What keeps a band saw blade on?

[Kevin McMichael]

I have a very old Sears band three wheel band saw. It was my fathers and has not ran since the late 50s. I purchased tires and a blade. The blade comes off when you turn it on. I assume a part has fell off?

[Frank Drew]

Kevin,

I've never used a three wheel bandsaw, but with bandsaws in general the band (the blade) stays in place due to tension and wheel tilt: The wheels have to be adjusted so that the band is stretched tightly between them, and usually one of the wheels is able to tilt front to back in order to keep the band tracking correctly on the wheels, not running off.

If you look your machine over carefully you should find handles or handwheels that will permit these adjustments.

[Myk Rian]

When setting the blade, unplug the saw.
When the blade is on, turn the wheels BY HAND and make adjustments to get the blade centered on the wheels, using the tracking adjuster.
Then make your final tension and tracking adjustments.

[Terry Beadle]

I have an older 12 inch Craftsman. It has a set screw with a nut on the upper wheel that you adjust to keep the saw blade centered on the crown of the tires. The set screw turns independently from the nut.

Mine is a two wheeled type. Your three wheeled type may have the same kind of adjustment screw on one of the wheels. With the saw unplugged !, hand rotate the tire while you adjust the screw until the blade stays centered on the tire crown. If you are running a 1/8th inch blade you may have to adjust it where the blade runs on the front side ( the side where the teeth point ) portion and not the center of the crown.

Once the blade is staying centered with the hand rotation, step back from the blade and turn on the saw for just a second. If it stays centered, then turn it on for 3 seconds and repeat until you can let the saw run and the blade stays put.

Then adjust your blade friction blocks and bearings for the blade you are using. The bearing should not touch the blade while the blade is spinning with no cutting load. This is some times set by using a dollar bill between the bearing surface and the blade back end. The friction blocks should be set just behind the gullets of the blade and can touch the blade or be 1 ~ 2 thou off the blade.

Good Luck !

[Kevin McMichael]

I figured it out. The rear wheel tilts to keep the blade tracking correctly. Thanks

[Dave MacArthur]

Well... the real physics answer though is that the band will climb towards a crown in it's wheel, due to more tension being exerted on the crowned side. Very interesting to watch old power-take-off leather bands on wheels. So, it's the crown that keeps it on and tracking, the wheel adjustment just lets you move the band-perceived location of the crown center.

Which is why narrow blades don't track too well on low-crown wheels like come on larger euro saws--there is not much crown, and the tension differential between either side of a 1/8 or 1/4" band may not be enough to overcome non-co-planer forces trying to throw the band off the wheel.