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View Full Version : Accurate chucking of timing belt pulley stock



alsinaj
09-05-2012, 10:06 PM
I need to part off a few hunks of timing pulley stock, then bore them concentric to the outer, corrugated surface. The grooves aren't friendly to dial gauges. Is there a trick way to do this accurately?

Don Young
09-05-2012, 10:37 PM
Turn and bore a bushing to slip over the pulley stock or use something like a thick feeler gauge between the stock and indicator. A close fitting bushing could mount the stock in a chuck and centered with the spindle pretty well. A suitable collet or soft chuck jaws bored to size would not need a bushing. If it's a reasonable thickness the bushing would tighten enough without being split. A button head on a dial indicator could be used also.

Mcgyver
09-05-2012, 10:55 PM
one of the wide flat tips in a test indicator would work well. If you don't have one, just use a DTI, go slowly and orient such that the drops off the edge rather than colliding - ie so its not acting like a ratchet.

http://www.grainger.com/Grainger/STARRETT-Indicator-Contacts-2ZUJ3 (wow those have gotten pricey!)

small.planes
09-06-2012, 03:42 AM
Unscrew the tip of a plunger type indicator, and them make a large flat button to screw into it.
You are only interested in relative, not actual measurements to center, so the button size is uncritical :)

Dave

Machtool
09-06-2012, 04:07 AM
I always do them by dropping ground dowel pin's in the tooth profile, pick a size that fits nicely in the flanks. Then 4 jaw chuck them, indicating over the top of the pin. It works even on timing pulleys with a tooth count that isn't dividable by 4.

Forrest Addy
09-06-2012, 05:12 AM
Set up a flap finger if 0.010 brass shim stock so it's tangent to and bearing against the pulley material. Place the indicator so the plunger contacts the point of tangency. The plunger follows the shim and doesn't drop into the slots.

That's Trick #1

Trick #2 Install soft jaws on a good three jaw and bore them to suit the major diameter of the pulley stock. Be sure there's a clean shoulder in the jaw bore.

Trick #3 Grip the pulley stock in the soft jaws, bump the overhanging end to concentricity, center-drill and support with the center. Face the centered end most of the way to the center. Flip the material around bumping the machined face firmly against the shoulder in the soft jaws. Part-off pulleys and machine to config, bore, leave the width a little long for a second op facing cut.

winchman
09-06-2012, 06:34 AM
It seems like it would be dangerously easy to force round pins between the teeth of the pulley while tightening the 4-jaw.

michigan doug
09-06-2012, 04:13 PM
I don't think he is suggesting you clamp on the pins, but just indicate off the pins. I've been wrong before though...

Finest regards,

doug

macona
09-06-2012, 05:23 PM
I use collets, 5C or 2J.

LES A W HARRIS
09-06-2012, 10:17 PM
I need to part off a few hunks of timing pulley stock, then bore them concentric to the outer, corrugated surface. The grooves aren't friendly to dial gauges. Is there a trick way to do this accurately?

Forrest's trick # 2, Most stock is made with topping hob's, so the O.D. of the pulley is concentric to the teeth.

Cheers,

oldtiffie
09-07-2012, 02:26 AM
This was for centering/checking reamer cutting edges but the principle is the same.

http://i200.photobucket.com/albums/aa294/oldtiffie/Sketches/Measurereamer1.jpg

macona
09-07-2012, 06:16 AM
The cogs on the belts generally do not ride in the bottom of the pulley's grooves but ride on the outer surface, so the outside is what really matters.

Machtool
09-07-2012, 08:02 AM
It seems like it would be dangerously easy to force round pins between the teeth of the pulley while tightening the 4-jaw.
With in reason, that would be correct. But only if you considered your self a hack, That's where you have to be known to be able to differentiate between delicate and squeeze the Fxxx out of a 4 jaw with a cheater bar.

Just saying, a correctly fitted dowel pin will often over come a belt flange. Doesn't apply in this case, as he is doing raw stock.