A z-error that I can't track down!

I mostly make thin two sided parts with X-Carve. Some areas of the part are only .030" thick. But my parts always turn out too thin. I’ve stiffened the machine on x,y, and z; calibrated it well, am very careful with zeroing, use a faced-flat backboard. After all that, the parts come out about .030 too thin, consistently.

Looking for ideas on what the cause might be. Hysteresis due to a worn delrin nut, perhaps; although it doesn’t seem to have any slop? Spindle deflection maybe? This is kind of driving me crazy.

Since you are cutting thin material are you certain that the material is flat to the flattened backboard across the entire material surface?

I dont know what program you are using but in easel and only easel I have to add .04 to every measurement. all other software i use the measurements are spot on. so I hope you get a answer because I would love to know.

Yep. Flatness of the baseboard with respect to the bit is well under .010 over the part’s work area. Thx.

I use Fusion 360 for CAD and CAM and send GCode with ChiliPepper. Thx.

I was talking about whether or not your material was held flat against the flattened baseboard.

If you are cutting a thin part thinner the way you hold it down is important, I would say try the CA glue and painters tape method on the first cut but making sure the 2nd side is held properly can be an issue too… I am not fully sure how precision these units can get also depends on the zeroing method to the face of the material, flipping over securing and then zeroing a second time could also be a factor.

Yep, washboard is flattened and 24x7x3/4" stock held down all around its perimeter. Thanks.