Concentricity

[gwarner]

I have a Rockwell lathe that uses 4c collets. The diameter of R8 collets is the same. The difference is the length and the taper.
In hopes of using abundant R8 collets I made an adapter that screws on my spindle and I matched the 16+ degree taper.
There is less than .001run out in my adapter because I turned it in place. All my 4c collets run true with out an adapter. The problem is not in the lathe
I'm certain the taper is correct as I set it using an indicator and the collets hold when I press them in lightly .
My issue is I consistantly get around .008- .010 runout on the R8 collets.
I made sure the collet puller is pulling straight as my first 2 tries threading the 7/16-20 with a die were off.
I cut the pullers threads on the lathe and it is now true.
What could cause them to be off this much? I'm stumped

 

[jbobb1]

Does the run out repeat when you remove and reinstall the same collet?

 

[gwarner]

Runout is close to the same for several collets. Tried different rods as well.
Same rod in the 4c and has less than .001

 

[jaek]

R8 collets have the front taper and the rear 0.9495” cylindrical section - does your adapter have both?

 

[gwarner]

The lathes spindle bore is that diameter and even has the key so where the cylindrical section goes is not part of the adapter.
The adapter threads onto the spindle and the 1" taper sticks out past that.
4c collets are 3" long(1" shorter) and have a different taper but same cylindrical section diameter.

 

[jbobb1]

No interference with the key in the spindle bore to the R8 collet?

 

[Mini Cooper S]

You might want to put a straight rod in a collet and run an indicator along the top and side to check if there is any wobble as well as runout. Just a thought.

Richard

 

[gwarner]

Thanks for the replies.
Pretty sure its not the key as both collets use it.
Great idea on the length of the rod.I'll try it when I get back down to the shop.

I played with it some more late yesterday evening.
One thing I noticed. If I tighten the collet then it averages around .008 runout.
If I then back off the tightener it drops to .001 run out. The item is still held in securely but the puller seems too loose.
Am I perhaps just over tightening them?
It not like I'm leaning on the wrench. About 1/16 to 1/8 turn after it seats.
My 4c collets I have a hand tightener and I get them as tight as I can.