[How do I?] True up ER32 Taper on R8 Shaft---FIXED

jocat54

Active User
H-M Supporter Gold Member
Joined
Dec 25, 2011
Messages
591
I bought a cheap R8 ER32 collet chuck and the ER32 taper is about .006 out of round. I have since bought one of better quality and very happy with it, but now want to fix the cheap one. (Can't help myself--just have to fix it)
How would you go about trying to bore the ER32 taper? I thought about just mounting it in the lathe using the chuck to grip the round part but that wouldn't really make it concentric to the R8 taper.
Ideas on how to do this?
 
Mount it in the mill spindle and grind the taper with a tool post grinder or shop made substitute. Set it up so you can set the taper with a sine bar and gage blocks. Before you do anything, check the mill spindle for runout and for loose bearings.


Thanks Bob. The mill spindle is good. I just couldn't figure out how to mount in in the mill and true it up---senior moment is what I'm claiming:D
 
See if Tony has a cylindrical grinder with an internal grinding attachment you could use.:big grin:
If you have an accurate way to chuck up and get the OD of the shank running true, all you have to do is rig up a grinding attachment on the lathe and use the compound to regrind the tapered bore. Rig up as Bob shows are regrind. Hum, I might try that on regrinding my spindle to correct the taper from misuse before me.
 
You chuck up a large enough piece of aluminum in the lathe , about 5" x 1 1/2" dia. I'd drill a clearance hole for 7/16" , then I'd drill the depth and size of the straight part of the collet , then I d turn bore the taper for r8 , fit the adapter to the bore . Then I'd take the chuck off machine and bolt the adapter into the piece in the chuck , after that's tightened I'd reinstall the chuck and set up to grind the taper internally . You can check it in the lathe because you didn't take it out of the chuck . Just how I'd do it in my lathe
 
I hacked up a fix so that the ER32 chuck is usable--about .001 runout,
I turned a 1.5 round bar between centers to true up the outside and then mounted it in the chuck and punch marked the location to the chuck (so I could remove and return to the same place in relation to the chuck) and then made a holder for an R8 arbor. I set the compound using a R8 arbor and dial indicator, same for the ER32. Mounted one of my other R8 in it and checked for run out--it was good.
Then mounted the cheap ER32 chuck and bored the ER32 taper. There is no hard metal on this, cut easily with brazed carbide boring bar. Checked it and still had
.008 run out:disgust:
Mounted it back in the lathe with center drilled short piece of .5 drill rod in the ER32 and turned the R8 taper just mounted in the lathe chuck and tailstock center.
I got lucky it has about .001 run out.:D



R 8.jpg R8.jpg R8-1.jpg
 
How true are the threads? An ER collet is a double angle collet. Both front and back tapers affect the alignment.
 
How true are the threads? An ER collet is a double angle collet. Both front and back tapers affect the alignment.


I think the threads are good, I have 4 ER32 nuts and they all screw on the chuck nicely and don't change the run out.
 
Last edited:
Back
Top