How to thread with no thread relief

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Griz
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How to thread with no thread relief

Post by Griz »

I was looking at the threading guide and have no idea how to thread a barrel with no thread relief on my lathe (Grizzly G4003G)...

Unless I am missing something I'd have to disengage the half nut and back out the cross slide at the same time which I don't think would be very repeatable and seems like a good way to chip a tool. Is there a good way to do this on my lathe?
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CMV
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Re: How to thread with no thread relief

Post by CMV »

Never tried it but I think you'd need to use a RH threading tool (flat on the left side so it can get against a shoulder) and run the feed in reverse. Not the spindle rotation just the feed direction. Would still need a little relief to get started in. Anyway, that's how I'd try to do it but I'm sure there's a "right way".
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57fairlane
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Re: How to thread with no thread relief

Post by 57fairlane »

Whats wrong with putting in a relief?

O.D. Grooving tool usually .060-.080" wide . . . whatever the width of the tool is, then back it up towards the muzzle end a full width and cut a 45* into the barrel and back towards the breech on the backside of the major diameter of the threads.
Historian
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Re: How to thread with no thread relief

Post by Historian »

Griz wrote:I was looking at the threading guide and have no idea how to thread a barrel with no thread relief on my lathe (Grizzly G4003G)...

Unless I am missing something I'd have to disengage the half nut and back out the cross slide at the same time which I don't think would be very repeatable and seems like a good way to chip a tool. Is there a good way to do this on my lathe?
As above use a right hand tool ... chips reel off to the right as it moves left.
As an exercise, on my Atlas 618, I tried it for kicks and the only way to do it was to disconnect
the motor/belt and turn the screw with a hand crank in the back of the head stock. No disconnecting necessary.

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Capt. Link.
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Re: How to thread with no thread relief

Post by Capt. Link. »

Either the barrel or the can will have a relief if the two will ever meet.Threading to a hard shoulder should be practiced.Disengaging the split nut and retracting the cross slide is the way its done.I like to do this at high speed when a novice is present just for the reaction.You have a option of starting at the shoulder with the tool upside down and run it in reverse out to the muzzle.The relief can be cut in advance or after.
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Doc Holiday13
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Re: How to thread with no thread relief

Post by Doc Holiday13 »

What's wrong with having a relief? Its better IMO to have the pieces that are being connected to mate on square faces
superstriker90
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Re: How to thread with no thread relief

Post by superstriker90 »

I'm not a gunsmith, but I am a machinist. Its tricky (I run very slow rpm's when doing this) but you can zero an indicator on the way of the lathe where you want the thread to stop, start thread normally, when it hits zero on the indicator, quickly back the tool away from the part while shifting machine into reverse. Never dis-engage half nut and allow lathe carrige to return to its starting point. This way is a must on some lathes ecspecially metric threads.
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CMV
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Re: How to thread with no thread relief

Post by CMV »

superstriker90 wrote:I'm not a gunsmith, but I am a machinist. Its tricky (I run very slow rpm's when doing this) but you can zero an indicator on the way of the lathe where you want the thread to stop, start thread normally, when it hits zero on the indicator, quickly back the tool away from the part while shifting machine into reverse. Never dis-engage half nut and allow lathe carrige to return to its starting point. This way is a must on some lathes ecspecially metric threads.
If I did that, I'd crash. Moving the feed lever directly from forward to reverse without coming to a stop will keep the machine running forward. Do bigger geared machines do this? I'd imagine that would be hell on the gears shifting the feed or direction lever into reverse while moving forward.

Would take forever but you can turn the headstock by hand with the feed & half nut engaged. Could get wherever you wanted and stop without risking crashing anything. Set for a higher gear or it will be hard turning the headstock. At least mine works that way - if everything is engaged, turning the chuck turns the leadscrew & moves everything along. You could feed in that way, stop at your desired spot, back off the cross slide, run in reverse under power w/o disengaging half nut, stop, feed in cross slide & compound, manually start spinning the chuck for the next pass. Rinse, repeat, until you have what you want.
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CMV
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Re: How to thread with no thread relief

Post by CMV »

Also, why no relief? Do you start your female threads with a little chamfer in the hole to ease mating? If you do, that chamfer where there aren't full threads anyway would be over the relief so you aren't losing anything.
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Griz
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Re: How to thread with no thread relief

Post by Griz »

I have been threading in reverse with an upside down carbide insert at high speeds. I get beautiful threads when I'm spinning at 1400 rpm or so, but I have to have a relief to start in and do it in reverse so I don't crash into the shoulder.

I can't quickly reverse my lathe as suggested, I'd probably pop a breaker if I tried that. I don't have any problems with picking up the thread again when re-engaging the half nut using the threading dial though.

My question was prompted because the AAC threading guide shows no thread relief on most rifle threads. I guess that's so that a peel washer will be centered if you were mounting a flash hider, but I like to just time the flash hider with the lathe and not use a washer. Is there any other reason why the threading guide shows no thread relief?
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