Gunsmithing Full-profile threading insert suggestions

[ptm121]

Hey guys,

I'm looking to try out full-profile carbide inserts for threading muzzles and tenons on my manual lathe. I normally use the upside-down method and thread away from the headstock, with the barrel held in spiders, so I can spin it pretty fast (hundreds of SFM, if needed). I'm hoping to get better surface finish and more exact thread profiles than my HSS tooling. My concern is that I might not be able to sneak up on the final thread size - I really like being able to kiss a thou or so off with my honed HSS tool, and get a really tight 3A fit. I ASSUME that material removal is non-linear as the insert reaches final depth and starts acting as a full form tool, so I won't be able to rely on the DOC per compound movement numbers I see on the first few passes to make the final cut.

Does anyone have a specific insert/holder family they have had good luck with, and speed/DOC suggestions?

Thanks!
-Phil

 

[Robert Gradous]

Iscar

 

[WVHick]

Arthur Warner HSS inserts and holders are phenomenal.

 

[bohem]

I don't use a full profile even in the CNC because it requires a tool change and offset tweak each time I change muzzle thread patterns.

The upside-down and backwards is pretty good though if you can cut in reverse (a CamLock or Taper Lock spindle instead of a Threaded spindle nose) then I liked to use an ID threading bar with an ER60 high rake carbide insert and you can get the SFM up just like the upside down way but you get to watch more closely.

The AR Warner inserts designed for cutting SS are the typical approach used on manual gunsmithing lathes and they do a very nice job.

 

[ptm121]

Thanks guys, I appreciate it!

 

[Gene Poole]

I have good luck with Iscar and Carmex. I've got a smattering of others: Kennemetal and no-names. All seem to work well for me at low speeds (75-125 rpm) with high-sulfur dark cutting oil.

 

[Wannashootit]

Just bought some ( as I've now gone almost completely to carbide with great results).
I haven't used them yet, but have been told that I need to turn my major OD five thou oversize- the last five will be taken off the OD on the final threading pass. We'll see how it goes...

In the interim, I switch to carbide stand-up inserts in my Warner tooling- and the results even at very low speeds have been excellent. I've also thought about threading upside down to increase speeds if needed, but haven't needed to. This surprised me, because I did find that that when turning, heavy cuts, about twice the speed, and the lowest feed rate on my lathe produced mirror surface finish even on stainless barrels. Just takes some experimentation.

 

[Wannashootit]

So, played with this for a few hours yesterday (24 tpi) to get the feel of it...
I thought (wrongly) that I'd actually be able to see a difference in material coming off the insert when it reached full depth, not so (at least for me).
So, after I realized this after the first "test", I turned the tenon to .015 oversize, then cut as I always have up to .030 on the compound infeed, where I'd be getting close to full depth. Then, a cuts of a few thou each time, miking over the threads after each until I got within .005-.006 and reduced infeed for the final couple passes until the diameter was within class 3 spec.

The wires confirmed the PD was correct. The threads are beautiful- personally, I didn't even see a difference when cutting wet or dry ( at least on my lathe, chicken cuts work better dry), most notably because the insert tops the threads no more scotchbrite needed- the tops are smooth as a baby's you know what...

Anyway, I'm sold on them so far...even made a couple of plug gauges for the drawer.

 

[ptm121]

Interesting, thanks for the info. I have some Warner partial-profile and Iscar full-profile stuff that just showed up with UPS. I’ll cut some threads on a junk barrel and see how it goes before I set up the AR10 that’s in the queue for a muzzle thread job.

EDIT:
In case anyone finds this in the future and wonders how it went…
Findings so far, on 4140:

• The Iscar inserts don’t like crawling speeds, but once I got over 20-30 sfm it was nice. 125-200rpm worked nicely, depending on diameter. I cranked it up and it got pretty bad at higher speeds. I’m not sure why – perhaps movement in my spider? I’ll try fast threading with something held more rigidly in a spider sometime.
• DOC is no problem. These are sharp and will take 5 tenths off, leaving a nice finish. 1-2 thou seems to leave a little smoother surface than a spring pass, but all DOC I tried work acceptably (in 4140)
• Oil doesn’t seem to make a lot of difference. It might be a little bit smoother with some Viper's Venom, but it’s hard to tell.
• The full-profile tool doesn’t get the crest perfectly smooth (like a file can), but it’s perfectly to dimension. One really nice thing is that now I can use the single pitch-wire measurement technique and be sure I’m not introducing error.
• So, I wasn’t able to get awesome surface finish, but finish is at least as good as my best HSS tools. I also didn’t lose ability to get a snug fit – in fact, I gained in that department. So I'm not disappointed, and will keep using these inserts for my most common pitches.