Belt grinder build, part 1
I wanted to experiment with building a belt grinder. But not having experience with one, I wasn't sure if it was something I had much use for, so I didn't want to build a typical belt grinder design such as Jeremy Schmid's, John Heisz's, Cosmas Bauer's, or this one.
And of course, out of wood, because it's what I know best, and quickest and cheapest.
I used some scrap MDF that used to be a headboard to cut some disks to make the main drive wheel out of.
For bearings mounted in a wheel, a press fit is essential or the bearing will work its way loose eventually.
The wheel will consist of three layers. The problem when laminating layers together is that they float on the glue and get out of alignment while clamping together. So I drilled two holes to fit screws (just large enough that I could push the screw through the holes), then aligned the layers and tapped the screws into the second layer with a hammer.
I clamped the third layer on, then carefully aligned it so the wheel did not wobble, then screwed the screws further in so they got into the middle layer.
I previously ground that 7/8" drill down so it made a hole to tightly fit the 22 mm bearing.
I also arranged it so I could push the wheel forward and back along the shaft so I could cover the cylinder and make sure its surface was perfectly parallel to the shaft.
The big wheel was slightly out of balance, but the bearings did not turn freely enough to balance it just by gravity. Previously I worked around this by letting it roll on smaller bearings inside the main bearing, but with these bearings just 16 mm inside diameter, the only bearings I had that were small enough were ones for router bits. I was going to put two of these bearings on a shaft, but then I had the idea of just mounting the router bits, with bearings in two pieces of wood.
My original idea had been to have the back column of the sander slanted so the top wheel would be forward enough for the front of the belt to be vertical. But if I use it with different lengths of belt and moved the top wheel along the post, the belt wouldn't stay vertical. So I made the column vertical and made the top wheel holder long enough to bring the front of the top wheel in line with the bottom wheel.
Tracking wasn't working very well. I wasn't sure why, but with everything held together precariously with clamps, I figured I should make it more solid before working on that some more.
I drilled some screw holes in the plate that has the stub axle for the lower wheel, used a short nail tapped into every hole to transfer the hole locations, then used those divots to locate pilot holes, then screwed it together, with just two screws at first.
But belt tracking adjustment still didn't work very well. I checked that everything was sufficiently square (it was). I found my bottom roller had a slightly negative crown to it, so I fixed that. That made it slightly better but still didn't fix the problem.
So I decided to investigate changing the tilt of the wheel, and the rotation about the vertical axis (yaw angle) independently. Both of those were able to change the tracking. But lifting the right side caused the belt to track to the left, while moving the right side forward also tracked it left. The way I had the slot, I lifted the right side while also moving it back. Those two caused opposite adjustments to the tracking, so they cancelled out. Oops! So I really needed a slot that slanted in the opposite direction.
So I threaded a hole into the back of the bracket using a piece of threaded rod with some slots cut into it with an angle grinder to act as a wood thread tap.
Before I go further with this build I need to figure out how to mount the motor, and that depends on which motor I'm going to use. I need to decide which of these three 1750 RPM motors I should use. I will have more on that next week.