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Thread: Amateur with tenon threading question-

  1. #1
    Join Date
    Jan 2008
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    Rochester, New York
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    Amateur with tenon threading question-

    Hi,
    I have a Grizzly gunsmithing lathe, and am chambering a Krieger heavy varmint barrel blank for my Nesika Bay single shot 6.5-284, F-Class type gun.

    I have cut the thread and the tolerances are good-- action screws on etc.-- At the shoulder end of the threading I had cut a threading relief cut just behind the recoil lug area with a cutoff tool to avoid problems at the shoulder end of the threading operation. The barrel I took off the gun (shot out after 1400 rounds) was chambered by a professional gunsmith, and he did not cut a relief cut at the shoulder end of the threaded portion of the tenon-- his threads just taper up and end very nicely.

    While both methods seem to work-- I am curious as to how the professional gunsmith managed to thread that tenon and have the threads end so beautifully without a threading relief cut.

    Thanks in advance for any responses.
    Bob

  2. #2
    Join Date
    Apr 2006
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    Kentucky-Home of the Kentucky Wildcats
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    Quote Originally Posted by rvander1 View Post
    Hi,
    I have a Grizzly gunsmithing lathe, and am chambering a Krieger heavy varmint barrel blank for my Nesika Bay single shot 6.5-284, F-Class type gun.

    I have cut the thread and the tolerances are good-- action screws on etc.-- At the shoulder end of the threading I had cut a threading relief cut just behind the recoil lug area with a cutoff tool to avoid problems at the shoulder end of the threading operation. The barrel I took off the gun (shot out after 1400 rounds) was chambered by a professional gunsmith, and he did not cut a relief cut at the shoulder end of the threaded portion of the tenon-- his threads just taper up and end very nicely.

    While both methods seem to work-- I am curious as to how the professional gunsmith managed to thread that tenon and have the threads end so beautifully without a threading relief cut.

    Thanks in advance for any responses.
    Bob
    Aquired skill. I still don't do it often as I thread with carbide at pretty high speeds, but after you get the hang of things, you won't need that wide a chicken groove. Mine are usually about 1 thread wide. Doesn't hurt a thing either way.

  3. #3
    Join Date
    Dec 2017
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    585
    not a professional.
    maybe he starts at that end, and turns in the tool as he engages the half nuts of the drive.
    no real clue

  4. #4
    Join Date
    Feb 2003
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    Houston, Texas
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    7,445
    One word. Skill. Most machinist that do a lot of threading get the hang of it. Using a flat side mount upright insert helps too.

    https://www.amazon.com/Dorian-Tool-T...1403319&sr=1-5

    I thread a 300+ rpm, and never cut a thread relief. Friends that watch me do so with a sense of panic.

    The reason I do not cut thread reliefs is because I set my barrels back about .025 on a regular bases.

    I do things a lot different than most. Being a machinist, I get the most difficult operation out of the way first. Thatís the chamber. Everything else is then worked from that point.

    In short, I establish the very best chamber possible, then do all the rest.
    Last edited by jackie schmidt; 02-28-2019 at 09:23 PM.

  5. #5
    Join Date
    Dec 2006
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    Branchville, NJ
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    I use the quick retracting compound like on the HLV-BK to pull the cutter as I disengage the lead screw.

  6. #6
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    Sep 2014
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    89
    I thread to an indicator on the lathe bed and can stop within .005 and retract the tool at the same time

  7. #7
    Join Date
    May 2006
    Location
    Hubert, NC
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    482
    If you decide to develop the skill of threading without a relief cut, practice on scrap material or barrel cut offs. I use an indicator with a magnetic base mounted on the way and picking up the side of the apron as it nears the end of the cut and set to make one rotation coming to zero at the point that the thread needs to end. I set the cross feed dial to zero at a position that I can retract it with a flip of the wrist and zero the compound dial at the tenon surface. I don't use a DRO, so I use the magnetic base indicator all the time. I have found it very difficult to watch a DRO and retract at the exact position. Experienced machinists can do this at faster speeds with a fair amount of practice. Start by threading relatively slowly and increase the speed as you gain confidence. Start each cut and watch the indicator as the tool approaches the shoulder. when the needle comes around to zero, simultaneously disengage the half nuts and retract the tool by flipping the cross fed dial handle.

