Within 8%, the below speeds can be used as suggested SFM for bimetal
hole saws for various materials. In other words, if 95 is the optimal
cutting speed for a 3.5" bimetal hole saw in mild steel, then we think:

SFM = RPM * PI*D/12

And we notice that PI* 3.5/12 = 0.92 which roughly equals 1 (within 8%
like I said). So for 3.5" hole saws only, neglecting the 8% error, the
equation becomes

SFM = RPM

and thus the recommended surface feet per minute for bimetal hole saws
can be inferred directly from the table below. To figure the correct RPM
for a bimetal hole saw of a different diameter in any other material use
the above formula.

Note this is only good for bimetal hole saws. Also, note it won't hurt
much to run a little slower. And yes, lay out your circle and drill a hole
tangent to your circle to allow chips to fall out. A real smart machinist
will drill this hole in the waste material :-)

Grant

Jedd Haas wrote:

I have just such a chart from a Blu-Mol "The Aggressor" Bi-Metal 3.5" hole
saw. I put it aside when I opened it last week, thinking it might be
useful someday--looks like someday has arrived rather soon. Here are the
recommended RPM settings:

Mild Steel: 95
Tool & Stainless Steel: 45
Cast Iron: 65
Brass: 130
Aluminum: 145