I think it’s pretty much agreed upon that a band saw blade automatically moves towards the crown the pulley.
Why is this? When I first suggested that it might be centrifugal force pushing the band outward, I was told I was wrong; but the person that told me that didn’t know what the correct answer was. (How very un-SDMB of him!)
Another theory is basically that the bands stays where it has the most friction. i.e. there is more to hold the band on the crown of the pulley than elsewhere?
While this question gets tackled, I’d like to also know what a crowned pulley works better than a non crowned pulley on a band saw. It’s my understanding that lumber mills use flat pulleys.
So, is there a simple answer to this or is this going to turn into another plane on a treadmill?
I have an ancient engineering book that explained the principle for belts. It also had a diagram showing the best place to cut a leather belt from the back of an ox
Thats really interesting I never knew it sought out the crown. I always take extra care in alighning my wheels to keep the belt tracking down the center. It causes blade drift if not riding on the crown.
I have trouble on my belt sanders with the sanding belt walking off to the side as I work then going back to center when I back off the material I am sanding. I wonder if a very slight crown on the wheels of a belt sander could help it maintain center better.
Antique farm equipment driven by flat belt from a pulley on a tractor depended on crowned pulleys to keep the belt in place. The tractor/steam engine and say, a threshing machine, might have their pulleys 30’ apart and couldn’t be aligned very well.
Pretty sure they’re crowned already. If they weren’t, you’d have to get the pulley alignment exactly right to keep the blade from slowly walking off on its own. The tracking adjustment on a belt sander is simply for getting the pulley angle “good enough” so that the crown can keep the belt centered.
Machine Elf. I have a 6X48 harbor freight sander. Several years of daily heavy use. The last few years all my belts are slightly too long to allow for the tensioner to properly tension the sanding belt. I have checked every related part for wear and can't find any. Is it possible the wheels have worn down enough to cause this? It seems highly unlikely but I am scratching my head at this point. The bearings are good. All the undercarriage parts relating to tension including mounting holes appear to have zero wear. There has to be wear somehwere?
I used to have the exact sander he’s referring to, and there is no tension spring. Instead, the upper pulley has left and right supports that can be raised or lowered by jackscrews to make up for a slack belt (and control tracking).
HoneyBadgerDC, my only thought is to check and make sure those black thumbscrews (above the adjustment) are fully loosened so that the jackscrews can rise up without any resistance? Maybe they are binding on the threads of the jackscrew and preventing you from raising the pulley enough?
Alternative explanation is that maybe your belts are all stretched? Have you tried a brand-new one? I use 36-grit shredders and do a lot of aggressive steel-shaping, so my belts never last very long before they get discarded. But if you’re shaping archery hardware, then I’m guessing your medium is wood, and you’re using gentle force, so your belts probably last a very long time.
I usually change belts fairly frequently as they clog up with some woods I use. I did find 2 small areas of wear. One is I have the wrong size pin in one of my axles, loosing maybe a 1/16 there, and the roller cam on the tensioner has close to a 1/16 th play, not sure how much it had when new. Going to change the pin right now and see if it helps.
