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Tapping a thread in steel is a useful workshop skill

This post is for people with little experience of working in metal. Tapping a thread is a useful workshop skill. It’s easy to cut threads in steel with a tap. You can use a drill and tap to fit a cutting bit to a tool shaft, assemble steel parts, or to make up frames for tool stands etc.

Drill the hole

Drill the hole for the thread using a tapping drill. This is just a normal twist bit the correct size for the particular thread. When drilling holes in steel, you need a bench drill with the speed set slow. This makes a hole that is square to the surface of the metal. When drilling metal like this it is essential to use a vice or clamp. The drill can catch when it cuts through, spinning the metal round and doing your hand no good at all.

The size tolerance is small, and accuracy is important. If the hole is bigger than recommended, the thread will be weaker, though the tapping will be easier. If it is too small, you will find the tap makes the hole bigger without getting a grip in the metal and cutting a thread.

The correct size of hole depends on factors including thread form and thread size. There are a lot of thread forms, such as Whitworth, BSF and BA, for which drill size tables are available online. I include here tables for the smaller metric threads and Whitworth threads that are commonly used in older machinery.

Taps

Taps come in all sizes and threads. You can identify the right tap to match an existing male thread such as a bolt by placing them side by side with the thread peaks lined up. Hold them up to the light, and you can see any mismatch further along the tap. If the diameter matches too, you probably have the right one.

Each thread type and size has three corresponding taps, though you don’t need all three for through holes. They differ only at the point. The first cut tap has a long taper to help start the thread, the second cut has less taper and the bottoming tap has none, because it works when the other taps have already made the start.

As well as the taps, you need a tap wrench.

Cut the thread

When tapping a thread, it’s necessary to align the tap accurately with the hole so that they are coaxial. A crooked tap will not produce a good thread. In shallow holes it is less critical, but the deeper you go the more severe any misalignment becomes, and the tap will break. The first couple of threads set the alignment. Don’t try to pull the tap straight once the thread has gripped the tap, it’s too late then. You can sometimes correct it by drilling the hole bigger at its opening and re-starting the thread further in.

A good way to start the tap squarely is to grip it in the chuck of the bench drill used to make the hole. That keeps it on track, but you have to turn it by hand, using the drill lever to keep gentle pressure on the tap so it enters the hole and starts self-feeding. Once the first cut tap is securely held by the thread it has cut, you can switch to the tap wrench. Just wind the tap in as far as it will go, taking care not to bend it. Small taps break easily. Then, if it is a blind hole, change to the second cut, which will go further in, then to the bottoming tap, which will complete the thread to the bottom of the hole. Before bottoming, clear out the swarf.

Another method for aligning the tap is to drill a clearance hole in a bit of scrap metal or wood and clamp it above the hole for the tap. The tap will slide through the clearance hole, which will hold it square. The clearance hole must of course be drilled square.

Lubricate the tap

Lubricate the tap to give a better finish to the thread. There are special compounds, but oil will do. The swarf cut by the tap has to be broken up as you go. To do this, advance a little then turn backwards a bit, going two steps forward and one back. If you don’t, the tap can get locked.

Blunt taps are hard to turn and may seize. You can sharpen them with a narrow, round-edge grinding wheel, but it is easier to replace them. Watch for this if buying second-hand taps, they were probably disposed of because they are blunt.

Metric tapping drill sizes

Tap                        Metric drill               Imperial drill

3 mm × 0.5           2.5 mm –

4 mm × 0.7           3.3 mm –

5 mm × 0.8           4.2 mm –

6 mm × 1.0            5.0 mm –

7 mm × 1.0            6.0 mm                      15/64

8 mm × 1.25           6.8 mm                      17/64

8 mm × 1.0             7.0 mm –

10 mm × 1.5            8.5 mm –

10 mm × 1.25          8.8 mm                      11/32

10 mm × 1.0            9.0 mm –

12 mm × 1.75          10.3 mm –

12 mm × 1.5             10.5 mm                    27/64

14 mm × 2.0             12.0 mm –

14 mm × 1.5              12.5 mm                    1/2

16 mm × 2.0              14.0 mm                   35/64

16 mm × 1.5                14.5 mm –

Whitworth tapping drill sizes

Size (in)                  Tapping drill size

1/16                          Number Drill 56 (1.2 mm)

3/32                          Number Drill 49 (1.85 mm)

1/8                            Number Drill 39 (2.55 mm)

5/32                          Number Drill 30 (3.2 mm)

3/16                           Number Drill 26 (3.7 mm)

7/32                           Number Drill 16 (4.5 mm)

1/4                             Number Drill 9 (5.1 mm)

5/16                           Letter Drill F (6.5 mm)

3/8                             5/16 in (7.94 mm)

7/16                           Letter Drill U (9.3 mm)

1/2                             Letter Drill Z (10.5 mm)

9/16                           12.1 mm (0.4764 in)

5/8                             13.5 mm (0.5315 in)

 

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Turning metal on a wood lathe. Small items are possible

Aluminium finial turned on a wood lathe

Turning metal on a wood lathe is possible, even though the wood lathe is not designed for it. Lathes are designed specifically for either woodturning or engineering purposes, rarely both. Heavily-built engineering lathes work better than wood lathes. Their tool holder rigidly clamps the cutting tool and moves mechanically. But if you don’t have an engineering lathe and aren’t too ambitious, you can turn many small items in brass, aluminium or even steel freehand quite successfully on a wood lathe. The finial shown above was turned on my Graduate Shortbed lathe, mainly using a small gouge. It was threaded onto a bit of 12 mm studding held in a chuck, with tailstock support, and sanded to an acceptable finish. It is about 5 inches tall.

There are problems to overcome. Holding the tool so that it cuts steel is difficult. The hardness of the metal resists the cut, and the cut is very liable to ‘chatter’. This is vibration that leaves a rough or ridged surface on the work. Working freehand, accuracy is harder to achieve. Without a tool slide, accuracy comes from the turner’s skill. Making true cylinders or flat surfaces accurate to a thousandth of an inch freehand is not easy. But many items don’t need such precision.

Interrupted cuts, such as turning the corners off something, are particularly difficult freehand because it is hard to control the cutting tool. It is risky, too. Some wood lathes have a proper slide rest as an accessory.

Preventing chatter

Woodturners are familiar with the problem of chatter. When turning metal on a wood lathe it is hard to avoid. To prevent chatter, you need a strongly built lathe, with good bearings. It must hold the workpiece firmly, with minimum projection from the headstock. For example, modifying a drive centre while it is in the spindle taper is easy. A similar job held in a chuck is harder, because the metal can move away from the cutting tool.

Use tailstock support whenever possible. A Jacobs chuck will hold small items. Light cuts using a robust and sharp tool, with minimum projection over the toolrest, should then produce an acceptable result.

