Inventables Community Forum

Help with undersized pockets

Ok guys, looking for some help here. It could very well be that I don’t actually have a problem other than a fundamental misunderstanding of how a CNC works, but I figured I’d ask anyway. I just got my X Carve about a week ago and I’m pretty new to CNC work in general.

So I’m trying to make a tray for holding all my work clamps and accessories. Rather than download somebody else’s I took a shot at designing my own. I measured all the pieces and added about a half a millimeter for clearance. I used Easel to do the design work and set it up for a single stage cut with a 1/8" upcut bit.

The problem I’m having is that my pockets are all about 1mm undersized. The ones in the picture should measure about 19.5mmx12mm

I’ve tried everything I know to do - adjusted belt tensions, adjusted V wheels, checked X/Y square, checked Z square to work surface, etc. It wasn’t all perfect and I had to make a few adjustments but none of it made any difference to the outcome.

I called customer support and they suggested I check the steps/mm calibration. I did this by installing a V-bit and bringing the Z axis down far enough to mark the wood, then bringing it up and moving the spindle over by 1 inch and measuring between the marks to confirm it moved exactly one inch. I checked this in both the X and Y axis and both were within a few thou, plenty close enough.

So the only thing I’m left with is maybe I just don’t understand how Easel calculates the tool path. Obviously I know that I can’t cut a square corner with a round mill, but I would expect to see more accuracy on the outer walls of the pocket, am I wrong here?

I downloaded a few files of where other people made a similar tool tray for the same parts and all their holes are actually oversized by about 1-1.5 mm even though their pictures seem to show a tighter tolerance. I’d like to not have to remember to oversize all my future pockets if possible, any ideas?

If you are cutting inside, outside or on pah could make a difference.

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Calibration is more accurate when done over a longer distance such as 20 inches.
Some causes are bit size, bit deflection or loose V wheels.

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I have found using a micrometer on my bit, entering that into the custom bit diameter and then actually simulating the cut gives me very accurate results. If its not in your bit width settings then I could imagine playing around with the width to see what number you actually need to input to make the size hole you require. good luck!

If the system have any amount of backlash or any sort of “give” => inside cuts are undersized and outside cuts are oversized.

First do what Mark suggest, measuring over the longest possible distance for each axis.