Timing Belts

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Originally Posted by Ricardoco

Evening Jonathan, thanks for the reply, I can drive 1 screw directly with stepper and pulley from one screw to other with pulley, i dont have a choice about the slaving. so option 1, and i will drive 1 screw directly with stepper.. Magic Thanks.

I do have lateral screw adjustment from 755mm to 765mm center to center so fingers crossed manufacturing tolerences should not be a problem..

Rick

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Am I missing something but, isn't it possible to locate the motor between the two lead screws and fit two pulleys to the motor to drive two belts?

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Originally Posted by boldford

Am I missing something but, isn't it possible to locate the motor between the two lead screws and fit two pulleys to the motor to drive two belts?

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That's tricky with a Nema 23/24 motor since the shaft is not long enough to accomodate two pulleys for 15mm wide belts. You could bolt two pulleys together, so one would overhang on the shaft, but that might be a bit much force for the motor bearings. Adding an extra bearing would sort that, but if you don't have access to a lathe or milling machine that gets tricky.

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Originally Posted by boldford

Am I missing something but, isn't it possible to locate the motor between the two lead screws and fit two pulleys to the motor to drive two belts?

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You are quite correct you could do that in a simillar way as stated in another post and have a V arrangement to cover tensioning, however i havnt mentioned it before but i have such a limited working space that there is only just enough room below the bed for the belt .. But thanks anyhow...hope that makes things a little clearer..

Rick

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Originally Posted by Jonathan

That's tricky with a Nema 23/24 motor since the shaft is not long enough to accomodate two pulleys for 15mm wide belts. You could bolt two pulleys together, so one would overhang on the shaft, but that might be a bit much force for the motor bearings. Adding an extra bearing would sort that, but if you don't have access to a lathe or milling machine that gets tricky.

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Bore 'em out then fix 'em on a common sleeve. The tension on the two belts would tend to cancel out if the thrusts are arranged to be reasonably opposite. The belts don't necessarily need to be the same length so the motor need not be centrally between the leadscrews.

Just my two-penny-worth.

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Originally Posted by boldford

The tension on the two belts would tend to cancel out if the thrusts are arranged to be reasonably opposite.

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Yes of course, but one of the pulleys is much further from the front motor bearing so there will still be a larger moment load on the shaft. Still, I'm probably being being overly cautious.

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Originally Posted by Jonathan

Within reason - using too small pulleys can stress the belt too much or risk leaving not enough belt teeth engaged with the pulley. I avoid using less than 15T pulleys for this reason.i

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If you look I said any belt that "suits" and obviously too small giving wrong tooth engagement wouldn't suit would it.?

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Originally Posted by boldford

Am I missing something but, isn't it possible to locate the motor between the two lead screws and fit two pulleys to the motor to drive two belts?

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Yes it is and that's how I did it first time but found it hard to get even tension on each belt.! It also means having the screws offset or one machined longer or like in my case where I hadn't allowed for this when machined due to originally going to use slaved motors screw extensions needed making.

The way I have it now isn't pretty but it works very very good and super reliable and easy to swap ratios.!

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Originally Posted by JAZZCNC

If you look I said any belt that "suits" and obviously too small giving wrong tooth engagement wouldn't suit would it.?

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True, hence I clarified for anyone who does not know that a small pulley not be suitable.