The tools

You can use a high speed steel woodturning scraper or a graver. A graver, which you can easily make yourself, was traditionally made from square section tool steel with a diagonal flat, leaving a long point at one corner. You could convert a triangular or square file, but a high speed steel tool bit would be better. A round high speed steel bar ground with a pyramid point would work. It would be similar to a woodturning point tool, but with a more obtuse point. Use a graver a bit like a skew chisel. Its edges (not the point) can plane off long, thin curly shavings from steel.

Brass likes tools with zero top rake, so responds well to scrapers. Tools leave a polished surface on brass. Aluminium turns with a graver or even a small short-beveled bowl gouge. Cutting speeds are lower than for wood, but because only small items are possible, the normal low-speed setting on the lathe is probably OK. Some metal alloys are more free-cutting and ‘turnable’ than others. A file will shape the item and remove chatter marks if necessary. Even on a lightweight lathe you can make simple shapes in steel using a file or a rotating grinding wheel held in a drill chuck.

Turning metal on a wood lathe is tiring, particularly with steel, because the tool must be held firmly up to the work. It helps to use a pivot pin in the toolrest to lever the tool into the work. This gives more control. If the workpiece is held rigidly, the pivot pin can help prevent chatter too. A heavy cut can increase it.

Safety when turning metal on a wood lathe

Turning metal freehand is hazardous, therefore precautions are necessary. It is essential that the workpiece is secure in the lathe. Chunks of metal flying out of the machine are even more likely to do you harm than are lumps of wood. Eye protection is a must. The swarf is sharp and hot – wood chips hitting your hand are annoying, but metal swarf can cut. Long strands could even catch your fingers and drag them in. Never clear away swarf while the lathe is running.

Turning with a scraper can make chips like little needles. They can get in your skin like splinters. But gloves are risky around moving machinery because they can catch and drag your hand in. Thin ‘rubber’ gloves that tear are safer. A bad dig-in could wrench the cutting tool badly enough to break it and perhaps cause injury. A file thrown back by the chuck jaws can injure you. They must always be used with a proper handle to stop the tang impaling your hand.

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Don’t forget dust extractor maintenance

This post is about dust extractor maintenance. It’s very easy to buy a dust extractor and forget about it. They are simple machines, but problems can grow slowly, so suction declines without you noticing.

Turning plastic

Not long ago, I made some wheels out of a commercial cutting board, one of the thick ones used in restaurants or on deli counters. I cut some squares from it with the bandsaw with no problems at all. I put each one in my self-centring engineering chuck and turned it to size and shape. A flat bit in the drill press made the holes in the middle. Back on the lathe mounted on a wooden mandrel to complete the turning. Job done. The plastic material, that I think may be polypropylene, turned very easily with a negative rake scraper, leaving a smooth, shiny surface off the tool. The only problem was the shavings. Long ribbons of plastic wound round the chuck, the mandrel and everything else, with the loose ends flailing as the lathe went round. So although there was no dust, I put the dust extractor on.

Later, it seemed to me that suction at the extractor inlet was not as good as it once was, so I cleaned the filter cartridge. This was a job I had been meaning to do for some time. There was lots of fine dust in it, blocking the pleated filter. I took it outdoors and used a brush and compressed air to get as much dust as possible out. I put it all back together and switched on. Much better!

Dust extractor fan guard

But was the suction yet good enough? Perhaps there was a blockage somewhere. My extractor is a cyclone unit, and at the outlet of the fan housing there is a grid to stop people putting their hand in and touching the spinning fan. I dismantled the ducting close to the housing to check it. Sure enough, long ribbons of plastic had passed through the cyclone and blocked the grid. It was surprising that air could get through it at all.

I knew what to look for, because once before when re-configuring the ductwork, I found the remains of a plastic carrier bag blocking the grid. Like the bag, the bird’s nest of ribbon was easy enough to remove. But this time I did my risk assessment and decided that although the grid removed one risk, it created another. The first risk was negligible to anyone with any sense, while the second was significant. So the grid had to go. I removed it, put the ducting back together and switched on. Now the suction is back to what it ought to be.

These are not the only times I’ve come across a problem like this. It’s possible for long splinters or other objects to get stuck at a bend so shavings build up, or for debris to accumulate at a low spot. And filters clog up from time to time. But often the drop in suction goes unnoticed, even if there is a vacuum gauge to check it.

So my recommendation is to make a point of scheduling maintenance, and to check suction at your dust extractor often. Whether you remove the safety grid is up to you. An objective way to measure suction would be useful. I shall have to consider a vacuum gauge.

Shavings trapped in dust extractor fan guard
Waste trapped by fan guard
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A homemade centre finder is easy to make and quick to use

One kind of centre finder on the market has a slot for a pencil to mark intersecting diagonals. These work well on squared timber, but are a bit slow to use on a batch of items. Another kind has a blade. You position the blank, tap it so the blade makes a diagonal line, then repeat. I’ve found that this type can easily start splits in the wood, and needs the end of the blank cut square.
The centre finder I used for a long time is simply a small wooden block. The block has a hole drilled that is a push fit for a short pencil. The hole is off centre. By turning the block on different sides there is some height adjustment. To use it, I put the spindle blank and the pencil block on a flat surface and mark a line across the end of the blank. Then I flip the blank 90 degrees and repeat to do all four sides. The result is a small square marked on the end of the blank, from which I can easily find the centre by eye. This is not super-accurate, but good enough for most purposes, and it is quick. I have several blocks in different sizes so I can pick the one most suited to the size of the spindle blank. The blank need not be square and the pencil block can mark cylinders equally well. The point of a nail works too, and stays sharp.
pencil block centre finder
Pencil block centre finder
adjustable centre finder
Adjustable centre finder

I’ve now made an adjustable version of the pencil block, with a pivoting arm to hold the pencil. The hole for the pencil has a slot through it and a pinch bolt to lock it.

To find the centre of a bowl blank, I usually use a hardboard disc of appropriate size. I have a lot of these in different sizes for marking out bowl blanks, and each has a small hole in the middle. I just lay one on the blank, and place it quite accurately by eye or touch. Then I mark the centre with a pencil through the hole.
chuck insert centre finder
Chuck insert centre finder
When I need more accuracy, I use a chuck insert centre finder. This is a short dowel with a steel point in one end. I turned the insert to fit inside the body of my engineering chuck. I put the chuck on the bench and adjust the jaws to be a sliding fit on the spindle blanks. The blanks must be square or cylindrical. A tap on the end of the blank pushes it onto the point to mark the centre. This is a good method to use when part of the finished item needs to be left square.
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The skew chisel. Learn to use it and see what it can do.

