Timing Belts

[Ricardoco]

Timing belt is the only type of belt to use here since it is critical that they remain synchronised. Various ways:

1) Short belt from motor to one leadscrew, long belt linking them with idler to tension it.
2) Long belt linking screws, wrap this belt round the motor pulley with idlers - so 3 pulleys on the one belt.
3) Two belts of a similar length going to motor placed in the middle, will make a 'V shape' so you can move motor to tension.

If you go for 1) then this 1595mm belt with 15T pulleys is 760mm center distance (or 1690mm with 34T pulleys is better as more teeth engaged on the pulleys), but that might be a bit risky when it comes to tensioning as if the center distance is slightly more, or the belt is slightly too short (possible due to the manufacturing tolerances) then the belt will not fit or may be damaged. It's safer to get a bigger belt then use an idler to tension it, problem is the next belt length up us 1690mm and the nearest with that over 760mm is 765mm which is too long.
If you go for 2 or 3 there's plenty of options.

Do you consider it critical to avoid slaving the steppers?

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

[boldford]

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

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?

[Jonathan]

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?

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.

[boldford]

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.

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.

[Jonathan]

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

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.

[Ricardoco]

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?

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