My first 3D carvings - random seam lines showing

I’ve been in the CNC game for a couple of years (Shapeoko 3 XXL) but everything has been 2D for me until about 1 week ago. Since carving in 3D I noticed some seam lines show up (see photo). I’m using a 1/16 ball nose bit at 56 feed rate, 0.006 stepover.

Do you know what might be causing this “seam line”?
Also, how many of you run 3D jobs at more than 1 angle as a standard practice? It doesn’t always seem necessary looking at time/cost/benefit but thought I’d ask.

As a side note I tightened the eccentric nuts for the v-wheels on my machine for the first time in a very long time (was definitely needed!) after I noticed this seam line issue on a 3D octopus I carved before this map. The issue remains. Is there something else maintenance related or settings related I should look at?

Thanks for your help

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The real experts will be here shortly I am sure.

But from experience, have you checked the V wheels and the V rails for debris? Seeing as this is along the X axis (guessing on orientation) in the same two or three spots, I am wondering if there is any sawdust packed on the rails causing the Z to lift slightly in those areas. I had this on my Y axis earlier this year and each time the CNC got to that spot on the rail, it lifted the Z up slightly causing a line in the work. Cleaning the top of the rails with a stiff brush and a little naphtha resolved my issue.

Just a thought…

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What does the 3D preview show?

Is there any regularity to the spacing of the defects?

Are the V rails clean and in good condition? The V wheels?

I’ve been lax on keeping things clean and there’s definitely plenty of build up so I will start there and report back… could definitely be the issue. The 3D preview is clean and I didn’t merge any datasets or anything that would cause that effect, so likely not an issue there.

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I have had similar results which I think came from backlash on Z. What type of Z axis do you have?

Backlash isn’t a thing for belt driven, but the Z plus can have it if the nut is worn.

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