Insert Holder Recommendation

[bigmojo]

Hello all.

Proud new owner of a 1941 LeBlond Regal 17 with a 1.5 hp motor and a top speed of ~480 RPM. - I know, slow, but i'm turning metal on a piece of history. She built submarine parts at the Manitowoc shipyard in WWII so I'm quite happy taking my time working on it. The lathe came with a Phase II 250-300 quick change tool post and 250-30x series tool holders. (Max shaft size of 3/4") I currently have a 5 piece set of Turning bars with 1/2 inch shanks and both TPMB & TPMW inserts. The TPMB and TPMW bits i have cut a very nice groove and thread like beasts, but they are less than ideal for facing or turning down SS.

I will mostly be turning mild and stainless steel. All of that said I am looking for some recommendations on a set of 3/4 shank bit holders and bits. - then again, maybe I'm not using the bits i already have correctly??

TIA

 

[Paul in OKC]

The holders you have should be fine. I would look to inserts more suitable to stainless, if that is what you do the most.

 

[bigmojo]

Thanks Paul. I have to admit there are way too many options, acronyms, and numbers for me to get my head wrapped around.

I have TPMB 321/322 and 433 inserts as well as the TPMW 222.

From what i have read:
A. I should stick with HSS bits as the lathe i have does not turn fast enough to take advantage of carbide
B. The 431 / 432 are better suited for facing and general turning

Would that be accurate?

 

[mikey]

I should think those TPMX inserts would work okay for roughing but they might be a bit of a challenge getting a good finish, especially at such low speeds. For stainless, HSS would definitely finish better for you and I personally would go with that.

 

[Wreck™Wreck]

Getting a nice finish on 303,304 and 316 stainless even at low SFM is the easiest thing that you will ever do with a lathe using insert tooling, chip control and tool life are a different matter entirely (the nest of unbroken chips may well drive you mad). For general turning and facing using one tool an 80° diamond or trigon insert will work well, triangles are not well suited to both operations with the same tool, flood coolant is essential.

 

[Dan_S]

.
From what i have read:
A. I should stick with HSS bits as the lathe i have does not turn fast enough to take advantage of carbide
B. The 431 / 432 are better suited for facing and general turning

Would that be accurate?

A) sfpm is what matters, A 8" diameter bar spinning at 480rm is roughly 1000 sfpm, and that's pretty fast for anything other than aluminum
B) that depends on the feed rate and the chip breaker.

This page will help you understand insert nomenclature.
http://www.carbidedepot.com/formulas-insert-d.htm

 

[Wreck™Wreck]

B. The 431 / 432 are better suited for facing and general turning

Would that be accurate?

The difference between Triangle 431 and 432 tools is the nose radius in 1/64 ths. The first number (4) is the inscribed circle in 1/8's, the second number (3) is the thickness in 1/6'ths. A 1/2" inscribed circle triangular insert used in a small hobbyist sized lathe is a large tool indeed.

As mentioned above, a triangular insert is not well suited to Facing and OD turning with the same tool in the same orientation due to the tool geometry.
The best option, short of changing tools, is to choose a shape that has the lowest acute included angles.

 

[mikey]

I own a 5-piece set that uses TPMX inserts and agree - you have to change tools to face and turn. They work but carbide doesn't finish nearly as well as a sharp HSS insert or a HSS tool in stainless, at least not for me and not at low speeds. TPM inserts have no chipbreaker so stainless will give you looong chips, another reason to change to a more modern tool geometry.

 

[bigmojo]

So if i am reading this right i would be looking at a CNMx32x?
That would give me an 80 deg diamond with 0 relief, reasonable tolerance, a .375 IC @ 1/8 thick thus fitting into a 1/2" holder.
Alternatively, since I would still need a new bit holder as the ones i have are all for T bits, i could get a 3/4" holder and would be looking at a CNMx43x bits? All in HSS correct?

Thanks all. In case nobody has mentioned it lately...this forum is awesome!

 

[Dan_S]

So if i am reading this right i would be looking at a CNMx32x?
That would give me an 80 deg diamond with 0 relief, reasonable tolerance, a .375 IC @ 1/8 thick thus fitting into a 1/2" holder.
Alternatively, since I would still need a new bit holder as the ones i have are all for T bits, i could get a 3/4" holder and would be looking at a CNMx43x bits? All in HSS correct?

Big tool holders & inserts are only really needed if you're going to take large depths of cut. Not to mention they cost more.

for example I run this set on my little 8" lathe, and it uses ccmt/ccgt 21.51/21.52 inserts.
http://www.grizzly.com/products/Glanze-Turning-Tool-Set-1-2/H5681

1/4" insets are usually rated for a depth of cut up to about 3/32"
3/8" inserts up to about 1/8"
1/2" a little over 1/8"

My recommendations would be to go with 1/2" or 5/8" shank tools that run ccmt/ccgt inserts. Take a look at this starter kit from AR Warner, it uses CCMW 32.52 t-15(a type of hss) inserts.
http://www.arwarnerco.com/p-15-kit-11-12-inch-turning-c-right-hand-left-hand.aspx

the benefits of these holders, is that you can also run CCMT, & CCGT carbide inserts that are cheap and plentiful.