Running a threaded spindle lathe in reverse to cut heavy threads in a blind hole.

I've got a D1-5 chuck right now but I seem to remember from my old Logan that there is a shoulder or taper that actually trues up the chuck when it bottoms out. Would a jamnut cause runout because the chuck would not be fully screwed on? Anyhoo, I don't think you want to spend the rest of your life afraid to thread a blind hole so this would be as good a time to learn as any. If I can do it, it can't be too difficult.
 
Thanks for the input so far, everyone. Anyone got an opinion on the left hand threaded draw bar through the spindle to lock the chuck?
 
pestilence said:
I want to make an ER32 collet chuck for my Logan 922, but I'm pretty scared of threading 2 1/4 - 8 TPI into a blind hole when I cut the spindle threads into it.

I'd really like to run the lathe in reverse so I can cut the threads going out instead if in, but I've read horror stories of chucks unscrewing themselves. If I go easy on it and make sure my chuck is tight, do I need to worry about it?

If I DO need to worry about it, could I get around the problem by making a thin jam nut to put behind the chuck? I figure if I screw the jam nut in behind the chuck and then lock it and the chuck together really well, I might get by for one job.

Anyone tried this before?

This will be literally the second time I've tried cutting threads on a lathe. Third if I end up making a jam nut. The first try went very well, but it was an outside thread with good clearance and much slower feed.
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I wouldn't do it. Even if it didn't fall off the spindle it could loosen enough to spoil the part. The only think I can come up with is putting a little Lock-tight on the last two threads before the chuck bottoms out against the spindle. I would suggest using more Lock-tight but you may want to remove that chuck sometime. Interesting challenge.
 
pestilence said:
Thanks for the input so far, everyone. Anyone got an opinion on the left hand threaded draw bar through the spindle to lock the chuck?
Click to expand...

I don't see a reason that a drawbar would not work, the challenge being how would you fasten it to the chuck securely? Assuming that the chuck has a thru hole... I guess you could tap a piece of plate and place it across the face of the chuck. As long as you have enough room to still put the part in the chuck, I guess it would work.

This still seems awfully complex, maybe a photo of the back plate/chuck in question? Perhaps there is some specific physical trait that you are concerned about?

-Cody
 
I would thread the inside of the chuck baseplate with a left hand thread then make a draw bar that would insert into the spindle before putting the chuck on. Then I'd screw it into the chuck from the back of the spindle and then draw it tight with a nut on the end.
 
I just took a look at the back of a chuck and of course I was being kind of a dummy thinking I'd thread the inside of the backplate, since that's what threads on outside my spindle, but there's still plenty of room to put some lefthand threads behind the jaws for a draw bar to engage in.

Maybe I could be a little less fearful of threading inside a blind hole if someone could tell me what the worst case scenario is if I screw up and crash the tool into the back of the hole. Does my split nut just jump off the lead screw? does the split nut die a horrible death and also mangle my lead screw? I plan to cut a relief, but I'm also pretty unlucky and not very skilled. I do have a back issue of Home Shop Machinst on the way and it supposedly has plans for a stop that will automatically release the split nut.

*shrug*
 
I'll 2nd what Tony Wells has said re cutting it normaly and having a few practice runs first. Are you using a HSS tool? Or Carbide? If HSS you will be abe to run the machine as slow as it will go which will make it easier until you get a bit more experience and the confidence that goes with that.
Machine a relief to run into and mark your boring bar so you know when to stop. After a few practice runs you will be wondering what you were concerned about.

Go for it.
regards
bollie7
 
Its too hard to predict the failure case but often, the leadscrew has a roll pin that is designed to snap. It depends on how your lathe is constructed. Best bet is to practice external threading for a few days and don't look at the cutting bit. Put a mark on the ways where you need to stop and just look at that. I use a kitchen refrigerator magnet -courtesy of the local pizza parlor. I've bveen thinking about making an air pneumatic disengage mechanism but after doing several internal and external threads a week for the last year, I'm not sure its worth the trouble.

Just start slow and work your way up. If its stressing you out, take a breather and try later when you're feeling better about it.

Ray


pestilence said:
I just took a look at the back of a chuck and of course I was being kind of a dummy thinking I'd thread the inside of the backplate, since that's what threads on outside my spindle, but there's still plenty of room to put some lefthand threads behind the jaws for a draw bar to engage in.

Maybe I could be a little less fearful of threading inside a blind hole if someone could tell me what the worst case scenario is if I screw up and crash the tool into the back of the hole. Does my split nut just jump off the lead screw? does the split nut die a horrible death and also mangle my lead screw? I plan to cut a relief, but I'm also pretty unlucky and not very skilled. I do have a back issue of Home Shop Machinst on the way and it supposedly has plans for a stop that will automatically release the split nut.

*shrug*
Click to expand...
 
Sorry if it's already been mentioned...I don't have time to read the whole thread....Mrs wants to go to the store. Anyway...all I ever do when threading into a blind hold is bottom the boring bar out in the hole, put a piece of white electrical tape or duct tape on it, dead even with the start of the part, and use that at a visual stop. Ok..gotta go.
 
Two things the old man said "thread slowly when on thin ice and don't" Tony Wells said it. If you ever ran a big loom you had better count
down to stop it been there done it & seen it. Loom shuttles typically travel around 60 mph & operator next to me did not count and shuttle
flew out and nailed the line supervisor >>>>>to the ER he went. So personally I have never tried it. And then a great big lathe like I have
it wont matter, little threads won't back off a heavy massive chuck. Even that one I do not.

ONE MORE THING; I cannot stress enough to cover all bases to everybody, comes a time When alone, the phone is 50' away YOU get
attacked by a wild machine like a bear in the woods WHO YA GONNA CALL. dont ask, I dont remember, when I woke up in the hospitol
cause stuppid things = equal hospitol.
 
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