Threading stainless steel

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So, I finished off the last SS blank and started on another, which was in the same order from the same company.

22 cal blank 30in x 1.25 diameter with 1-16 twist rate for 22lr revolver barrels.

I only do these for my own use to sleeve existing -105mm barrels to 110mm OAL.

It's a pain in the butt but it's a lot easier than profiling a complete barrel to duplicate the original. Usually I just make up a new barrel with a different profile, with flat sides that I can do between the lathe and milling machine.


Anyway, the new blank is HARDER than its predecessor.

Both barrel blanks were hammer forged. One was centered at both ends and about the same hardness as ballistic steel blanks. I didn't look at the second bbl in the box until I was ready to use it. One end had the bore centered and the other end had the bore about .075 in off center. Not a big deal other than I had to take the chuck off, put on the face plate with a center, attach a dog leg and set the barrel up between centers to turn the whole thing into a usable barrel blank. I guess I could have cut off as much as I needed but WTH it was all set up and ready to go, so I just did the whole thing.

Anyway the darn thing was DIFFERENT concerning its hardness.

I bought these blanks from a sale several years ago, from a reputable company whom I had dealt with before and since without issue.

I don't know if anyone here remembers the Black Star barrel blanks. They were hard and tough to cut/chamber/thread. Still, it was still possible to cut smooth threads.

This new blank is not only hard but it's giving me issues when it comes to cutting SMOOTH threads. I hate galled/rough threads with a passion.

I've tried both HSS tooling as well as properly ground carbide bits. Of course with lots of lube. Yes, I've tried different speeds.


I have a Grizzly back gear lathe that is about 15 years old. I also have a quick change unit and both are very good units. I have an attachment that allows me to go as slow as 10rpm for the quick change.


Any ideas????


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About all I know about stainless is that it work-hardens while you’re working on it. That could have happened. Different alloys work-harden faster than others. Could be that the steel was hardening in response to the tooling passing through it, making subsequent passes more difficult or impossible.

Can it be annealed without screwing the whole thing? Any professional metallurgists here?
 
What are you using for 'lube'?

Actual cutting oil? Water soluble? Motor oil?

You may have to jack the speeds up well beyond the terror level to get it to cut well. Carbide insert threading tool, water soluble coolant meant for use on stainless. Thread on the backside, with an upside down tool, cutting away from the headstock, if you don't have a threaded spindle nose. Or you might just be hoopered.

I am sure that inconsistencies in stock are about the biggest PITA barrel makers face these days. Maybe less so for a hammer forging outfit, but still...
 
Tool geometry, cutting speed, and lube, are all factors to be considered. I like cobalt bits which are ground to minimize chip load. Experiment with angles. I like Rigid dark threading oil. I like to run at around 250 rpm. Feed in at 30 degrees.
 
I too like a 'sharp' tool with good relief, Rigid dark oil, 30 degree feed, and a slower rpm... depends on your lathe... 250 or less.
 
Slower isn't always the solution. If you're getting a rough finish (that's not caused by vibration), go faster until you start burning up tools. Easier said than done on a manual I suppose.

You could also grind two tools, one for each flank, to reduce your cut pressure?
 
Does a good sharp file touch it, or does it skip right over without leaving a mark at all?
Good carbide will cut the hardest of hardenable stainless's, and I kinda doubt that barrel is in the 50+HRC.
Hardened material usually cuts super smooth and shiny like a mirror and doesn't tear, its the soft stuff that does.
So, something is going on.
 
SND said:
Does a good sharp file touch it, or does it skip right over without leaving a mark at all?
Good carbide will cut the hardest of hardenable stainless's, and I kinda doubt that barrel is in the 50+HRC.
Hardened material usually cuts super smooth and shiny like a mirror and doesn't tear, its the soft stuff that does.
So, something is going on.
Click to expand...
I agree,
File has about 65 HRC, if file doesn't cut blank fairly easy then HSS threading tool is to soft for the job.
The best tool to thread SS that work harden is Sandvic (Swedish) coated threading insert.
Self ground carbide tools don't have chip removing grooves so chips intend to pile one on top of another and burrs appear.
Threading any material with bit that cuts mostly either right or left edge brings trouble free machining especially in SS.
For threading SS tennons about 1" dia, if you stay at 120-150 RPM the coated inserts don't need any cooling what so ever.
GR8 2c worth....
 
For barrels, I finish the threads with the E-Stop button in and in neutral. 1 thou or less cut a couple of times takes all the roughness out and it is very easy to spin the chuck by hand. Also, the fit is very nice since there is no roughness to mess with your feel. I suppose it would therefore gall less when assembled as well. I blame the lathe having too little preload on the spindle bearings.
 
gunrunner8 said:
I agree,
File has about 65 HRC, if file doesn't cut blank fairly easy then HSS threading tool is to soft for the job.
The best tool to thread SS that work harden is Sandvic (Swedish) coated threading insert.
Self ground carbide tools don't have chip removing grooves so chips intend to pile one on top of another and burrs appear.
Threading any material with bit that cuts mostly either right or left edge brings trouble free machining especially in SS.
For threading SS tennons about 1" dia, if you stay at 120-150 RPM the coated inserts don't need any cooling what so ever.
GR8 2c worth....
Click to expand...

