How close can you mount the countershaft?
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  1. #1
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    Default How close can you mount the countershaft?

    Is it possible to shrink the footprint a few inches with a modified tensioner and a shorter belt? Is the only limiting factor the making it so the motor doesn't hit the lathe when the belt tensioner is disengaged?

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    Clearance for a taper attachment may be an issue if you have one or ever plan on installing one.

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    Belt power transfer is limited first and foremost by the amount of surface contact, and the least contact always occurs on the SMALLER of either the drive or driven sheave.

    As you mount the shafts closer together, the arc of contact on the smaller sheave decreases, and the larger sheave increases. The smaller getting smaller means the contact surface of the smaller is under higher stress.

    It doesn't seem like it'd be that serious, but draw a very large and very small circle, put them just a fraction of a hair apart, and draw the belt path, you'll see how dramatic the contact reduction IS.

    So the answer is: Farther you get, the better the wrap, and closer you get, the less you'll be able to transmit.

    Will it impact you? Pull 'em close, wrap a string, and mark the sheave... now move it back, mark it again (with different color ink), and measure the circumference of both, and compare the change.

    You can BEAT this, by installing idler sheave on one side (the slack side, usually) to increasewrap, but with added stress on the belt (having to make a flex in one direction, and back the other).

    If you're not asking for much belt power in the first place, it won't matter. If you're already slipping the belt, then it might... all depends on magnitude and load.

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    I'd consider moving the jack-shaft assembly closer forward, but also higher so that the standard length of belt would still fit and there's no loss in pulley contact

    Ultimately, if all you're saving is a couple inches, I'd live with it and set it up as the manual says. If you really need to save space, get a lathe with an under bench drive, or an old overhead jack-shaft. You could probably make an pair of overhead hangers for your current lathes jack-shaft easily. On most of the overhead driven lathes I've seen in old books and manuals, you didn't even need to loosen the belt to change speeds. You guide the belt from one step to another by hand while it's running (just don't tell OSHA).

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    Quote Originally Posted by M.B. Naegle View Post
    You guide the belt from one step to another by hand while it's running (just don't tell OSHA).
    Man, I'd never do that - even if the boss said it was a condition for my job. I've seen way too many videos of people being pulled through their lathes. It's surprising at just how little power is needed to crumple a human body.


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