Smooth z-travel increment?

For those who do a lot of non-axis-planar or smooth curves with their projects, what is your sweet spot for z-increments? While I predict that cutting in smaller depths per pass will shape the project better for less sanding smooth, I also believe every reduction in z-travel increase number of passes on the total project, which can be tons of time better spent.

While this is not as much of an issue with the M4’s increased speed, it certainly isn’t a sprinter either. I’m sure everyone has their preference, would love to hear your thoughts.

(I’m also assuming the smallest z-travel increment is likely 1/64" for practical purposes)


Another option for smoother curved surfaces is to use a ball nose endmill like this:

It won’t leave sharp edges which makes for less sanding too

a profiling pass (x/y lines with variable Z) also goes a long way to reducing
the sanding.

but remember, with a maslow style machine, the sled rides on the workpiece, so
this can only be done for areas significantly smaller than the sled.

David Lang


Great point, @dlang is very correct. Rather than cutting in steps you want to cut a back and forth pattern (like mowing a lawn) and have the z-axis vary it’s height continuously as you are cutting to get a smoother surface. A ball nose endmill will still help to reduce the amount of tool marks that you see.

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There we go with me assuming asynchronous z axis adjustment…

I totally see the value of the ‘lawnmower method’. What about if the project had a contour that changes direction on all 3 axes simultaneously, ie. A circular band on the x/y that has a wavy z-depth? Does adjusting in all three planes simultaneously create issues (Provided the sled level is managed)? My thought is possibly more lateral stress on the bit and a higher chance of bit wear, but if it was just for a small section of the project and done slower maybe that is mitigated?

the bit doesn’t care what direction it’s cutting, so feel free to run it through
whatever twists you want. The machine will move all three axis however the gcode
instructs it, so the machine isn’t the limitation (other than the sled support
as mentioned earlier)

the limitation is in the CAM software, it usually has countour mode (cut a level
at a time in steps the way you were initally describing) and a profile mode
(lawnmower type passes with the height varying.

David Lang

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You may already know this…

Similar concept to what dlang mentioned is to have a ‘roughing’ pass and a ‘finishing’ pass - depending on the CAM software etc. it may have different names.

The ‘roughing’ pass assumes a hefty end mill to go quickly through the material and hack out most of it. Normally done in steps down through the z-axis following contours. Obviously ‘quickly’ on a ‘not M4’ Maslow makes everything a bit relative.

The ‘finishing’ pass assumes a smaller smoother end mill, often a ball nose, and its path will go across the previous contours. Potentially several passes in different directions.

Obviously, all of the above depends on the CAM software.

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