Why would a pocket cut be smaller than designed?

CNC Machines Shapeoko 5 Pro
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I’m making a kids balance board and I cut two pockets 18.5" long x 0.715" wide. The idea being I would place another curved piece/support legs inside that pocket to balance on . When cut out, the pocket was about 1/32" smaller than designed on all sides. Is there a reason why this might be? Does it have to do with how the tool path is calculated? My tools are all the same diameter and the support legs that were cut at the same time were a perfect 18.5" long (as designed). The tool I used for the pocket is listed as the correct diameter (0.25") in the tool library, so there’s no issue there.

The only thing I can think of is that I do a roughing and finishing pass on all my contour cuts because of the chatter I get in baltic birch. Would this also affect pocket paths? All the interior walls of the pocket are smooth and don’t have any chatter marks or other indication of a problem, except they’re just smaller than what I was expecting.

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  • Is your cutter the same diameter as selected in your software (have you actually measured the cutter in case it was mis-labelled etc)?
  • Do you use software which has a “stock to leave” feature?
1 Like
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  • Yes, same diameter. The second piece I cut was perfectly in-spec and I haven’t had any other issues with normal contours. It’s just pockets
  • I use Carbide Create, so no.
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