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Lathe maintenance

It’s easy to overlook the need for lathe maintenance. That applies to other workshop equipment too, here is my post about dust extractor maintenance.

Recently I have noticed a problem with my lathe. The tail stock has become harder to move, and so has the toolrest holder (the ‘banjo’). I tried lubricating the bed, which helped, but it was still not as it should be. The movements should be as near effortless as possible. Time for some more serious attention!

Closer examination revealed a deep scratch along the bed. A bit of grit must have got caught under the tail stock. I could feel the raised metal along the line of the scratch. The bed of my lathe is steel, not hardened. I don’t know if a cast iron bed would be affected the same way. The underside of the tail stock had a corresponding scratch. I removed the raised metal from both quite easily with a coarse diamond hone. With a little lubrication, the tail stock now slides freely.

The scratch did not go as far as the part of the bed where the banjo normally sits. But I used the hone to clean that part of the bed too. The underside of the banjo felt smooth, but I dressed it gently with a smooth file. With lubrication, that moves much better now. I cleaned the thread of the locking lever with a wire brush, and oiled it. I also adjusted the tension of the cam lock. That was just a matter of tightening the nut below the clamping plate enough to let the banjo slide without sagging too much.

The toolrest

Another bit of lathe maintenance that should be routine is to dress and polish the top of the toolrest as often as necessary to make sure the tools slide smoothly. Some people rub a bit of candle wax on the top. That helps, but I find it forms small lumps that the tool has to jump over.

I made an oiler to lubricate the toolrest. It’s just a short bit of steel tube containing a roll of fabric sticking out at one end, with a wooden stopper at the other. I put machine oil in the tube to saturate the fabric and it lives on a magnet on the tail stock. A quick wipe of oil on the toolrest, or sometimes on the tool itself, makes the tools slide easily, and there’s not enough oil to make a mess. The late John Jordan once said that lubricating the toolrest is the only thing that can make you a better turner without having to practise. Being able to move the tools without friction or other resistance makes it much easier to achieve the intended shape in the finished turning.

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Spalted beech

Back in 2020 a large beech tree fell in a storm. It was growing in a private garden in Mill Hill, and I was able to get a lot of useful timber from it. The tree was rotted at the base, so it was no surprise that it fell. Higher up, the fungus had caused some spalting, and I used the wood from this part of the trunk to make a number of bowls. The branches were still sound, unaffected by the fungus. With a friend, I cut them to manageable lengths and stacked them in a patch of woodland on site. We wanted more spalted beech, so we put them on a bed of dead leaves on the ground. We covered the pile with more dead leaves because we wanted to slow the drying. This would encourage fungal growth and at the same time minimise splitting.

The branches (small logs) ranged from about 175 mm to about 250 mm in diameter, and up to about a metre long.

The harvest

Now, more than two years on, nature has had more than enough time to do its work. so we opened the pile and made some test cuts with a chainsaw to see how the logs were getting on. Sure enough, they were all spalted. Today I started work on some of them back in the workshop.

Here are some of the logs that I brought back. They are still quite wet, but much lighter in weight than before. They smell strongly of mushrooms, and their bark is loose and soft in patches.

Some of the logs really looked as if they had been lying on the ground for a couple of years

Processing spalted beech

I began by cutting each log down the middle using a band saw. This was my first real sight of the spalting. There was some cracking at the ends, but I was able to trim this off without too much waste. It helps to cut thin slices and flex them. Any concealed cracks then show up. I then cut the halves into chunks for bowls, and the bits that still had cracks I cut into spindle blanks. They will end up as boxes, decorative cones or bud vases. The smallest offcuts I shall turn into wooden mice.

This is one of the short log sections that I cut while it was standing on end. The spalting looks promising. Hanging under the bandsaw table is an old wooden clamp that I use to hold round timber. Cutting round timber on the bandsaw without clamping can be hazardous because the blade can make it roll and jam. Cutting centrally along the length of the log is safer because the force of the cut doesn’t make the log roll.

