775 Pro Coupling

[Richard Wallace]

Originally Posted by R.C.

If your looking to do that, then its the same as buying the GT2 pulley here:

http://www.wcproducts.net/gt2-timing-pulleys-belts

Can you point me to a C-C distance calculator that works with the GT2 3mm 12 tooth pinions that WCP sells? The one at SDP-SI only goes down to 16 tooth.

I would like to use this pinion to drive a 44 or 45 tooth pulley from SDP-SI. Will exact C-C set up work, or will I need a side tension system to keep six teeth of the pinion engaged to the belt?

[ajlapp]

In the past I've just emulated the Versa strategy.

I used the VexPro "c" collar from the Versa and just reamed the pulley to 8mm then applied clamping force from a set screw.

[AustinSchuh]

Originally Posted by Richard Wallace

Can you point me to a C-C distance calculator that works with the GT2 3mm 12 tooth pinions that WCP sells? The one at SDP-SI only goes down to 16 tooth.

I would like to use this pinion to drive a 44 or 45 tooth pulley from SDP-SI. Will exact C-C set up work, or will I need a side tension system to keep six teeth of the pinion engaged to the belt?

It's actually pretty easy to do in Solidworks. Draw out the belt as a bunch of arcs with a diameter of (3mm * num_teeth / pi) and straight lines. Use the Path Dimension feature (It's in the drop-down menu in the sketch menu under the Smart Dimension tool) and select all the lines. Set the path length to (3mm * num_belt_teeth). Done!

For short belt runs, you might want to remove a couple thou. We tend to just run exact c-c and move on. For longer ones or more critical ones, we add a tensioner.

[Richard Wallace]

Thanks for the CAD trick -- I will get one of the students to try it!

An equivalent old-school method uses pitch diameter circles and tangent lines connecting them to calculate the wrap angle on each pulley, and then get center distance from the resulting two arcs and two lines. One such calculator can be found here: http://www.gizmology.net/pulleysbelts.htm

Using that one I got 4.773 inch C-C for a 110 tooth belt connecting a 12 tooth pinion to a 45 tooth pulley at 3mm tooth pitch. Will check that against the CAD result before we cut holes in metal. Measure twice ...

[AustinSchuh]

Originally Posted by Richard Wallace

Using that one I got 4.773 inch C-C for a 110 tooth belt connecting a 12 tooth pinion to a 45 tooth pulley at 3mm tooth pitch. Will check that against the CAD result before we cut holes in metal. Measure twice ...

Our favorite reduction is a 56 : 12 with a 67 tooth belt. I think we might have had 6 of them last year. I love GT2 since there is such a safety factor that it isn't a huge issue if you don't get everything else perfect. (6 teeth of engagement is 180 degrees. I try to target at least 120.)

[asid61]

Originally Posted by Richard Wallace

Can you point me to a C-C distance calculator that works with the GT2 3mm 12 tooth pinions that WCP sells? The one at SDP-SI only goes down to 16 tooth.

I would like to use this pinion to drive a 44 or 45 tooth pulley from SDP-SI. Will exact C-C set up work, or will I need a side tension system to keep six teeth of the pinion engaged to the belt?

You can change the type of pulley to "timing pulley stocks" to get down as low as 6t. You also have to go to Metric instead of Inch.

EDIT: I got the same result but with only 5 teeth in engagement.