Lots of woodturners fear the skew chisel. Skews dig in alarmingly, seemingly without any warning or provocation. Some people don’t use them at all. But can you really call yourself a woodturner if you can’t use a skew chisel? It’s perhaps  the most useful and versatile tool of the lot for spindle turning, so it is worth persevering with it. Just watch Woodturner21’s videos on YouTube to see what the tool is capable of.
You probably already have some idea of how to use the skew chisel for cutting beads and planing a cylinder. You can find the basic principles in turning books and DVDs and I don’t mean to repeat them. All I can tell you is what you already know – that you need lots of practice – and show you how to get the most from it.

Tuning up

First, tune up your skew chisel. Although you can use different grinds, the default has a skew angle of about 70 degrees and a bevel length of about 1.5 times the thickness of the tool. A long bevel makes it easier to see what you are doing, though can make the chisel cut in deeper when you get a catch. Make sure the edge and the points are really sharp, and not rounded over.
A long bevel and straight cutting edge are easier for sharpening on a diamond hone. But it’s OK to use either a straight edge skew chisel or a curved one straight from a grinder. Platform sharpening is probably the easiest method. Try the edge on your thumbnail – if the edge or the point slides without biting in, it’s blunt. Make sure you keep the chisel sharp all the time you are using it. You must grind away the sharpness from the long side edges of the tool so they slide easily on the tool rest. Nowadays you will probably find this has been done at the factory if you buy good quality tools.
If possible, use a strong, rigid skew chisel of about 10mm square to practice beads (dealers sell these as ‘beading and parting tools’. You can easily grind it to a skew angle), and one about 18mm wide for planing. Of course other sizes work perfectly well. But a short edge gives less scope for catching on a bead while cutting on the point, and a wider tool helps keep the long point clear on a cylinder.
Now check your tool rest. Make sure it is smooth. Rub it with a bit of wax to cut friction. Set it a little higher than for gouge cutting. This puts the skew’s handle in a more convenient place for you.

Set up the lathe

Have the lathe running slowly so you can see what is happening at the point of cut, and you don’t feel threatened by the spinning wood. Put on your face shield, just in case. Later you will probably want to use higher speeds.
If you are nervous, use a conical fixed centre (one without any teeth) in the headstock and a revolving one in the tailstock. Make a pilot hole about 6-8 mm wide and deep in the headstock end of the blank. The cone centre will give friction drive only, with nothing else forcing the wood round, and is safer than holding the wood in a chuck. You can adjust the tailstock until the friction is strong enough to drive the blank but it will stop turning if you cut too deep or have a bad dig-in. A ring centre will also drive the work safely, and doesn’t need a pilot hole.

Practice

Practice on soft timber.  Start with a blank you have roughed down into a cylinder of about 40mm diameter and about 150mm long. You may find bigger pieces intimidating, and long or thin ones whippy, neither of which is helpful. Choose a blank that is straight-grained and without knots.
Don’t try to make any specific item at first, just keep making beads and planing cylinders. Make beads of about 12-18 mm wide. Use a parting tool first to make a clear space either side of each bead for the skew chisel to work in.
Use the short point of the skew chisel for cutting beads, although it is possible to use the long point or the edge. Stick with the short point until you are happy with it – later you will try the long point and may end up preferring it. I think the short point is easier to start for many people.

 Rough out the shape of the bead

The first few times, use a scraper to make a shallow bead shape that you can then follow with the skew. The scraper seems easier, but don’t be tempted to keep on with it. When you see the difference in the surface the skew makes, you will understand why. Then, with the lathe switched off, present the skew to that rounded surface, first at the top and then moving down to the bottom of the curve, keeping the point in its proper cutting position as you go. The chisel will begin almost flat on the rest and twist over. After you have made some shallow beads, try some that are fully semicircular. On these, the tool will end on its side. See how you have to move the tool to keep the point in the right place. Repeat the movements round the curve, so your muscles begin to learn the action.
Although you will be cutting with the point, the bevel must float (not press) on the cut surface to support the tool. Twist the skew as you go round the curve to keep the point in the cutting position. The edge will be close to the wood, but don’t let it touch. If it touches when the lathe is spinning you might get a catch. When rolling the bead with the edge, the movements are slightly different.

Make a cut

When you are ready, switch on and take a cut round the roughed-out bead. Go slowly so you can see what is happening. No rush. As slow as you like, if using a high speed steel chisel. Carbon steel can overheat if kept in the cut too long. Take a thin shaving. Steer the point all the way round the curve, repeating the movements you started to learn earlier. Try for a smooth, even cut and don’t put pressure on the wood.
Pay attention to the handle movements. They are what you are practicing. As you try to go round the curve, you may have a tendency to complete the movements either too early or too late. Either will make a poorly shaped bead.

Repeat

Don’t work too long on one bead, cutting too deep into the wood, because if the blank gets thin it will start to vibrate. Start a new one. You may find one side of the bead easier than the other. Concentrate on the easy side first, making half beads, until you understand the process and feel ready to change over. When you get a catch, correct it with the scraper or start again on a fresh part of the blank. This is because the damage can interfere with the free movement of the skew.

Planing cuts 

Planing uses the edge of the skew chisel. Keep the long point up, clear of the wood. Have the cutting edge at about 45 degrees to the lathe axis, because that gives a slicing cut with the shaving coming off near the short point. The key is to keep the bevel floating, without pressure, on the freshly planed surface. It’s easy to let the handle lift a little, and immediately you will get problems.
At first sign of trouble, lay the handle lower. Feel for the sweet spot in which the cutting is smooth and quiet and easy. If the handle is too low, the edge just lifts out of the wood, so does no harm. As long as you pay attention to keeping the bevel in contact and the long point clear of the wood, you should not get digs when planing. At the ends of the blank, let the cut run off the wood, not onto it, as there will be no bevel support at that point
When you can plane a cylinder without problems, you can practice steering the cut to round over the end – this is another good way to make beads.
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A ball cutting jig can be made from a machine slide.

