View Full Version : Straight bit more accurate than spiral?

05-04-2016, 01:45 PM
Hello, recently I have noticed that when using a straight bit my dimensions are more accurate on a profile cut than when I use a spiral bit? The spiral bit is always off around .02" on one axis and "01 on the other. And this is with a new bit. Is this normal?

05-04-2016, 04:47 PM
I was thinking that deflection would be greater with a spiral-flute tool than with a straight-flute one, but it shouldn't be that much. Grain direction might account for some of the difference you're noticing between cutting on the two different axes, or it might have something to do with your machine. To eliminate that possibility, try rotating the wood piece 90 degrees and running the program again, measuring to see if the error moves or stays with the same axis. You might also check to see if the spiral bit is really the size it claims to be.

05-04-2016, 07:58 PM
I know onsrud bits - especially 1/8" - are smaller than advertised - which I find extremely annoying at times. So using an end mill as a drill bit has ended poorly before (ie if I try and insert a 1/8" drill bit into a hole drilled by a 1/8" end mill, it does not fit).