Hey Outlawtaz, thank you.

I do not know enough about belts to give you an educated answer.
However, I did talk to an engineer with the Belt Corporation of America some
time ego and he told me that most belts have the majority of stretch within the
first 10 hours of use. Then it tapers down and stretches little for a long time
until material degradation starts and then it picks up again until the belt breaks.

One of the main reasons I wanted to explore the power nut system is that I think that it is
much less effected by belt stretching and belt backlash than other conventional systems.

Let me give you an example:

I am going to compare a standard pinion/rack drive system which most people
use here and which is basically an industry standard. All numbers are rounded.

Let's say there is a 0.01" of belt 'looseness' in the rack and pinion drive.
The big pulley (60T) has a pitch diameter of 2.256" which equates to a circumference of 7.1".

0.01" relative to 7.1" would be a 0.00141 ratio (0.01 ÷ 7.1).

So, 0.01" of belt backlash produces a backlash at the big pulley at a factor of 0.00141 of circumference.

The pressed-in steel pinion has a pitch diameter of 1" which equates to a 3.142" circumference.

3.142" circumference at a factor of 0.00141 equals to a backlash of 0.0044" at the rack.


Let's say there is a 0.01" of belt 'looseness' in the power nut drive.
The nut pulley (40T) has a pitch diameter of 1.5" which equates to a circumference of 4.7".

0.01" relative to 4.7" would be a 0.002 ratio (0.01 ÷ 4.7).

So, 0.01" of belt backlash produces a backlash at the nut pulley at a factor of 0.002 of nut lead.

The 1204 ball nut has a 4mm lead which equates to 0.158".

0.158" of lead at a factor of 0.002 equals to a backlash of 0.0003" at the screw.


I just hope I am not wrong with my math and, if I am not, a rack and pinion drive seems to have
at least ten times more backlash than a power nut drive for a given belt looseness.

Another possible advantage would be the pulley ratio. A 1:3 reduction (20T to 60T) means that
the small stepper pulley just provides the necessary minimum amount of tooth engagement and
the belt has to be fairly tout to avoid belt jumping.

For the power nut, there really is no need for a gearing (38T to 40T) and the belt can be run
looser to minimize friction and wear without belt jumping.

Somehow, your questions always seem to require elaborate and lengthy answers.