Turning a sphere freehand will test your skill, particularly if you need two the same size. If you want more than one or two and don’t want to do them freehand, you can use a simple homemade or commercial ball cutting jig. I make lots of balls in a range of sizes, and for me a jig that lets me produce them quickly and accurately is essential.
The most basic ball cutting jig is simply a clamp to hold a cutting tool, with a pivot to allow the tool to swing through a quarter circle or more, all fixed to the lathe bed.  The cutting tool is sometimes adjusted in the clamp, or there could be a sliding adjustment so the clamp itself moves. But every commercial ball cutting jig I have seen is a bit flimsy or lacks easy adjustments. The cutter is usually advanced just by pushing it forward by hand. Sometimes there is no adjustable stop to control the finished ball size.
I made a heavy-duty ball cutting jig. It does a very good job cutting balls and can also make hemispherical hollows. It was easy to make, but would not have been so easy if it was not based on scrap parts. The key component is a machine slide such as top slide from a metal turning lathe. These can be obtained from dealers in old tools, or from Ebay. Mine has a rack and pinion lever feed. This is ideal because it is fast to use, but screw feed would be fine. I made the rest of the ball cutting jig from bits of scrap steel. The construction details depend on what lathe and machine slide you have so I can’t give more than guidance. Assembly would probably only involve drilling, tapping and bolting together.
homemade ball cutting jig
Jig set up on Graduate shortbed lathe
If you would like to make a ball cutting jig like this but have never done any work with mild steel before, don’t worry. Think of the steel as like very hard wood. You can cut it with a hacksaw, or if it is thick, drill a line of holes close together and saw through them. Drill the holes with a twist bit in a drill press because it is difficult to drill freehand, even with a power drill. You can cut screw threads in steel with a tap by screwing it into the correct size hole.
The ball cutting jig (see cross-section plan below) consists of the following components, starting at the bottom and working up:
  • A clamping plate that will hold the jig to the lathe bed, allowing it to slide and lock
  • A locating block (not shown on plan) that fits the lathe bed so the jig can slide along parallel to the bed without sideways movement. This makes locating the pivot point with reference to the ball centre much easier as you can just slide the jig along to the right place. You have to make sure the centre of rotation of the jig passes directly and accurately under the turning axis of the lathe. The short bed on my Graduate lathe has a slot that is offset a little, so I offset the jig to match. The locating block is not load bearing, it just positions the jig before locking down, so wood would do.
  • Next is a pivot plate sitting on the lathe bed. Make it thin, but rigid. The thinner it is, the more clearance space you have and the larger the ball you can make. A steel disc about 10 mm thick and 100 mm across would be ideal. Mine is much thicker, because that is the scrap that I had at the time.
  • A rigid slide support platform sits on the pivot block. The mating surfaces of the pivot block and the slide support platform are the pivoting plane. The ideal for the support platform would be a strip of steel of width to suit the slide, and 12 mm thick. If the strip is too short it limits the ball size unnecessarily. I rounded the end of the support platform to clear the headstock.
  • The clamping plate, guide block, pivot plate and slide platform are all locked together with the pivot pin. This could be a 12 mm or larger steel rod, threaded where necessary. Firmly anchor it in the pivot block. You could screw it into a tapped hole in the pivot block and secure it with thread lock compound. This provides two separate clamping actions – one from below to lock the jig to the lathe bed and another from above to adjust the swivel tension.
  • The pin passes down through clearance holes in the guide block and clamping block. This allows a nut and washer to pull the pivot plate down on the lathe bed, positioned by the guide block and held by the clamping block. Above the pivot block, the pin passes through a snug-fitting clearance hole in the slide platform.
  • Above that are a washer and two nuts that lock against each other to set the pivot tension. The pin should preferably be unthreaded where it passes through the slide platform. This is a bearing surface for the pivoting movement. But even a screw thread should give adequate guidance, assuming the hole is a snug fit. The top of the pin needs to have its centre marked to set it exactly beneath the centre of the ball when in use. I turned a point on mine. If the ball turning jig is not lined up properly, the ball it makes will not be perfectly round.
  • Bolt the machine slide to the slide support.
  • The moving slide carries the tool holder. The tool holder on mine came from another old machine, but you could make a similar one by bolting three bits of steel together. It stands on a raising block to bring the tool to the lathe centre height. Having it a little low allows you to use different cutters, with shims. If the cutter is not on centre height, the ball will not be spherical.
  • You need an adjustable stop for the slide movement. How you do this will depend entirely on what slide and other parts you have. I used a bit of threaded rod with two adjustable lock nuts, passing through a clearance hole in a bit of metal attached to the slide. The cut stops when the metal contacts the adjusting nuts. By counting movement of the nut flats, I can adjust the cutting depth and size of the ball very accurately.
limiter for homemade ball cutting jig
Lock nuts limit the slide travel
The largest size of ball you can make depends on the clearance above the top of the swivel point and the travel of the slide. If you make a ball from a cylindrical blank, the clearance needed is more than the radius of the ball. Even more so if you use a square blank, And you have to allow for projection of the cutter.
tool holder for homemade ball cutting jig
Tool holder
 To use the ball turning jig, position the swivel axis directly beneath what will be the centre of the ball. I normally make hemispheres with the blank held on a screw chuck, so position the swivel pin beneath the face of the chuck. I glue the hemispheres together to make perfect spheres. Advance the cutting bit, an ordinary round-nosed scraper. Pull the slide round to make a cut, then advance the tool for the next cut. When set up, I can very quickly make lots of identical half balls.
hemisphere cut with homemade ball cutting jig
MDF hemisphere cut with homemade ball cutting jig
A ball cutting jig of this kind cannot make a whole ball in one pass. You must hold the blank in the lathe, so the cutter cannot reach all the surface. It could make most of the ball for finishing off by hand. Or you could move the ball in a chuck so the cutter reaches the uncut parts. If you hold the blank in a chuck the cutter could do 75% or more of the circumference in one pass. It would leave just a single chucking spigot. If you hold the blank between centres, it leaves two smaller spigots.
A traditional way of hand turning spheres is to put the roughed out ball between two female cone centres. The spigots project sideways for turning off. Using this same method, you could finish the ball with the jig. It should leave a perfect ball if set up correctly.
 Cross-section of ball cutting jig
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Graduate lathe, a great machine for bowls, though not without faults.

The Graduate lathe was designed in consultation with Frank Pain, one of the first turners to write for the amateur. He was a professional of very long experience and knew a thing or two about lathes and woodturning.

I bought my Graduate lathe many years ago. At the time it had little competition. It was perhaps the most solidly built machine available for non-industrial use, and the lathe you bought if you wanted the best. It was intended primarily for use in schools, back when schools taught woodwork, although my own first turning experience at school was on a Myford. Ray Key, another well known turner, described the Graduate as being ‘head and shoulders above the rest’.

This lathe comes in a long bed and a short bed format. Mine is a short bed, better for bowls and boxes because it takes a larger diameter and you can stand in front of the work without bending. It can be used for spindle turning, though not very convenient for this, and the maximum workpiece length is short. I have now bought a larger machine, but happily used this lathe for bowls and any larger work. It was a great improvement over the small spindle lathe that I owned at the time.

One problem with the Graduate lathe is that its centre height is low. Most people would want to raise the height. I had a welded triangular platform standing on steel pillars made for mine. This brought the centres up to elbow height, which is the normal standard. It also increased the footprint a little, making it more stable. I have not found it necessary to bolt the machine to the floor.

It came with a 3/4 horsepower motor and 4 pulley speeds with a range from 425 to 2250 rpm. This was not suitable for the large discs that I later began making for globe stands, which needed more power and a lower speed. I therefore upgraded with a bigger motor and a Variturn variable speed drive and had a special large steel faceplate made for these jobs. This goes on the left hand end of the spindle and allowed me to turn discs of over a metre in diameter. I installed the Variturn kit myself. It’s a great addition, quiet and smooth, but the lathe still lacks power for very large work. It copes with large bowls, but I prefer a 2 or 3 HP motor to let me work faster.

