I've lost count of the times when I have been mid project and thought, what I really want now is a nice big fat disk sander. With them you can make precise angles in wood and metal. You can produce brilliant outer edge curves, and very accurate circles. You can quickly remove material and flatten off stock that's too small to be safely planed, or thicknessed. You can sharpen tools, tidy up rough edges, deburr and square up, and do extreme toenail manicure (just in case you're insane, I'm not really recommending that last one).
In short, a disk sander is an awesomely useful machine to have in the shop!
Like most of my instructables, this one is mainly made from reclaimed materials.
Where is the bill of materials and tools used?? For this 'able it didn't make so much sense. a) because I'm using lots of strange materials that I have fished out of skips, and b) because I was experimenting with tools and techniques quite a lot. And c) if you're planning to build one you're going to read this all through and get an idea of what you need anyway based on what you already have available, right? I'll give tips on what might be useful reclaimed sources along the way.
If you're still not convinced you neeeed a disk sander, fly on ahead to the various steps on 'Use' to give you ideas and tips on what cool things you could do with one.
What makes a good disk sander?
OK so lets say you're thinking of buying one - what would you be looking for?
I'd say you'd want: a very strong solid base, good quiet, smooth and vibration free running, along with a perfectly flat and accurate work table with a parallel mitre slot. A tilting table seems like it would be a nice feature - but not at the expense of solidity. Something user friendly and safe - safety is obviously important.
Personally I'd want it BIG too. 500mm (20") abrasive disks are about the biggest economically available here in the UK, so that seems a good size to aim for. Having a nice big disk doesn't just mean you can sand bigger stuff, it also means you have a bigger range of abrasive speeds. That is, you can vary the material removal rate by choosing how far out from the centre of the disk you present the workpiece: towards the outer edge will be exceptionally aggressive, with the abrasive moving many times faster than say half way out.
When we look at fulfilling all those requirements in a bought machine, the cost is over £1.5k - which is quite a bit (eeeek!) - so lets make one from some rubbish!
I started with a 1kw single phase induction motor that I rescued from a broken floor scrubber/polisher we found in the skip. I was well pleased when I got it home, dried it out, and tested it. It went really well with very little vibration or noise, running at 1450rpm. At that speed, at the edge of a 20" disk, the abrasive will be travelling at roughly 38 meters per second - which is very fast!. But not too fast :D
This motor had a face mount, the design would have varied quite a bit if I was basing it round a foot mount motor.
I did some modification and used the housing/flange mount that came with the motor. To sit the motor horizontal I needed to support the rear end of the motor with something. For this, I glued two ply pieces together and routed a circle in them. Follow along with the notes on the photos for the whole story.