    Actions that use a recoil lug allow you to stay farther from the shoulder. Most custom actions have about 2 threads removed at the front of the action so you need to get close to the shoulder but not run right up to it. It is important to practice enough that you can retract the tool at very nearly the same point every pass as going too far risks chipping or breaking the cutter or insert. If you retract a little too soon one pass, the next pass needs to cut twice as much at the end.

    To be successful, you need a thread insert that is not too wide to allow you to come close to the shoulder without cutting into it. Your lathe needs to work smoothly and have the gibbs adjusted so that the dials are not too stiff. The cross feed needs to not have excessive backlash.

    It does take practice and there are plenty of "Professionals" that never develop this skill. It isn't necessary at all, but it is a mark of skill and a source of pride once you acquire it.

  8. #8
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    Idaho
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    Donít know about gunsmiths, but some machinists make a slight relief cut, then thread toward the tailstock. Takes out the guesswork, perfect start every time and canít crash the lathe .... unless you fall asleep for a few minutes

  9. #9
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    Many of the pro smith's have a threading stop on their carriage, they're skilled too.

  10. #10
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    Dec 2015
    Location
    Nampa Idaho
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    Chicken Groove

    Quote Originally Posted by mwezell View Post
    Aquired skill. I still don't do it often as I thread with carbide at pretty high speeds, but after you get the hang of things, you

    won't need that wide a chicken groove. Mine are usually about 1 thread wide. Doesn't hurt a thing either way.
    I haven't heard that term before......I like it.

    Mort

  11. #11
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    Quote Originally Posted by Mram10 View Post
    Donít know about gunsmiths, but some machinists make a slight relief cut, then thread toward the tailstock. Takes out the guesswork, perfect start every time and canít crash the lathe .... unless you fall asleep for a few minutes
    I know folks that do this. It is possible with some machines to mis-engage the half nuts and there is no room for error here. You can destroy a nearly finished threading job in a fraction of a second. Some machines are very positive on the half nut engagement and some are not. I personally want to see the top of my insert as it cuts so I can be sure it hasn't become damaged or chipped and is cutting well.

  12. #12
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    Quote Originally Posted by MilGunsmith View Post
    I use the quick retracting compound like on the HLV-BK to pull the cutter as I disengage the lead screw.
    You say "like on the HLV-BK." What lathe are you using? I've seen the Hardinge setup and it is sweet. The spindle diameter is pretty small on those machines but you can do most sporter size barrels through the headstock.

  13. #13
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    Quote Originally Posted by SGS View Post
    You say "like on the HLV-BK." What lathe are you using? I've seen the Hardinge setup and it is sweet. The spindle diameter is pretty small on those machines but you can do most sporter size barrels through the headstock.
    I use the HLV-BK for sporter and sniper barrels, and a Clausing 1565 with a 2" spindle bore for the large barrels. I have a retracting attachment on the toolpost of the Clausing.
    Last edited by MilGunsmith; 03-02-2019 at 03:09 PM.

  14. #14
    Join Date
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    Tennessee
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    Tenon threading to a undercut is fine even on barrels where a recoil lug is used or even on a really fancy BR group barrel.

    BUT, if you will bring your slightly retracted threading tool to where you want it to stop then make a very visible mark on the left bedway at the carriage wing, the practice with the tool slightly retracted, practice stopping and retracting the tool while just watching the carriage wing as it gets to that mark on the bedway you will find that you can stop the tool EVERY TIME within about 0.005" of the same place.

    Just takes practice and confidence. Like Pro Bass fisherman Gerald Swindle says, PMA. Positive Mental Attitude...i.e. you gotta' have self confidence in whatever you do.

    /

  15. #15
    Join Date
    Jan 2009
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    14
    I was having a similar issues as you with a similar lathe. I know this may not be an issue your having but Iíll get to that..... I was having problems with my threads looking like . I did a ton of research and found that single phase lathes leave an awful finish on parts. I changed my belts that helped. I still wasnít getting the finish I was seeing everyone else getting so I did a 3 phase upgrade using a vfd. Boom problem solved I could even go down to 1 RPM to thread if I wanted. I then tied the brake option to a micro switch now I can stop on a dime.

    https://youtu.be/Ncc72aKgzVY

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