Although the Graduate lathe was a great machine in its day, and performed very well for most of my work, it has some weaknesses. The shortbed version seems to have been a design afterthought. For all its good points, its design leads to some problems.

The strange tailstock causes some problems. It is not used on the long bed machine. I didn’t often use the tailstock, so the problems I describe below rarely caused much inconvenience in practice.

The curve of the tailstock casting increases the distance between the centres. It is partly hollow, being open at the back. This causes lack of rigidity, and you can sometimes see it flexing as the work turns. The tailstock position sometimes falls where the two bed slots join at right angles to each other. In this position it is not properly supported. Both the foot of the casting and the locking plate below the bed are too small to bridge the slots at this point – an obvious flaw. You can see this in the photo below. I used an extra-large washer below the bed to help bridge the gap.

Graduate shortbed lathe
Graduate shortbed lathe showing unusual tailstock and crossed slots in bed.

The curved casting has its foot closer to the headstock casting than its centre point. This means that when you want the point close to the headstock the locking lever below the bed will not turn. The headstock casting obstructs it. This means that you can’t always give a shallow bowl blank on a faceplate tailstock support. You can’t pin a disc against a faceplate with the tailstock.

The tailstock ram is just a screw (hollow, to take a No. 2 Morse taper) with a cross hole for a tommy bar to advance and retract. I made a winding handle to use instead of a tommy bar. The alignment of the screw on my lathe is not good. The upper part of the tailstock twists in the casting. A pin locks it, and there is enough play to throw the centre slightly out of true.

The toolrest holder casting is also curved and hollow, as shown in the photo. You can mount it in either of the two slots in the bed, with the same problem at the point where the slots meet. I find however that it is normally set in the cross slot clear of the junction. When the tailstock is in place, the feet of the two castings and their locking levers below the bed can sometimes get in each other’s way.

The tool rest holder also lacks rigidity to some extent. The foot of the casting is not directly under the tool rest stem, which allows slight flexing. The holder can slide along the bed slots and swivel, which ought to give free movement of the rest. But as it swivels, there are times when you cannot put the rest in the right position. and the toolrest locking handle, which is another tommy bar, can foul a large workpiece. With the tailstock removed, which is how I usually have it, the toolrest holder has more freedom of movement and there is rarely a problem in practice. The rests themselves are excellent for faceplate work – rigid, and with a good slope and narrow top. They are not so good for spindle work if you like an underhand grip with a finger behind the rest.

The headstock consists of a single iron casting from floor level up. The shell is heavy and robust, with a thin wall. Bolts attach the cantilevered beds to it.

The lathe came with an outboard bowl turning bed on the left of the headstock. But the inner and outer beds are the same height, so there is no more capacity when using the left hand bed on the short bed model. You cannot use the tailstock outboard. The spindle rotation originally was fixed (now reversible with the Variturn), so the threads are different and accessories aren’t interchangeable. Turning on the outboard side is in the reverse direction to the normal anticlockwise. Left-handed turners might like this. It can make some cuts easier, for example when hollowing bowls.

The outboard spindle thread is the opposite hand to the inner side. Because of this, if you reverse the rotation, the chuck is likely to unscrew. But the outboard bed is at least a convenient handle when moving the lathe. It would be useful for large diameter work when attached to the long bed lathe.

With the inboard bed removed, you can turn large pieces inboard. The limiting factor is when the headstock casting gets in the way. It bulges out half way down to accommodate the motor. Without the bed, a free-standing toolrest is essential.

With the left hand bed removed, you can turn even larger pieces outboard. I have used my Graduate lathe to turn built-up oak discs of 60 x 1100 mm. The lack of power was a problem though.

Both beds come off easily by removing the fixing bolts. There are dowels to align the beds accurately when replacing them. One person can do this with the help of a temporary wooden prop to help support the weight during this process. Some people set up a disc sander on the outboard side. The bed is then useful to carry the sanding table.

Conclusion

No lathe is perfect. The Graduate lathe in its short bed version is in some ways a poorly designed and under-powered machine. But because of its mostly great build quality the lathe performs very well and can do excellent work. Any of these bowls could have been made on the Graduate. You may sometimes come up against its eccentricities. But it is usually a delight to use and a Graduate lathe is still a good buy. It’s far superior to most of the cheap lathes on sale now. I used mine for many years and was always able to find a way to overcome its limitations. I have never used the long bed version, which has a more traditional toolrest support and tailstock. It should be excellent for spindle work, though limited for bowl turning.

 

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Choosing a lathe for woodturning

It’s easy to get it wrong when choosing a lathe. That can greatly restrict the work you can do, or prevent you enjoying woodturning, the very thing you are buying it for. There are so many machines on the market, some of such poor quality that they can only be used for very light work. How do you choose between them?

To perform well, a lathe must be designed well and made well. Top quality doesn’t come cheap, but even inexpensive machines can be compared when choosing a lathe to see which is the better buy. Good quality lathes last indefinitely and often a used one is a better choice than a poor quality new one, even if you have to replace bearings or scrape off a bit of rust or change the motor from three phase to single phase.

Few suppliers advertise that their lathes are of poor quality, so you have to make up your own mind which is best. You can consult other turners, but when you are choosing a lathe, it’s your money. The best approach is to make sure you understand what makes a good machine. When you have examined lathes from different price ranges you will see the differences and be able to make an informed choice.

The perfect lathe  does not exist, and never will, because so much of the design of a lathe involves compromises. For example,  a short bed lathe takes up less space and is easier to use, but will limit the length you can turn. Nor is there such a thing as a beginner’s lathe or starter lathe. Either a lathe is a good one or it isn’t, and a beginner is not well served by a poor quality machine that causes problems in use. You can compromise on size or variable speed if cost is important. But don’t compromise more than you have to on build quality. Weak components and poor manufacturing tolerances may make the lathe almost unusable for anything but very light work.

Here is a checklist.

Size

The first thing to consider when choosing a lathe is size. A big lathe is the most versatile, as although you can do small work on a large machine, the opposite does not apply. Many of my bowls could have been made on a small lathe, but not all. Bigger lathes, made primarily for more experienced turners, are also usually of better quality. The biggest can still do small work, though they sometimes cumbersome. For example the toolrest holder and tailstock will be heavy to move.

But if you have limited space or budget, a good small machine will be fine for small work, and the better ones are very capable. The smallest machines, micro lathes, should only be considered if you have a particular need for one, for example if easy portability is critical. Even if you only want to make very small items, a larger machine will probably be easier to use. Drill-powered lathes are also unsuitable for general use, because of their light construction and the noise they make.

