Making hollow 26-inch bandsaw wheels
This is the upper wheel of my 20" bandsaw, made of two pieces of 3/4" plywood glued together. But all that plywood adds inertia, which makes starts and stops a bit slower. It also makes the saw heavier. So for my bigger 26" bandsaw build, the wheels would be 70% heavier still. So I wanted to try making the wheels hollow to make them lighter.
I could also cut holes in the solid plywood to make it lighter, but that would make the wheel act more like a fan, which will in turn whirl around dust more. Another approach would be to make them of one layer with wider flanges, but on my 18 bandsaw I found that shape tends to guide dust behind the inner tube tires.
Then rough cutting the circles out with a jigsaw, and finishing the cuts on a bandsaw. This could of course be done with a jigsaw as well, but I already have some bandsaws, and a bandsaw is a better tool for that!
Having cut out the circles, I laid it out for twelve spokes. I started by drawing two lines at 90 degrees, then got the 30 degree increments by using my beam compass to mark 60 degrees from the lines intersecting at 90 degrees.
Every second spoke piece is pointy towards the middle to fit between the other spokes.
With the wheel balanced on the head of the screw, I checked the balance. I added a small block of wood to balance it. This is just an approximate balancing. I will have to re-balance the wheels once they are all done, but by that point, I won't be able to add a weight to the inside.
I made sure that all the rim pieces came from the same piece of wood, so they would have about the same density and not throw the wheel off balance. The spoke pieces are also all cut from the same piece of wood.
I always give the plywood a light sanding where it's glued for critical glue-ups. Not because the surface needs to be roughened up, but because atmospheric grime deposits gradually build up on surfaces, which can reduce glue and paint adhesion. and a light sanding gets rid of that.
I used all six of my new long reach clamps that I made for a recent table top glue-up to clamp closer to the middle.
Then some of my older long reach clamps to glue closer to the middle, and some weights for the very center.
In retrospect, I could have drilled those four holes in the spokes through the top layer and put bolts through those holes to help clamp it. Also a bolt and a big washer through the center axle hole would also have helped clamp. Sand bags would also have been useful for the clamping.
Using these four bolts, and some threaded knobs, I glued a flange to the side of the wheel. This flange is a spacer so the bearing flanges will be further apart, which should give the wheel more side-to-side stability.
After clamping it with the four knobs, I realized I could just barely fit my dovetail clamps through the center axle hole for additional clamping.
Surprisingly, I managed to set the circle cutter set to the right diameter on the first try. I set it with a caliper, taking the 52 mm for the bearing, divide by two, gives 26, add half the diameter of the 6 mm center drill, so 26+3 = 29 mm, then subtract 0.2 mm to make it tight. So I set the callipers to 28.8 mm, then with the callipers measuring from the center drill bit to the edge of the cutter head, set it to that.
The circle cutter cuts slightly bigger the deeper it goes, just the way the cutter is angled. To minimize this, I drilled to half depth, then flipped the workpiece over. Using the hole from the cutter's center drill as alignment, drilled in from the other side.
The bearings are a tight fit, and I had to use my vise to press them in. The vise doesn't reach to the center point, is I kept pushing a little bit, unclamping, rotating the flange 90 degrees, and squeezing some more, until the bearing became flush with the wood and I couldn't press it any further.
The bearing needs to be in very tight because as the flange spins around the axle, from the flange's point of view, the axle is pulling back and forth as the wheel turns, and if that bearing can at all budge from repeated back and forth, it will work its way out eventually. So it needs to be in there very tight. If you can press it in by standing on it, it's too lose.
Spinning the flange and bearing on the shaft, I couldn't see any wobble. Very satisfying!
I drilled four screw holes near the corners of the bearing flange and put screws in them, but not far enough for the screw points to come out the other side. I then put the flange onto the other flange already on the wheel, and fastened a beam compass to a piece of wood stuck into the bearing.
Swinging the point of the beam compass around, I adjusted the radius and flange position until the compass point traced my old circle exactly. That way I could be sure the flange was positioned on center.
And then using the four bolts through the wheels to clamp the flange in place, with the beam compass still fastened so I could check the position, though with the screw knobs in the way I could only swing the beam compass through less than a quarter turn. Maybe if my reference circle had been much bigger, I could have reached over the knobs and been able to check with the knobs in place.
Maintaining center is important. If I was off by a few millimeters, I had enough margin that I could have trimmed the edge of the wheel to still make it centered and the correct size, but the hollow space in the middle would be off-center, which would throw the wheel substantially out of balance.
Spinning the wheel, I checked for side to side wobble. With the second flange only positioned by friction, I kept tapping it with a mallet to move it to eliminate the side-to-side wobble as well as I could. I got it down to less than 1 mm.
Once I was satisfied with the alignment, I used the same screw-point divot trick to lock the alignment of the flange. Then removing the flange I added glue and put it back on, using the screw divots for alignment.
And why not do this whole procedure with glue on in the first place? Became the glue is very slippery, so it drifts out of alignment as it's clamped. And the glue's drying time is limited, so it's best to work out the alignment before applying glue.
Having said that, after I clamped it on with glue, it was off by a little bit and I had to tap it some more to fix that.
Making the drive pulleyThe next step is to turn (lathe) the wheels to true them up. For that I need to spin them with a motor, so I made the drive pulley. I rough cut it out of a sheet of 3/4" plywood with a jig saw, then spun it against a running table saw blade to get it precisely round.
After that I cut a 1/4" slot around the circumference on my new router table.
But the sides of the v-belt groove need to be slanted, so next I tilted the tilting router lift to match the sides of the belt and routed each side grooved.
Doing this on the router table felt much safer than making it on the table saw, though if you don't have a tilting router lift, the table saw is the way to go.
It turns out I had it 1-2 mm off center, but for a temporary setup, I didn't care that much.
I had to take about 6 mm off the wheel after I trued it up. I had left too much margin. I turned one side down to the size I needed, periodically measuring the circumference until it was right, then turning down the rest of it to size.
Checking it for round-ness with a dial indicator held against the wheel slowly spinning. The dial indicator needle moved back and forth by nearly 0.010" (0.25 mm) Too much. Each segment had a high and low spot because the chisel grabbed better when it was cutting into the wood grain than out of it.
Bandsaw tires from inner tubesI bought some larger sized inner tubes for the bandsaw this time. 1.75" bicycle inner tubes would have been enough, but Princess Auto had these, which were for fatter tires and maybe thicker.
After cutting the inner tube open and cutting out a wide strip from the outside of the tube, I cleaned off the chalky powder from the inside. This powder is there to keep the inner tube from sticking to itself while folded up, but for a bandsaw, I want the rubber to stick to the wheel, so the powder has to come off.
Then mounting the inner tube over the wheel. I start by clamping it to one side, then stretching it across and clamping it on the other side. Then I stretch one side to across to 90 degrees from where I clamped it on either side, then pull the quarter sections over the wheel. After that, I stretch the mid point over on the other side and repeat.
This way I don't end up with an unevenly stretched inner tube, which should make the thickness of the inner tube more consistent as well.
I will later varnish these wheels, which will make the rim better for the inner tube to stick to.
With the wheels done, I figured it would be fun to see if I could make a bandsaw blade track on them. So I mounted the second wheel further down the bench, put a blade on it, and spent some time getting the alignment just right.
Next: Making the bandsaw frame
As usual, the video got a lot of comments, and a lot of those were repeated in different forms many times. So I made a video answering some of these questions.
Next: Making the bandsaw frame