A short log cut while standing on end

Not too bad, though other logs were better

The spalting in the other logs varied. Here are some examples. Some had zones of colour, others had the typical wandering black lines. Beech is one of the best woods for spalting, and spalted beech is great stuff!

This piece has some soft patches but should still be usable.

We cut this crotch section on site with the chainsaw

The fungus and spalt lines can sometimes be visible directly under the bark.

The same block after roughing out shows the lines more clearly. I like the zigzag pattern.

Some of the blanks, showing the zones of colour

The roughed out bowls ready for drying

Below is the pile of 30 spalted beech bowls roughed out. I had to reject 3 or 4 because they had soft patches that would have been very difficult to turn to a good finish. Two years was really a bit too long to leave the logs, but you don’t know what you have until it is processed. No doubt the results depend a lot on the weather conditions – warmth and rain probably speed the fungal growth.

I’m happy with this lot though. After they have dried, which will take at least some weeks, they will go back on the lathe for their second turning. I look forward to the finished result!

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Getting rid of sanding scratches

Many bowl makers use sanding discs in an electric drill to sand bowls. The idea is to start with a coarse grit disc, then use a succession of finer grit discs to remove scratches left by each previous one. Each disc leaves its own scratches, getting finer and finer as you work through the sequence. But it can be hard to tell whether a scratch was made by the current disc or the previous one. If you sand with 120 grit, then go on to 180, which disc are the scratches from? If you go from 120 to 100 or 150 grit, those discs will be more effective than the 180 at getting rid of sanding scratches. But the smaller the interval, the harder it will be to tell them apart.

Sometimes you can overlook the deepest scratches until the last stage, or even until after you have applied the finish. If you miss the deep ones from the coarser disc they can show badly later.

There is a simple method to distinguish between them. A particle of grit on the upper part of the disc will be moving from left to right as the disc spins clockwise. If the part of the bowl being sanded is moving upwards in the lathe, the scratch that particle makes will run diagonally from top left to bottom right. The angle will depend on the relative rotation speeds – running the lathe slowly will make the angle easier to see. If you reverse the rotation for the following disc, its scratches will run from top right to bottom left. When you can’t see any scratches running the other way, that disc has done its work. Reverse the rotation again and go on to the next one.

You can reverse either the lathe or the drill to give this result. You can also switch between the upper and lower quadrants of the sanding disc. Either way, you will be able to spot deep sanding scratches more easily.

Another benefit is that reversing the direction helps remove projecting fibres. This applies also to hand-held sandpaper, which leaves vertical scratches. This method of getting rid of sanding scratches is not applicable to hand sanding.

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Sharpening band saw blades

Band saw blades last quite a long time, but they don’t stay sharp forever. Probably most people throw them out when they get too blunt to use. They just put in a new blade. That makes sense. Who has time for sharpening all the teeth on a band saw blade?

A blunt blade isn’t safe (though nor is a sharp one if care is not taken!) because it makes you push too hard to force the cut. Blunt blades shouldn’t be used. Re-sharpening means a potential saving in cash if not in time. And it can save delay if you don’t have spare blades to hand.

My Startrite 352 has a blade 112″ long, and I normally use a 3/8″ or 1/2″ blade with 3 teeth per inch. That’s 336 teeth per blade. Despite this, I like to sharpen them. It only takes a few minutes, and the sharpened blade cuts about as freely as a new one.

Reasons not to re-sharpen blades

I can’t sharpen the teeth very accurately and uniformly without proper equipment, so the re-sharpened blade is not as good for precision cutting. But that is rarely necessary for the rough work I do. It would be possible to make a jig with a click detent to ensure proper tooth placement, and stops to limit the grinding depth. Sharpening does reduce the amount of ‘set’, so the kerf will be narrower.

The blade isn’t new after sharpening. Blades eventually break, sooner if they are thicker and the bandsaw wheels are small. Metal fatigue makes the blades brittle. There is usually some warning that a blade is about to break. A crack develops, and you may hear it clicking as the crack goes through the guides. You may also see the blade moving backwards and forwards in the guides when not actually cutting. If you carry on cutting, there will soon be a loud bang as the blade breaks. A bit scary, but it never seems to do any harm. If you re-sharpen a blade it will extend its life, but you are then more likely to have it crack and break in use. It’s possible to repair a broken blade, but the whole length will be brittle and I don’t think it’s worthwhile. It will soon break again.

