Re: [CAD_CAM_EDM_DRO] Timing belt pulleys -- manufacture

A question or two for you John:

When you machine the cutter, is it REALLY necessary to put a radius on the
bottom? Wouldn't a flat bottom with nearly square corners give more
clearance?

It would appear a cutter made as indicated above could then be used to cut
ANY size (number of teeth) pulley. Is that correct?

Smoke
-----Original Message-----
From: John Stevenson <machines@...>
To: CAD_CAM_EDM_DRO@egroups.com <CAD_CAM_EDM_DRO@egroups.com>
Date: Saturday, November 11, 2000 4:42 AM
Subject: [CAD_CAM_EDM_DRO] Timing belt pulleys -- manufacture

>As an introduction let me say what we do. We build special purpose machines
>like Ink Mixers and Pencil production machines to name the most popular.
>We use poly vee belts now as being more suitable for our work but before
>that we used a lot of timing belts. As a lot of our work is one off's
>development plays a large part and before invertors we would spend hours
>changing pulley ratios to suit the machine. To this end to save time and
>costs we made our own.
>At the time we couldn't find much info on these, no WWW and manufactures
>kept information close to their chest. So I worked backwards from known
>pulleys and got our own formulae sorted out.
>Now I have shelves of books on the design of these and just looking through
>them last night all the calculations that are so freely in print work out
>exactly to the ones we arrived at in about 79 - 80
>Truly gratifying to read the penciled in corrections in the margins of
>these earlier books.
>
>Initially we used to use a fly cutter as that was all we had. Later we made
>a milling cutter similar to a gear cutter with 12 teeth. These were all for
>the L series 0.375" pitch BTW.
>We put the small radius on the bottom but as it was a lot harder to produce
>we left the top radius off and actually formed this by polishing the
>finished pulley on a course wire wheel. This deburred it and also took the
>sharp edge off the top to give a decent radius.
>We also found very little difference in tooth form between small and large
>pulleys so decide to just use the one cutter, hopefully the belt taking up
>any errors. in experience we found no problems. We ran up to about 3 Hp on
>1" wide belts up to 1500 rpm, and on the smaller belts and pulleys we also
>ran cutters in excess of 9,000 rpm. For these we usually used the XL 0.200"
>pitch series.
>As proof we have pencil sharpening machines in production that work at
>22,000 pencils per hour. These have now been in service for up to 15 years
>and are just coming back in for refurbishment. The pulleys are still OK and
>won't be changed.
>
>As I said earlier we now use poly vee belts which are not suitable for
>CNC's as they aren't timed but if I was going through all this again I
>would seriously look at the HTD range of curvilinear belts. Not having
>studied them in great detail but it looks from a couple of simple
>calculations that you can drill a series of holes and then turn the outside
>off to get a pulley. A far easier job. I may even look at this in more
>detail.
>
>As most of the people on this list are hobby types and would probably be on
>the XL series, possibly even the MP series I would have no qualms about
>producing my own with a form tool as the speed and HP required are well
>within anything these can handle.
>--
>
>Regards,
>John Stevenson
>Nottingham, England
>
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