# Modifying a R8 Shell Mill Arbor



## TomS (Jul 16, 2018)

I have a Ultron Snap Change tool changer on my CNC mill.  This setup works great but the downside is new tool holders are expensive, especially their shell/face mill arbor.  Not wanting to spend upwards of $140 to $150 for one holder it hit me that I might be able to modify an R8 arbor.  I figured worst case is I scrap a $15 import arbor.

I mounted the arbor in a 1" 5C collet and supported the outboard end with a live center.  Believe it, or not, I had about .0002" TIR on all of the machined surfaces.  In this picture I'm machining off about 1-3/4" of unnecessary material.



This is a picture of a OEM tool holder.  The critical dimensions are the location of the built in pull stud in relation to the R8 taper.  



Here's a close up of the built in pull stud.  If too much material is machined off the inside face of the pull stud the holder won't be pulled into the spindle R8 taper tightly.  Leave too much material on this face and the gripper won't fully close and lock into position, and the holder falls out of the spindle.  The tricky part is getting this holder to lock into the spindle with the same tension as the other holders.



Here's the finished product.  I had to set it up a few times to take skim cuts on the pull stud face to get it right.  In the end it turned out nearly perfect.  The needle on my .0005" DTI barely moves with the holder mounted in the spindle.


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## TomS (Jul 17, 2018)

I just realized I posted in the PM forum instead of Project of the Day.  If the moderators want to move please do.


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## TomS (Jul 18, 2018)

This has worked out so well I'm going to modify a JT6/R8 and a JT3/R8 arbor.  The OEM holders are less expensive than the shell mill arbors but still cost about $100.


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