fit of an R8 arbor

[wrenchcruncher]

I bought a mill about a year ago & have used it alot with various R8 collets and a 2" face mill. When i draw any of these up with the drawbar they will seat in the quill, and for removal i need to loosen the drawbar & tap it to unseat the tool. I just bought a 3" face mill & when i draw it up into the quill it will seat with no runout but as soon as i loosen the drawbar it begins to drop out of the quill without being tapped. Is this ok?. I have been told it is, but i am worried about damage to the quill if it is not ok.
I was told an R8 is not a press fit taper such as a morse taper, is this true?.
thank you

[rustamd]

morse taper is self locking, while R8 design is not, (i'm guessing it was aimed at production work, designed to take less time to change tools)

[wrenchcruncher]

Thanks Rustamd. Thats what I thought, just didnt want to do any damage to the quill

[jhowelb]

The R-8 collet must compress around the tool it is intended to hold, the taper at that end of the collet causes that compression. Your mill won't compress so it just drops!

[Geof]

Possibly you might want to check the fit on the taper. Take out the little screw that goes in the keyway on the R8 shank so you can turn the taper in the spindle and then use marking blue to see if the shank taper matches the spindle taper nicely. I have found that some cheap R8 shanks are a bit off on the taper and these ones do not lock in as well as the shanks that have a very good fit over the whole length of the taper. The runout can still be okay because this is just an indication of how concentric everything.

With a poor fitting taper you may not get enough driving torque from the friction between the shank and spindle and with a face mill doing an interrupted cut it is possible the shank could spin in the spindle. This would shear off the little pin because it is not intend to take any driving load and it could also gall up the inside of the spindle as well as making everything so tight you would have a devil of a job getting it out.