Need Help!- Ugly Threads

[G. Hager]

I am a newbie here. I have been programming and running a Nakamura Tome TW 20 twin Spindle lathe for many years. I picked up the programming on my own as an operator. The problem I am having is I am cutting M5 X 8 threads on 303 stainless steel with a groove cutter. I am being forced to cut the threads on the back side as there are several small close tolerance bores on the front end. Therefore I cannot get a profile threader in that small space. The part itself is very small and the thread area is only .150. The thread is good and the gages go right on, but I do not like the appearance of them. I have tried cutting anywhere from .004 per pass to .002 per pass (G32) at S.S. of anywhere from 400 to 600 and everywhere in between. They almost look torn. I have tried changing inserts to no avail. Any suggestion would be appreciated. The "real" engineers where I work can't help me here either.
Thanks. I can't seem to add a photo from my computer. E-mail me for a rough one. peanut2339@yahoo.com
G. Hager

[HuFlungDung]

I'd look critically at the clearance angles ground on the tool. It sounds as though you might have a slight rubbing problem which would indicate not quite enough clearance on one edge. It must be close though, or the threads would not likely gauge right due to deflection at the rubbing edge.

[jess fuqua]

are you using carbide, do you program with G76, what is your spindle speed are you chattering, oil helps alot too.

[G. Hager]

Originally Posted by jess fuqua are you using carbide, do you program with G76, what is your spindle speed are you chattering, oil helps alot too.

I do not have a auto canned thread cycle(G76). I have programmed each pass, G32. The tool is carbide. It is a ThinBit, made for metric thread. I have tried several spindle speeds ranging from 450 to 600. Same result. The machine does not have oil coolant. It has flood coolant. Heat is not the problem.

[jess fuqua]

your rubbing or chattering and not going fast enough.
I think your spindle speed should be around 2000 rpm for that small of hole, thats about 80 sfm, thats slow for carbide also you could be running over your chips too.

good luck