I know there has been some discussion on this topic, and I have read it, but I believe my problem might be a little different.
I tried 1/8" drill-holes, using the 1/8" cutting bit to various depths. I observed the so-called "Wood-Pecker dance", used by the CW unit when drill depths are greater than some threshold, presumably to clear dust. Between attacks of the cutting bit, the traction belt moves back and forth. I was assuming this was an accuracy-improving maneuver on the off chance that drilling shifts things a bit (I'm only guessing and giving the unit the benefit of the doubt). Common sense says it should have to move, but there you go. So, in the end, my drill-holes were oval shaped, with a major axis at a consistent angle to the y-axis (about 30-45 degrees). Even on the first attack, which sinks to a depth of about 1/8", I'm pretty sure the oval pattern was already established, so I DON'T think the traction-shifting caused the problem (although the fatness of my 1/4" drill holes MIGHT be due to this behavior).
One explanation for this behavior might simply be that my Quick-Release chuck might be bent relative to the z-truck. Could have happened during an unpleasant discussion I had with the machine over a stuck bit. If the bit itself were bent, you would expect the whole bit to move in a conical motion (they call it "play-out", no?). It would produce oversized holes as opposed to oval ones. But if the whole chuck were at a small angle, the bit would spin straight within the chuck and the z-truck would lower for the drill attack, but the slight angle would produce an oval hole in the direction of the bend as the entire cutting bit hit the wood slightly "sideways". Just one theorey.
On the minus side for my theorey, a deeper hole would be more oval than a shallow one. I did a 1/4" depth hole and it it wasn't noticably more oval-shaped than a .8" hole. Could just be my eyes.
So if my "bent-chuck" theorey is correct, is there anything I could do about it? Maybe remove and re-place the chuck? Is there a screw adjustment somewhere to "right" things up between the z-truck and the actual chuck-bit linkage?
Let's assume my "bent-chuck" theorey is bogus (what are the odds?). Is there a common, well-understood reason for oval drill-holes that I'm overlooking? Will "calibrating" the machine address this issue? I finally have a 3/8" double-flute, straight routing bit with a flat head, 1/2" shaft and 1 1/4" depth (don't think THAT didn't take some hunting down). If I calibrate, what are the measurement characteristics that should improve?
Any thoughts?
Cycollins