Re: Timing belts

--- 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."

Belts have several advantages: they are tolerant of dust, don't need
dirt attracting lubrication, have no critical shaft speed and
alignment of the drive mechanism can be downright sloppy and you still
get good results.

I build CNC metal puncing machines. See aircastle.biz I use belts
becuase there is no side force on the drives while punching. I get
repeatability of .0005" due to belt stretch: way better than need for
my purposes.

Gates GT style belts are very good. There are other makers, just
forget the trapazoidal shape teeth, which have backlash.

Don't apologize for belts; they are very good choices in the right
applications.