On Wednesday 21 September 2016 01:15:54 Chris Albertson wrote:

> Actually drilling the timing belt is not a bad idea.   The older MXL
> type belts used a trapezoid tooth belt but the new high torque "HTD"
> Designs use circular profile teeth.    They really are bater and
> transmit more torque with less belt tension required.   Even newer
> designs are GT2 and GT3 and they use circular test also.  It seems
> counter intuitive at first that round teeth would hold more force. 
> But the load is more distributed the the tooth profile lack street
> concentrators (corners)  Any new design should be using g the HTD or
> newer profiles
Humm. All I have done with the small round teeth stuff has failed in 
relatively short times.  Even the OEM motor in its OEM mounting could 
make it hop teeth and burn up both the teeth on the belt and the black 
plastic pulley on the motor.

However, after mounting my jackshaft in the same manner as the OEM motor 
was mounted, I now understand that it is not the most rigid mount, and 
does allow the motor, or my jackshaft, to flex enough that it finds the 
slack to start the destruction process.

So now my jackshaft has an adjustable screw sticking out of an added boss 
on the load end of the shaft that is in solid contact with the bottom of 
the bed, and located directly in line with the reaction force of pulling 
a heavy cut.

I also changed the "gear" ratios so as to get another 300 revs when the 
backgear is in low. That reduces the pull on the belt at the same time. 
I don't recall having the backgear in high unless cutting alu since.  
Top revs in high gear for TLM is about 1500, low gear around 750-800.

> This is the tooth design I was thinking of when I said "ball end"
> mill.
> While on the subject I found a neat program that will let you design
> almost any kind of gear (yes ANY kind, even non-round ones) then then
> it creates G-code to make it.
> http://www.gear2motion.com
> I've not used it myself and likely will not as it seem to run only in
> MS Windows.

I have to wonder if wine or crossover will run it. When I have some time 
(whats that) I might find out.
> On Tue, Sep 20, 2016 at 2:20 PM, Martin Dobbins <tu...@hotmail.com> 
> > 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.
> >
> > 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

Thanks Chris.

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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