What is causing these weird lines in facing operation?

[Mikell]

Hi guys, I've just ran a facing operation on some Oak with both the kit 6.35MM end mill and a 12.7MM face mill and I'm getting these odd lines in my cuts. I put the facing operation together in Fusion 360 and it uses both climb and conventional milling - it appears that when the mill changes direction it bites a little bit deeper into the wood than the other direction - not sure which is which. I've tried various depths of cut, but this effect occurred when I used an 8MM stepover with the 12.7MM face mill and when I used both a 6.2MM and 4.5MM stepover with the 6.35MM end mill. Reducing my stepover to half the diameter of the cutting bit seems to negate this effect, but should this be necessary?

My spindle is pretty close to square (0.1MM out over 20CM on both axes)

What causes this? Should I cut from only one direction for a final facing operation?

Thanks!

[WillAdams]

Grain tearout, or a natural void in the wood

[Mikell]

Hi Will, thanks for the reply - what's the best way to deal with this? Should I just reduce my stepover as I have been to reduce the effect?

[DanMc]

Unless I'm trying to hog out material really fast and I'm not worried about appearance I usually use .4 as the stepover ratio.

[CrazyBillybob]

There's also a chance that your Z axis isn't 100% Square to the material. This would cause one side of the bit to dig a very little bit deeper than the other.

[Mikell]

Thanks everyone - I'll reduce my stepover to .4 and go from there. My spindle is squared so I don't think it's that, but I'll check again. Might try only climb and only conventional cutting too.

[CrazyBillybob]

My spindle is squared so I don't think it's that, but I'll check again.

If your Spindle is square, make sure the work piece is held down tight! because if it's not on the same plain as the spoil board you will get artifacts like that. Even if the "top" and "bottom" of the work are not parallel you can see this some. Smaller step over will help it be less noticeable.

CBB

[Schruminator]

Oak is known to be really porous (like soda straws running through the wood), so wood species may be at play here as well.