Chipout-abatement strategies

I’m embarking on a project that requires a lot of very fine cuts in plywood and I’m wanting to eliminate chipout of the surface as much as possible. I’ll be using a 2-flute spiral upcut .0625" endmill.
I’ve got a few strategies for this that I’ve come up with (and some tested), but I’m interested what other ideas people have.

I’m going to pre-finish the surface of the material (water-borne poly or lacquer) prior to cutting anyway, I’m thinking/hoping this helps hold the fibers together.

Scoring pass
Run two jobs per cut: The first an extremely slow (15IPM) and shallow (.005"), then follow up with full-speed/depth passes for the remainder. Idea being that it will score the material on the first pass, then not chip on the subsiquent ones.

Downcut endmill
Obviously, this is AN answer. I’ve got a couple in the right size, but I have a lot of linear feet of cuts to do and downcutting is just very hard on the mills. I also worry that this would result in some bit wander and the cuts need to be as precise as possible

Scoring pass with a Downcut endmill
Make the first shallow (.01") pass on every part with the DC endmill, then switch the tool out for the UC mill. My concern here is yanking around the steppers during toolchange and ending up a few thou off in some direction.

Putting a masking material of some kind (tape or film) overtop the surface of the material. I’ll use painters tape on wood when I need to help reduce chip-out, but I’m worried about this gumming up the endmill.

Those are all my bright ideas, mostly untested… eager for feedback…

Use two separate files and re-home after the toolchange?

You’re talking for the downcut/upcut idea? Yea, that’d work in theory… I don’t know, never had good luck with the precision there. Always seems to end up out by a few thou here or there

I just finished a largish (for me anyway) project may from maple plywood. The maple plywood cuts much better with less tear out than cheap plywood. I did a large amount of V carving, and the final cut out profile was done with a 1/4" single flute straight bit. I think I pulled something like 60ipm+ with that and saw no tear out. The bit I used came from the Inventibles store. Worked really well. That is actually their recommendation for plywood. I used a downcut bit on another project, lesser quality plywood and it didn’t really look all that good and as you mentioned it was Slooooooow!



If you are worried about the machine moving off your zero you can easily take care of that by homing the machine and setting g28 to your official zero. At any time you expect the spindle to have moved you can rehome and move to g28. It should be exactly the same place everytime. Or at least my machine works that way.

Here is the sequence in case you are not used to this process and this may help others.

Setting your g28

  1. Home the machine
  2. Move the machine to where you want the zero and set your zero or use a block to set all your zeros.
  3. Type g28.1 {ENTER} which sets the g28 value in your controller to that exact zero location. I normally dont worry about the Z axis and have it up to make sure it inadvertently doesnt hit my material when moving from the home position. Just make sure you have set your Z zero before do the cut if you didnt.

You can now do your first cut. When finished you change the bit and do the second cut if nothing moved. If you are concerned that it moved you do the following.

  1. Home your machine
  2. Type g28 {ENTER} - this will move you machine from the home position and back to your g28 fixed position
  3. Set your Z-axis by your normal method.

Do your next cut.

There is also another indexing location like g28. It is g30 and works exactly the same way. These store the exact machine position based upon the home position and are very reliable in my experience.

Hope this helps someone.


Nice write up @bonch. Yep, I’m familiar with workoffsets and the “how” of making it work, just always found the S3 lacks the consistency to hit the mark. Curious if this is/was just my machine, or if everybody else can hit home, then hit an offset and have it be ON ±.001? Maybe I just need to tune up.

I topcoat before routing all the time. I like to do at least five coats. There will still be some fuzzing, but I very seldom have issues with chipping. I’m using a Freud 70-103 engraving bit in baltic birch.


@Boothecus, what do you topcoat with? Sprayable polyurethane?

I can’t say I can hit +/-0.001" consistently as I’ve never tried that level of accuracy. I can say that I made a jig for engraving Christmas ornaments a few months ago and did 50+/- ornaments front and back over the course of 2-3 weeks and never rezeroed my machine other than homing at the start of the night and resetting Z for different material thicknesses. I also used spray poly before cutting on these as it does seem to hold everything together a little better with less “fur”. The fur that is left usually swipes away pretty easy with a brass wire brush and 320 sandpaper.



It depends. I brush on either Minwax oil-modified, water-based polyurethane (Lowes) or Minwax polycrylic (Home Depot). It depends on whether I want the final finish to have the natural yellow tint of polyu or the blue tint of polyc. I don’t spray any more because I don’t have an effective overspray exhaust system I can do in my condo attached garage shop. I also do a lot of coats pre-CNCing because I’m often painting the grooves, and having a lot of topcoat allows me to be sloppy painting. I can just sand off the slop and the poly protects the layers beneath that.


Thanks much @Boothecus.

Have you tried a compression endmill. They are upcut at the bottom and downcut at the top. Also using an endmill designed for plywood would help. I have found endmill quality plaws a big factor in cut quality. Check out amana they have great quality but your going to pay for it. I too topcoat to reduce tearout.

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