On Tuesday 20 September 2016 17:20:32 Martin Dobbins wrote:

> Gene wrote:
> >The ball end wouldn't be the tool for the job as the bottom of the
> > gullet has sharp corners except for the OEM belt of a 7x12. And
> > there >are 2 common face angles in >use and I've not the memory to
> > quote whether its 14.5 degrees or 20 degrees for the face angle per
> > belt tooth style.
> >
> >Bigger than xl is probaqbly 20 degrees but that leads to belt hopping
> > if not tighter than a drum so I'd assume its 14.5 on the xl as they
> > will rip the teeth off the backing >before they'll hop a tooth,
> > assuming the shaft centers can't flex.
> Absolutely no experience with timing pulleys here :-), and of course
> from that perspective it's always "how hard can it be?"
> No cnc abuse in this video just a lot of old British iron, but where
> do you get the tooth profiles from? "You can see the belt manufactures
> details or get the profile for the cutter by curving the belt to the
> required diameter.?" (from the comments below the video)
> https://www.youtube.com/watch?v=kCiujbcrQzc
> This fellow just drilled some holes, but since he glibly points out
> that in his case it was pure math to decide drill size and spacing, it
> *must* be OK.
So-so. Doing it with the right size drill (and one that does not randomly walk 
as it starts) would do a usable facsimily of a belt profile from 50+ years ago 
if he then turned off a little more than half the holes diameter.

> https://www.youtube.com/watch?v=vJaacHN-A0Y
> I posted this without a thought to the serious matter at hand, and
> just hope it brightens up your day.
> Martin

The HTC (IMO) is not the most horsepower way even if marketing did call it HT 
for High Torque. I'll have to admit he got an excellent fit though, tight 
machine and spotting drill.  It has a higher tendency to climb the face of the 
tooth after a bit of wear than the "squarer" profiles do.  OTOH it could be 
because I have destroyed quite a bit of that profile of tooth and belt in The 
Little Monster, a 7x12 I cnc'd years ago.  Things are somewhat more dependable 
after swapping pulleys for xl belts.

As always, YMMV.

Cheers, Gene Heskett
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>
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