Re: [CAD_CAM_EDM_DRO] Timing Belt Sizing

Hugh: I am currently running 3/4" "L" series belts with 12 tooth and 24 tooth pulleys. Even the knee feed(z axis) has a 3/4" belt.
This one really should be a 1" belt but I was having trouble finding a 12 tooth in 1" . So I will use a 1" 14 and 28 tooth pulley on
the knee. My motors are about 1200 oz. in.. I was drilling some very big holes with the x axis(angle head) and had no problems. One
drill pass was from 1" to 1 3/4" . The program went haywire and went rapid feed into the piece. It just pushed it down the table. It
was a piece of cold rolled clamped very tightly to the table.
Those big pulleys would be overkill. Particularly with only 785 oz. in. I will try to find a 1" kevlar belt for the knee at some
point since it is pushing a good bit of iron up and the kevlar won't stretch as much. I hope that this helps, Carey.

Hugh Currin 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
>
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