Internal Threading a blind hole with a threaded chuck?

I'm thinking my solution for now is going to be using my Beall collet chuck, which really tightens down very securely, and giving it a shot. I am cutting softer materials, almost always smaller diameters, light cuts. And I'll wear shoes instead of my Crocs. My "real-world" context does not include the need to cut internal threads in steel; brass, possibly at some point for a particular part, but it would be small. The other advantage of the Beall is that I can work very close to the chuck and have much greater flexibility to turn my tool angle, than with the 5" 3J, and not worry about losing a finger or three. Further, the Beall does not capture ebonite and acrylic string swarf, so the instant birds nests they create are avoided.

Thanks for all the good advice!
Tim
 
pontiac428 said:
He's concerned about the chuck coming off of the threaded spindle in reverse. It's a legitimate concern, but probably not a real-world issue, it takes a bit of a whack to break the chuck loose from the spindle nose compared to the lighter loads from cutting a single point thread.
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I agree. I had read all sorts of scare stories about chucks falling off.

In my case, the back plate and spindle have provisions for clamps. This prevents the back plate from coming off, although it would do nothing to prevent slight loosening. I always use the clamps. However, I have never found in use, that the back plate gets loose. Even when threading in reverse. Typically I need to use a lot of torque to remove the back plate. It requires wrenches. The only times it has been easy is when I deliberately didn't snug the back plate to the spindle nose. I don't do that very often, since that increases run out. The thread in my picture is 8 TPI in cast iron. There was no evidence of my chuck loosening. At least for my lathe, threading in reverse is a viable technique. I tend to take it easy, and relatively slow, no herky jerky stuff.

Other lathes that do not have any spindle clamps may be different. However, if the back plate or chuck has good lockup to the register, I'd think the issues would be very, very minimal. If the back plate is always hard to remove (not stuck due to other reasons, but having very good lockup to the register) then I'd think it would be relatively safe to proceed. However, that is up to the judgement of the machine operator.
 
This is what I use to keep the chuck from unthreading. I call it a chuck keeper. The only caveat is that the threads on the keeper have to be different from the threads on the spindle. The threads on the spindle on my lathe are 1 1/2x8tpi and the threads on the keeper are 1/2x13tpi. The different threads will work against each other keeping them from unscrewing.

IMG_3943.JPG
 
tmenyc said:
I'm thinking my solution for now is going to be using my Beall collet chuck, which really tightens down very securely, and giving it a shot. I am cutting softer materials, almost always smaller diameters, light cuts. And I'll wear shoes instead of my Crocs. My "real-world" context does not include the need to cut internal threads in steel; brass, possibly at some point for a particular part, but it would be small. The other advantage of the Beall is that I can work very close to the chuck and have much greater flexibility to turn my tool angle, than with the 5" 3J, and not worry about losing a finger or three. Further, the Beall does not capture ebonite and acrylic string swarf, so the instant birds nests they create are avoided.

Thanks for all the good advice!
Tim
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You can make a handle to fit on the left end of your spindle and turn the chuck by hand. Wind the chuck with the leadscrew engaged and listen for when the tool stops cutting - this tells you that your tool has reached the undercut. Or set an indicator at the depth you need and wind the spindle until it reaches zero.
 
Parlo said:
You can make a handle to fit on the left end of your spindle and turn the chuck by hand. Wind the chuck with the leadscrew engaged and listen for when the tool stops cutting - this tells you that your tool has reached the undercut. Or set an indicator at the depth you need and wind the spindle until it reaches zero.
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Back when I had a threaded spindle lathe this^^^ is basically how I did. I killed the power with about .060 to go (depending on thread pitch) and it coasted to about .030". I just used the chuck key to thread the last 30 thou. by hand. I used a 2 inch DI mounted on my carriage stop to keep me posted.
 
Epan -- good advice, thanks. i'm going to try finishing by hand next. And yes, I'm already using a 2" DI for that purpose. It helps.
Tim
 
You could also use a carriage stop. That is what I use. As the carriage approaches the stop I put a piece of paper between the stop and the carriage. When I can't move the paper I disengage the half nuts. With a little practice it becomes a learned motor skill to disengage the half nuts at the same time as the paper can't move.
 
You can also slow down time. To reduce the time constant on the lathe, retard the space-time continuum by decreasing spindle RPM. I know it's not as exciting as a supreme being's capabilities should be, but from the machine's perspective, you are the divine singularity.
 
pontiac428 said:
You can also slow down time. To reduce the time constant on the lathe, retard the space-time continuum by decreasing spindle RPM. I know it's not as exciting as a supreme being's capabilities should be, but from the machine's perspective, you are the divine singularity.
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In the limit, control the spindle speed with a hand wheel. But yeah, slow things down, and some things get a lot easier - it also boosts your confidence.
 
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