[How do I?] Thread Crest Override - ???

[Bamban]

I am still totally puzzled, I did a threading exercise again with the half nuts engaged all the time and the thread got messed again, so I flipped the work piece, barrel stub and cut it and threaded it for an AR 15 tenon, 13/16 x 16 TPI, to have something to meaningful and I am quite familiar with the AR 15 tenon, I've done a few AR barrels for my own use on my 1236. This time I did the half nut engage/disengage/engage method, the outcome, though the not the best looking thread, is acceptable and in fact I cut the thread so I can screw the barrel extension.

The problem occurs when the half nut is engaged all the time, looks like.

 

[Paul in OKC]

Reversed the tumbler.

My guess is right there is your problem. Once you disengage the lead screw in any way (which you do when you shift the tumbler) you take the chance of loosing the 'timing' of all the gears. You will get lucky, but rarely through a whole thread cycle. Use the thread dial, and hit the same number each time you engage the half nuts. If you don't want to try that, then pull out and stop the spindle, leave the nuts engaged and reverse the spindle back to your starting point.

 

[Bamban]

My guess is right there is your problem. Once you disengage the lead screw in any way (which you do when you shift the tumbler) you take the chance of loosing the 'timing' of all the gears. You will get lucky, but rarely through a whole thread cycle. Use the thread dial, and hit the same number each time you engage the half nuts. If you don't want to try that, then pull out and stop the spindle, leave the nuts engaged and reverse the spindle back to your starting point.

Thank you. We were typing at about the same time. I did exactly as you said and the outcome is as expected. I could not reverse the spindle. The reverse switch is actually wired and set to FWD so I don't accidently put the spindle in reverse. I was told that the screwed on chuck might unwind itself unless there is hold down set screw to lock it in place.

 

[RJSakowski]

BamBAM, You cannot disengage the gears when threading. Using the thread dial won't help you. If you can't reverse your motor, you will have to wind it back by hand (ugh!).

 

[Bamban]

BamBAM, You cannot disengage the gears when threading. Using the thread dial won't help you. If you can't reverse your motor, you will have to wind it back by hand (ugh!).

RJ,

Thank you.

I am just showing my ignorance, thinking that as long as the half nuts are engaged I am good to go. Good education for this newbie. I do the half nut engaged threading on my 1236, but I can reverse the spindle on that one.

 

[RJSakowski]

At the speeds that threading is done , there is little danger of unthreading the chuck by running in reverse. If you are concerned about doing so at high rpm, then a second switch could be added to prevent running in reverse unintentionally. I don't know how your spindle is set up. My Grizzly 10 x 22 has two clips which hook into the spindle to prevent unthreading. Maybe you could do something similar.

 

[Bamban]

Here is the spindle set up to the chuck. The back plate just screws on to the spindle. I and thinking about installing a nylon set screw on the back plate to bite on the spindle thread. I do like the 2 switch set up to run the spindle in reverse and only active when threading.

I would like to see your spindle set up on your 10x22

 

[RJSakowski]

BamBam, There is a groove cut into the O.D. of the spindle. The two chuck locks tighten into that groove. Here is a picture from the manual.

 

[Bamban]

RJ,

Thank you for your patience and help.

Unfortunately my spindle does not have a groove and there may not be enough space to make one.

 

[brino]

Bamban,

Don't worry at all about "showing ignorance" here. We are all at different levels and everyone is treated fairly.
All I see is someone learning by doing; I respect that and I believe most people here do.

Honestly, I do NOT recall this wrinkle in the threading process being discussed, so it is great to shed some light on it.

Another option is to remove the chuck and turn between centres with a faceplate and dog driving the work.
Of course this only works if you can stand to have a centre hole on both ends....
While it is true that the faceplate may also only be screwed onto the spindle, it typically has much less mass and therefore much less inertia.
Also in the unlikely case(because of low speed as Bob mentioned) the faceplate does unscrew it is captive and cannot skitter across the floor.

hmmmmm, if you are really concerned about it, it may also be possible to build some kind of "draw bar like" device to use with the chuck to ensure the chuck cannot come loose
-I say "draw-bar like", because it is not actually pulling any tapers together, just locking the spindle-to-chuck threads
-it would block the spindle thru-hole meaning only short items could be threaded
-this device could use left-handed threads, lock washers, jam nuts, etc. to ensure that it cannot unscrew accidentally

-brino