I took the workpiece off of the spoil board, and I can see that the spoil board wasn’t perfectly level either, so that added to the issue. On the left side, at the origin, the 6.1mm cut went into the spoil board 0.4mm. On the right side of the cut, where I measured the 4.0-4.1mm original cutting depth, it just barely touched the board. So my original thought of missing 1mm/5.1mm is exaggerated. I was really missing 0.6mm/5.1mm.
Are you sure your board is not warped a bit from clamping down the edges?
I’m pretty sure. The board was definitely warped, but the origin was right next to a clamp, so I think all the warping would have moved it away from the spoil board, so it should cut deeper.
The down cut bit also pushes the board down and the tool up causing opposite flex of gravity, think of the whole thing like a spring being pulled down by gravity any help opposite of gravity is exagerated.
The drilling was done with an upcut bit, and they also didn’t make it through. Drilling has it’s own trouble fighting gravity too though.
either way .1mm is about 10x’s too little overshoot.
Yeah, I am seeing that now. That doesn’t bother me here, where I’m trying to cut the boards out, and drill all the way through. I’m more concerned about what that means when doing something like a carving operation with a v bit. Really, I’m happy with any quality at all, just trying to look for signs of problems with my build or techniques. I’m also hoping folks will chime in with, “What! That’s way too much error” or “What! That’s awesome, I wish my error was that low”, or “What! That’s exactly what I would expect!”
Maybe I should tighten the anti-backlash nut down a lot 🙂