Sharpening options

The teeth on the band saw blades I use alternate with left set, no set and right set. They are all sharpened straight across at 90 degrees to the blade body, regardless of their set.

Over the years, I’ve tried various methods for sharpening band saw blades. Here are some of the options.

The first choice is whether to sharpen the blade in the machine or out of it. Doing it in the machine means the blade is held securely and can be moved on to the next tooth without losing alignment. However, access is better when the blade is removed.

Sharpening in the machine

Hardened teeth cannot be filed, so grinding is necessary. You can grind the leading face or the back of the tooth. You can use a small diamond or carbide burr in a Dremel tool inside the tooth hook. I found that the diamond burrs wear quite quickly. If you choose their diameter to suit the tooth shape, another blade may have teeth of a different profile. You will probably have to work from the right of the blade (access may be difficult from the left), which means the burr turns toward the point of the tooth. That makes it prone to climbing over the point, which damages the tooth. I’ve also tried cylindrical stone grinder points, but they wear too rapidly even if you slide them across the tooth to even out the wear.

This method allows you to put the burr into the tooth gullet and use it to lift the blade to the next tooth during the sharpening of the first tooth. They are quite fast and effective when all is going well. But if the burr is too small, it’s easy to grind the hook without actually touching the point. The tooth is pointing down, so not easy to see the result of grinding. If the burr is too big, or you slide it to reach the point, that’s when it climbs over the point and ruins it.

Grinding the back of the tooth

The back of the tooth can be touched up in the machine too. You can use a small grinding disc in a Dremel to cut back the point until you remove the wear. This can work well too. The difficulties are maintaining a consistent angle, taking off the same amount from each tooth, and making sure the following tooth doesn’t touch the grinder until it is in the right position.

If you grind a tooth more than its neighbours, it won’t touch the timber so won’t do its share of the cutting. I’ve found it very easy to take the point off the following tooth by mistake. You need a steady hand, but you can make up a simple jig to hold the Dremel. It can slide along the fence or in the table T slot. This controls the angle, but doesn’t stop you taking too much off, and the blade has to be advanced manually to get to the next tooth. Again, I found it easy to grind the point off by mistake. Here is an example of such a jig.

Visibility is better when grinding the backs of the teeth in the machine.

Sharpening outside the machine

If you lay the blade on a flat surface you can sharpen either the hook or the back of the tooth, using a Dremel. You can see what you are doing, and I found it easier to avoid mistakes this way. The burr can run off the tooth points, so is less liable to spoil them.

I preferred to use a bench grinder for sharpening band saw blades. I set the grinder platform to 90 degrees and turn the grinder at an angle to the bench top (making sure it is secure) to allow the blade to take the proper angle to the wheel. You can easily make an angle setting jig to ensure accuracy. An error in the platform angle might cause the blade to drift when cutting. Depending on the position of the grinder you may not have to turn it.

Then I hang the blade over the platform at an angle to suit the tooth and touch the back of each tooth against the wheel. This is a quick process and visibility is good. If I rush too much, mistakes do happen, but a small number of badly ground teeth have little effect on performance. Even with a fine wheel the grinding action is aggressive, so a slow speed grinder would be ideal.

I found a thin grinding wheel and set it up in the lathe. With a diamond wheel dresser, I shaped the wheel profile to fit the tooth gullet. Then I could drape the blade over the toolrest, set at the proper angle to the wheel, and quickly sharpen each tooth. This worked better than using the bench grinder, though it was necessary to rig up supports to keep the blade horizontal.

I have now started to use a cheap chainsaw sharpening machine (which I bought to sharpen chainsaws, but it didn’t work very well for that). It has a click detent for moving the blade along, a slot for the blade to fit in, and an adjustable stop for the grinding wheel. The machine is largely made of plastic and not made to high precision. None of the adjustments are very repeatable. But the grinding wheel comes down at the right angle to sharpen the tooth gullet, and the indexing is quick. It should be possible to improve the repeatability. Even as it is, the result is the best yet. The sharpened blade cuts smoothly and well.

