Finishing pass chipload?

So I know to aim for 1 thou chipload when machining. Don’t make dust, right?

What about a finishing pass and/or spring pass? Are these exceptions? Is it permissible to take these really light cuts to get a nice surface finish in aluminum? Or should I be doing more math, and how do I figure out what kind of “stock to leave” number I should aim for?

My guideline for stock to leave is it should be greater than the largest defect/deflection/deviation one is seeing when making the roughing pass.

Based on that dimension one can determine if multiple passes are feasible, and if so, what thickness they should be, and based on the width of material being removed, what sort of chipload should be workable.

Ooof that sounds complicated. Any videos on this topic? NYCCNC?

or just make dust for the finishing pass…
it is what I end up with normally, since usually I do both a smaller stepover and a very shallow depth for these… (say 0.2mm depth at 25% to 33% stepover)
small stepover + shallow depth give me a nicer finish, and that’s the point of the finishing pass for me


Do folks run a full DOC to finish a wall? I did so - 10mm DOC, and previous op left 0.1mm radial stock. Seemed to run without issues.

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you can even do the floor and the wall in one go that way

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Ive found that in 90% of the case for Aluminum, ramping down for finish wall contours usually leaves the best finish.

Also for stock to leave, Will has it right. Usually works out to 0.020-0.010 and on the upper end if you need to add in a semi-finish for 3d work


Oh that’s interesting, so if I understand correctly:

  1. Do your contour (however really) down to your desired depth, leaving 10-20 thou radial
  2. Run another finishing pass, 0 stock to leave, but keep your DOC stepdown settings as well

Well it really depends on part geometry

Usually I’ll rough with both axial and radial stock to leave then perform finishing toolpaths to the flat areas with radial stock to leave that matches the roughing. Then come in and ramp down wall and leave a very small amount of axial stock so that it doesn’t mess with the floor finish. Really depends on many things and tolerances as well. You can ramp a bit more aggressively on the finish pass but IMO its not worth saving seconds, 1-2 degrees works well and is very reliable.

For the most consistent finish cuts, you’ll want to minimize load spikes.

oh yeah, chipload

Don’t worry a whole bunch about chipload on finishing passes, just keep it reasonable

above 0.0005ish is a good rule of thumb. Reason is, you aren’t creating a bunch of heat during finishing so chipload isn’t make or break like roughing. Tool load is more important imo

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