Rigidity

When choosing a lathe and comparing machines, look for:

  • a strongly constructed headstock with a large diameter headstock spindle, mounted in heavy-duty bearings that are well separated. The spindle nose thread should have a wide register at the back to support the chuck butting against it. Except on small lathes, the spindle should accept number 2 or larger morse tapers.
  • a strongly made tailstock,  that on bigger lathes can accept number 2 or larger morse tapers
  • a robust tool rest and support
  • a substantial and rigid bed
  • a strong and stable stand or bench that will support the lathe without shaking.

Look for key components made of cast iron or heavy welded steel. Cast aluminium, thin pressed steel or light weight tubular components may not be rigid enough, and heavily stressed screw threads in aluminium can wear rapidly.

Cast iron or steel bed?

It is often said that cast iron is the best material for lathe beds because it suppresses vibration, and there is some truth in this. Lathes with flimsy, light weight beds made of pressed steel are really only suitable for light work. Steel tube beds or solid steel bars can flex and vibrate, but the heavier and stronger (and shorter) they are, the better the lathe will be. Cast iron can be brittle, so is usually made quite thick and heavy out of necessity, which tends to be a good thing. A heavy cast iron bed with good cross-linking webs connecting the sides will be the foundation for a good machine.

But some top end lathes have steel beds. Heavy steel plate is welded to a heavy steel tube, round or square. The assembly is large enough to prevent twisting and flexing. Vibration on these is not a problem.

The tool rest and holder

When choosing a lathe, pay particular attention to the design of the tool rest and its holder (sometimes known as the banjo). These are key components and any weakness will prevent smooth, chatter-free cutting, particularly when using scrapers. This is specially important if the lathe has a swivel headstock as you may have to extend the holder far off the bed. The greater the overhang, the stronger the components needed to resist flexing under load. Some may bend or even break if the tool catches. Avoid rest holders with lightweight jointed swing arms. If the holder has a cam lock, it needs a heavy and rigid eccentric spindle, otherwise the clamping force will vary depending on where the holder is. Access for adjusting the tension should be easy. The hole for the toolrest stem should be deep as this will help prevent it flexing under load.

The toolrest itself should be heavy and strong in proportion to its length, with a large diameter stem. But the most heavily built rest will flex if it is too long and only has a single stem. You need a robust rest but one with a narrow top, to put the fulcrum for the tools close to the wood, minimizing tool projection. A flat top to the rest hinders proper tool movement because there are two distinct pivot points when tilting the tool.

Grip

Many turners like to use an underhand grip to anchor the tool and improve control, so the shape of the rest should allow you to grip the underside with your fingers (though some sacrifice this for the sake of greater strength, and many turners prefer the overhand grip). The rest holder and locking levers must not obstruct tool movement, when the handle is low. For this reason, it is good to have alternative positions for the stem locking lever. The side of the rest that faces you should be steep, so the tool handle can drop low enough anywhere along the rest, including directly over the stem.

The lathe should have a short and a long rest as well as the standard, as all are useful. The long one may need a second rest holder. The rest should be capable of being positioned as close as possible to the lathe axis so tool projection on thin spindles is minimised, and should be easy to move.

Tool rests can be replaced if necessary.

Weight

A heavy lathe shakes less when spinning an unbalanced piece of wood. Weight comes from strong and rigid cast iron/steel construction. The stand or bench that the machine sits on must also be strong and heavy,  but it may be possible to add weights to the stand to improve stability. The lathe will be more stable if it stands on a concrete floor.

Construction quality

Machines with strong and heavy components are usually OK. But there are some points worth checking when choosing a lathe.

  • Make sure that the spindle and motor pulleys have keys fitted into slots to secure them. Some makers rely on grub screws alone, which work loose and become a constant annoyance.
  • All-over machining of the pulleys will help them run smoothly, without vibration. Check that pulleys align properly.
  • Choosing a lathe with poor quality headstock spindle bearings, power switch, electronic variable speed controller and motor can lead to trouble later. Look for components of a recognised brand, not the cheapest that the maker could find. You want them fully enclosed to keep dust and chips out, and the motor fan cooled and rated to run continuously. Cheap motors run hot.
  • See that the top surface of the bed is smooth and true. A bed with a flat top may be easier if you want to fit accessories such as a steady rest. Be sure that the headstock and tail stock can line up accurately with each other. Any apparent error could be due to an uneven floor causing the bed to twist slightly, and easily corrected.
  • Make sure there is no detectable play in the tailstock ram when extended and locked. Also that the tailstock slides freely but locks immovably to the bed. The revolving tail centre must have no play in its bearings when under load (this is a replaceable item).
  • Make sure that the headstock spindle has no play or end float – fit the faceplate and see if it will move.
  • Make sure also that the tool rest holder and the tool rest itself move freely and lock immovably at all positions. Some will lock when close to the lathe axis but not when further out.
  • The screw threads that lock the toolrest and tailstock ram should be generous in size and snug-fitting. The points of the locking screws should not cut into the metal. The handles should be strong and preferably of steel, not plastic.
  • Poor paintwork and sharp edges on the castings suggest a lack of attention to detail at the factory.

Choosing a lathe for ease of use

It’s important to consider ergonomics when choosing a lathe. Good ones are designed for ease of use, and fit your particular needs. Look for spanner-free adjustments. See that the locking levers don’t get in the way (particularly the one that locks the toolrest stem – try it with the holder in different positions). Make sure that they are robust. Plastic levers will break in time. Levers adjustable for angle are useful. It should be easy to remove the tool rest holder from the lathe. Ideally this should be possible without removing the tailstock or dismantling anything.

If you are choosing a lathe primarily for making bowls and boxes, you may find it much better to be able to work from the front of the piece without having to bend over the lathe bed. A shortbed lathe, or one with a swivel or sliding headstock or with outboard turning provision lets you do this (though short bed lathes obviously sacrifice capacity, and you never know what lengths you may want to turn in future). But other turners are happy to work over the bed and don’t mind bending. A swivel or sliding headstock also prevents obstruction of the tools when the handles hit the lathe bed.

There should be an indexing arrangement for a swivel headstock so you can quickly return it to parallel. It is possible for debris to get under a swiveling or sliding headstock, affecting its rigidity and alignment. This could affect the tailstock too. I have not found this a problem in the lathes I have owned, but good design would minimise the risk. In particular, the headstock should not tilt when you loosen it. As long as it sits flat on the bed it will be difficult for chips to get between the metal surfaces.

When turning spindles, you will need to get close to the work. Make sure there is no obstruction to your feet that will force you to bend forward. If on a bench stand, the lathe should be well to the front, as consistent with stability. A gap underneath for your toes is good, though it will accumulate shavings.

The height of the lathe spindle is important if you use it for hours at a time. The usual rule is to have the axis at, or a little above elbow height. Then you don’t have to bend. But it depends on the individual. You may have to experiment to find the most comfortable height for you. Some lathe stands are adjustable for height. But it is normally possible to raise the lathe on blocks or to stand on a platform when working.

