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 are:
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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 are:
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?
Also -- and the more easily broken tool is the one which costs more.
What lubricant? For aluminum, kerosene or WD-40 are good choices.
:-)
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.
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.
Ouch! Cheap! (Well -- Busy Bee, after all, not a serious machine tool supplier.)
Ouch! Even worse.
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.
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.
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.
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.
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.
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.
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