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Chuck sizing template for bowls

Chuclk tenon sizing template

This is a very simple workshop aid. So simple that I hesitated to post about it. But it eliminates the risk and possible errors associated with using dividers. I made some of these chuck sizing templates to help beginners during my bowl turning classes, but they are so convenient that I now use them for my own work too.

A chuck sizing template helps you to make the chucking tenon or recess on a bowl the right diameter for the chuck. It should fit when the chuck jaws are almost closed, because that’s when they have the best, non-marking grip.

The usual method is to use dividers set to the correct diameter to scribe a circle on the work. If the dividers are set correctly, if both points fall on that circle and if the points are on the diameter (that is, not too high or too low on the work), the circle will fit the chuck. This method works well, but takes practice. It can be risky, because only the left point should touch and it’s possible for the points to catch in the spinning wood.

As an alternative, I made some templates from offcuts of 6 mm MDF. They are just small rectangles, with widths to suit the chuck jaws. You could add a millimetre or two to the ‘correct’ size to give some allowance for error when cutting the tenon or recess. They aren’t adjustable, so each set of jaws needs its own templates for marking a tenon and recess.

Using the chuck sizing template.

The end of the template has a mark in the middle. I hold that mark to the centre of the spinning wood, which can be highlighted with a pencil if necessary. Then I use a pencil to make a circle the same diameter as the template’s width.

It only takes a moment to mark the circle. And it’s the same each time with no need for measurement or setting dividers. You need separate chuck sizing templates for each set of chuck jaws. But a benefit of that is you can try the templates against the bowl blank to select the best size.

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Drying bowl blanks

Drying bowl blanks on racks indoors

Probably most bowl turners generally use blanks cut from green wood. They either make green turned bowls or rough outs to be turned again when dry. Some work with dry, seasoned timber, from which a bowl can be made in one session. Drying bowl blanks for that purpose may be easier and quicker than you think!

Most of my own work uses green wood. But in my bowl turning classes I rely on dry bowl blanks that I buy from turning suppliers. My students generally work with a blank of about 7 inches by 2 inches (175 mm x 50 mm), which I find is a good size for a beginner to make a useful small bowl. These blanks cost a significant amount, and sometimes turn out to have defects. So I now make my own. Cutting and drying bowl blanks is a process that I quite enjoy.

Cutting the blanks

I start with a log big enough to yield the size needed. 250 -300 mm diameter is useful, and as long as I can handle. The longer the better because there is always some waste due to end splits, but I don’t have lifting equipment. I use a small Alaskan chainsaw mill and my band saw to cut planks. There are plenty of videos on YouTube showing these mills in use, and even how to make them.

My mill is a commercially made one. I made a simple wooden “ladder” that I attach to the log. The mill slides along the rails as the chainsaw makes the first cut, clear of the pith which is the main source of cracks in the timber. The saw cuts straight, leaving a flat surface that guides subsequent cuts. I use an inexpensive electric saw from Screwfix. It’s self sharpening, which is very helpful, because ripping is tough on the saw and grit in the bark soon blunts it. I haven’t found it necessary to use special ripping chain.

On larger logs, I use the mill to make further cuts, but if the pieces are manageable I take them to my Startrite 352 band saw. On the band saw, I trim the pieces to about 180 mm wide, then saw planks 50 mm thick. I turn the log to its best orientation for maximum yield, and can usually go on to saw spindle blanks from the off cuts. The saw is somewhat underpowered, but does a good job as long as the blade is sharp. It’s quicker than the chain saw and makes a narrower kerf, minimising waste. I use a 12 mm 3 TPI blade.

Drying the blanks

I seal the ends of the planks with two or three coats of PVA, then stack them outdoors under cover, with spacers to allow air to circulate. After a few months, I cut discs from the planks, cutting clear of any cracks that may have developed. I microwaved a few discs in an attempt to speed drying, but not only was this a slow process, those discs all split. I allow the other discs to finish drying indoors, but don’t seal the edges or give them any other protection.

