Turning a timing pulley

[bgolash]

Hi
I am attempting to turn the ID of this timing pulley and it looks like I off to
a bad start. I pulled my first chip and it seems I`m not taking a uniform
cut off the complete surface. I did indicate the face of the pulley but with
the style of indictor I have I was unable to check the ID for concentricity.
I`m hoping for some tips from the experts here. I don`t have any accessories
like a face-plate so all I have to work with the chuck you see in the
picture.

Regards Barry

[mxtras]

Here's what I did.

I turned a small post to fit the original ID of the pulley then put the pulley on that and held it in place with a bolt and a large washer. I then skim cut the OD of the thin flanges true and to a common diameter (I had more than just one pulley to do).

Then I took a small length of aluminum tubing or pipe and bored it so that the flanges fit snuggly and against a shoulder. I drilled and tapped three screws on the tubing for clamp screws which fit in the root of the pulley's notch. I then used small pieces of aluminum welding wire between the clamp screws and the pulley and snugged it in place and bored the ID.



Scott

[NC Cams]

Three options:

1. I'd look for a cheap dial indicator from Harbor Freight or the like and simply dial indicate in the bore (if it isn't FUBAR'd). Once you do that, you're home free.

2. IF the ID is screwed up, dial inicate the od off the high points of the teeth at 120 deg or 90 deg points, shim A/R to get negligible runout and then bore the ID.

3. Finally (and my preference), you can chuck at the OD over centerless ground dowel pins that are large enough to "bridge" the gap 'tween the pulley teeth. This will get you closer to the pitch dia of the pulley which is what you're trying to make run concentric to the pulley axis. You can then indicate over the OD of the dowel pins, eliminate runout and then rebore ID.

[WhiteTiger]

Your problem is you are locating in your chuck on the belt guide flanges.

Were I doing it, I'd take a piece of pipe larger than the pulley, turn it inside and out to a uniform thickness, then cut three shims out of it. Put one shim between each chuck jaw and the pulley itself (where the teeth are), and you'll be concentric to the limit of accuracy of your chuck. The shims of course have to be thicker than the exposed depth of the belt guide rings.


Tiger

[ViperTX]

You should indicate on the ID....the OD is usually a pressed on piece of aluminum.....indicate on what you're trying to machine...

[MarkT]

Much Similar to Tigers suggestion, I normally undercut softjaws provide clearance for the flange guides. Then I bore the jaws for a good fit on the O.D. of the pulley itself. Normally I can bore jaws with a close enough fit to run true. If you do need to indicate, indicate the surface that has a relationship to the feature you are machining. If perpindicularity is called out to the face, indicate the face then machine the perpendicularity to the indicated surface. If you have material on the face you can remove, kiss that prior to removing the part after you have bored it. The perpendicularity at that point would be as true as your machine is capable of cutting (assuming it does not move in the chuck while being cut). If runout or concentricity is called out to the O.D., then indicate the O.D. and machine the bore to it. If you can or need to cut both, do the bore then I.D. chuck or mount on an arbor style fixture and skim the O.D.
Good Luck!
Mark T

[smoa1980]

Like stated above you need to dail in the Id since that is what you are cutting. If you ahve a lathe then I dail inicator is a must have. dail in the front of the bore and then the back. It is easier to use a 4 jaw chuck to dail something in.

[ViperTX]

bgolash....Hey Barry here's a solution that I came up with....stick a pointed center in the tailstock and use it to center the pulley on the chuck....then check it with a indicator as you manually turn the chuck.

[bgolash]

Hi
Thanks to everyone for their suggestions. To be truthful I decided against potentially screwing up the timing pulley. I ran off to a machinist and he came up with a few suggestions for the timing pulley that I would never had thought of. The Littlemachineshop spindle has a 1.625 ID collar to set the preload. The machinist mentioned that we should shoulder the collar for a slip fit to the pulley. This would allow me the ability to change pulleys if needed.
He also made provisions for a setscrew in the side of the pulley and also cut a key way in the side of the collar to secure the timing pulley. It all worked fine. Thanks again!

Regards Barry

[N4NV]

Yesterday I found myself having to enlarge the bore of 2 timing pulleys. I used Whitetiger's suggestion and it worked great. You can see what it did in this other post.

http://www.cnczone.com/forums/showth...450#post146450

Vince