From: Robert Bastow <Tubal_cain@hotmail.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Grooving 300-series stainless - carbide essential?
Date: Wed, 04 Nov 1998 02:56:34 GMT

Curt Brown wrote:

> Is it practical to make deep (3/8), narrow (1/8) grooves in 300
> series stainless _without_ using carbide?
>
> Thanks
> Curt

Your material is showing all the symptoms of work-hardening. There is no way to
"overcome" this..but it can easily be "undercome"  ;^)

The secret is to take a cut deep enough to get "under the skin" of the surface
hardened by the previous cut. And NEVER let the tool "dwell" even for an instant
without cutting.

This takes a little experimenting..and a lot of confidence/courage when parting
off or cutting grooves.

First, make sure your cross slide moves smothly with no trace of play in the
ways. Reduce overhang and increase the rigidity of your tool/toolholder. Lock
every carriage movement not in use.  Be sure the headstock bearings are
correctly set up.  In other words totally eliminate any cause of
chatter...Chatter in itself can produce work hardening in a hurry!!

Now sharpen and hone your HSS parting tool..razor sharp!! grind the front quite
square (any angle to the front..such as is sometimes suggested to "remove the
pip" only results in imposing a side force on the tool as well as producing a
chip that is wider than the groove..not a good idea)

The front clearance should be around 5-7 deg and must NOT have any flat to it
(Work hardens). side clearance should be a little greater than for MS say about
five deg/side..again, honed and razor sharp.  Top rake should be 5 to 10 deg.
Its a trade of here as you want to "slice" off the metal with a minimum of
pressure (to reduce the depth of WH)...but you can't afford to weaken the tool
too much.  Make the tool from the largest section of HSS that you can and keep
the blade you grind to minimum length.

Set the tool EXACTLY on C/L..if you must err..go below C/L. If you go above you
are creating excess pressure that will cause WH)

Set your work in the chuck or collet with a minimum of overhang, even if it
means resetting for every groove.  If you can, arrange tailstock support. The
objective is to eliminate deflection = shallower cutting or rubbing = work
hardening!!

Now comes the gutsy bit.  Reduce speed to about 2/3 of that normally recomended
for that material/diameter, arrange a full flood of lubricant and GO FOR IT!!
You have to feed in at a quite aggressive pace..to "get under" the hardened
surface you are constantly creating. You must not hesitate or slow down until
you reach full depth and you must instantly reverse out without "dwell" when you
hit the right depth.

I suggest you practice a bit on a piece of similar material and find the best
automatic infeed rate for the job.

Approached like this it should be a piece of cake.

Robert Bastow