Until I tried drying bowl blanks like this. I would have expected all the discs to crack. But the process has been very successful. The woods I have used so far are apple and oak (both from standing dead trees, so probably already with a reduced moisture content before planking), ash and cherry. I weigh the discs at intervals until they stabilise, which seems to take about three or four months. I now have lots of bowl blanks either fully air dry and ready to use, or well on their way. Hardly any have cracked, and those used in my classes have been very satisfactory. All are similar in size. It may be that the process would not be so successful if the blanks were larger.

Some of the blanks warped as they dried, but I expected this. They are still usable.

Encouraged by this, I sawed some beech and cut some of the planks into discs immediately with no preliminary drying. Most of those discs cracked after about three or four weeks indoors. No surprise there!

It remains to be seen whether the beech planks now drying outdoors yield useful material. But I should be able to cut spindle blanks, if nothing else.

Conclusion

I shall continue to experiment, but at this stage my conclusion is that the discs should not be cut from wet wood. Some preliminary drying is necessary, but the planks don’t have to be fully dry. The total drying time is measured in months, not years. 

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Dust extractor maintenance

I’ve written before about the need for regular dust extractor maintenance. An extractor with a filter is not ‘fit and forget’. My extractor is a cyclone unit and since I removed the internal wire grid that avoids the low risk of accidental contact with the fan, it is less prone to blocking up. After considerable use, it still seemed to be working OK. But when I checked the filter recently I found a great deal of fine dust in it. After cleaning it, the extractor worked a great deal better. Not really a surprise!

The deterioration in performance had been so gradual that I had failed to notice it. I needed an objective measure of performance and a proper dust extractor maintenance schedule. Just putting my hand in front of the inlet now and again to see if there is still suction is not good enough.

Measuring air flow

Performance equates to air inlet velocity and filter effectiveness. Dust build up in the filter actually improves its effectiveness, but it cuts the air flow. The flow can be assessed by measuring the vacuum in the pipe. A vacuum gauge permanently installed as part of the system, with an easily visible readout, would be ideal. However, I opted to measure the speed directly with an anemometer. A digital anemometer can be got very cheaply. I bought this one from Amazon.

It was impossible to get a consistent reading from it just by holding it in my hand. I folded a bit of steel strapping to make a holder for it, with a hook that clips on the edge of the extractor inlet to secure it at a fixed short distance inside. I take it out again after each reading.

The reading itself is less important than changes in the reading over time. So I noted the indicated air speed just after I had cleaned the filter. I can take further readings at intervals as dust starts to build up again. This will tell me how long it takes for the speed to drop by, say, 20%. Then I can schedule a regular filter clean in my calendar.

It was interesting to see how far from the inlet the suction extends. The answer is not very far at all. A small diameter inlet is only effective when very close to the dust source, which is not easy to achieve at the lathe. The 7 inch inlet I have at the lathe does provide quite good air flow at the tool tip where the dust is generated.

Cleaning the filter

Cleaning the filter was straightforward. I took the cartridge outdoors and stood it on end. Tapping it with a wooden batten dislodged the dust cake and it fell to the bottom. In some places the pleats were close together, and those areas took more tapping. I also used compressed air. At first, the supply of dust coming from the filter seemed almost infinite, but eventually it slowed down.

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Improved bowl depth gauge

Something you definitely don’t want to do when hollowing a bowl is cut too deep. Less disastrous, but still a problem, is not cutting deep enough, because too much wood in the bottom leaves the bowl too heavy. Many turners assess the thickness of the bottom by feel. But on larger bowls, fingers don’t reach far enough. Even calipers, like these, don’t measure the thickness where the chuck prevents access. So a depth gauge can be useful when making bowls.

Parallax error

The simplest depth gauge is just a pencil. You sight across the rim of the bowl, put the pencil in contact with the deepest point, then grip it at a point that is in the same plane as the rim. Then you hold the pencil against the rim and sight across the bottom of the item. This works, but parallax error means it’s not very accurate. And if the chuck jaws are in a recess, you can’t see how deep that recess is.

