Sunday, September 13, 2015

DIY Disc Sander

Last year I bought an old DeWalt radial arm saw, and I broke the motor mount while trying to disassemble it. It looked like the aluminum casting had a void in it - and tapping on it with a hammer didn't help.

I figured I couldn't use the motor in the hanging orientation, but if I flipped it upside down it would still work for something. I drilled through the casting in a couple of places and put inset screws to make the mount solid.

I decided it would work well as a disc sander.

I bought a buffing plate from Harbor Freight for $4. I comes with the same 5/8" threaded arbor mount as the saw.

I put it on tight, then added the arbor nut to make sure it would stay that way. I mounted a 3/4" plywood disc to the plate and turned it until was well-balanced and just over 10" in diameter. It has almost no vibration, lending to a very heavy motor, mounted on a large plywood base.

I added a worktop with a 2" vacuum port. It's boxed-in around the disk to capture all the sawdust.

You really need dust collection on these, or you get quickly get a lot dust in the air. I made the table removable (of course), and also slightly adjustable. This way I can set the gap between the table and the pad to get the best vacuum. It's currently at about 3/16 and works great - no dust escapes. I have learned to leave some air gap when making vacuum baffles like this to keep the air velocity up.

The motor is 1/2 horsepower (10 amps / 120 volts) and 3400 RPM.

By my observation, and I've checked on it - older motors have a lot more actual power for the stated HP rating than new ones. Old ones where typically under-rated for the working power, and new ones are often a bit over-rated for "developed" power - apples and oranges. So a 60 year old 1/2 HP motor that runs well is going to be more like a 3/4 or 1 HP new motor. Just my opinion - buy old and buy American when ever you can.

For this set-up, the motor has all the power I will ever need. I can feed the end of a 2x4 into it with a lot of pressure and it won't bog down.

The RPM is about double that of a typical commercial model, although you can buy them in this configuration. There are two issues: power and speed of material removal. As I said, I have no trouble with power. I like the high-speed material removal - I have a 60 grit pad on there and that's what I'm looking for.

Here's a short video showing how it works (my first video)...

It grinds away the stick about as fast as I can feed it. There is absolutely no dust with the vacuum system on.

Costs: I'm calling the cost of this project $13, since the motor was left over from another project.
- Electrical parts: $3
- Sanding discs $6
- Buffing plate $4

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