Sandvik inserts and holders will likely be prohibitively expensive for the average home gamer, or even small shop. They work awesome (There's nothing better than their laydown 266 system and 1125 insert grade), but they're definitely pricey.
 
Cheaper and still good option for laydown threading inserts is Vardex, I buy those through KBC. You can buy the inserts individually instead of being stuck buying a whole box as is the case with sandvik and others.
 
Could try set your compound rest at 29.5 deg from straight and take your cuts with it so that you only have tool pressure on the front of your insert. Can help with stainless.
 
I am using Rigid Dark cutting oil.

I have tried suggested speeds

The tool is sharp carbide and set on the holder at an appropriate angle, which I've used several time before with stainless.

Because I've been using carbide, I haven't bothered feeding from an angle. I haven't had to in the past but it is certainly worth trying.

This stuff will cut with a Nicholson file but not as easily as another stainless stub I have to compare it with.

When the plant I used t work at shut down, I was allowed to take as much tooling for my lathes, milling machine, drill press, grinders as I could carry in my pick up.

I have stuff that I could never have or would have purchased. Sandvik carbide inserts, Aloris quick change tool post with a half dozen interchangeable holders, a 24"x24"x six 2 in deep drawers full of HSS and Carbide tip cutting tools as well as instert holders that allow quick change out when a cutter breaks etc. Full tooling for my milling machine as well.

I have never used the threading inserts. Now would be a good time to get familiar with them. There are several different sizes and profiles to choose from.

Lots of great, easily understood information here.

My sincere thanks to all of you that took the time to impart your valuable knowledge, not that I would have expected any less from any of you. Still I do appreciate it.

Tomorrow will be a learning day.

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Instead of using Ridgid Dark which is an old school high sulphur oil for carbon steel, try Ridgid Extreme oil which was formulated especially for threading stainless steel because of the galling issues. Feedback that I've gotten says that it works way better than even Ridgid Nu-Clear.
 
I use a water soluble cutting fluid, in a tin can. with a brush to apply.

I want to say Cutswell 55, but the label is long gone. It was one of the few I could find that wasn't only available by the 5 gallon bucket at the time.

A little goes a long way. It is supposed to be a 2 to 5 percent mix, but I just slop a little water into the can and rehydrate the oil into an emulsion and stir it up again.
 
Feeding on the angle lets the tool cut on one edge only and gives the chip someplace to go. I think tool geometry is very important and many commercial inserts and brazed tip tools are just plain wrong. Some of the brazed tip tools couldn't be made any worse on purpose.
 
Leeper said:
Feeding on the angle lets the tool cut on one edge only and gives the chip someplace to go. I think tool geometry is very important and many commercial inserts and brazed tip tools are just plain wrong. Some of the brazed tip tools couldn't be made any worse on purpose.
Click to expand...

I fully agree with you on commercial brazed tip tools.

I haven't used any of the thread cutting inserts yet but as soon as the company leaves I will be trying a few out. I don't have any issues with the carbide inserts when I'm cutting threads on regular steel barrels, nor have I had any issues with other stainless barrels before. This particular blank is hard to cut. Likely my inexperience is the issue. If I had another, I would just set it aside and work it out later. I don't and as we all know, those darn things don't come cheap.

I miss the days when I could order lengths of rifled blanks out of the US that were 1/2 inch diameter to use for barrel liners. You could get a half dozen of them for the price of one larger diameter blank. Those days are long gone and lamenting them won't make it better.

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chroma-tap is the best cutting oil i have ever used, i have used it to cut 2" npt in pre hardened 420 stainless by hand with no galling many times. have you considered cutting shallow on the lathe and finishing with a quality die? only other thing to suspect is looseness somewhere in the tool
 
Ex3dy said:
chroma-tap is the best cutting oil i have ever used, i have used it to cut 2" npt in pre hardened 420 stainless by hand with no galling many times. have you considered cutting shallow on the lathe and finishing with a quality die? only other thing to suspect is looseness somewhere in the tool
Click to expand...

I suspect you mean a thread chaser?????

I finally did a lot of experimenting and cut the threads with the lathe in reverse at higher speed. All of my cuts were very shallow and I had to make a lot of passes to get the proper finish I wanted. Still it worked well and I did end up getting some cutting oil from a commercial shop for the job. The fellow at that shop is a good guy and gave me about a litre of concentrate to mix with water. I don't know what it is, other than it came out of a pink 25 liter bucket. 1-10 mix ratio and it's very slick on stainless.

My tool base is rigid as are the tool holders, when locked in position. It's an Aloris.

I just wasn't feeding fast enough. This is one occasion when there is a "to slow" for best results speed.

I will look for Chroma-tap.

Thanx

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