Mini Mill R8 spindle

sounds like your problem is the same as the one I have with my Grizzly mill - the part of the spindle where the end of the R8 collet ends up (bit closest to the threaded end) is ever so slightly undersize. Some collets go in ok and can get drawn up by the drawbar, others will do what you describe. nothing to do with the pin in the spindle. For my ER25 collet chuck I blued it up with Dykem and carefully knocked down any parts where the dykem was removed. Did that a few times until it would seat. One day I'll very carefully take a sand paper lap to that part of the spindle and see if I can open it up a tiny bit so that my other collets work.
 
Mattthemuppet2, I was also going to suggest the Dykem or perm marker to tell where the problem is. I even had a couple of the R8 that had burs in the grove that rubbed a bit.
You need to see where the problems is before you start working on the spindle other than cleaning, I do see a small bit of light rust that could be cleaned with scotch bright and wd40 but does not look that bad. but take care of it now while searching for the problems before it gets worse.
 
  • The pin and grove look good - nice clearance (especially since I got ride of the burr on the shank)
  • Cleaned the spindle bore and the shank very well and then applied a light oil to both.
  • Was able to get the shank in ok - with a little "juggling"
  • Once in good, I moved the shank in and out of the bore a few dozen times; that seemed to help.
  • Found a good spec on the R8 shank.
  • Then got out the telescoping gauge and micrometer and did some measurements as follows. (Mine in red)
  • r-8_spindle.gif

  • I set the gauge starting at 0.955", which was loose, and started working my way down.
  • So it appears that the finished end (top of the bore) is just barely a slip fit
Thanks to all for the suggestions -
 
I'm thinking you want to leave the spindle throat-to-collet fit fairly tight to be sure the drawbar pulls the collet straight up and doesn't cant it to the side while seating it in the spindle. The drawbar on my machine rattles around in the spindle when there is no collet attached and there is no way to really accurately center it. Without the close collet-to-spindle fit in the throat, it could cant the collet enough to affect tool runout.

You said it was difficult to get the shank out while you were taking the spindle apart. That is normal after it has been drawn up tight with the draw bar. Typically, you will have to tap on top of the drawbar to dislodge the collet after you loosen the drawbar.

Tom
 
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higgite said:
I'm thinking you want to leave the spindle throat-to-collet fit fairly tight to be sure the drawbar pulls the collet straight up and doesn't cant it to the side while seating it in the spindle. The drawbar on my machine rattles around in the spindle when there is no collet attached and there is no way to really accurately center it. Without the close collet-to-spindle fit in the throat, it could cant the collet enough to affect tool runout.

You said it was difficult to get the shank out while you were taking the spindle apart. That is normal after it has been drawn up tight with the draw bar. Typically, you will have to tap on top of the drawbar to dislodge the collet after you loosen the drawbar.

Tom
Click to expand...

Thanks - That's why I was asking about the "range of normal!" I'll leave it alone.

On a positive note - I went out yesterday and checked the spindle runout (0.001" indicator) - outside and inside barely move the needle.
Put the R8 shaft in, with Jacob's chuck, 1/4 drill rod hardly any movement at all.
 
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