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QSIMDO
01-05-2017, 03:19 PM
I've not much experience with the procedure but I've been reading up & watching videos so I can play Machinist on TV ;)...no, really, I need to
perform my first serious internal threading operation and I'm impressed with all the tooling available.

I have a .75" bar and just ordered a .3125" blank but I've been hearing the Siren song of insert tools for this purpose.

Some use a lay-down insert, some use upright...most of those I couldn't use because the thread will start well inside the bore.

Anyone care to offer up a treatise on what works where and how?

TIA

BCRider
01-05-2017, 04:03 PM
What do you mean "most of those I couldn't use because the thread will start well inside the bore."? I'm also not sure what you mean by lay down vs upright insert. Are you talking about flipped over so you cut on the back side using reverse?

If you're working down deep then I suggest a lot of practice first on a more open bore and where you can see what is happening. If you're working down a deep bore where you'll be totally blind you will be literally "running on instruments".

The other issue with a threaded hole at the end of a deep bore is that you have no way of "testing" the thread for size. To nail down the numbers you'd need to do a mock up on some exposed bore where you can test fit the part that screws into these thread.

Is there any way you can machine the part the other way around so the thread is out on the open end of the bore? Or machine it as you plan but part it off and re-center it so the bore to be threaded is open to view and for size testing?

If that can't be done you would need a start groove to put the point and a finishing groove wide enough to ensure you don't crash the cutter at the far end. I'd bring in the tail stock to work as a hard stop for bringing the carriage back to the beginning so you are sure the cutter is located at the starting groove. And set up a mag base with an indicator pointer for the far end stop groove to indicate the point for disengaging the threading. After that you just need a whole lot of thought and trust while working 100% blind. And if you're working with a thread that needs to keep the thread lever engaged all the time (metric) then all I can say is good luck with that. You'll need a stop groove long enough to allow for the cutter advancing during the spin down of the lathe without crashing into the far end of the bore.

All in all I would REALLY look into options to allow you to bring the thread out so it's done from the open end.

As for what tool to use that's your choice. But I don't see a 5/16 thick HSS cutting bit in the end of a 3/4 bar being very good. If the top of the cutter is at the center height of the bar you've got just a small 1/16 thin finger on the bottom to clamp it. Far better a 3/16 sq too bit so you have a thicker lower side "D" shape for holding the cutter in place. Save the 5/16 cutter for a 1" or larger diameter boring bar.

If you make your own boring bars one advantage of inserts for the smaller sizes like 3/4" and smaller is the inserts are quite thin for their size. And that means more metal left to support the insert compared to using square HSS tool blanks. Your 3/4" bar being a good example. Even with a 3/16 cutter you only have a "D" shaped finger below that is 3/16" thick and quite narrow to support the cutter. Not an ideal solution by any means. But a natural for a 5/16 or 1/4" size IC insert which is 1/8" or less thick. I've yet to go with inserts but when I do I suspect that one of the first adoptions will be for my smaller boring bars just for this reason.

PStechPaul
01-05-2017, 05:10 PM
Assuming the bore has a bottom, you would first need to bore the full depth to the minor diameter of the female thread, and then further bore to the major diameter of the thread to the depth where the threads will start. This will provide clearance for the major diameter of the male threaded part that will screw into the bored part. It might be best to make a groove at the bottom of the bore, also at the major diameter. It would also be advised to start threading from the bottom out, in reverse for a RH thread, so that there will be no chance of crashing the cutter.

Do you have a specification drawing for the mating parts?

J Tiers
01-05-2017, 05:19 PM
A "lay down" insert is on the bar like a regular one, on the topside. The profile is cut in it from the wide side.

A "Stand up" insert is attached on the SIDE of the bar Or perhaps the end), the profile is ground on the insert tips on the thickness

The bars in his case may be too big to fit inside. I am not sure about the "start well inside", maybe there is a narrow area down in which is threaded?

A threading profile can be ground into a regular HSS blank from the side, and the blank ground away to give clearance. The threading "point" then reaches around inside to do the cutting. For smaller bores, a tap may be best.

BCRider
01-05-2017, 05:48 PM
A "lay down" insert is on the bar like a regular one, on the topside. The profile is cut in it from the wide side.

