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Belt to my motor keeps shifting.

I finally got my letterpress all set up. My motor worked great and my leather belt is perfect. I have the belt connected to the flywheel and to a kimble motor. Here is my issue, when i turn on the motor the belt does not stay in place. after about a minute the belt shifts and is almost half way off the wheel and i would imagine only a couple more minutes it would fly off. The belt is tight and seems pretty straight on. Why would this be a problem? I assuming i need to 100% confirm the wheel and motor are straight on, but what other issues could it be? Anyone ran into this problem? Another note, i have my press elevated on about 2 inch thick to even out the weight of it in my shop but the motor is on the ground so could the lower motor be the issue? Thanks in advance!

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I wrap the pulley on my Kimble a few times in the center with electrical tape to create a “crown.” This is enough to keep the belt from wandering - everything else being equal!

The crowned roller is a good idea. Alighnment is bound to be the primary problem, but that should be easy to resolve. Also I’ve found that too much tension can sometimes be a problem.

John Henry
Cedar Creek Press

Lower motor is not an issue. The flywheel does not care about the elevation. Only that it is aligned front to back and that the motor shaft and flywheel shaft are parallel.
Flat belt power transmission became pretty much a lost art when steam power was replaced by electric motors. All flat belt wheels/pulleys were crowned. The metal was machined that way. While the platen press can be powered by a belt on the flyheel, it was not intended to be done that way. Thus the flywheel was flat.
Scribe a mark in the center of the flywheel and all around the circumference. Wrap two strips of electrical tape around the flywheel butted to your mark. Place a third strip over the center of the two. Voila.Crown

You could always fit a crowned pulley on the motor ,if you have one kicking around the place , or take the above mentioned option with tape .
If you have crowned pulleys on the press and this happens turn the drive belt round 180o one side of the belt may have stretched a little .
180 degrees.

Thanks everyone! I crowned it, and it works perfectly!