Center to Center Distance in Power Transmission

[Adam.garcia]

Originally Posted by compwiztobe

What are some of the known tolerances on tension and the center to center distance?

I can only speak for the area where I have experience. I've spoken to many people around the FIRST and CD community, and they have said that it is a general rule of thumb to follow these tolerances:
Single-Speed Gearbox: +.000 - +.001 in.
Multi - Stage Gearbox: +.002 - +.003 in.

You can find more information about tolerances (and even a Center to Center Distance Calculator) here:
http://wcproducts.net/how-to-gears/

Hope this Helps!

[Aren Siekmeier]

I'll speak to some our own team's specific experiences:

Our 2012 intake was driven by a 1:1 timing belt (16t XL sprockets) from a P60, and the center to center distance was calculated assuming circular sprockets and their published pitch diameter, as well the outer loop distance of the belt (not sure why). We ended up with a belt that could have been any tighter, which was probably not efficient or very healthy for the mechanism (though I have a relative lack of experience with belts). I don't think the tolerance was particular good in this case, however... And sorry I don't have more numbers, I have none of the CAD in front of me at the moment.

On an off season project last summer we had a chain reduction between 10t and 42t sprockets (#25 chain). We used the center to center distance given by a chain path in Solidworks (using the pitch diameters supplied by Andymark) that was a multiple of the pitch (.250). This was of course also assuming circular sprockets. We wound up with very loose chains that would not have functioned properly without tensioners (perhaps as expected because of the irregular 10t sprocket). The tolerance on this should have been excellent as we had the plates done by CNC (probably .001 or 2, but I wasn't directly involved in that spec).

[artdutra04]

For timing belt center to center distances, I've always used the SDP-SI Belt Calculator to easily run through various options of available belts and sprocket sizes. The timing belts used in FRC don't stretch any appreciable distance, so I always use the exact CTC distance and have never had to use a tensioner.

[chadr03]

I have measured a few AndyMark gears for tooth thickness and they have all allowed for .005 to .010 of backlash at standard centers which is about where you want to be these types of transmissions. I would recommend a -.000 to +.003” CD tolerance on gearing.

Just remember a little bit of backlash is a good thing. You will destroy a gearset quickly if they are in a tight mesh.