I purchased a slitting saw and an arbor to make - well, slits. The first
slit ever I made was using a Dremel abrasive disc in my mill. It worked
really well but I am told that it is not a recommended thing.

So here they a

http://busybeetools.ca/cgi-bin/picture10?NTITEM=B044

http://busybeetools.ca/cgi-bin/picture10?NTITEM=T747025

I tried to make a slit in an aluminium block to make a boring bar holder.
The first thing I noticed that the saw did not run concentrically (instead
of 'vrrrr" it went 'vroom, vroom'). I finished the cut (using a lubricant
and a slow speed). The slit looked awful, but this was partly my fault as I
forgot to lock the Z-axis in all the excitement. Anyway, it is functional,
so no real harm done.

I had a close look at the arbor and at the saw. The saw does not have a key
slit (proper name?) contrary to the picture, just a circular central hole.
The diameter of the central hole is 0.872" allowing for my calipers reading
0.001" under. It appears perfectly circular. The tooth length measured from
the inner aspect of the central hole varies by 0.008".

The run out of the arbor shank in a mill 1/2" collet was less than 0.001".
The run out of the 7/8" ring, however, was 0.015".

I put the saw on the arbor and noted a slight laxity of the fit on the 7/8"
ring. I tightened the whole thing as I would normally and then measured the
"run-out" of the teeth by checking them carefully individually. The run-out
was 0.030".

The questions a

1) Is this situation common?
2) Is it acceptable (I cannot see it myself - right now I am cutting with
only a few teeth - maybe when they wear out the other teeth will start
cutting ;-)
3) Would purchasing the same system from an "industrial" vendor be more
likely to perform satisfactorily?
4) Is this sort of arbor a good thing anyway? Would another type perform
better?
5) Is there anything in the setup of the saw I could have done to make it
run concentrically?

Thanks,

--
Michael Koblic
Campbell River, BC

On 2009-07-13, Michael Koblic wrote:
I purchased a slitting saw and an arbor to make - well, slits. The first
slit ever I made was using a Dremel abrasive disc in my mill. It worked
really well but I am told that it is not a recommended thing.

So here they a

http://busybeetools.ca/cgi-bin/picture10?NTITEM=B044

Cheap tool.

http://busybeetools.ca/cgi-bin/picture10?NTITEM=T747025

Also -- and the more easily broken tool is the one which costs
more.

I tried to make a slit in an aluminium block to make a boring bar holder.
The first thing I noticed that the saw did not run concentrically (instead
of 'vrrrr" it went 'vroom, vroom'). I finished the cut (using a lubricant
and a slow speed).

What lubricant? For aluminum, kerosene or WD-40 are good
choices.

The slit looked awful, but this was partly my fault as I
forgot to lock the Z-axis in all the excitement. Anyway, it is functional,
so no real harm done.

:-)

I had a close look at the arbor and at the saw. The saw does not have a key
slit (proper name?) contrary to the picture, just a circular central hole.

They are more common on larger ones (say 1" or larger), and for
long arbors for horizontal mills where multiple cutters and spacers are
mounted between the end which goes into the spindle and the end which is
supported by a bearing.

The diameter of the central hole is 0.872" allowing for my calipers reading
0.001" under.

Hmm ... that should be 0.875" (7/8") for a standard size. But
note that your calipers will measure undersized for inside measurements,
and how much undersized varies with both the diameter of the hole and
the thickness of the contact edges of the calipers inside jaws.

It appears perfectly circular. The tooth length measured from
the inner aspect of the central hole varies by 0.008".

Ouch! Cheap! (Well -- Busy Bee, after all, not a serious
machine tool supplier.)

The run out of the arbor shank in a mill 1/2" collet was less than 0.001".
The run out of the 7/8" ring, however, was 0.015".

Ouch! Even worse.

I put the saw on the arbor and noted a slight laxity of the fit on the 7/8"
ring. I tightened the whole thing as I would normally and then measured the
"run-out" of the teeth by checking them carefully individually. The run-out
was 0.030".

This was in a position where the run-out of the arbor adds to
the run-out of the hole -- and perhaps the slop as well.

Try rotating the saw to different positions before clamping it
and checking the runout. You should be able to find one where it is
minimized (though likely never zero, unless you have 0.007" of slop in
the fit from the blade's hole onto the step of the arbor, in which you
should be able to tune out the slop.

The questions a

1) Is this situation common?

Even with a good arbor and good milling cutter or slitting saw,
*some* runout is to be expected. You only wind up cutting on all teeth
with a fairly aggressive feed -- on a machine rigid enough to support
it. And you will probably need a key in the arbor to handle the loads
from an aggressive cut -- and a matching key slot in the blade or
milling cutter.

2) Is it acceptable (I cannot see it myself - right now I am cutting with
only a few teeth - maybe when they wear out the other teeth will start
cutting ;-)

Take the time to tune out the errors in the arbor and the saw,
and you should be able to make it better -- but there will always be
some error audible with a light feed.

3) Would purchasing the same system from an "industrial" vendor be more
likely to perform satisfactorily?

Much Better, at least. Or you could make a *single-sized* arbor
to fit the saw you have -- and hope that the runout is better than the
0.007" you measured. I've never had one of the multi-step ones, but I
have made single-sized ones for projects before I got the Horizontal
mill.

4) Is this sort of arbor a good thing anyway? Would another type perform
better?

A single sized arbor, machined to be concentric on your lathe
(lots of careful work there). (Hmm ... does your mill have a R8 collet
spindle nose? If so, there are two-step arbors with some rings of
both sizes and with keys. The two sizes are 7/8" and 1" in the ones
which I have seen.

5) Is there anything in the setup of the saw I could have done to make it
run concentrically?

Yes -- try rotating the saw blade so its runout cancels part of
the runout of the arbor, and then slide the loose fitting blade around
to see how close you can come to truly concentric. And then leave it
assembled for future use, and make a new abor for the next slitting saw,
and get it from a better quality supplier and maker. (Someone like
Cleveland or the other industrial makers for the saws and conventional
milling cutters.

Good Luck,
DoN.

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