Re: [mill_drill] r8 collets
- Maybe that's it for some. I've a habit of positioning the collet by hand until it seats against the taper, then spin the draw-bar nut by hand until it "makes up", then finish it off with what's usually about a 1/4 - 1/2 turn with a wrench. The key prevents the little twist on the collet one needs to do by hand to get collet seated up quickly. The friction between the tapered surfaces is enough to keep the collet from turning as you tighten by hand, if your draw-bar & collet threads are as clean as they should be. When I got my chinese bench mill, I did have to clean the draw-bar threads and true up the draw-bar shaft to be able to do the quickest tool change possible for me. But then, I digress from the key issue. (pun sort-of intended) Also helpful, is matching the wrench sizes for the draw bar, and your vise/clamping tooling.Phil R
From: Jerry Durand <jdurand@...>
Sent: Monday, April 1, 2013 12:43 AM
Subject: Re: [mill_drill] r8 collets
On 03/31/2013 10:39 PM, philr_77378@... wrote:I'm one of several people I know who made lot's of one-off parts over the years using different vertical mills equipped with R-8 spindles. I don't recall anyone making mention of a benefit from the set-screw in the spindle. Most of machines I worked on had it removed. I wonder if it helps when you have a power draw-bar? I saw or heard more stories of gauled up spindles and tooling as a result of it's presence than of it's absence. I never ran a tool on these types of mills that needed "registration" or any key assisted orientation of a tool tip. It would be interesting to hear how someone out there may utilize this universal R-8 feature.
I would think the idea is to allow the collet to be loose and still be able to tighten the draw bar. Otherwise you'd have to hold the collet to tighten it up. Of course spinning the collet might be a faster way to install one!
-- Jerry Durand, Durand Interstellar, Inc. www.interstellar.com tel: +1 408 356-3886, USA toll free: 1 866 356-3886 Skype: jerrydurand
- Hi Folks,
I probably missed it, thought this was the thread about the pin being
long in import mills. The drawbar may be too long, so the threads are
bottoming out before you pull the collet closed. Add a few washers
under the head if this is the case and see if it helps. You can make a
shoulder washer for the top of the spindle for a nicer job.
On 04/02/2013 03:02 AM, John Herrmann wrote:
> Robert -
> I know this is now a relatively old thread, and maybe you've found the solution already. Nevertheless, here's my two cents' worth:
> Given that
> (1) your collets don't close when reefing on the drawbar
> (2) you only see a small amount of taper contact when using dykem
> (3) the collets seem to work OK when you wrap the taper
> I'd say that somebody's (sorry, forgot who first said it) suggestion about the collets being a bit too long has a lot of merit.
> You can check this pretty easily. Pick one of your new collets. Make sure there's no grit or burrs in the slots, and that you can close the slots by hand before putting it into the spindle. Now put the collet in the spindle *without* a mill inside. Tighten the drawbar (fingers should be enough). The gaps in the collet should close up pretty much all the way. If the drawbar seems to "hit bottom" (ie, become hard to rotate) before the collet closes, that's evidence the top of the collet is being stopped from moving upward as far as it should.
> If that's the case, you can try grinding a bit from the top of one collet and repeat the test. If it closes further or all the way, you've verified the problem and the fix. Proceed to grind all of them, and you're good to go!
> - John Herrmann