Think I Wrecked my Drawbar

[SteveHGraham]

I think I've outdone myself. Today I had a coax indicator in the mill, and I was turning the spindle with a wrench. I forgot the wrench was up there and turned the mill on at 50 RPM. The wrench got stuck against something and kept tightening the drawbar. I turned the mill off and realized what was going on.

I was able to turn the drawbar, and the indicator came out of the collet, but the collet seems to be stuck in the mill. I have no idea what I did. I am thinking the most likely thing is stripped threads on the drawbar.

I have banged on the top of it with a hammer, but the collet does not seem inclined to move. I very much doubt that the collet spun in the taper. I saw no indication of that.

What now?

[SteveHGraham]

The brake no longer does anything. I'm hoping there is a shear pin in there somewhere.

[SteveHGraham]

It looks like the drawbar had two pins in it. I yanked on the top part, and it came out of the mill. I thought the bar was a solid piece, but there is a top section which APPEARS to slip over something down in the head. There are two pins intersecting each other inside this hollow thing, and it looks like they're both gone. The ends that went in the piece are there, but if I poke a screwdriver down into the part, it doesn't hit the middle parts of the pins, so I think they were snapped away.

If this is right, I might be able to make a tool to keep the spindle from turning while I loosen the collet, and then maybe I can get the drawbar out for repair or replacement.

[BadDog]

If you are turning the normal way, it would loosen, not tighten.

The draw bar pulls up against that top of the spindle as a thrust surface. If the top half of the draw bar is pulled off, then that takes the thrust surface with it. If it DID tighten excessively, you are never going to turn that collet in the spindle. More so if you still have the key/grub in there. I may be wrong, but I think the likely best course is to get a nice sized rod, just small enough to go down the spindle bore where the drawbar passes, and thack that remaining piece of draw bar soundly. Or, if the bore is big enough, it might be better to use a piece of pipe or the like to slide over the draw bar and go down to the collet shoulder to whack that directly, thus eliminating the risk of a columnar failure in the remaining drawbar. But you don't want it to fit TOO closely or swelling could make it a permanent fixture.

And lock the quill first.

Unless I miss my guess, that is the only way you will get that collet out of there.

[BadDog]

I just re-read and noticed you got the coax out, so I guess it did back off some or that coax wouldn't come out. That starts to sound like a coupler inside hung on a shoulder. Not sure what to make of that, but if so, and the collet is loose enough, and the grub/key is out, you might be right about turning the collet to get it lose.

[GlennW]

We really need a live video feed from your garage!

[SteveHGraham]

All is well.

My brain gradually started working, and I realized the answer was to bang on the top of the remaining bit of drawbar. I grabbed a piece of 1" aluminum rod, jammed it in the hole, and smacked the bar. Out came the drawbar and collet. I had to put the collet in a vise and put Vise Grips on the bar to get it unthreaded. No scratches or damage.

In other words, I did pretty much what you suggested.

Tomorrow I'll see if I can get the pins out of there and put new ones in. In the meantime, I am ordering a spare drawbar.

Thanks for the assist anyway.

[SteveHGraham]

The pins came out pretty easily. They're very soft. I should be back in business tomorrow.

With those soft pins, this must be the safest mill in the world. It didn't even hiccup when it snapped them off.

[John Evans]

I'll admit to the same boo boo . Just wait untill the wrench is still up there and you lower the quill !! Wrench is
LOTS harder than your head ! OUCH !!!

[SteveHGraham]

I have done this twice since 2009. The first time, the wrench had the common courtesy to fly into the wall instead of shearing the pins.

I learned a lot from this. I read about the key in the R8 taper, which can be involved in misadventures like this. Some people say it does nothing good and can do harm. I wonder if that's true. Supposedly it can get jammed and cause a lot of problems.

Seems to me that if you don't have a key you're more likely to spin a collet and ruin the taper, but then what do I know? I'm just the guy who leaves the wrench on his drawbar nut.

[SteveHGraham]

Incidentally, you can Ebay a new drawbar for about $19, delivered. I expect to get this one working, but next time I do this, I want to be able to get back to work fast.

[BadDog]

It doesn't take much for the screw (aka "key", in loosest terms) to bugger a collet, then you'll have great fun trying to get the collet out. My understanding is that, like the tang on a MT drill, it is for aid in installation/removal, not for driving at all. So if the collet's going to slip and you expect the screw to make the difference, you are already screwed. I find it trivial in the extreme to hold the collet to the taper when tightening or loosening the drawbar as long as you keep your tooling (mainly the threads) clean, which you should be doing anyway if you don't want to have more problems. And, you get the added benefit of just fitting the collet as you choose without worry about aligning the blasted keyway. My screw/key left my R8 spindle years ago, and I've never regretted it for a moment.