Why is my first pass always ~4mm deeper than my next passes?

I’m extremely new to Easel (and CNC work) so this is probably going to be something obvious that I’m missing. What’s happening is that my first pass is plunging in roughly 4mm more than whatever I set my ‘depth per pass’ to.

So let’s say my depth per pass is set to 1mm, the first pass will rip through at a depth of 5mm (4mm+1mm) and usually break my bit, and then the next passes will be the standard 1mm. What this means is that my final piece (if my bit survives) is always 4mm deeper than intended.

I’ve realised that I can ‘rectify’ this problem by deducting my intended depth of pass (1mm) from the 4mm it overshoots on the first pass and then raising my ‘work zero’ position by that amount (so 3mm).

But that’s not ideal :sneezing_face:

I’m using a Sainsmart Genmitsu 40-40 Pro

And I’ve uploaded my gcode file

Untitled_roughing.nc (1.1 MB)

what is your Z probe thickness and what is it set to in your software? IF it is set 4mm thicker than it really is than that would cause the initial plunge to be 4mm deeper than intended.

Another somewhat common issue on the cnc’s with very little Z axis travel distance is the Z lifting after the probe sequence, crashing into the top, loosing steps and from then on it’ll be the amount of steps lost deeper than intended… However I would expect this to be a varied amount and not exactly 4mm every time across different boards… So I’d check the probe settings and keep an eye on the Z movement during the prove cycle as well just to be able to rule that one out.

That’s sorted it mate, thank you so much :grin:

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