Shopmade Disc Sander Advice Needed

[Tom Porter]

Several years ago, I bought a used jointer and the seller had an extra motor he threw in for free. I've never needed the motor for the jointer. The label on the spare motor is illegible but it appears identical to the one installed in the jointer and that label is legible. I'm considering using the motor to make a disc sander. If I have an area of expertise, this isn't it, but I have an idea how to do what I need. However, I need a little advice. The motor is 0.625 HP with an RPM of 3450. That seems a lot faster than most commercial disc sanders. Am I asking for trouble? If the major drawback is that this thing will be very aggressive as a sander, I can live with that. If it's possibly dangerous, that's another matter. And as long as I'm asking questions, how large a disc can I get away with? Obviously, I'm not thinking about a 3 foot diameter disc or some such insanity but 16" would be pretty cool.

[Bill Dufour]

I made a 12 disk sander but 1/2 that rpm. get the largest pulley you can find. drill 3-4 holes near the rim. I took a piece of solid core door, cut a circle on the bandsaw, and bolted it to the pulley nice and flat. Turned the outer rim round with a lathe chisel and glued on a sandpaper disk.

[Richard Coers]

You better calculate the surface feet per minute for a 16" disc at 3450rpm. You will likely have a sander that is hard to start because of the disc mass. You will need a balanced disc or else the sander will want to walk at that higher speed. You will have a sander that will burn just about every wood species, if not with a fresh disc, it certainly will once the disc is even slightly dull. That kind of speed will dull the abrasive quickly from the heat and the discs will quickly be fouled with resins. This will be even worse for finer grits of abrasive. Heat kills sanding discs. Do some shopping, the cost of 16" discs are quite pricey. I have a commercial 20" sander, I have the experience.

[Tom Porter]

Yeah, that's my concern. High RPM in the middle is going to lead to really high speed at the edge of the ring. Pretty much the reason for my question. I'd like to have a disc sander and hate to have an unused motor just sitting around collecting dust but I also don't want something that's more trouble than it's worth. Of course, if I were to build it, I bet my jointer motor would quit immediately after that and I wouldn't have a replacement.

Thanks for the advice.

[Mike Henderson]

You don't need to mount the sanding disk directly on the motor. Get a shaft and a way to mount the disk on that shaft. Then use pulleys to give you control of the speed of the disk. You could get two stepped pulleys so that you could experiment with the speeds and choose the speed that works best for you. I made a shop-made disk sander and used 12" disk just because they're easy to find. But it depends on what you plan on sanding with it. I only do small stuff.

Mike

[Chris Fournier]

I like where you're going with that motor as a disc sander project - projects are great fun! I have a General 100-5 disc sander that I restored from the castings up and it is a super valuable piece of equipment in my shop for wood and metal. If I have learned anything over the years it's that heavy machines are good machines especially if you're planning to spin a 16" disc! I'd suggest that a restoration of a 16" disc sander would be the best way to get a useful machine and save this motor for another project. Not to be a naysayer but even those import 12" rigs are next to useless in my opinion. Too light, too much vibration...

[Tom Bender]

That speed and hp is an unworkable combination. You can however build a lower speed sander as Mike suggests. If you belt it down to 1/4 speed is should work ok. And you can change for a bigger motor later. At 900 rpm a 16" to 20" sander should be good, though not for major stock removal. The disk is where to focus, it should be very flat and fairly heavy.