A sliding dowel set in a crossbar will measure the internal depth more accurately. Such a simple depth gauge is very easy to make, and lots of turners use one. But there is still the same difficulty when assessing the amount of wood remaining in the bottom.

When making this gauge, drill a hole the same diameter as the dowel in a bit of scrap to make the cross bar. Saw a slot along the crossbar, dividing the hole and going an inch or two beyond it. Insert a screw (not visible in the photo below) on each side of the dowel to adjust the grip so the dowel is held with just the right amount of friction.

Make a measuring stick to suit the chuck

Using the dowel gauge with a separate measuring stick can greatly reduce error. Cut a wooden rod to length so that when placed in contact with a suitable fixed point, it extends about one inch beyond the chuck jaws. That fixed point may be most convenient if it is on the headstock, but it need not be as long as the distance from it to the jaws is constant. The contact point must be far enough off the lathe axis for the rod and dowel to clear the rim of the bowl while they are parallel to the axis. For wider bowls, or if the front of the headstock does not have a vertical surface, something standing on the lathe bed could act as a reference point for the stick, as long as it’s always put in the same position.

Mark a scale with 1/8 inch intervals on the last inch of the rod, beginning exactly level with the outer face of the jaws. You may need a separate rod for each different chuck.

Using the improved depth gauge

Place the crossbar across the rim of the item and adjust the dowel to touch the deepest point. This tells you the internal depth. Move the gauge so the dowel is outside the bowl, with the crossbar still touching both sides of the rim. The crossbar must be long enough to enable this. Put the measuring stick next to the dowel. The scale will then show the thickness of wood remaining above the chuck jaws.

Improved bowl depth gauge
This bowl has 1/8″ of wood remaining above the chuck jaws

You can also use the rod to preset the dowel in the crossbar. When the bar touches the rim, the bowl depth is complete.

If the jaws are in a recess but don’t bottom out in it, or if the inner surface of the recess is not flat, an allowance has to be made.

 

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Taking up woodturning

Using a lathe, you can make objects that are both beautiful and useful, often taking only a few minutes from start to finish. The process is fun, and no other form of woodworking is so immediate in its results. But if you are thinking of taking up woodturning, how do you start?
There are four things you need to become a woodturner: a workspace, the equipment, some timber and the necessary skills.

The workspace

This you probably have already, or you would not be considering taking up the craft. The space determines what you can do. Woodturning can be messy, and you need somewhere to store materials and valuable equipment, so the workspace is the first thing to sort out. A proper building that is secure, insulated, heated, powered, dry and well lit is ideal. But most people get by in a garden shed, basement or garage, and do great work.
Whatever you have, do your best to allow nothing in your workspace that does not relate to turning – no bicycles, lawnmowers etc. They take up the space that you as a turner will need, and detract from the proper dignity of the craft. And unless your workspace is large, try to find somewhere else protected from the weather for the wood pile.

The equipment needed for taking up woodturning

When you are taking up woodturning, the essentials are:
  • A lathe with a stand or a bench, and a chuck. The lathe should be the most substantial one possible. If you start with a cheap, flimsy machine, you will soon want to replace it. If space and budget are limited, a good quality mini lathe is fine, though it will restrict what you can do. A good used machine is much better than a poor new one.
  • A grinder for sharpening. Blunt tools will not give you the results you want.
  • A sharpening jig for gouges, though you can learn to sharpen gouges freehand if you take the trouble.
  • Some basic turning tools – a good start would be a small spindle roughing gouge, a 3/8″ spindle gouge, a small and a larger bowl gouge ground at different angles, a square nose scraper, a round nose scraper and a parting tool
  • An instructional DVD or book.
  • A face shield and dust mask
  • Sandpaper and the usual workshop tools – screwdrivers, power drill, tape measure etc.
With these, you can make bowls and vases, boxes, all kinds of spindles, and lots of shavings. Later, you may need a bandsaw, a chainsaw, a drill press, a dust extractor, power sanding equipment, additional turning tools, buffing equipment and lots more. No woodturner ever has all the equipment they would really like.

