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What tool holder to cut up to a live center?

LOL. The only insert fatter than a W trigon would be an R round. No wonder you are having access problems.

1) Try a narrow diamond like a V insert. You can get holders that will put the centerline of the narrow corner at 45 degrees or very close.
1) Get a "CNC center" with a small diameter center extended axially for clearance between the work and the tailstock.
 
The narrow inserts can have a small radius. Make sure you have an insert that doesn't need an excessively fine feed and isn't overly delicate. If it's a one-off, this is where a properly ground HSS tool is the quickest answer.
 
I use a lot of DNMG-432 (55°) or a VNMG-332/331 (35°), the 55° is a lot stronger.
 
This is more then the one off, I really need a better solution when this scenario comes up that's why I don't have a problem getting the proper tool holders now. That said I did do some cutting with a brazed carbide tool bit and man... is 4140PH gnarly stuff. Dark blue chips coming off.
 
Kenscabs: You will always be disappointed with brazed carbide tooling. They are not much. Get a insert tool of your choice. No comparison to the former. Use coated inserts. You will have a little initial expense, but much better results. Perhaps you are running it too slow. Good luck.

JH
 
You can tune up brazed tooling on a diamond grinder until the cows come home and it still won't be as good as a properly chosen insert. At least it will have the benefit of costing more than the insert. :D Just IMHO.
 
No the brazed carbide trial was just to get in close to the center. I have a couple of insert tool holders on the way. Speaking of speed, I find on my chart at least, a SFM of 350 to 400 for 4140PH so at 1 1/4" that's 1070-1200 rpm. Seems pretty fast for such a hard material. Using .004 feed .050 doc.
 








 
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