Re: Timing Belt Sizing

Hi hugh, i have been studying belts for a few weeks. First the belts
you are looking at are the worst ones the XL, L, H, ect, these use a
trapazoid tooth. The next series of belts is the HTD series. This
HTD series has a round tooth profile and is much better than the
trapazoid version (gates is droping the HTD line). The best belt to
use is the new PowerGrip GT2 belt by gates. It is stronger than all
the others and has a modified round tooth design. I have been
working with gates to pick out the best belt size. In the first
round with them i gave them a much to large of a hourse power figure.
and got back the following results.

"I ran the life estimates for the 5mm pitch belts and the result are
as follows

56T - 112T with a 5MR-750-15 belt life approximatley 7000 hours
(cd = 6.24")
40T - 80T with a 5MR-625-25 belt life approximatley 8000 hours
(cd = 6.27")

As far as any of the 8mm selections, we are unable to run life
estimates at this point. We are still developoing the test data to
support life calculations.

These estimates were run at 2 hp @ 1000 rpm with 1 1.7 service
factor. If you have any additional questions, please call me."


56T = 56 tooth
112T = 112 tooth
5MR = belt 5mm pitch
750 = belt lenght
15 = 15mm width
25 = 25mm width
cd = center distance

At 10,000 hours of belt life gates recomends you go down a size.

I also learned something astounding. When you increase the diameter
of the smallest pully by 10%, you double the belt life.

And when you increase the belt lenght buy 10% you increase belt life
by 10%.

Also the smaller the pitch the less backlash you have.

The cost for 5mm pitch, 15mm wide or 25mm wide sprockets are within a
couple of dollars of each other.

I think i will call gates back and have him run the numbers using
1/2HP at 1000 RPM. The steppers i am thinking of using can devolope
this much HP.

Gates also makes 2mm and 3mm belts in the GT2 series.


Wally K.

--- In CAD_CAM_EDM_DRO@egroups.com, Hugh Currin <currinh@O...> wrote:
> Mechanical Inclined CNCers:
>
> Here is my second of three questions.
>
> I'm retrofitting a Bridgeport copy for X & Y CNC. I'm using
> 785 oz-in steppers with 5A stepper drivers from Camtronics.
> I plan to connect the steppers to the ballscrews with timing
> belts of 2:1 reduction.
>
> When I run the numbers for a timing belt I find I need a
> 1.0" wide L belt with pulleys of at least 28 teeth and 56
> teeth. This is a driver pulley of 3.3" diam and a driven
> (leadscrew) pulley of 6.6" diam. OR, a 1.0" wide H belt
> of 14 or 16 teeth/28 or 32 teeth. These have diameters of
> about 2.5" and 5.0". The H could be smaller but you run
> into number of teeth in contact problems.
>
> I used Machinery's Handbook for calcs. I used a service
> factor for machine tools of 1.8. This is probably for a
> spindle drive but I don't think excessive for a stepper
> motor drive. Stepper motors aren't smooth.
>
> But this still seems excessive. What are others using for
> the timing belt reduction on Bridgeport sized machines?
>
> Thank you in advance.
>
> Hugh Currin
> Klamath Falls, OR