It may not be worth your time, Pete, but many types of general purpose hole
saw teeth can be resharpened, possibly a couple of times to like-new.
The hardened tooth area may only be a narrow band of coil stock "saw" welded
to a mild steel cup/body of the hole saw, so this will limit the number of
times the teeth can be resharpened.
By just lightly kissing each tooth face in the gullet with an abrasive disk,
the original sharpness of the saw teeth can be restored.
Alternating the radial angle of the "grind" (pitch angle is probably
consistent for every other tooth) is how most of the teeth are ground when
they're new.
So when I discovered that they could be resharpened, I started by grinding
every other tooth at the same angle for one rotation, then going around once
more, grinding the other angle. Again, grinding is just the slightest amount
of tooth material being removed.
One wouldn't need to have a sophisticated cutter grinding fixture. I used a
cheap spin index, a magnifier lamp and a Dremel tool with very good results.
As you already know, most general purpose hole saws aren't manufactured to
tight size tolerances.
Your practice of making a test hole in similar material is a good method of
finding out the real hole size.
As you suggested, slower spindle speeds may dramatically increase the
cutting life of the hole saws.
Clearing away the chips is also of major importance (which you've addressed
by adding smaller holes near the finished hole size), since the teeth may
end up just skidding on the work material if the tooth gullets are full of
chips.
--
WB
..........
metalworking projects
www.kwagmire.com/metal_proj.html
"spaco" wrote in message
...
I am using my old US Machine Tool vertical mill. It's about a 1800# knee
mill. Plenty stiff when all locked down. I know I am on the high side of
the speed range at 350 rpms min. speed. Someday, a VFD is on my list if I
can ever figger out how to spec one out. I still have the original 3 phase
motor which I replaced with single phase when I got it.
Yes, I learned that "edge hole" trick recently. It makes a tremendous
improvement in cutting rate and saw life. Much less pecking needed, of
course.
I use the dark brown sulphurous stuff. I buy it at the hardware store
as "pipe thread cutting oil".
I will look at the links you suggest.
And yes, I used to do it using the "several tool change" method, but with
the hole saw, I can do in 3 or 4 minutes what took me almost 20 minutes
the "old" way. In "the old way", I had to go up to my largest twist
drill, 1 5/16" and then bore from there. I really learned how to hold my
breath for a long time using that HUGE (to me) bit at 350 rpm. to go 1
1/2" deep!
As it is, tolerances are such that I have to try to come close, but
undersize with the hole saw, then to the boring bar for the last cut.
Normally, I am close enough that once I adjust the BB for the job, I can
leave it set there and just plug it in, bore, and go back to the hole saw
for the next one.
-----Interesting problem, though: Recently I bought some new hole saws, I
from each of 4 well known mfrs. 3 of the 4 had on tooth hanging out,
producing an OVERSIZE hole---- wasted one part!!.
The Starret brand turned out to be best by a long shot over the other
three. I chucked the "bad" ones up carefully in the lathe and ground off
the offending tooth or two with the tool post grinder.
In future, I will take a test cut on new hole saws in scrap, even
though the Starretts have all been right on. And, for what it's worth,
these 1 3/8" hole saws tend to cut 10 to 20 thou oversize.
Pete Stanaitis
------------------
F. George McDuffee wrote:
=======
What are you using to drive the holesaws? One trick on hole saws
is to drill a hole or several holes just inside the finished
diameter so the swarf has somewhere to go. Easy to do on a mill,
less easy on a drill press. Also what coolant are you using?
For what looks like a better price on an annular cutter see
http://www.drillsandcutters.com/hssanho1dia224.html [60$]
http://www.ameritradeco.com/page/961257 [75$]
Also if this is not a high volume job how about a silver and
demming drill? You would have to change tools several times, but
this could be less cost. [c.28$]