[Les A W Harris]

Thanks guys. Been there, and when clicking through the "Partview" feature for both specs & cad files, I stumbled across this:



Not all samples displayed the above, but both the 30 and 71 grove (among others) in the 8mm pitch x 12mm width, did. Needless to say, because of the critical nature of the profile, I'm a little dubious because of the warnings.

The GT2 Polychain did not exist when I last cut cogs, I downloaded the design data & Patent data, the [x~y] co-ordinate equations are listed, and one could crunch the numbers to get the form, tolerances are given in the spec.

As posted the form is a kind of involute so each tooth count is different in form, I expect they are normally hobbed or shaped, Ash Gear has tools for most of the older types, but one has to enquire for this form, [proprietary].

In the Gates PDF downloads is an interchange doc showing the differences.

So, in my opinion the CAMBAM form is not correct.

Gates drawings are representative, not actual form, as each tooth space is different for each number of teeth, apparently they can not display the true form in a cost effective manner, because then we could just download, make a form tool and mill it that way.

As this is for yourself, not for resale you could crunch the numbers to get the profiles you want and make form tools to mill them.

Cheers,