Turning insert coating advise

[Pistolero]

This is probably something that only Keith is going to be able to help with, but anyone that
has insight, please chime in.

I am looking at some replacement threading inserts, 16ER A60 type. Which, as I understand the
designations means a #16 size insert, which has a 3/8" inscribed circle, and a A60 thread cutting
tooth, which is partial profile, 60 degree. Partial profile will make the root of the cut thread
correctly, but, unlike a full profile cutter, you have to have the starting workpiece diameter
turned to final OD of the thread in advance. With full profile, you can only cut one TPI for
a cutter, since you are cutting bottom AND top of thread at the same time, therefore depth and width,
so TPI, of the thread is fixed, only works for one (? or a very narrow range) of TPIs. I want a wide range
of TPIs, so A60 partial profile seems right, most flexible. ER means external threads, right hand.

All that lead-in is just HOPING that I understand this part correctly - and if not - want some
correction of any misconceptions here, first off.

The real question is the coating codes. Gold (assumed to be TiN) coating is coded SMX30, and another code,
which is black in color, is coded SMX35. One source says that black coating (without refering
to the SMX35 spec, darn it) is (IIRC, lost the URL of that page) was TiAlN.
Looking at some Chinese inserts, and the typical cryptic semi-English info says
"Black coating for steel stainless steel, general effect is good. Code (SMX35) "

Sounds good, assuming a missing comma after "steel", but wonder if anyone knows ACTUALLY
what SMX35 coating means, or is it a proprietary code rather than some industry
standard? Searching on SMX35 gets lots of PNs of inserts.....no info beyond that
cryptic, semi-English, ultra short sentence.

??????? Hall of mirrors for a relatively new person to the whole indexable tooling
world. I understand that there are a number of very hard PVD/CVD coatings over
carbide, not totally clear if just any of them are OK for general machining...mix of
alloy steel, mild steel, aluminum and brass.

Is a particular coating really bad for any particular material?
Or, just ignore the whole damned coating thing when running garage-wimpy-amateur
low cut depths and feeds because which coating you use is only important for max
cut depth and max feeds used in commercial operations where 10% more parts per
hour is a big deal?

Bill

 

[fiver]

your gonna cut the coating off anyway right?

the black is also a nitride coating, but it needs to be burnished through use to be at it's most effective as a surface lubricant.
I have had a couple of swage dies coated with it.

 

[Pistolero]

No, not cutting off the coating, this is on the cutting tool replaceable insert
that does the actual cutting. Carbide underneath, coating on top.

Here is a screen grab. These are TiN coated, I assume.



Bill

This one looks to me like a full profile type, see the little part to left of the
tooth that will cut the proper top on the thread...only works at full depth, so
only for one TPI. This is just a screen grab to show the general concept of
indexable threading tools.

 

[Ole_270]

The coatings are designed for use on high rpm, high production CNC lathes. Unless your a real whiz at throwing levers on an engine lathe, I doubt you'll see too much difference in them. In some cases, with the low rpm us mortals would use to thread with, a good old fashioned high speed steel tool ground to a positive rake would give better surface finish without as much tearing of the steel from the low rpm. It's been years since I got to twist the dials on an engine lathe, worked my way into programming CNC mills and really miss the lathe work. Now retired, so I'm out of touch with both.

 

[Pistolero]

So, you are saying that HSS cutter will give better surface finish than these insert type cutters
regardless of coatings?
I do thread at low speeds, of course.

Bill

 

[Ole_270]

Like I said, it's been years since I turned any metal, but with the lower rpm typical in an engine lathe a properly ground hss tool can give better finish than the insert types like your picture. HSS tool can be ground and polished to a sharp edge, carbide typically has a honed edge break because of it's brittleness. The earlier coatings back when I was turning added a little roughness to the surface of the carbide that didn't help low speed finishing. The coating adds lubricity, wear resistance and heat resistance. The carbide will far outlive the HSS, but the HSS can be sharpened. Surface finish will depend somewhat on material to be cut, some are more finicky than others.

 

[KeithB]

My 2 cents worth: Full profile inserts are great for a single specific pitch. Most have a positive rake so they make really clean threads in almost anything, but of course they won't work for another pitch. If you have a laydown type toolholder but buy a universal insert for it it too should have a slight positive rake. As you say it cuts the root and flanks but not the profile at the thread crest.

My universal threading toolholder uses a triangular insert mounted on its side, and as far as I can tell it has 0 rake. A little harder to get a really smooth finish on the thread flanks but possible with care.

I've used carbide inserts that were both uncoated and coated with various materials. For manual machining I've never noted too much difference. It seems to me that the cutting fluid makes a lot more difference than the insert coating. As has been pointed out you're not going to be able to thread at automated machine speeds so the wear from high speed machining should be pretty minor.

Gotta give a +1 to Ole_270's comments, with a caveat about the "properly ground hss tool". Yes, but so many people, myself included, do such a poor job grinding tools freehand that a sharp carbide insert tool is always going to do a better job.

Bill, buy a couple of inserts of each coating type and test them out.

 

[smokeywolf]

Bill, I agree with nearly all of what Ole_270 says about carbide inserts, with the exception of, "The coatings are designed for use on high rpm, high production CNC lathes.". Coatings are beneficial on most cutter materials in both manual and NC applications.
Coatings increase resistance to heat, edge breakdown, provide a small degree of lubricity and deter chip-welding.
The only insert materials I would stay away from in a manual shop would be powdered metal and ceramics.

Been so long since I've sourced inserts, I can't begin to remember the codes for the different coatings. Can say that I usually opted for the more impact resistant (for intermittent cuts) grades of carbide with TiAlN coating.

 

[fiver]

the gold is a titanium nitride coating.
it's just like the coating on drill bits. [usually marketed as, and IMO cut better as, high speed bits]

 

[Brad]

Bill, I don’t look to much at the coatings as I am not pushing the tooling enough to notice a difference. I know I won’t pay extra for a snazzy coating.

 

[Pistolero]

Not intending to just 'pay more', I more wanted to be fairly sure that paying a lot less for a different
coating wasn't just super dumb. Like 10 triple point (three cutting edges) inserts for about $6.29
against the same number, same basic spec, but different coating for $17, or a different
coating for $18. Now, even the most expensive is $1.80 per insert, or 60 cents per cutting
edge, dirt cheap, China direct mail. Cheapest is 20 cents per cutting edge.

Seems like worth getting a package of the cheapest and the most expensive (still cheap) and
see if I can tell any difference. May be a lifetime supply anyway, 60 cutting "teeth" should last
a long time.

Thanks for the info. I can grind HSS reasonably well, and can take stuff to a friend who has
a really nice green wheel grinder with a miter table to get angles correct and consistent.
I have some HSS that I ground there, and they seem to work fine, too, but a bit larger. I had
a very small threading job, ground a special tiny HSS tool which worked. But with preground
carbide inserts for $0.60 per cutting edge, seems too cheap to pass up. Also things like an insert
6mm boring bar that will cut down to .354 ID for $5.35??!! Inserts are 10 for ~$6, two cutting
edges. Have a hard time passing that kind of deals up.

eBay 172866300283
eBay 152797830051
eBay 152640680135

This guy's eBay store is unbelievable.

A different seller. Note what I call a chip breaker edge shape....I think.

eBay 302469294340

Bill