The headstock spindle and tailstock ram are best hollow. This allows you to use a knock out bar, and you can drill long holes on the lathe.  It’s nice if the tailstock taper is self-ejecting. An easy and effective spindle lock for the headstock is important so you can remove chucks. Provision for dividing is useful for some work. But the division holes should not double as the spindle lock, unless they and the locking pin are substantial. Otherwise the holes will soon wear.

A headstock handwheel that lets you turn the spindle is useful when inspecting  the work or winding on chucks. The tailstock handwheel should be generous in size and operate freely. A place to keep calipers, sandpaper etc is useful. There is often a flat top on the headstock for this. You also need somewhere to fix adjustable lights. But these aren’t necessarily on the lathe.

Unless you know you will not need to turn pieces bigger than the capacity over the bed, when choosing a lathe go for one with provision for outboard turning. Or one with a sliding or swivel headstock. You can use a freestanding tool rest, but they are often unsatisfactory. Unless they are rigidly locked to the lathe, they can tilt or bend inwards, causing a catch. Sliding headstocks and outboard toolrests may need more space in use. You need access to the ends of the bed and you may have to remove the tailstock. The tailstock cannot be used with a sliding headstock when it is moved right to the end of the bed. Nor when the headstock swivels.

Motor power

Choosing a lathe with insufficient power will slow you down. A 1/3 horsepower motor is about the minimum for a small lathe. It will do for small spindle work and for small bowls when cuts are light. Under-powered lathes stall easily, which is annoying. One horsepower will do for medium size bowls. It is enough for large ones if you use the low-speed pulley setting and take light cuts. Two to three horsepower will let you work at a natural pace on large pieces without stalling the motor. Large motors may need permanent wiring rather than just a domestic style plug and socket. Large motors are less safe for a beginner, because they can apply a lot of force to the tools.

Noise

The lathe itself should run quietly, though when cutting there will be more noise. You will soon tire of rattles and bearing noise. The lathe should have an induction motor, not one with brushes and gears. The drive belt should not be tensioned solely by the weight of the motor. This can cause it to bounce, which can lead to noise and vibration. To avoid this, there should be a lock for the motor. The motor should, ideally, be directly below the spindle to minimise shaking.

Speeds

When choosing a lathe, look for one with a good range of lathe speeds. Low speeds, preferably down to 200 rpm or less, are more important than high. This is because it is unsafe to spin unbalanced chunks of wood fast even on a heavy machine. If the wood is sound, balanced, secure and not too large, turning at higher speeds is usually best. But you will get used to whatever maximum speed your lathe has. Many lathes these days have electronic variable speed, and this is a great feature. Even more so if it goes down to zero and can reverse the lathe. The very low rpm you can get from a good variable speed unit can be useful. It helps if you want to apply finishes to work while it is still on the lathe or to sand green-turned bowls.

But step pulleys work well, provided that it is easy to adjust the speed. It should not be necessary to go behind or underneath the machine, unlock covers or use spanners. Even with good quality electronic variable speed, it is very useful to have step pulleys. This is because their lower speed settings give more torque. You can often upgrade a lathe to electronic variable speed, but at significant cost. Some lathes have mechanically variable speed, with lever-operated cone pulleys. I have little experience of these, but they may be unreliable unless well made, and may cause rapid wear on the belt. The unit on the lathe at my turning club has not held up well. Adjustment is only possible when the lathe is running.

Accessories

Make sure the lathe is ready to accept headstock and tailstock accessories. Choosing a lathe with a non-standard spindle nose thread will make it hard to find chucks. Avoid machines that do not allow use of Morse taper fittings in both headstock and tailstock.

 

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Homemade long tool rest

A homemade long tool rest can be a useful accessory. It’s a great help if the tool rest is longer than the spindle you are turning by at least 25 mm at each end. This extra length gives tool access to the ends of the spindle, and it’s much easier to turn sweeping curves accurately if you don’t have to keep moving a short tool rest. Lathes don’t usually come with a very long tool rest as standard. One can often be bought as an accessory, at substantial cost. Over a certain length, a long rest needs two stems to keep it rigid and stop chatter.

It’s quite easy to put together a homemade long tool rest and a second holder to support it using hardwood. A wooden tool rest is pleasant to use, and was standard in past times. You will need to remove the sharp side edges on skew chisels to protect the wood. But that’s necessary for steel rests too. If the rest gets a lot of use, you may have to plane or sand the top smooth from time to time. If thought necessary, a metal strip or bar could be fixed on top with epoxy.

The stems

Make the two stems of round steel bar. One needs to fit your existing tool rest holder. The other can be any size because you will drill the holder to fit. The length should bring the top of the rest to the proper height when in the wooden holder.

I made mine by drilling a hole in one end of each bar. I used a tapping drill that matched a bit of threaded rod. The rod was tight in the hole so it would stay secure. Inserting the rod about 25 mm deep and projecting about the same distance seemed about right.

More simply, you could just glue the stems into holes about a quarter of the way along from each end of the wooden rest. The main thing is to make sure the stems are parallel to each other and securely held in the wood.

The rest

My homemade long tool rest began life as an oak table leg, about 600 mm long, 40 mm thick and 50 mm deep. I find it quite strong enough. I planed the front to make a slope.

The holder (banjo)

Use hardwood, say 60 mm thick, and drill a blind hole, say 45 mm deep, at one end for the second stem. Wood will probably not be strong enough to take a locking screw that will bear on the stem and hold it firmly, so that limits height adjustment. You could make a saw cut in the holder and put in a clamping bolt to squeeze it and make it pinch the stem. A second bolt would be needed on the opposite side of the stem This would reinforce the holder and stop it splitting when tightening the clamp. Or you could just put a spacer in the hole under the stem to raise it a little.

Saw a slot in the holder that will fit over a clamping screw to hold it on the lathe bed.

A steel version of this holder could have a locking screw to allow easier height adjustment.

The clamp

Now make a clamping block that will fit your lathe bed. Its design will vary because all lathes are different. Mine is made of thick MDF and fits between the ways. It has a projecting lip underneath. A bolt passes through the block and is long enough to reach up through the wooden holder. A washer and nut clamps the holder in place on the bed.

homemade long tool rest
Homemade long tool rest

Plan of homemade long tool rest

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Harden steel using these simple methods

It’s sometimes useful to know how to harden steel. Although it’s possible to do woodturning with very few tools, I can never resist trying something new. Sometimes I buy tools, but often I make them myself. Back in the days before commercial tools were available, turners knew how to harden steel and temper it. They made their own tools out of high carbon steel, or got them from the local blacksmith. The best way to harden steel and temper it is to do it properly by modern methods. This requires the right steel for the job, with careful control of temperatures and timing and the rates of heating and cooling. But acceptable results can usually be obtained using the cruder methods described here.