A "Stand up" insert is attached on the SIDE of the bar Or perhaps the end), the profile is ground on the insert tips on the thickness

Thanks. I don't recall seeing a "stand up" style insert up to now. So I went looking at images of "stand up inserts" and all I can say is that it's quite the eye opener.

PStechPaul
01-05-2017, 06:27 PM
It seems that the "stand-up" style is what would normally be expected for external threading. The following discussion shows what it looks like and how to make an insert holder:

http://castboolits.gunloads.com/showthread.php?315449-Making-a-standup-threading-tool-holder

http://www.fototime.com/83C76AA55BD7385/standard.jpg

The lay-down type is turned 90 degrees:

http://www.latheinserts.com/1-2-LAYDOWN-THREADING-TOOL-HOLDER-6-SER-500-F16.htm

http://www.latheinserts.com/images/1341262763045-934724145.jpeg

Illinoyance
01-05-2017, 06:58 PM
For single point threading on a manual machine the speeds are way too slow for carbide to be needed. The only advantage of carbide is the convenience of a pre-ground tool. Also, full profile inserts are only available in carbide.

I always use HSS tools for ID threading. The 5/16 bit in a 3/4 bar is a good combination. You can rotate the bar in the holder to put the cutting edge on center as long as you grind the bit bit to compensate for the angle. I also like the Everede bars for internal threading in addition to boring.

In industry they would normally use carbide threading tools for everything. They can't afford the downtime of grinding their own tools. Accuracy of the thread form is assured in carbide inserts, not so for offhand ground tools. In a home shop you can usually afford the time to grind tools offhand.

Laydown inserts will fit into a smaller bore than on-edge inserts of the same size.

Toolguy
01-05-2017, 07:03 PM
Nice summary, Illinoyance.:)

38_Cal
01-05-2017, 07:18 PM
From your description, it sounds like you're threading the bottom section of a blind hole, which means that you can thread the entirety of the hole (so you can see what's happening at the start of the hole) and then bore out to the clearance diameter for the unthreaded depth you'll need on your project. This will allow you to check the female thread against the male piece that engages it for proper fit on a section you can see rather than working "on instruments". Good luck!

Magicniner
01-05-2017, 07:26 PM
For single point threading on a manual machine the speeds are way too slow for carbide to be needed.

I thread "away from the shoulder" and "from the bottom of the bore" on all "manual machine" jobs using a Myford Super 7 with the appropriate feeds and speeds for inserted carbide tooling.

One should not confuse one's own ability with that of the machine,

- Nick

J Tiers
01-05-2017, 07:46 PM
For single point threading on a manual machine the speeds are way too slow for carbide to be needed. The only advantage of carbide is the convenience of a pre-ground tool. Also, full profile inserts are only available in carbide.
....

And for materials that quickly dull the HSS.

Juergenwt
01-05-2017, 08:09 PM
What material dulls HSS at a slow speed used for inside threading?

J Tiers
01-05-2017, 08:14 PM
4140 prehardened material, for one. It dulls HSS fairly quickly just in general. When threading, if obviously will be depending on how much threaded length there is on a piece, what thread size, what you call slow, and how many pieces.

For a short thread, on one piece, don't worry.

polaraligned
01-05-2017, 08:19 PM
I would think work hardening stainless steels also when you are sneaking up on the final thread size and not taking a deep enough cut.

BCRider
01-05-2017, 08:21 PM
From your description, it sounds like you're threading the bottom section of a blind hole, which means that you can thread the entirety of the hole (so you can see what's happening at the start of the hole) and then bore out to the clearance diameter for the unthreaded depth you'll need on your project. This will allow you to check the female thread against the male piece that engages it for proper fit on a section you can see rather than working "on instruments". Good luck!

I got the impression that it was a minor ID sized hole he would be working in. But yes, if I'm wrong and he's working at the far end of a clearance size hole I heartily concur that it would be best to simply thread the entire length and bore out the clearance later.

JCHannum
01-05-2017, 09:11 PM
I use the Everede bars for boring and threading. The inserts are available in both HSS and carbide.

Arthur H. Warner makes a wide selection of HSS insert tooling that duplicates the more common carbide inserts.

http://www.arwarnerco.com/

QSIMDO
01-05-2017, 10:43 PM
I got the impression that it was a minor ID sized hole he would be working in. But yes, if I'm wrong and he's working at the far end of a clearance size hole I heartily concur that it would be best to simply thread the entire length and bore out the clearance later.

