BP disaster: snapped r8 collet?

"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message


First, let me say that I ran all of the ideas presented here to my buddy, and he seems to think the collet/nut is on so tight that most will prove unviable. I myself was in favor of Clay's idea, with epoxy.
The thread of the drawbar is protruding past the r8 nut, so KT's idea above is not viable.
But, the suggestion to just tilt the head got my buddy thinking, and we are going to drill out an aluminum round bar to fit the 7/16 thread of the drawbar, and use this round bar as a guide for an aircraft drill, and just drill out the whole thread/nut portion with a 7/16+ drill.
We will of course lose the draw bar, but he has another one anyway.
Still open to more ideas, or criticisms of this strategy.
The moral to the story is, No more two-piece R8 collets!
Hopefully from all this those that didn't realize R8 collets came in multiple styles now realize the danger of these two-piece disasters-waiting-to-happen. goodgawd....
Appreciate all the good ideas, will let everyone know what happens. Might not get completed for another day or two.
--

Mr. PV'd

Mae West (yer fav Congressman) to the Gangster (yer fav Lobbyist):
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Where *did* I put that left-handed 13/16" hole saw?
:)
--Winston
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Winston wrote:

This'll have to do. Several layers of electrical tape to protect the taper and you're good to go, yes?
http://www.tungstencarbidegritedge.com/proddetail.php?prod "MMTCGRITHOLEBK
--Winston
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volley in

I'm still not clear how the drawbar could've extracted the nose of the toolholder, and be jammed to the end of the thread. If it jammed, it would've stopped before the collet completely separated.
Unless... unless the drawbar TWISTED the part in two... but how was it assembled? If it was swaged together, that couldn't happen.
One thing in your favor, though. You could _try_ any one of the several suggestions without wrecking anything, then resort to the drill if you must.
LLoyd
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On Jan 22, 3:39pm, "Proctologically Violated"

In that case jamming the nut remnant upward with pipe might lock it tight enough.
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Lloyd E. Sponenburgh wrote:

My understanding of this CLASSIC Bridgeport disaster is that the cause was the collet cross-threaded, due to wear probably on the drawbar's threads. Does he have a power drawbar unit? I doubt this would happen when manually wrenching the drawbar.

Yeah, I think that IS the scenario. The threaded insert isn't really put in that tight. Just a bore in the back of the collet, and the slug is dropped in and the collet peened over a bit.
I don't think you will find ANY R-8 collets that aren't made like this.
Jon
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Jon Elson wrote:

I've just looked at all my R8 collets and they all appear to be one piece, no insert. They are all of Taiwanese or Chinese origin I suspect. Looking at the drawing of an R8 collet in my BP manual it appears to show an insert threaded into the back of the collet but the drawing isn't that clear.
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    --Betcha bought that collet from Enco didn't ya? Next time get Hardinge collets; you'll be glad ya did..
--
"Steamboat Ed" Haas : Do us a favor and rescue
Hacking the Trailing Edge! : a doggie or three...
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Proctologically Violated wrote:

Classic problem. No, disassembling the head or spindle will NOT easily get you to where you can get it apart. That is the last resort.
First, do you know whether the thread has seized up, or did the collet just pull apart? If the latter, I'd first suggest trying to jam the collet back onto the dangling part in the spindle. If you can get it to partially mash together, and the thread is normally loose, you should be able to unscrew the drawbar in a jiffy. If the thread has seized, then you do have a problem. Is this a 1J or 2J machine? On the 1J (step pulley) the top of the drawbar is almost accessible, on the 2J is is buried WAY down in the varispeed.
If a 1J, here's the procedure, assuming a standard hand-operated drawbar. Remove two bolts and take the motor off. It weighs at least 75 Lbs. Disengage feed worm for the power quill feed (little crank on upper left side of head.) Remove 3 nuts below belt housing, and you can then lift the belt housing straight up and off the spindle spline. Be careful to not bend spindle. The top of the drawbar should be pretty well exposed at this point. Be sure to not get metal shavings into the bearings when sawing.
The procedure is pretty similar on the 2J, but you have to unload the springs on the motor pulley and do some other stuff to get the varispeed belt off.
Jon
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