RE: [CAD_CAM_EDM_DRO] Re: Timing Belts and Pulleys

HI Jon

I thought most the stuff in the US was pretty good quality, sorry to hear
your pulleys are not so.

The ones in the UK I get are normally from DAVAL, in aluminium or steel.

If you measure from the hole to the edge of the pulley there are large
errors, but if you put a slip gauge on the teeth and measure to that you
won’t find an error with a simple calliper.

Pilot bored is normally about a ¼ inch or 5mm hole in the middle, they are a
little cheaper than fully bored pulleys. You drill or bore the hole to size,
add a key way, or grub screw drilling into the flange and your good to go.

They are also available cheaper without the belt guide flange.

We also have very much larger holes and bolt a friction clutch into some,
just in case the machine hits the stops hard the belt survives.



Regs Mark



_____

From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Jon Elson
Sent: 20 November 2006 00:52
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: 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





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