That's what I meant when I said the insert bars I was seeing were too short.
There's a larger diameter where the bar mounts into the tool holder than where the insert is held and it's the same distance away from the work as the tip of the tool.
Only good if you thread in from the end.

But thankfully you guys answered a question anyway!
The threaded section in this 1.5" ID tube is in the center 1" of a 3" length.
Thread the whole thing and bore the end after!
Aces, thanks!

BCRider
01-05-2017, 10:55 PM
And it sounds like you need to buy or make a longer boring bar to reach in far enough.

JoeLee
01-05-2017, 11:04 PM
Unless I missed it.........what is the depth and dia. of the hole you need to thread??

I entered "well into the bore" into my Vardex threading program and it came back and said no match!!

JL............

BCRider
01-06-2017, 02:29 AM
Joe, read post #17

J Tiers
01-06-2017, 09:49 AM
That's what I meant when I said the insert bars I was seeing were too short.
There's a larger diameter where the bar mounts into the tool holder than where the insert is held and it's the same distance away from the work as the tip of the tool.
Only good if you thread in from the end.

But thankfully you guys answered a question anyway!
The threaded section in this 1.5" ID tube is in the center 1" of a 3" length.
Thread the whole thing and bore the end after!
Aces, thanks!

How does that help?

The tool still has to reach the same distance through, it would seem. The only advantage is being able to see the threads at the end better. But there is no guarantee that the threads in the middle are the same. Boring has a tendency to end up with a slight taper from the end, due to bar deflection, and internal threading uses the same sort of tool.

Mcgyver
01-06-2017, 11:12 AM
agree with Jerry. You've got lots of room so can use a large bar. I'd grind a bit of hss to use in the style of bar that takes short little pieces of sq hss.....or in a pinch braze one on to the end of a round bar.

QSIMDO
01-06-2017, 11:19 AM
How does that help?

The tool still has to reach the same distance through, it would seem. The only advantage is being able to see the threads at the end better. But there is no guarantee that the threads in the middle are the same. Boring has a tendency to end up with a slight taper from the end, due to bar deflection, and internal threading uses the same sort of tool.

Because I need to thread it in this set up then remove it to it's ultimate home in another lathe for the final operation.

Damn, J, I wouldn't lie to you!

Black Forest
01-06-2017, 11:20 AM
That's what I meant when I said the insert bars I was seeing were too short.
There's a larger diameter where the bar mounts into the tool holder than where the insert is held and it's the same distance away from the work as the tip of the tool.
Only good if you thread in from the end.

But thankfully you guys answered a question anyway!
The threaded section in this 1.5" ID tube is in the center 1" of a 3" length.
Thread the whole thing and bore the end after!
Aces, thanks!

I woiuldn't thread the whole thing. That to me would be a big waste of time. You are only talking 2" deep at the back side of the threads. That is not a deep hole especially in that big of a bore. If I was doing this I would put a sharpie mark on my bar when it was at the start depth and and another one at the finished depth. Zero my DRO at the start of thethread location and then just thread to the required depth. Easy job done. And I only use lay down carbide inserts for threading. Slam bam thank you Ma'm!!! But I live in the civilized world and make metric threads. Leave the half-nuts engaged and have at it. And if I couldn't easily test the mating part I would make a mating part with the correct external threads and use that to test if I didn't trust my self to hit them correctly with the DRO or dials.

old mart
01-06-2017, 05:18 PM
I only use carbide inserts, 16er/nr,*in this size they go to 8tpi, 60/55/acme/trapezoidal. You can get holders down to 12mm/1/2" square for external and the internal will probably thread down to 1" bore.
As mentioned, some practice on soft tube would help, and doing some external threading, say on a piece of aluminium with the ends reduced. This would be an inside out version of the actual job.
Just checked, 16mm internal holder can thread in a 20mm hole.

J Tiers
01-06-2017, 07:42 PM
Because I need to thread it in this set up then remove it to it's ultimate home in another lathe for the final operation.

Damn, J, I wouldn't lie to you!

That's fine... I just don't see how it helps, unless you are using the extra threads as part of a fixturing setup, or the like.

Without knowing more of the reasoning, it seems easier to bore it out to depth and then thread what's left.

You know your workflow better than we do.... maybe it IS better for you.