Re: Timing Belts and Pulleys

> If they have been hobbed, or done on a gear gear generator of any type, they
> will (should) have used the pilot bore as the mandrel datum.
> If the cutter doesn't "crown" the tooth crests, then the outside could be "out".
> The root dia. and general profile should always be true to the pilot.
> Dave Pope.

Many are hobbed as a stick and then parted off and the hole added after.
It's still down to supplier and quality control. Soft jaws are the way to go as you grip on the part that need to run true.

John S.

> ----- Original Message -----
> From: Steve Blackmore
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Sent: 20 November, 2006 9:30 AM
> Subject: Re: [CAD_CAM_EDM_DRO] Timing Belts and Pulleys
>
>
> On Sun, 19 Nov 2006 18:42:32 -0600, you wrote:
>
> >Steve Blackmore wrote:
>
> >>I just chuck them in the "Griptru" or 4 Jaw, clock the bore central then
> >>bore them out.
> >>
>
> >If the original bore is off-center, then you have made an eccentric
> >pulley. Not a good idea where
> >positioning accuracy is important. On a number of pulleys, the runout
> >of the bore was
> >CLEARLY visible! So, I either use an indicator on the major OD or
> >something that will
> >guarantee centering the teeth. Also, on flanged pulleys you can't
> >assume the flanges
> >are concentric to the teeth.
>
> I'd stop buying off that manufacturer Jon, and buy concentric pulleys.
>
> Steve Blackmore
> --
>
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>
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