Threading fit issue, tapered?

[jareese]

Hello all - I'm running into an issue where the left side of my threads are tighter than the right side, and I'm wondering what I can do to correct this.
(I am threading barrels for muzzle brakes and actions) I'm seeing this on both ends. Typically the last .100-.150 thou is too tight to continue to thread on and once I get the threads to a point where I can thread the mating device on, the beginning of the threads are pretty sloppy. Still within spec, but looser than I prefer. (2A+ fit)
When I do a taper cut test, I'm only out about .0006-.0009 over 6 inches so I don't think it's related to that. I'm not taking heavy cuts when threading, so deflection should be at a minimum. What else could I check?

Thanks much.

 

[mmcmdl]

Single point then run a good die over the threads if neccessary . Did you take any spring passes ?

 

[jareese]

Single point then run a good die over the threads if neccessary . Did you take any spring passes ?

Always do spring passes
I don’t have, nor will I buy die for these, single point only.

 

[GeneT45]

Sounds like the barrel flexing to me. Threading can apply significant pressure, and you won't see that doing a taper test. How are you fixturing the barrels? I often use a brass crown protector and thread the muzzle end with tailstock support. Chambers / shanks I cut with the barrel through the headstock. No taper issues in either case.

Other things to check: is your compound locked (if plunging with the cros-slide) or gibs appropriately tight (if advancing with the compound)? Either compound or cross-slide moving backwards could cause a taper.

GsT

 

[jareese]

Sounds like the barrel flexing to me. Threading can apply significant pressure, and you won't see that doing a taper test. How are you fixturing the barrels? I often use a brass crown protector and thread the muzzle end with tailstock support. Chambers / shanks I cut with the barrel through the headstock. No taper issues in either case.

Other things to check: is your compound locked (if plunging with the cros-slide) or gibs appropriately tight (if advancing with the compound)? Either compound or cross-slide moving backwards could cause a taper.

GsT

I have minimal stick-out and if I do, then I also use a brass tip on my tailstock. I also run through the tailstock and my TBAS. I'll look at locking the compound once. I've switched to straight plunging in an effort to try and figure this out.. No change in doing so.

Like I said - I'm still within thread spec, but I want it better and I know I can do better. I just need to figure this out.
Thanks for the tip!

 

[markba633csi]

Check for burr. Single pointing always raises one. Check the major and minor diameter closely. Check the thread profile with
a magnifier.
I made a crude minor gauge once with a pair of xacto blades fastened together
What type of threading tool?

 

[derf]

What kind of lathe do you have?

 

[WobblyHand]

This is going to sound dumb, but was the tool holder locked down tight? That has happened to me more than once. Forgot to lock it down correctly. Different tool holders may have slightly different lock up points, due to minor differences in their machining. So things seems ok when you are using it, but actually the tool is moving or deflecting a minute amount.

Were you using a four jaw chuck, a collet, or something else? I'm assuming you are indicating it in, but assumptions are dangerous. Were you indicating on the bore or the barrel? Sorry to ask these simple questions. Was a jaw loose when you were finished, or less tight? If the barrel was eccentric, or the bore relative to the barrel there could be asymmetry. Are you using a set tru chuck? Are the screws tight?

There are many ways that things can go wrong. A lot are just something has loosened up, or not set correctly. Look for the simplest causes first, proceeding towards the hardest.

 

[benmychree]

Tool set a bit high?

 

[jareese]

Answering the last 4 questions -
Threading tool has been a mixture between a standard laydown, and a Mesa Tool vertical (threading away from headstock).
Lathe is an Eisen 1440EV
Everything is tight - Aloris Toolpost
Chuck is a True Bore Alignment System with a Gator 6 Jaw - barrels are indicated in as close to zero as possible - typically only reading .0002-.0005 when done dialing in. After threading, all is still tight and dialed in within range.
Tool height and squareness verified.