Tool order to minimize tear out

Hi everybody!

Big thanks to the whole community, you’ve already answered so many questions I didn’t even know I had.

On to today’s issue, Im making a family establishment sign for my girlfriend’s boss. 1" Thick black maple, top surface painted white then masked. All cuts are 2mm deep, 1mm DOC.

My goal is to minimize tear out and any other damage to the white raised letters, my thought is to start with a Ø1/32" bit to first machine all the contours than follow with an Ø1/8" or Ø1/4" to finish the roughing.

I can see the Ø1/32" will have more engagement as it is constantly cutting into untouched material, so I should run a little slower. Is there anything else I should be considering with this approach? Is it even worth it?

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Since nobody else is fielding this, I’ll give it a shot. I hesitate because I’ve only just started my CNC experience. That said, I’ve oodles of experience with routers and, on my Nomad, have successfully cut a complicated snag with tiny (0.25 mm) branches that I was happy with. My approach:

Do the rough work first. Cut a little “fat” around the lettering. By this I mean leaving the lettering a bit thicker such that you trim off the excess with your finish pass using the 1/32" mill. The way you cut fat with CC is to create a new bit with a slightly larger diameter than the one you will actually use to do the roughing. For my work I made this diameter about 0.06 mm larger. But, for me, the 1/32 bit was my roughing mill so you might try an increase of 0.1 mm. [Others appear to recommend about 0.5 mm increase:


I suspect this is contingent on the scale of your project.]

[Edit: removed reference to climb cut]

As always, test using a small sample of your design.

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The M4 will just reverse the spindle (if your machine has that capability). That could cause a typical end mill to rub and increase the chance for fire. You’d have to change your end mill to reverse the direction of rotation.
A climb cut would change the direction the router is moving through the stock. If CC can’t do that, Fusion 360 can.

@Tyson Fusion 360 can create finishing toolpaths using “rest machining”. I wouldn’t recommend using a 1/32" end mill with full engagement (blazing its own trail through the workpiece). Leave a small bit of stock after your roughing pass and come back to clean it up with a finishing pass. Tearout will also be a function of the wood type and grain direction.

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Probably not the best answer for you, but if you continue to do jobs like this, buy some down cut endmills, they are amazing for pocketing and leave clean edges with no tearout. This will have the most effect in my opinon. I have also had good results cutitng pine with a straight flute endmill.

I’m away from my computer but fusion has an option for roughing and leaving radial clearance, which allows for a finishing pass, My suggestion would be to get some scrap material and just cut a few small pockets and experiment. try with no finishing pass, then with something like a 0.001" finishing pass, and just see what the results are. Also maybe trying a very small DOC for the first pass may help too,

As was mentioned, each timber will react differently, RPM, speed and feed may also effect tearout, so it may take some experimenting to get it perfect

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OK, I’m officially embarrassed. I somehow equated reversing bit rotation with reversing feed direction. I am in my “golden years”, must be it.

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