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10-32 single point 303 stainless

jlakes85

Aluminum
Joined
Sep 10, 2011
Location
Northern NJ
I'm trying to cut this at 100 rpm using a carbide kennametal insert. When I get within the last .005 pass of the 0.036 thread depth, the entire thread starts to tear out. Using plenty of cutting oil. Any suggestions to correct this?
 
What is your chip load per pass? You said "When I get within the last .005 pass". In my experience, 303 is shit to thread.
 
Is the insert you are using designed to cut this material and thread size? Brand new and sharp?
How many of these are you cutting? How far out of the collet/chuck?
What kind of lathe?
Are you feeding in compound on angle? Or is this CNC?
Starting guess would be .005 is too much for last pass.
You'll want a tool that is very free cutting, in my experience.
 
It's probably tearing at the previous passes too. Try upping the rpm. Been there and done that too. :cryin:

Machine Shop Practice Vol. 1 (Karl Hans Moltrecht) Chapter 13 - Cutting Screw Threads on a Lathe. That's what I refer to every time there is a doubt. It mentions that the final few cuts are .0005 - .001. It also describes about cleaning up the backside (right side)that is being burnished.

I knew a old time German Machinist who started out in Germany during WWII. He did not use that front side/back side method with a 29 degree angle, He just cuts at 90 degrees straight in. Works for him.
Groeger Special Tooling.
 
.005 per pass is a lot for that skinny root diameter, likely flex is the problem. Also unaware that Kennametal made a super sharp uncoated insert that you'd need for this. If you're using a coated insert it'll never work.
 
.005 per pass is a lot for that skinny root diameter, likely flex is the problem. Also unaware that Kennametal made a super sharp uncoated insert that you'd need for this. If you're using a coated insert it'll never work.

Yeah it will. Give me a break.
 
I too have had problems with 303 and found it worth using HSS tools lapped to a razor sharp
finish. I have just parted off 2000 components in 3mm 303 with a simple HSS blade with no regrind. You must also get the tool dead on centre.
 
There's good 303 and bad 303. With the good stuff, this should be dead easy but the last passes should be a couple thou at the most. Make sure your tool is on center and the work isn't deflecting. With bad 303, I dunno, use a die head?
 
I hope you missed a 0 in that 100rpm...
Speed it up, pointy insert, smaller doc, and advance the cross slide a bit so it only cuts on the leading edge (you can set it to 29.5 degrees if you really want to). Helps keep the tearing to a minimum.
 
There's good 303 and bad 303. With the good stuff, this should be dead easy but the last passes should be a couple thou at the most. Make sure your tool is on center and the work isn't deflecting. With bad 303, I dunno, use a die head?

Where does bad 303 come from? I've never machined bad 303.
 








 
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