Making wheels for the 20" bandsaw
This is the first part in a series about building a big 20" bandsaw, the construction of this one will be similar to this 16" bandsaw. This will be my fourth homemade bandsaw. Previous bandsaws: one two and three
It helps to make the wheels for a bandsaw out of good quality plywood, but I like to make use of old crap I get for free. I'm using some shipping pallet plywood. Here marking it up with my beam compass ...
I needed four circles (each wheel has two layers), but unfortunately, the plywood wasn't big enough to cut four whole circles out of it, so I'm using my dowel jig to join the pieces together from multiple parts.
I clamped a stop to my workpiece. That way, by placing the jig against the stop, drilling through, then flipping it over, and drilling again, I can effectively index the position to get consistent dowel spacing.
Another two pieces, cut near the center, for another disk. I'm using the same method with the block to index the dowel jig, but this time indexing off both sides to accurately space six holes (I could have drilled up to eight holes spaced this way).
Before gluing layers of old plywood together, it's always a good idea to sand the surface to expose fresh wood. Over time, the surface can get all kinds of microscopic grime deposited onto it, which makes for poorer glue adhesion, even if it looks clean.
I put a lot of clamps around the perimeter, plus my long reach clamps to clamp near the middle. You could also use some wood screws to clamp it together near the middle, or use some clamping cauls.
Making the bearing flangesI then went shopping for shafts and bearings: some 1" shafts and bearings with a 1" hole and 52 mm outer diameter. These are the same bearings I used on my 16" bandsaw six years earlier, and they have served me well.
Note that the workpiece is clamped down. When the circle cutter breaks through, the pilot bit in the center no longer holds the workpiece, so it has a tendency to get thrown around if not clamped down.
A circle cutter like this is difficult to adjust to a precise value.
After several tries I had a hole that was a fraction of a millimeter smaller than the bearing. I was barely able to get the bearing part-way into the hole with a mallet. I then used a vise, pushing the bearing in a millimeter at a time on one side, then rotating the workpiece, pressing again, and so forth until the bearing was flush with the wood.
Having successfully inserted a bearing in the test piece, I was satisfied with the fit. The fit needs to be very tight.
I cut four bearing flanges out of Baltic birch plywood. Then marking the center in each one by drawing a line a fixed distance from each edge with my beam compass. I prefer this method of establishing the center because it's less error prone than trying to draw a line exactly to the corners. It also helps to check the size of every piece.
Some caution about mounting bearings like this. When the bandsaw is running, twice the blade tension pulls on the bearings. As the wheel turns. the direction of pull of the blade changes with respect to the wheel. So it's like the wheel is continuously yanked back and forth and side to side against the bearing. The bearings need to be in the flange considerably tighter than the forces they will encounter or they will work themselves loose eventually.
If you make the holes too small, and you use a spindle sander to open them up slightly, unless you are very consistent about it, you may mess up the bearing. The bearing outer ring is only so stiff, so, if forced into a not-quite-round hole, it will assume that shape.
Then rounding the edges on my edge belt sander
Mounting the wheel flangesDrilling a 1 1/4" (30 mm) hole in the middle of the wheels. This hole provides clearance for a 1" (25 mm) shaft. I'm using a drill guide to get this square (the wheel is too big to fit in the drill press). This hole, having several millimeters of clearance to the shaft on all sides, is not that critical, so this could also be drilled freehand.
I also need four threaded knobs with a 3/8" thread. Such knobs are hard to find, so I'm using some 3/8" coupler nuts and pressing them into slightly undersized holes in pieces of wood. (3/8" is roughly 10 mm).
I drew a circle on the wheel before drilling the center hole to help guide where the flange needs to go.
In previous bandsaw builds, I drilled much larger holes and inserted bar clamps through the holes in the wheels, but the bar clamps had a tendency to push the flange off to the side slightly as they were tightened. These hold-downs avoid that problem.
Checking wheel wobble by holding a piece of wood near the rim while it spins. Unfortunately, the glue set firmly before I had a chance to tweak it to my satisfaction. I still had about 1 mm of lateral wobble. A bar clamp at an angle wasn't enough to overcome the glue.
For the second wheel, I clamped and tweaked the flange position without applying any glue. I then drilled pilot holes and added two screws to fix the flange position, removed the flange, added glue, then used the screws to get the flange back in the same place. This procedure was much less stressful.
Truing and crowning the wheelsI screwed on a temporary pulley for spinning the wheels. This is a temporary pulley I used during my first bandsaw build, though I cut a hole in it to fit around the flange.
I made the pulley by cutting a round disk out of plywood, then using the table saw to cut a slot around the circumference. I didn't bother bevelling the sides of the slot — it's only a temporary pulley.
If you are not comfortable cutting the slot around the perimeter on the table saw, you could also use a router with a slot cutter bit, or glue together three thinner layers of plywood.
Checking the size. I'm using a flexible tape measure (not the sort that extends straight out) to measure the circumference. I want a diameter of 50 cm, minus 1 mm tire thickness, so 49.8 cm diameter. That works out to a circumference of 156.4 cm. With a floppy tape measure, circumference is easier to measure accurately.
After getting it down to the right diameter, I turned a "crown" on the wheel. Basically, a peak in the middle of the wheel. This helps keep the blade tracking on the wheels.
Making the drive pulleyThe lower wheel will have a large drive pulley attached to one side. To offset the drive pulley a little, I'm gluing on a disk of plywood.
I put four screws on it near the middle to help clamp that disk in place.
After the glue dried, I removed the screws
Then making the wheel for the pulley. This wheel is 24 mm thick, consisting of 18 mm Baltic birch plywood and 6 mm Baltic birch glued together. I'm cutting a hole in the middle to fit around the wheel's bearing flange.
After that, sucking up all the shavings with my dust collector.
Balancing the wheelsThe next step was to balance the wheels. After all the turning, the bearings ended up spinning freely enough that I could just put the wheel on the shaft and watch which side tended to move down.
I used some scraps of the plywood I made the wheels with, stacking them on the top rim of the wheel to get a sense of how much wood I had to remove.
Bandsaw tiresBandsaw wheels have a rubber "tire" on them to prevent the blade's teeth from wearing away the wheel over time. I'm using a 16" bicycle inner tube as my tire. I slice it open along the inside-most part of the tube, also carefully cutting around the valve.
Inner tubes typically have powder on the inside to keep the rubber from sticking to itself. But we want the rubber to stick to the wheel as much as possible, so after slicing them open, I washed them with soap and warm water.
Stretching the tube on can be tricky. I clamped the inner tube to one side, then stretched it across to the other side and clamped it there. Then, turning the wheel by one quarter turn, I can pull one side of the tube up and around the wheel at a time. After that, I removed the clamps and adjust the position.
I'm still planning on adding a few coats of varnish to the wheel, so the inner tube will have to come off again for that. I'll varnish the wheels when I varnish the frame, so that will come later.
Next: Making the bandsaw frame