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Strange Carbide Insert Internal Threading Tool Geometry

I'm going to honestly suggest that with the smaller dia having it rotated gives the clearance required. Look at the posted picture and you'll see that if set correctly as with larger boring bars the the support of the cutter will contact on the smaller ones.

This is a compromise to achieve function based on size (or lack of it).
 
The rake angle looks correct to me - looks aggressive, but it is needed for small bores (as has been explained by others).

One thing that could be a problem (perhaps it is only the picture’s fidelity?): looks like the tip is chipped off. It will not cut if that is the case. Rotate the insert to a new cutting edge.

2CE0E0CA-4A6B-4789-A33A-060F9825DDDD.jpeg


As an aside - I do have off shore threading / boring bars that came with their own inserts. I have gone ahead and replaced the inserts with high quality ($$$?) brand name ones. Made all the difference and reduced headaches in the long run as the carbide seems better in the brand named ones.
 
YotaBota said:
If that set has the 8/10/12 mm bars I recently bought the same set. I've used them over the last couple of days, 5/8- 18, and have worked okay, the carbides break easy but that could be me. I used them for about 90% of the thread and then finished off with the tap.

I thought the angle looked weird as well but it seems to work.

What thread were you cutting and what DOC?
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I've been less than impressed with the quality of the carbide inserts supplied on Amazon , break easily & they even look crappy.
 
Gearhead88 said:
I've been less than impressed with the quality of the carbide inserts supplied on Amazon , break easily & they even look crappy.
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What carbides are you using and do they fit the holders @YYCHM and I have? I'd like to try a decent quality carbide.

Hard to tell if any of the Amazon inserts are any good, they all look the same.
 
I think mine is similar. They appear to have negative rake relative to the shank flat, even as shown on insert sketch, but if I recall the insert tip itself is upturned slightly that reduces the rake somewhat. I should check. To make it confusing there is also a smaller (finer pitch) insert series that has zero rake shank datum & possibly zero rake inserts. I don't have those.

Raising/lowering the tool height changes the equivalent rake from a cutting perspective, but also slightly changes the resultant thread form. That might not amount to much, I'm not sure. But I think they are intended to be centered or very close to. The way that big boy manufacturers alter rake is with anvils which reside between toolholder & insert. Its been a while since I was in Carmex catalog for example but I seem to recall beyond a certain size the anvil was effectively zero anyways. After that you get the appropriate anvil for the job in order to use the same $$$ holder. This (absence of anvil0 is kind of indicated on the clone specs. I think they just mill the toolholder to compensate for 'no anvil'.
 

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YotaBota said:
What carbides are you using and do they fit the holders @YYCHM and I have? I'd like to try a decent quality carbide.

Hard to tell if any of the Amazon inserts are any good, they all look the same.
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The quality of the available inserts vary on Amazon , you can find better , longer lasting inserts but you will pay more for them . For every example of quality name brand you might find , there are dozens of knock off that crumble easily . Theres no shortage of hucksters in Asia selling low grade crap . Some times I feel like a sucka when I open the package , I've started to be more careful , what's obvious is a lot of the suppliers just don't give a shit about quality , or copying designs that may be copyrighted .
 
As far as I know, which isn't all that much really, all insert boring bars or internal threading tools will incline the insert to provide clearance.

On solid HSS boring bars, when boring small holes, I've had to either grind the bottom side of the bar, or raise the boring bar as high as possible, and rotate the tool so its tip is on center.

In the attached picture is a number of different sized boring bars, and the two bars on the right are threading tools, (a left hsnd, and a right hand).
 

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Ok, I checked my insert boring bars and they incline the insert as well. Even my external threading tool inclines the insert.

So how does one set tool height in this situation?
 
thestelster said:
No different. Set center at the tip of the insert.
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That would then imply that I needed to use a smaller bar? Is there a rule of thumb for relating bar size to bore size?

@RobinHood was right about the pictured insert being chipped.

BTB - This was my fist attempt at internal threading. I was trying to make a single pointed 1/2-13 nut and bolt. I end up with a bolt that threaded into a commercial nut ok, and a nut that thread onto a commercial bolt ok, but my bolt and nut didn't cooperated with each other all that well. Close but pretty tight.
 
