Edges are very fuzzy/lots of tearout. Normal? How to improve?

Hi!

I’m just getting started to actually use my mpcnc that I’ve been building since Nov or something…

Anyway, I tried to cut a coaster in oak using a 1 flute upcut bit.
Now, it finished OK, but I get a lot of tearout/fuzzy edges as seen in these photos:


After a quick sanding it looks a lot better

Now, does this look normal? Can I improve this in some way?

I’m using Fusion 360 and the thing in the middle is using a 2D Adaptive roughing pass which leaves 0.5mm as stock to leave. Then I do a finishing pass with 2D Contour, removing that last 0.5mm.
For the ring around it I do something similar but with a 2D Pocket and 2D contour.
Then another 2D Contour to cut the coaster from the workpiece.

I’m using a depth of cut of 1mm for my roughing passes, and these settings:

Any advice on how to improve? Or is it as good as it gets without buying a downcut bit or something?
I’m using a Makita rt0700cx5j by the way.

Thanks!

Other than possibly adjusting your feeds/speeds to see if you can improve the outcome, cutting with an upcut bit will do that and a light sanding should clean it up.

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Yeah, the easy fix is a downcut bit. Shouldn’t be any issues with that path, but they can really pack in the chips on deeper cuts.

A sharper bit, and/or a downcut but would help. You could also try putting blue masking tape on it. That might reduce the chips that get broken off.

If you go with a downcut, they don’t pull the chips out, so something like a drill or plunge operation can make the bit wobble. When I use a downcut, I just mark the holes with a 2mm poke and then finish on the drill press. I also have a long ramp when plunging (45deg).

If you go all the way through, the downcut can push chips down on the other side, but it is not as bad as it is on the top with an upcut bit.

Thanks! I bought some downcut bits and just tried it out. Wow, what a difference!

However, I got another problem this time. I don’t know if I was just unlucky but it looked like the bit caught on to something, jumped around and destroyed my beautiful coaster :slight_smile:

Any ideas what might have happened and how I can avoid it in the future?


Was that where it plunged?

No. It just happened in the middle of the cut :confused:

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Bummer. I don’t know what causes that.

I would consider some sort of chip evacuation assistance (maybe an air blower?) for downcut bits. They’ll tend to pack the chips into the bottom of the cut rather than ejecting them. I’m guessing what the bit “hit” was actually a bunch of chips getting pulled back into the cut.

Yeah maybe. I was working hard with my shop vac though so it shouldn’t have been that much. But who knows. I will try again and try to be even more aggressive with the vac!