Amateur with tenon threading question-

R

rvander1

Guest
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
 
rvander1 said:
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
Click to expand...
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.
 
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
 
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-..._5?s=industrial&ie=UTF8&qid=1551403319&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. That’s the chamber. Everything else is then worked from that point.

In short, I establish the very best chamber possible, then do all the rest.
 
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I thread to an indicator on the lathe bed and can stop within .005 and retract the tool at the same time
 
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.
 
Don’t 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 can’t crash the lathe .... unless you fall asleep for a few minutes
 
Chicken Groove

mwezell said:
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.
Click to expand...

I haven't heard that term before......I like it.

Mort
 
Mram10 said:
Don’t 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 can’t crash the lathe .... unless you fall asleep for a few minutes
Click to expand...

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.
 
MilGunsmith said:
I use the quick retracting compound like on the HLV-BK to pull the cutter as I disengage the lead screw.
Click to expand...

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.
 
SGS said:
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.
Click to expand...
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.
 
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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.

/
 
I was having a similar issues as you with a similar lathe. I know this may not be an issue your having but I’ll 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 wasn’t 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
 
I do it a little different. I thread to the shoulder watching my Trav a Dial and then disengage the half nut. I then casually retract the cross slide. It leaves a thread relief that you can't see unless you look very close. Everybody has their own method and we do what we prefer. One of my buddies and a forum member made up a proximity sensor tied into his DRO and VFD on his old oriental lathe. When he gets to his programmed point on his DRO his VFD, with braking resistors, instantly stops the spindle. He retracts the spindle, does not disengage his half nuts and reverses the feed. Know you crank in your cross slide to "0" and crank in your compound and turn it on as the half nut is still engaged.
 
I had NO idea a 3 phase had anything to do with finish on threads! I always touch mine with a thread file or emery cloth to pretty them up. Great info.
 
I don’t use a thread relief, but I do make a tool nose radius relief at the shoulder. This isn’t required if the lug opening or receiver face is chamfered sufficiently.
On integral lug receivers I thread at 750 rpm and pull out .005” before the edge of the insert crashes into the shoulder. With a separate lug, I thread one thread pitch under the lug.
 
A problem I've had

is my half nuts don't always engage totally so one can get "Chowered up" threads very easily. The gearing setup for me to cut the threads I need for tenons ends up giving me a fast feed rate and before one knows what they have, Chowdah! Perhaps there is a way to slow the feed rate down but I have yet to figure out how to do it and still know I'm cutting the thread pitch I need.

The only thing about the otherwise great lathe I bought is the danged change gears! Perhaps someone can help me out with slowing the feed rate down? I use HHS cutting tools for threading. My lathe doesn't have a conventional gear box on it. The lathe is a mid 90's Central Tool 13".

Thanks,

Pete
 
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