Fixturing a step pulley for boring

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rfdes

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As a beginner it seems that the simplest problems are the biggest challenge.

I have a small (~3" dia) 3 step pulley with a bore (0.5") which needs to be bored for a bushing. The pulley appears to be a machined, cast iron, pulley that has been painted to prevent rusting. I need some direction as to how and mount this in the lathe for boring. It seems that the obvious thing is to mount it in the 4 jaw and indicate off of the bottom of one of the vee grooves. However, it seems that the pulley may/may not lie parallel to the 4 jaw due to the roughness of the machined casting. Also, I'm concerned that that I will be holding the pulley only against the outer edges which doesn't seem stout enough to me.

With the pulley bore be only 0.5" or so, how would one indicate against the bore? Is this a viable option?

Your help would be appreciated.
Thanks - Jim
 
I would make a snug slip fit plug to fit the bore with about 2 " of overhang and indicate off that...close to the pulley and then out farther to see if it was running true.

David
 
You should be able to make the pulley run true even though its a casting. Even if one part of it doesn't touch the chuck face the jaw will hold it in. I would indicate it off the middle of one the vee groove sides not the bottom. The belt shouldn't ever touch the bottom so some may not be true. Just my thoughts...Bob

alum 045.jpg cc5.jpg
 
I would use a DTI Dial test indicater in the bore. As far as holding it, it would depend on the pully. Post a pic would help.
 
I agree with Bob. Indicate to the belt grooves. FWIW - I was taught many years ago, when I was an apprentice, that you should avoid dialing in a part using a surface that you will machine away, e.g. the bore of this pulley.

Tom S
 
Thanks to all... This weekend, I will attempt to indicate to the groove and see how it goes.

I certainly appreciate all of the advise.
Jim
 
rfdes said:
As a beginner it seems that the simplest problems are the biggest challenge.

I have a small (~3" dia) 3 step pulley with a bore (0.5") which needs to be bored for a bushing. The pulley appears to be a machined, cast iron, pulley that has been painted to prevent rusting. I need some direction as to how and mount this in the lathe for boring. It seems that the obvious thing is to mount it in the 4 jaw and indicate off of the bottom of one of the vee grooves. However, it seems that the pulley may/may not lie parallel to the 4 jaw due to the roughness of the machined casting. Also, I'm concerned that that I will be holding the pulley only against the outer edges which doesn't seem stout enough to me.

With the pulley bore be only 0.5" or so, how would one indicate against the bore? Is this a viable option?

Your help would be appreciated.
Thanks - Jim
Click to expand...


Put a piece of 1/2 inch drill rod in your tail stock drill chuck.
Slide the pulley bore over the drill rod and slide the tail stock forward.
Carefully tighten the outer rim of the pulley with a four jaw chuck.
Slide the tail stock back and forth and make sure that the drill rod inserts into the pulley hole smoothly.

Dial indicate the pulley hole to make sure that it is within your tolerances.
Insert a bigger drill into the tail stock and make a larger hole.
Use a boring bar to make a perfectly sized hole.

Hope this helps.
 
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