I can't say I have taken a slot cutter off the shelf that showed .003-.004" run out, cut with it, then had it ground concentric, then cut the same stock with it again using the exact same parameters to witness first hand any observable differences
I have. Well, all but "the same stock" part. New/other stock.
I agree, cutting on all 3 or 4 or close to it is probably "better". Since they are present and accounted for anyway.
The book "Chisels on a Wheel" addresses the effect and the discrepancies can be tiny, yet have observable results in the finish in apps such as mouldings.
I believe multi toothed cutters cut better if all of the teeth are actually cutting their share. That may not apply or manifest itself in observable results for all operations, but I believe in general it is a sound concept. I was helping someone over the phone recently who was using a 6 wing cutter that had around .010" TIR. The concept of buying a 6 wing cutter due to the perception they are better for our needs than a typical 2 wing router bit, but the runout is so bad only 2 or 3 teeth will be doing the cutting just seems odd to me.
OTOH, the only reason to buy more teeth is to cut (feed) faster.
No cutter will ever be as concentric and cut as smoothly as a dynamically balanced single lip (tooth) cutter, at the correct feed speed. However, that feed speed will be limited by a lot of factors. At that point, you add teeth (& HP) in proportion to the increase in feed desired. People are often confused that extra teeth are for smoothness. It will never work that way compared to a (balanced) single tooth, at the optimum feed. But the more teeth added, the faster the cutter can be fed with average discrepancies. (I agree - if the teeth are present, they should be working)
When I was using the Makita router I set up a boring bar on my CNC and wrote a program to grind the taper of the router (router was on, no collet installed in case this sounds puzzling) to improve the runout of the router. (Thanks Neil!) I now have a quality spindle which cost quite a bit, with nice collets.
Nice!
I know turning a cue isn't the same as cutting an inlay with a .005" endmill, but after all that effort I don't care to be satisfied with one tooth of a 3 wing cutter to do all of the cutting. This is even more so given my first go round doing this I found a place that ground the cutters at a very reasonable rate.
With some wing cutters it can be astounding how far from concentric some teeth are with each other or with the bore. Even worse are often metalworking slitting/slotting blades. Years ago it was a revelation when i broke one mid job and had to set up and sharpen an old one to finish. Suddenly, compared to the new blades, the re-sharp was smooth, cut on all teeth, just purred through the rest of the job. I had thought the arbor was bad! I make and modify a lot of tooling, including stellite and carbide tipped tools and slotters for myself, and for a contractor who sent me millwork (woodwork) projects for decades. The specialty tooling is for their install crews. There's nothing overly complex about the tooling, but some can take days' worth of scale labor out of a multi-month project, so it is worth a lot of money to them that would not make sense "retail".
If you can grind spindle tapers, why not make your own arbors, sized for a push fit for the cutters, and use a straight, non-threaded section where the cutter seats? Some i make are flush cutters, so the arbor is threaded (tapped) internally for a #10-32 or sometimes 1/4"-28 FH socket screw. The arbor stem needs to be counter sunk, and the cutter body itself the same, for a true flush cutter set up (cutter that will cut right down on the end, like a face mill) with the head of the 10-32 screw flush below the cutter teeth. For peripheral cutting only, that part (full flush) is not necessary. I like 4140 prehard for arbors, but drill rod will work though not quite as strong.
Also, i was not joking about evening up high teeth with a hand (diamond) hone. I hate setting stuff up on the T & C grinder for one at a time, and it is not fool-proof that it will correct things it the cutter is not both face and top ground. Or maybe done top only, very carefully, with a repeatable finger rest. The hand hone can get them all exact, in the spindle the cutter is running in, relatively rapidly. I note the high tooth by the dust and varnish build up, hone it, and run some more. Do this over a period of time and the cutter will be very sharp and very concentric. If the preference is to get them all concentric, right now, use a DTI indicator and hand hone while keeping track. Naturally the safety bulletin message is "ALWAYS unplug the machine while hand honing the cutter"
smt
