Bandsaw refinements

I have been using my homemade bandsaw as my main bandsaw for over two months now. I still use my cast iron bandsaw with a 3/16" (5 mm) blade from time to time if I need to cut some really tight curves, but I really prefer to use the homemade one for everything else. My homemade saw cuts much faster and it's much better at containing the sawdust. I have however made some refinements, so here is what I have done to it.

Fixing wheel creaks

After I built my bandsaw tension gauge, I realized that my bandsaw tension was well below the limit of what the blades

could withstand. So I got myself some new stronger tension springs, and cranked up the tension.

While the frame of the bandsaw could easily handle the tension, I heard faint creaking noises from the wheels when I slowly turned them by hand. On further investigation, I found that my upper wheel was creaking slightly. I mounted a dial displacement indicator to the wheel, and was able to measure a .001" pop back and forth of the cast iron bearing flange with respect to the wheel. That in itself is pretty insubstantial, but I knew that if it creaked back and forth, this would surely work itself loose over time!

The nature of the problem was that my cast iron flange bearings were not rigidly enough attached to the wheels. I had mounted them at a 45-degree angle to each other, so I couldn't just replace my wood screws with washers with bolts going through the wheel to press them together. I didn't really want to do that anyway, because as the wood expands and contracts with humidity, the bolts would eventually become loose too.

The cast iron wasn't glued to the wood. Mostly, the flanges were held in place laterally by four blocks of wood that I glued around the flanges. For 150 pounds of blade tension, these blocks proved to be inadequate.

So I set out to make new wooden flanges. Although wood is not as strong as cast iron, I knew I could count on a really good bond between a wooden flange and the wooden wheel.

I reused the bearings from my self-aligning bearing flanges. The bearing had an outside spherical surface of exactly 52 mm in diameter. But my Forstner drill bit set is in imperial sizes, and the closest I had was 2", which works out to 50.8 mm. So I had to expand the holes with a sanding drum on my drill press. A drum sander would have been better, but I don't have one.

I expanded the hole enough to be able to get the bearing into the flanges with a very tight fit. The fit needed to be tight or the bearing would be able to work itself loose again. For industrial applications, any bearing mounted inside a wheel is always mounted with a press fit for this very same reason. A setscrew simply wouldn't do.

Having replaced the bearings and flanges, the new bearings were in a position just a fraction of a millimeter from where the old ones were, so the wheel needed re-truing and re-balancing.

I had previously trued the upper wheel by mounting it on my extra long drive shaft of the bandsaw and spinning it up that way. But I had since shortened this shaft to its final length, so that wasn't an option anymore. So I made a temporary pulley, and attached it to the upper wheel with a pair of wood screws. This was enough to spin up the upper wheel on my workbench. Using some chisels on the wheels, in a lathe-like fashion, I turned it to run true again. When I checked the wheel with a dial indicator, it was within a range of 0.002" (.05 mm) all the way around.

I also found a slight bit of creak on my lower wheel. The 7'8" shaft fit reasonably rightly in the 7/8" hole, but apparently, not tightly enough. So I figured, why not just glue the shaft into the wheel? If the glue holds all is well. If it works its way loose, I can always get that shaft out and try something else. Worst case, I'd just have to make a new wheel.

Rim shape refinement

I found that with the inner tube bandsaw tires stretched over the wheel, there was a natural inside pocket that formed between the rubber inner tube pulling over the edge, and the edge of the rim. This gradually filled with sawdust. The enclosure tends to contain lots of airborne sawdust, and centrifugal force would force some of it into this pocket between the inner tube and the wheel.

So I added these little blocks of wood to occupy this cavity, so that I wouldn't get as much sawdust collecting in the wheels.

If I build another bandsaw, I'll just make the wheels thick enough that they won't need rims, and I won't have this problem again!

Truing the drive pulley

Looking for sources of vibration in the saw, I realized that my back pulley did not entirely run true. I had cut this pulley out on the table saw, as opposed to turning it on its shaft.

The temporary upper pulley that I used to turn my upper wheel worked out reasonably well. So I mounted the temporary pulley to my lower pulley. That way, I was able to spin up the lower pulley without having a belt on it, so that I could use my turning chisels on it to turn it completely true.

But on turning the pulley, I slipped with the chisel and it caught on the spinning pulley, stopping it instantly. But my lower bandsaw wheel, spinning on the same shaft acted as a flywheel. The momentum from the lower wheel ended up breaking the screw that I used to protrude from the pulley into a hole in the shaft.

So I figured the solution was to just drill a hole through the shaft and put a bolt all the way through. Unfortunately, I tried to do that with a hand drill and broke a drill bit in the process. So I tried to drill another hole 90 degrees to my first hole, and broke another drill bit, probably because I hit the remnants of my broken drill bit from the first attempt.

If I wanted to try drilling a third hole through my shaft, I'd have to get a new shaft first. But in my quest to eliminate creaks, I had just glued that shaft into the lower wheel! So replacing the shaft would entail making a new lower wheel. While this was certainly an option, I really just wanted to put my bandsaw back together and start using it again.

So I ground a keyway into my shaft using an angle grinder. I used a block of hardwood as a guide, but overall, it was a pretty freehand operation.

I also filed a keyway into my pulley with a hand file.

For a key, I just used a big machine screw, which I ground flat on two sides, and hammered it into the keyway. I left the screw's head on so that I'd be able to pull my key back out for unmounting the wheel.

On my second bandsaw design, I just put the pulley directly on the wheel, so that eliminated the whole issue of coupling a wheel to a shaft.

Faulty lower main bearing

Finally, after a few weeks of using my bandsaw, I sometimes heard a knocking sound as the bandsaw was spinning down. By process of elimination, and by carefully listening in various places, I finally realized that the noise could only be coming from my lower flange bearing. Other than a slight knock, the bearing was still functioning perfectly. But it was another thing that I figured would go eventually, so might as well replace it now.

That bearing has to take the force of the entire blade tension times two. Plus that force is amplified a little bit because the lower wheel is cantilevered out from the bearing. So effectively, that bearing gets twice as much load as any of the other bearings in my saw.

Bearings of this size are usually rated for a side load of over 10 kilonewtons, which works out to well over 2000 pounds. My bandsaw, tensioned to 150 pounds, would only apply just over 300 pounds to the bearing. So that should be well within the load rating of a good quality bearing. The problem is, I was using cheap Chinese made bearings bought at Princess Auto.

I wasn't sure if these cheap bearings are all that poor, or if I just managed to get a dud. So I bought another cheap bearing for $8. I mounted the new bearing in the cast iron flange I used with the old one. These self-aligning bearings can be removed from their flange or pillow blocks by turning them sideways by about 30 degrees in just the right direction. This is best done by holding the flange in a vise, inserting a shaft, and tapping it sideways.

The mating surface between the flange and the bearing is actually spherical, so they fit tightly at any moderate angle.

If the new bearing ends up developing a knock as well, I'll get a good quality bearing from a bearing store. Those cost around $25 each. It's only the lower front bearing that has developed a problem though. The other bearings aren't loaded as heavily.