Z-Axis cutting deeper than it should

What would cause my z-axis to cut deeper than it should? The material is .6 in thick, and I set my depth to .58 and it still cuts through the material, no matter what I do.

If your material is exactly .6" thick, the only thing I can think of is maybe when you set your Z position that you’re setting it lower than just the top of the material. I have a bad habit of setting my bit “into” the material instead of just barely touching.

Upspiral bits will draw the bit down into the material that much. Particularly on an unmodified or poorly adjusted machines. I always just put a spoil board down under my work and let it go all the way through for easier finishing.

Try the same settings with a down spiral. Also, if you do not have a z touch plate for zeroeing, you can chuck your bit into your collet, barely tighten it, lower it to just a hair above the surface, loosen your chuck so your bit drops to the surface and then tighten it. Do this in the same spot with an upspiral and a down spiral bit with the same cut and you will get a feel for the amount of flex induced by each.

@AndrewWatkins - well, there are many possible explanations. First, you’re only dealing with .02" - a poorly calibrated machine will likely yield that much error. Second, have you measured your material? Is it uniform thickness throughout? Have you ensure your waste board is 100% true across the span of your cut (both X and Y)? Have you stiffened your machine? As @Tarry_Brindle mentioned, homing Z a little too low can result in the same outcome. Are your eccentric nuts tight? Is your spindle mount tight? Have you calibrated your Z axis for precision (e.g., mine is set at $102=188.909 (z, step/mm) ). All things to consider.