Everything Is 1/32" Too Small

I have a new X-Carve with the 500mm rails and DW611 router. I did all the tuning steps I thought were necessary: adjusting the motor pots, tweaking the step size to move the router an exact distance, etc. And things seem to be working pretty well, except that whatever shape I carve seems to come out 1/32" too small. It is not a scaling issue since, for example, a 1" square and a 5" square both come out small by the same amount. I have made shapes directly in Easel and also imported G-code from VCarve and get the same results. The shapes come out very consistent, so I’m not losing steps, etc. I measured the bit diameter and it is exactly as specified. What am I missing?

Thanks,
Scott

What size bit are you using? Is it possible you are cutting on the line versus outside?

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It was a 1/4" bit, so that wasn’t the problem. I did check that I was in the right position relative to the line.

I had a similar issue early on and to fix it you need to adjust the variables $100, $101 and/or $102. I don’t remember how far each variable change is, but there was a thread about it on here somewhere. Anyway those settings fixed the issue for me (sorry I couldn’t be more help but it was like a year ago).

Brian

Thanks for the replies. As I said, I checked both those things. The bit measures exactly 0.250" with calipers; I will double check and try another bit to be sure, because that seems like the most likely thing. I adjusted the $100 and $101 values and get the correct movements in each axis. Plus that should make a 5" square smaller by a different amount than it would a 1" square since it sets the scaling.

I remeasured carefully on the cutting portion and it is 0.246", so it is a tiny bit small. I will try your test when I have a chance and also try setting the bit size to the exact measurement, and also try another size bit to compare. Thanks for the tips.

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Don’t measure the actual bit (no matter how careful you are, you can damage the cutting edge) — instead, cut and measure a slot.

To continue that, you could cut a diamond-circle-square test block and evaluate it to determine the runout for that endmill in that spindle, in that machine.

http://www.shapeoko.com/wiki/index.php/Calibration_and_Squaring_the_Machine#Diamond_Circle_Square_Test

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Finally had more time to investigate this. After measuring the width of a single line cut from the 1/4" bit, it does indeed measure narrower than 1/4" by about the required amount to make the cuts I was measuring too small by the amount I saw. Thanks for the help!