On 2010-06-02, Gerry wrote:
I need to slit a piece of mild steel 0.500" thick and 0.875 deep to a
0.652 hole. This will be a clamp to attach to a motor shaft. Never
used a slitting saw before, therefore I am asking for any advice.
Using a drill/mill with a 3X1/16X1 30 tooth saw. Thanks in advance

You *could* go into _Machinery's Handbook_ and look up all the
formulas. But for convenience, my old McDonnell Douglas feeds and
speeds calculator (slide rule type, plus built in lookup tables for
materials) says:

ALLOY: SFPM: Chip load per tooth
Annealed alloys: 70-90 0.006
Soft carbon steel: 80-120 0.007

Let's be conservative, and pick Annealed alloys, so for the middle of
the range (80 SFPM), and a 3" diameter cutter, you want about 102 RPM.

And for 30 teeth, you want about 1.83 in/min feed rate.

Now -- the first question is whether your drill/mill can get
down to 100 RPM. If not, you will be burning up your cutter.

This is really the sort of thing at which a horizontal spindle
mill excels, and I have my doubts about a mill/drill (or drill/mill as
you show it). The fact that "drill" is before "mill" in the term
suggests that it is more optimized as a drill press, and may not have
spindle speeds slow enough for your task in steel.

And the inches/minute feed rate presumes a power feed, which you
are unlikely to have.

What kind of spindle does this machine have? There are arbors
for use with slitting saws and narrow mills which fit R8 spindles. If
your machine has a Morse spindle, I'm not so sure what is available.

Use a cutting fluid -- at least something like Rigid high sulfur
threading oil (sold for pipe threading). At this slow a spindle speed,
you probably won't be throwing the coolant around at least. :-)

In any case, I would advise not going much more than about 1/16"
(the width of your cutter) of depth per pass -- especially until you get
the feel of your machine under this kind of loads. And it sounds as
though you won't be doing enough cutting of this sort to really get the
feel of it.

Good Luck,
DoN.

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