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Grinder platform angle setting jig

Sharpening is one of the essential skills for woodturning. Most turners use a grinder to sharpen tools, and platform sharpening is probably the best method for skews and scrapers. But each type of tool needs a different grinding angle, so a grinder platform setting jig for each angle is very helpful. For example, a skew chisel will usually have a more acute angle at its edge than a spindle roughing gouge, which in turn will have a finer edge than a scraper.

Each of these tools can be ground while flat on either the grinder’s own tool rest or a separate platform rest, which just has to be set to the correct angle. One way to do this is to blacken the existing tool bevel with a marker pen then adjust the platform until the bevel comes into full contact with the wheel, which is inched round by hand so that the ink removed will show the accuracy of contact. Or you can just match the bevel to the wheel by eye, looking from the side. But in either case, any error can be cumulative. It will be repeated and possibly amplified next time the tool is ground. This can lead to a gradual change in the bevel angle.

I use an easy-to-make grinder platform setting jig that gives a consistent, repeatable result very quickly. It consists of a scrap of plywood with two projecting screw heads that align it to the wheel rim, and a straight edge at the bottom to which the platform can be set. The jig is very easy to make and use. A different one is needed for each tool type and thickness (thicker blades contact higher on the wheel rim and because of its curvature will be ground to a sharper angle than thinner ones). Use plywood thick enough to take the screws in its edge without splitting, but no dimensions are critical. All you have to do is set the platform angle as you wish, perhaps copying an existing tool angle, then cut the plywood so it rests on the platform with its edge fairly close to the wheel rim. Insert the two woodscrews (as far apart as the wheel guard and platform will allow, and angled so they are radial to the wheel axis. Drill pilot holes to prevent splitting.) The screws are optional, but if used, they can be turned in or out to fine tune the fit or to compensate for wheel wear. If necessary, the inner edge of the plywood can be cut away to follow the wheel rim more closely.

To use the grinder platform setting jig, loosen the platform, place the two screw heads in contact with the stationary wheel rim, bring the platform into contact with the bottom of the jig and tighten up again. Every time you sharpen the same tool, or another of the same blade thickness, the angle will be just the same, making for quick results and saving tool life.

 

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Wet sanding is messy, but prevents dust and clogged abrasive

I recently did some wet sanding to improve the surface of some sycamore bowls that already had a Danish oil finish that had dried a bit rough. I used fine ‘wet or dry’ abrasive with white mineral spirit as lubricant and got some good results. After wiping clean, the surface was silky smooth. I applied some more finishing oil afterwards and they are now ready for buffing. Today I have been making some lignum vitae boxes out of old bowling balls. Lignum vitae is a very hard wood with a waxy content that clogs sandpaper like the dried oil finish on the sycamore bowls. I tried wet sanding here too, using water this time. I just held a wet bit of kitchen paper to the freshly turned surface at the same time as the abrasive. You could use a spray bottle. The result was lots of mud that sprayed off and made a mess of my turning jacket, but a very good surface was quickly achieved on the wood. No dust and no clogging. I started at 180 grit, then 240, and finally 320 which gave a fine matte surface ready for further treatment. It is important to use good quality¬†abrasive, particularly if using ‘wet or dry’ silicon carbide paper. The cheap grades tend to shed particles and leave black specks embedded in the wood surface.

It was club night at my turning club last night. There was an interesting demo of making a spalted birch log into a hollow vase. The wood was very poor – I would have thrown it out – with advanced spalting and terrible tear-out. But the finished product was surprisingly good. The demonstrator used lots of quick-drying cellulose sanding sealer to harden the fibres before final turning to shape. Sanding with an unpowered rotary sander made lots of dust but left a quite reasonable surface.