Using End Mill as a Drill

[marklazarz]

Just finished a Brian Law clock (clock 24) and I used a 1/8" up spiral router bit to do a lot of the machining and noticed something interesting.  All of the 1/8" holes I programmed as drilling tool paths were slightly oversized, yet the larger holes I programmed as profile tool paths using the same cutter were the correct diameters.  I took the cutter and measured it and checked it for distortion and everything seemed fine.  I then put the router bit in a drill press and drilled some holes and they were all slightly oversize (say 0.001" or so).  I then put a 1/8" drill bit in the drill press and drilled a hole - perfect.  Has anyone else noticed this phenomenon?

[BobL]

Mark;

Congratz on finishing your Brian Law clock, post a picture if you can, love to see it.  As to the oversize drill hole, could it be you have a slightly warped router bit or maybe it's the spindle itself?


Cheers
Bob

[marklazarz]

Mark;

Congratz on finishing your Brian Law clock, post a picture if you can, love to see it.  As to the oversize drill hole, could it be you have a slightly warped router bit or maybe it's the spindle itself?


Cheers
Bob

Checked for warping, dimensions and runout.  Same results on drill press so it must have something to do with a hole being drilled with a flat bottom cutter.  I will post a photo of the clock on the "Ticker" board when I put the finishing touches on it.

[Nate]

Same results on drill press so it must have something to do with a hole being drilled with a flat bottom cutter.  ...

That, or chip clearance.  (Square nose bits are known to wobble when plunge cutting like that though.)

[marklazarz]

I think Nate is correct.  Slight wobble with no guiding point would be my best guess.

[ArtF]

Sounds logical to me..

Art