Re: Timing belts

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "aircastlebiz" <john@a...> wrote:

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "mmeyers1111"
> <mmeyers1111@y...> wrote:
> > I'm building a 3ft by 4ft router. Has anybody successfully used
> > timing belts to control gantry movement and could you recommend a
> belt
> > type and a supplier? Should I expect backlash problems controlling
> > movement over a 4 ft distance? Other problems?
> >
> > The belts and pulleys seem to be relatively inexpensive, it seems
> > relatively simple to implement, and gantry speed could be changed
> > easily with pulley diameter changes. How come timing belts don't
> seem
> > to be used more for cnc router control?
> >
> > Mike
>
> There are reasons why belts are not common, but they are not great
> reasons. Backlash/stretch is one, but you can deal with it by using
> belts with the rounded teeth to control backlash. Clamp both ends of
> the belt and have the motor travel along the belt like a flexible rack
> and pinion. Use idler pulleys on either side of the motor pulley to
> bend the belt arround. This cuts the belt length and the stretch in
> half. Another reason is lack of mechanical advantage. A screw will
> move the gantry .2" or less per turn of the motor, while a belt drive
> move causes a 1" or more mover per motor turn. This is fine if you
> want fast rapids. If you need more force, add two more pulleys and a
> belt to "gear down."

I have flip-flopped on belts or screws many times.

Screws requrie machining the ends, an expense or a PITA.

belts require gearing the drive pulley down so an additinal set of
pullies is needed, an expense.

A drive system with GT2-15mm belt width and 5mm spacing will find an
28 tooth drive pulley for the belt as about the minimum that will fit
on a 1/2 shaft. That means 1.709 OD (Per SDP's site) and that means
5.36" per gear rotation.

A leadscrew will have 5 or 10 rotations per inch so can often be
direct drive.

So, the question is what is easier to make, the belting driven section
with belt ends and a motor pulley reduction system, or machining screw
ends and making a screw that has not axial movement.

If they are equaly hard or equally expensive, which will deliver more
accuracy or more power ?

Dave