Friday, 14 June 2013

Make your own sharpening disk

Do you have a problem with blunt tools? Do you hate to have to lug a grinder to demonstrations? If so, this may be an answer to the question you've not yet asked.

A sharp tool is safe; a blunt one is dangerous because a sharp tool does what you expect it to whilst a blunt one requires force to make it do the job; which is dangerous because it is not as predictable. Enough blurb, let's get on with the job.

  1. If you don't have a screw chuck, then it's worth making yourself one. You need a way of fixing a MDF plate to your lathe, and a screw chuck is the quickest. It's a block of wood with a screw through the middle. But any way you figure out for holding the MDF plate is fine, even if it's bolted to a faceplate.
  2. Glue a sanding disc to the MDF (I used wood glue) and leave it to dry for at least 24 hours in summer, or 48 in winter. If the glue isn't dry it'll be a mess. I'd suggest leaving it as long as possible. The MDF disc doesn't have to be round, and the centre doesn't have to be exact.
  3. Fix the disk to some mechanism on the lathe. I used a screw chuck, which is a home made piece of wood with a hole drilled down the centre and a screw through it. I hold the block in my 4 jaw chuck, but screwing it onto the faceplate would be as good if not better, but a little slower.
  4. Next I turn the lathe on and cut away the MDF to make a circle (it's safer than a spinning square).
  5. Now you have your sharpening system. Remove the tool rest, and keep the tool as low as possible, preferably under the centre. That way the disk pulls the tool from you, rather than pushing it at you. There is no chance of a dig in at the 6 o'clock position.
  6. Wear eye protection!

    Sparks fly off in all directions

  7. With a little practice you should be able to get those tools nice and SHARP. I used an 80 grit disc, but in hindsight I think a 120 or higher grit would have been better. I can glue a finer grade to the back of the disk and reverse it to just touch up the tools. The 80 grit seemed a big aggressive, but gave a good finish.

I hope this helps. It was quite fun to do. I should say that I had tried this before with a plain piece of glass paper, but the paper back dissolved in the glue and the glass grains fell off and was useless. So the key is obviously a good aluminium oxide disc.