General question about re-installing a chuck

[poorboy]

A quick question - I have a buck set-tru chuck that I adjust where the TIR is measured around .0003 (or so). If I remove the chuck and install it later on - I see that the TIR has increased to around .0015 (or so). I am assuming that this is normal ? Do most people re-indicate their chucks and re-adjust them after re-installation ?

thanks

Adam

 

[SLK001]

What kind of mount do you have? Increases in runout can be caused by an "unclean" mounting surface or debris in the way.

 

[benmychree]

Probably depends on what type of spindle you have, mine are screwed on and I would expect to re adjust when reinstalling, with other styles of spindles, if they are reinstalled with the same position, the tendency would probably be less, also, who really needs .0003" concentricity anyway? I have doubts that they were rated to that degree of repeatability as new.

 

[davidpbest]

If you have a CamLock type spindle, make sure you mark the chuck and the spindle housing so that the chuck is clocked identically each time it's installed. You want the same CamLock pin to go into the same hole on the spindle each time the chuck is installed. Here's an example of a chuck and spindle that have a proper indexing mark on each component.

 

[poorboy]

I have PM-1340GT lathe using a D1-4 camlock. I have marked the chuck and spindle (as David mentioned above), but it seems that upon reinstallation of my buck chuck the TIR increases (all surfaces have been cleaned). I was just wondering if this is normal or not.

Adam

 

[Asm109]

Its a 3 jaw chuck, they are not perfect. Use when you don't need perfect. If you have a critical cut to make, take the time to dial in the set tru feature. Otherwise make chips.

 

[mikey]

I have PM-1340GT lathe using a D1-4 camlock. I have marked the chuck and spindle (as David mentioned above), but it seems that upon reinstallation of my buck chuck the TIR increases (all surfaces have been cleaned). I was just wondering if this is normal or not.

Adam

Try this. Mount your chuck and then adjust it to have minimal run out with a precision pin. Mark one of the jaws and the pin with a Sharpie so they align, then dismount the pin and then the chuck. Now reinstall the chuck and pin, making sure you line up the Sharpie marks and try to use the same amount of torque you used to tighten the pin in the chuck the first time.

You should have nearly as little run out as you did when you first adjusted this pin.

Now, does this matter? It depends. If you're doing a production run with the same exact diameter stock then an adjust-tru chuck is useful for accuracy; once you adjust it the run out for the part should be very low and as long as you're using the diameter stock the chuck is adjusted for then run out should be the same for every part. BUT if you are using the chuck to hold parts that are different in diameter from the diameter the chuck was adjusted for then run out will increase, regardless of whether the part is smaller or larger than the original part the chuck was adjusted for.

A 3 jaw chuck used for first operations will be dead on accurate for all first operations, regardless of the nominal diameter of the stock being turned. Where an adjust-tru 3 jaw comes in is when you need to use that chuck for a second operation for some reason; that is, you're re-chucking an already turned part and need to realign it with the spindle axis.

Just keep in mind that for most lathe work where the diameter of the stock varies or is not previously turned/ground, AKA first operations work, an adjust-tru chuck is superfluous and concerns about accuracy of the chuck run out are pointless. Just use it and be happy.

 

[poorboy]

I also found out that if I only use the master pinion to tighten the work, I can re-install the chuck and the TIR is reduced to .0005. Not sure why, but it is repeatable.

Adam

 

[ddickey]

So the problem was you were not using just the master pinion?

 

[poorboy]

Yes the TIR went down dramatically after I switched to only tightening using the master pinion. I tried removing and reinstalling the chuck multiple times and only tightening using the master pinion I get a TIR of less than .0005.

Adam