10 Questions You Should to Know about Threading Inserts

I'm gonna make some of my fellow machinists roll their eyes but bear with me. I'm gonna talk about what works great for home machinists and budget minded folks that still want nice quality results. You do not need expensive holders to use carbide threading inserts for gun work. There is production machining in a workplace and there is gunsmithing.... 99.9% of any gunsmithing is not taking 12" od heat treated material and plowing off .200-.400" depth of cuts off it. Small 1/2" TCMT style toolholders with decent thread inserts (carbide) like the ones in the attached pictures from ebay work very well on small lathes like the g and you don't have to buy 10 at a time or spend $200.
Look back 2 pages to the thread pictures I posted a few days ago. They were all done at home, with Single Phase Power, on a 2hp, chinese, Grizzly g lathe. I bought that lathe new for my home work shop 12-13yrs ago and have used the heck out of it since. Still a great machine for its intended purpose. I manage an all manual-machine machine shop in the mining industry and Do I buy Grizzly machines and chinese tooling for our industrial shop? No; the Neanderthals would destroy them in 2 weeks. but we're not talking about that here; that is heavy work, this is gunsmith talk.
I know toolholders and inserts are complete alphabet soup to home hobby machinists. Trying to figure out each manufacturer's "code book" is a real pain. So, I'll attach some short cuts here to maybe get you started.
Search Ebay for: 5 pc 1/2" Lathe Indexable Carbide Insert + Turning Tooling Bit Holder Set (this is $32)
The inserts included with these are junk for gun work and light finishing. You need sharper, less tool pressure inserts for the small, less rigid parts. For threading get a few 16ERA60 Inserts(the ER stands for External RightHand). They will cover everything from 16-48tpi and that's most of your Gunsmithing threads. Get a AG60 to do up to 8tpi but the A60 will get you closer to shoulders so they're the better way to start (unless you're doing Mausers). When you feel frisky jump up to the full profile inserts. I keep 8,16,20,24,28, and 32tpi on hand for my gun hobby work at home and use A60 and AG60 inserts for everything else. They are the bomb and once you use them, you'll never go back. But you do not need them to make a quality thread.
For general turning, get TC"G"T16T308 inserts not "M" inserts. Those 1/2" holders above will use both the thread inserts and TCMT16T30.. size inserts TCMT and TC"G"T interchange in the same holder. Think of the "G" as "Ground-like ground sharp" and the "M" as "Molded-not so sharp but heavy duty for big cuts". Most work can be done with a TCGT16T308 . A .......304 has a finer nose radius and you'll need a couple of those around too. (they're also called TCGT32.51 when you're shopping ebay.) TCGT32.52 is the bigger nose radius and the 308 size. I won't get into what those numbers really mean, not enough room/need here for that right now.
I'll use Ebay again to illustrate examples. The following would be a good start for threading inserts:
Search Ebay for: SECO CARBOLOY 16ER A60 S25M CARBIDE LAY-DOWM THREAD INSERTS (9Pieces) ($51/9inserts)


Search Ebay for:
SECO CARBOLOY 16ER A60 P30 CARBIDE LAY-DOWM THREAD INSERTS (3 PIECES) ($21 shipped)


Here are aluminum inserts, Inserts for Aluminum are generally very sharp with a high rake. While not necessarily recommended for steel, they do work really well on 416SS barrel steel and most normal steels. They just do not last as long. But most threads and cuts for gunsmithing are not very long unless you're profiling a barrel. And for the cheap cost of the inserts($1.50each if you shop hard), who cares if they do not last as long! Buy 20 at a time(60tips) and go to work. They also leave nice finishes and can usually shave a ." off a part if you need to. Don't overlook them.

These Kennametal examples are decent for steel too:



Hope that helps some of you get an idea of what to look for. I am not associated with anyone of those Ebay sellers, just using them for examples as to what to look for. Those little 1/2" toolholders work just fine and are plenty heavy duty enough for anything that you should be putting in a 12x36 etc. lathe. I only check in every couple days so if I don't respond to a reply right away, I'm not ignoring you. Thanks and happy smithing.

I have an inexpensive Grizzly lathe, a GG. I've switched to an inboard spider to keep the workpiece as close the headstock as possible. I use a laydown full profile threading insert and make threading passes as prescribed in the Standard of Depth of Cut document for American UN external threading.

There does not appear to be a problem with the threading work except for the way it looks. I used to use an on-edge HSS threading tool with similar results. I thread at the slowest speed my lathe will run - 70 RPM. I use Viper's Venom on the last few passes but not the first ones lately.

I am guessing this is some kind of chatter. You can see what looks like ridges in the valleys of the threads. What is causing this?

View attachment

Thank you,
Hank

Hank,
I miss read you first post. Sorry for high jacking you thread with a long tooling blog since you're already using lay down tooling. Tooling isn't your issue. If your part is supported both sides of the headstock and working close to your spider chuck, that shouldn't be a problem either. I'm assuming you are using the compound to adjust the depth of cut? If not, and you are only using the cross-slide, I would quit doing that and try make the transition to using the compound. And if you are using the compound, I would bump the compound feed angle down(On your particular lathe. If following Old US "How to Run a Lathe" guidelines, they tell you 29.5degs. That won't work on your Grizzly and often overlooked. The degree wheel is positioned differently on asian machines. We use 29degrees on our old Monarchs at work.) to 57-58degs and give it a try. Sometimes it helps to keep the right side of your insert dragging a little to help stabilize it. My Grizzlies sweet spot is 58degs. It won't make a difference to the thread profile in the end.

I've heard that carbide inserts like deep cuts and fast feeds, and have experienced much the same with what little turning I've done with carbide inserts.

How does this reconcile with threading with carbide inserts, since it is neither deep nor fast?

I've got a project coming up where I want to cut some 7/8-20 OD threads close to a shoulder. I'm seriously considering purchasing a right-handed ID threading tool, running the spindle and threading screw in reverse, and threading on the back side of the work, away from the shoulder to avoid crashing. But many such tools are indexable.

What to do? I do almost all my threading with carbide (and turning too!). There is not really a minimum speed limit for carbide, the big difference is the maximum speed you can cut. There are exceptions for super hard materials because you are aiming to generate enough heat to soften the metal locally in front of the cutting edge, but this doesn't apply to most of the cutting in the home shop.

If you find carbide is not working well for a particular application, you may want to look for a sharper insert with a ground edge (edge sharpness is also the reason why many move to HSS). These are often advertised as being for aluminum but they work very well on soft steels and stainless as well. I see it is easy to find the 16ER threading insert with this edge geometry, although I haven't tried them personally yet. I usually thread at 100rpm but might go down to 50 if I am feeling nervous.

The selection of the insert to your application really makes all the difference in the world.

What material are you cutting?