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YYCHM said:
Ok, I checked my insert boring bars and they incline the insert as well. Even my external threading tool inclines the insert.

So how does one set tool height in this situation?
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Hopefully my answer here will be better informed that that stupid reply I gave last night....

SOMETIMES with internal threads, it helps to be a scooch ABOVE center. I cannot give an amount. It's sorta trial and error. The problem is clearance for the tool in small bores. If the tool is on center, it's bottom section will sometimes contact the bore below center because the ID is rotating TOWARD the tool below center. By cutting slightly higher, you provide more clearance for the bottom of the tool. Because the ID is actually moving away until it reaches 90 and then back below that.

I totally agree that it should normally be on center. But sometimes it just doesn't work. Big IDs do not have this problem.

The fact is that I have a few boring bars and inside threading tools where I had to grind a bit of the tool away to get clearance EVEN THOUGH I was totally within their specifications limits. Maybe if I had spent more money on the tools, they would have been just fine.

FWIW, I also agree with your observation and the comments of others - that tool looks tipped too much to me too. The top of the insert actually looks like it is tipped up vs the work. Maybe try a better insert? Or try using a boring bar holder like @Darren suggested earlier.
 
YYCHM said:
That would then imply that I needed to use a smaller bar? Is there a rule of thumb for relating bar size to bore size?

@RobinHood was right about the pictured insert being chipped.

BTB - This was my fist attempt at internal threading. I was attempting to make a single pointed 1/2-13 nut and bolt. I end up with a bolt that threaded into a commercial nut ok, and a nut that thread onto a commercial bolt ok, but my bolt and nut didn't cooperated with each other all that well. Close but pretty tight.
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For sizing the bar to hole, the specs should tell you what the minimum bore dimension is. If no specs are provided, then set your bar's top flat level, then set insert tip height to center. If it does not fit into your bore you intend to thread, you have to go to a smaller bar.
 
YYCHM said:
Is there a rule of thumb for relating bar size to bore size?
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Not that I know of. However the specification for the tools themselves (see my other note a few minutes ago) usually gives a minimum bore size for the tool.

FWIW, that tool looks WAAAY too big for a 1/2" threaded hole. Especially since the original hole before threading is smaller still.
 
@YYCHM - sometimes it helps to drill a hole the size you want and then hold the boring tool or threading tool up to the back side of the hole with a light shining on the tool so you can stick it in the bore and see the fit from the front side of the hole. Sometimes it's amazing what you can discover from tool rubbing to clearance to angle errors.
 
YYCHM said:
That would then imply that I needed to use a smaller bar? Is there a rule of thumb for relating bar size to bore size?

@RobinHood was right about the pictured insert being chipped.

BTB - This was my fist attempt at internal threading. I was attempting to make a single pointed 1/2-13 nut and bolt. I end up with a bolt that threaded into a commercial nut ok, and a nut that thread onto a commercial bolt ok, but my bolt and nut didn't cooperated with each other all that well. Close but pretty tight.
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You are cutting to tighter tolerances, commercial nuts and bolts are to the looser side. Here is where it is important to have gauges to set your tolerances.
 
your "it fits but doesn't" was a recurring issue for me as well.
A few points to consider:

1. An A60 insert is not intended for coarse pitches., most listings are wildy optimitic about their range. Too wide for fine pitches, too narrow for coarse pitches. On my A60's the tip width is typically .008" where a 13 tpi thread wants .0094" at the root (.125*pitch). You can fake this with compund parallel to the Z axis and offsetting slightly on a finish pass.
2. External thread depth is typically .6134* pitch, internal .5413*pitch, but it still requires proper tip width. A60 might not be able to go deep enough at coarse pitches without topping the threads.
3. Carbide bits don't like running in reverse, did you chip yours by running the spindle in reverse to back it out without winding the cutter clear?
4. Measuring your external thread with wires should confirm the above.

This is one time that the Machinery's Handbook is worth looking at, the thread proportions are fairly simple once you digest them.
For your desired pitch AG60 is a better bet, but again the tip width matters.

I generally end up putting the insert on my optical comparator, measure tip width and pass it by the d-bit grinder for correction depending on the thread I need.

Gerrit
 
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