6x48" belt sander build
Going through my collection of shafting and bearings, I decided to use some 12 mm shaft for the main shaft, mainly because I already had some bearings that fit it precisely. I decided to use some cheap 3/8" steel rod for the idler roller's shaft, the same stuff I used for my jointer parallelogram mechanism
The main roller on my existing belt sander is coated in rubber. I figure that was a good idea, especially because on my strip sander the belt can slip if I don't have enough tension.
I bought some inner tube that I wanted to cut into strips to line the roller with, but when I cut it open I realized the rubber was thicker on the inside of the donut, so I couldn't use it.
The main drive drum is made out of layers of plywood, which I cut out on the bandsaw. My homemade bandsaw, of course.
The photos shows doing this by hand, but in reality, I just used my existing belt sander to do most of them.
I turned and rounded the drum by mounting it above my small table saw sled and spinning it with a drill while slowly pushing it over the blade.
It took quite a bit of tweaking to get the shape I wanted for the drum. The drum is slightly bulged in the middle like a barrel (crowned is the proper term). This will help track the belt in the center. I shaped that crown by mounting one side slightly higher on the table saw sled to cut the cylinder into a cone shape, then mounting the other side higher to cut a cone from the other end as well. But in the end, it took several tries to get it right, and the drum ended up a few millimeters smaller than I was aiming for.
Trying to stretch even a 3 cm long section of inner tube onto the drum was too difficult. So instead, I coated the drum in caulking. I got this idea from John Heisz in his quick and dirty bandsaw mill build video.
I also milled this one to be a straight cylinder (no crown). Belt sanders tend to have just one of the drums crowned. I read somewhere that some have found that this works best for a 6x48" belt sander, though I didn't experiment with this myself.
The inner tube also had some ridges from seams from the mold. I shaved these off with a sharp knife (my homemade knife).
With the rollers made, I printed out 1:1 top and side views from my SketchUp CAD model using my BigPrint program. The printout covered 8 sheets of regular letter (8.5x11", similar to A4) paper.
It's expensive plywood, and if you were to build cabinets with it, the costs could add up quickly. But for a machine like this, I only end up using about $10 worth of the stuff.
The bearings I'm using have a 32 mm outside diameter. It turns out, this size makes for a tight fit in the hole from my 1.25 inch Forstner bit (1.25 inches is 31.75 mm, so I guess the drill drills slightly oversized).
I had the foresight to chisel two gaps next to the hole to pop the bearing back out with two screwdrivers after pressing it in the hole.
Pressing one of the main bearings into its mount. Before pressing that in, I drilled two extra holes all the way through which will enable me to push the bearing back out if I need to later. You can see one of these holes in the picture at right.
So I cut a fraction of a millimeter off the side of it on the table saw to bring that edge into square. I set the fence on the saw by placing the piece to the right of the saw blade, then pressing the fence against it. Then pulling the piece out, starting the saw, and pushing it through to cut about 0.1 mm off the workpiece.
There are of course drill bits that will do this in one go, but I don't have one, and with just a few holes, it would hardly be worth the effort to adjust one of these (and then it still might not have the right combination of shank and pilot hole diameters that I want)
Another crossbrace goes here to help hold the parts square. I have the screws already in it, and I'm tapping it against the wood to get the tips of the screws to mark where the pilot holes need to go.
The part that the idle roller mounts to (with the slot in it) slides between two layers of plywood, but the way this turned out, it would have been a tight squeeze, so I had to make some shims to add more space.
Due to some slight misalignment, the shaft turned a bit tight in the blocks. To give them a bit more tolerance, I ran the drill in the holes while slightly pivoting the block side to side. But the drill got caught and ripped a substantial gash in part of the block. The shaft is still held securely (the gash isn't all the way through). So I'll just leave it like this. If it wears out, I can always replace the bearing blocks.
Now mounting the part that tensions the belt. It pivots on a screw, and the short arm is pulled with a threaded rod. A nut goes on the end of the threaded rod. I made a block of wood that this nut fits into to keep it from spinning as the threaded rod is turned.
I had the idea of using two T-nuts in the slot to adjust the tracking. The prongs of the T-nut, against the edge of the slot, prevents them from turning with the shaft. But this turned out to be a bad idea - the prongs get caught as the slot moves left and right when adjusting tension.
This method of adjusting tracking worked, but it was difficult to adjust, so I ended up redoing how tracking and tension adjustments work later.
I have a 2.5" (73 mm) pulley with a 1/2" (12.7 mm) hole to mount on the 12 mm shaft. Using some plastic from a pop bottle made for a shim to snugly fit on the shaft. The shim, being transparent, is hard to see in this photo.
Now powering it with a 1/2 hp induction motor and trying out the sander. It works!
But that's enough for now!
Neal Week's belt sander
Lucian's oscillating spindle sander