Tool steel

Turning tools are now rarely manufactured from carbon steel, but it is still used for many other purposes. Even for turning tools, it still works as well as it did when the old-time turners made their living with it. You can buy high carbon steel in various grades from steel stockholders, some suitable for hardening in water and others in oil.

Scrap carbon steel is easy to find. If you want to harden steel for tool making, springs, files, saw blades, masonry nails, crow bars, cold chisels, woodworking chisels, old screwdrivers, plane irons and many other things are steel that is suitable for reworking. I have used the tines of an old garden fork and the rings from old ball races. Keep in mind that if you put the tool under significant stress, steel that has or may develop cracks is unsuitable. For example, the valleys between the teeth of a file are weak points where cracks can start.

If you are using scrap, old steel is often the best choice because some modern steel alloys may not respond well to these basic heat treatment procedures. One way to tell what you’ve got is to touch the steel on a grinder. Lots of bright bursting sparks like a child’s ‘sparkler’ firework mean it is probably high carbon steel. Try a bit of mild steel such as an ordinary nail for comparison. It will also make a lot of sparks, but there will be fewer bursters. The use of the metal before it became scrap is a clue – if it was subject to a lot of stress, the metal is probably high carbon steel. But there is a continuum of carbon content – to be sure, test-harden a piece before making the tool.

Low carbon mild steel

Ordinary low-carbon mild steel is not suitable for most cutting tools. You cannot harden steel of that kind, and it will not keep a sharp edge. To harden steel, the metal must have a high enough carbon content. The metal is harder than wood, and a cutting edge on mild steel may last long enough for a one-off job. But if the edge is thin it will just give way under pressure. You can case-harden mild steel. This gives it a very thin layer of higher carbon content on its surface. Then you can use it for some light-duty cutting tools provided you don’t grind away the hardened skin when sharpening. To case-harden, coat the metal with a special compound before heating. You can use mild steel as a holder for inserted or brazed-on cutters.

Equipment needed

To harden steel, you must first make it hot. You can use a magnet to check that it is hot enough for hardening – when the magnet stops attracting it, the steel is ready. More simply, just get it red hot, which is also the temperature needed for hot forging. The bigger the piece, the more heat you will need. If the item is small, you can harden steel using a burner on a gas cooker. You can use a charcoal fire with a blower to supply air.  You can do a lot with a reasonably powerful blowtorch. Larger pieces of steel may dissipate the heat as fast as it is applied, never getting hot enough. If using a blowtorch, you can stack a few dry bricks to make an enclosure to retain the heat.

A simple forge burning solid fuel or propane is not hard to improviseThere is video on YouTube about making a simple but very effective propane forgeI made a forge that burned anthracite and worked 7/8 inch bar without too much trouble. More recently I made a propane forge using just two insulating fire bricks and a blowtorch, and was able to bend steel strip of about 2 inches width and 3/8 inches thick.

Hot forging

If you make two pieces of steel white hot, you can weld them together by hammering. Hotter still, the metal will burn and spoil. But these temperatures are harder to reach with the sort of equipment described.

If you want to do any hot forging, you will need something to use as an anvil, a hammer, vise and heavy pliers. You may also need a hacksaw, angle grinder, file, bench grinder and a drill press. To work thick steel, you will need heavier tools and a forge.  If it’s hot enough, it’s surprisingly easy to bend steel using a vise or wrenches, or to hammer it into shape on an anvil. You can forge ordinary mild steel in the same way.

Annealing

Some scrap carbon steel is too hard for sawing or filing into shape. You will have to anneal it to make it softer and workable. To do this, the first step is to make the metal red hot. While it is hot, you can forge it. Don’t try to work the metal when it has lost its red heat or it may crack. You have to strike while the iron is hot. After any forging, get the steel red hot again and then anneal it by cooling it slowly. The slower it cools, the better – traditionally the metal was left to cool buried in hot ashes. If using a propane forge, you can just leave the metal to cool in the forge so the residual heat will slow the cooling. You want the whole piece uniformly softened, so try to heat and cool it evenly.

When cooled, the annealed steel should be soft enough to file. Check that all parts are soft, then carry out whatever further operations you need. Shape the tool, including rough grinding the edge.

Harden the steel

To harden steel, heat the part to be hardened bright red hot again, if possible ‘soak’ it in the heat for a bit, then quench it. It’s the rapid change from red hot to cold that will harden steel. You can use various quenching liquids, but a bucket of water will usually do the trick. Plunge the red hot metal straight in, and swirl it about to cool it as rapidly as possible. If the steel warps or cracks when quenched, try using oil instead of water, or use different steel. If using oil, fire precautions are necessary. Use a metal container, not a plastic bucket. The hot steel will heat and ignite the oil, so have a metal cover handy to extinguish the flames.

You don’t always have to harden all parts of a tool to the same degree. If it must withstand stress in use, you can leave the bulk of it soft, for toughness and strength, with just the cutting tip hardened.

After quenching, the steel should be glass-hard and a file will just slide off it without cutting. Don’t try too hard with the file, the hard metal will soon make it blunt.

Tempering

The freshly hardened tool will be brittle. If you were to use it in this state, the edge could chip or it could shatter. For most purposes, you must heat it one more time to temper it before use. Tempering takes away the brittleness. It makes the metal tougher, but softer. The higher the temperature reached during tempering, the softer and less brittle the steel will become. Each tool has its own optimum compromise between hardness and toughness.

Before tempering, clean up the metal using abrasives. You want the steel bright and shiny for this stage. Warm the tool very carefully above, not in, a clean flame. Watch the bright metal surface carefully as it heats up. Let the heat start away from the edge and creep towards it, aiming for a uniform temperature over the surface. The edge and any other thin parts will heat up too fast if exposed to the heat directly.

Watch the colour change

As it gets hotter, you will see the bright steel change colour. It will go from silvery to a pale yellow, through brown to blue and then to grey. You have to catch the moment when the colour you want reaches the edge. Normally a pale yellow-brown colour at the edge of a cutting tool is about right for cutting wood, but different tools may need other colours. A blue colour will leave the steel tough and strong, but not hard enough to keep a cutting edge. (Springs are tempered to blue, and some steel components such as screws are blued for decorative purposes.)

Don’t let it get too hot

If you let the metal get too hot you will have to repeat the hardening stage. You can repeat the annealing, hardening and tempering without harm to the metal. But too long at high temperature can tend to burn out the carbon from the surface layers. When the colour is right, quench the tool again. It is then ready for final clean up and sharpening before being put to use.

Sometimes you need more accurate tempering, for example if you need a larger piece evenly tempered. You can do this by heating the item in an oven at a set temperature, or in oil. You will need a thermometer for these methods. They allow for soaking at the proper temperature, which may give better results.