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  • Flat belt tracking

    I've built a tube coping machine that is near competion. It's using a 6" wide abrasive belt. I made it so I can adjust the tacking while running, but the belt still likes to wonder off to one side or the other. I'm going to crown the drive roller but not sure how much. Is there a formula/rule of thumb, or is it just trial and error?
    Thanks.

  • #2
    Phil,
    I think the rule of thumb is 1/8" of crown per 12" of roller width. It's not very critical, and the crown can actually be a slight taper. I've had good success with putting a few wraps of tape around the center of a pulley to make the belt track.

    On this machine: http://www.oldengine.org/shows/semta97/jul19_13.jpg

    In the case of drive belts, it's important to have the pulleys properly aligned to keep the belt on if it slips a bit. The crown will make it track, even under a bad misalignment condition, as long as there's no slippage. A bit of slip will cause the belt to come off immediately, however.

    The tape trick would probably work great for you.

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    • #3
      Thanks, experimenting with adding some tape right now. 1/8 per foot is on the radius or diameter?

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      • #4
        I used a small flat belt on a grinder recently and found some sites with info:
        http://www.lhup.edu/~dsimanek/scenario/crowning.htm
        http://www.visusa.com/belt_tracking01.htm

        It takes relatively little crown to cause the belt to track. One site recommended the drive pulley be crowned and the driven pulley be flat - their opinion was that if both were crowned the belt could get unstable and move back and forth. Too much crown can also cause instability - I ran into that initially

        John

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        • #5
          Phil,
          I think the 1/8" per foot is on the radius. That is, if the pulley has a 12" wide face, the crown should be 1/8" high.

          Both pulleys can be crowned, and in fact should be if there's a possibility of misalignment, as on the sawmill that I linked to. If it's a fixed setup, that's not necessary, but I can't see the harm in it.

          <<Jim>>

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          • #6
            My experience is similar to Gadgets ... I was building 2" belt sanders and kept having stability problems --- slightest bit of pressure on belt would cause it to wander all over. Ended up making a wheel with just the barest of crown and gained stability.

            The tape idea is great, that'll tell you what you need without taking too much off, guessing at amount of crown needed.
            If everything seems to be going well, you have obviously overlooked something........

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