The materials

In the beginning, you can buy ready-made turning blanks. It’s what many people do when first taking up woodturning. But this is the most expensive way to buy wood. It is better to convert small logs and branches to turning blanks yourself, at no cost. You will enjoy turning unseasoned timber, and found timber can be the most beautiful. A band saw will pay for itself. You will soon find you have more timber than you can turn, and will need somewhere to store it, protected from the weather while it seasons.
For practice, almost any timber will do. But it is easier to turn wood that is straight-grained, free of large knots, decay and splits, and not too hard. It’s a mistake to buy tropical hardwoods when you are starting out. They are beautiful, but harder to turn than species such as oak and ash, which are just as attractive.
You will also need finishing materials, such as a can of danish oil.

The skills

A turner must be able to prepare the wood, sharpen and use the turning tools properly, and come up with pleasing shapes for the finished items.
When you are taking up woodturning, you have to develop these abilities. Study the books and magazines, watch the DVDs, take lessons from me or anyone else with the experience, and join a turning club. If you practice, you will improve. Practice some more. Eventually, practice makes perfect. Learn from people who have gone before, then go your own way to establish your own style.
There are two options for a turner. Some people use a lathe simply as a means to an end. They use any turning methods that get the result they need. As scraping tools are comparatively easy, that’s what they use. It’s a pragmatic approach that can make a lot of sense. With a little practice, and on suitable timber, scrapers can give excellent results. But they can sometimes leave a very poor surface, so that heavy sanding is needed. This can show in the finished product.
Others set out to learn the more difficult tools – gouges and chisels, as well as the scrapers. They value the craft for its own sake. These tools are quicker and more versatile in use. There are very competent turners who rely on scrapers and get great results. But getting to grips with the other tools pays off in the end.
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Homemade calipers are helpful when turning bowls

Getting the wall of a bowl the right thickness is very important. The wall doesn’t have to be the same thickness all the way down, but it must look right and feel right. An experienced turner would likely rely entirely on their sense of touch and not use calipers at all, at least for small bowls where their fingers can reach the bottom. But calipers can help, and simple, non-adjustable homemade calipers are useful. They are quick to make and use. Calipers are, of course, normally adjustable, and made of steel. But adjustability is only necessary if you need to get the wall to a specific thickness. I find that when using ordinary steel calipers to check the wall of a bowl, I usually set them to more than the thickness required anyway. By watching or feeling the gap between the point and the wall, I can tell how the thickness changes. I made a batch of these non-adjustable ones to help with the teaching I do at the Camden Town Shed, where money for equipment is limited. I often use them instead of normal calipers in my own workshop too.

Material for homemade calipers

I used scraps of 6 mm MDF. This is unlikely to scratch the finished surface of a bowl. But with care in use, other materials would be fine. Dimensions are not at all critical, as long as the central cut-out is big enough for the caliper arms to reach down to the bottom of the bowl. They could be made in any size.

Making the calipers

I cut the blank to a circle with a band saw and found the centre. I then pinned the disc to the jaws of a chuck with the tailstock. This is a very quick method of mounting thin discs in the lathe. Friction from the chuck jaws drives them. I trued up the edge of the disc. Turning MDF is dusty work, but very easy with a scraper. Then I marked an off-centre circle and cut the middle out with the band saw. The entry cut is at the narrowest point. I sanded the inner curve with a drum sander, but this, like the turning, is purely for appearance. Hand sanding, or no sanding, would work just as well.

Then I enlarged the entry cut and sanded the points. The gap should be a little more than the likely wall thickness, say 12 mm for walls of 10 mm. The size of the gap is not critical, but should not be too big. Although these calipers have no adjustment, it would be easy enough to cut them in half, glue  a couple of scraps from the centre cut-out to sandwich the wide end of one of the halves, and drill for a small bolt, washers and wing nut.

When one arm slides down the bowl’s inside wall, the gap between the other arm and the outside of the bowl clearly reveals changes in thickness. I drilled a small hole for hanging the caliper on a nail – it slips off if the large hole is on the nail.

homemade calipers