Re: [CAD_CAM_EDM_DRO] Re: Timing Belts and Pulleys

Mark Vaughan wrote:

>I've bought many piloted pulleys and bored and keyed them to size.
>
>I have never found one where the bore is really out of centre at least not
>that you could measure with simple machine shop kit.
>
>
>

I have bought them at various times from W. M. Berg, SDP and McMaster-Carr.
ALL had easily measurable runout! Just use a dial caliper from the bore
to the
OD and take 3 measurements at random around the circumference. I've never
seen one that was better than a few thousandths of an inch, ie. easily
measured.
The sintered iron XL pulleys from McMaster seemed to be the worst, I
guess the
sintering process may lead to variable shrinkage.

>Nowadays to bore and key them we use an EDM wire machine, it's easier for
>the keyway.
>
>I have had some measured on a CGM, and the pilot is normally within 3 to 5
>micron of the teeth, but not true to the outer belt guide rim, which is
>perhaps what you are experiencing, but practically doesn't really matter.
>
>
>
>If you are buying them piloted and out of centre, I hope you are demanding a
>low price since they would appear to be seconds. The whole basis of buying a
>pulley with a piloted bore is that the bore is centre and true to allow
>simple machining.
>
>

I'm not sure what you mean by piloted. Most of them have hubs with
setscrews, and some
standard bore like 1/4 or 3/8". There are also hubless sprockets with
taperlock hubs that
are supposed to be much more accurate. They are also vastly more expensive.

I didn't make any demands because I intended from the start to bore them
out.

Jon