Made a test cut in pine for a ring dish. I think it came out ok, but still needs sanding. There was a knot on the backside of the material that i didn’t see until started cutting. There was some deflection around where the knot was then settled out once passed it.
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Nice
The weird thing is that the previous test one i made full size and the bottom of the dish was flat… same file.
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Something must have moved. It might even be the wood. Kiln dried has a lot of built in tension. Some parts are pushing one way, and the others pushing back. When you cut away half the wood, it can find a new natural twist.
That’s interesting. It’s very symmetrical. I originally thought that was your intention since it looks like a shell. Looks nice either way but I like the added texture. 
It was pinned and clamped. Sounded a little different when it got to the knot, then after it passed it, went back to normal . You can see the line across the flippers. Just weird. The alignment was dead on front to back since started using steel dowl pins into spoil board.
It would be interesting to try it again (I say, from my office chair).
The fact that it is pine and there is that knot makes me really think it was the wood shifting. Unless you made a witness mark on the wood before hand, I don’t know how you would tell that it shifted. But you also would have a hard time telling that it didn’t. Which is why this theory is hard to kill.
I did an engraving in a cabinet door a long time ago and as the wood was removed, the panel bowed up and the cuts were deeper in the middle. Wood movement was the best explanation, but I can’t confirm.
Four steel pins into the spoil board and four aluminum clamps, pretty confident the material didn’t move. But I agree, will definitely try it again with a much nicer wood. 
Although, it was close to mid span of my mpcnc. 2x3 foot workingbarea with 3/4" emt… flex is posible culprit. Still very happy with the test results!
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The entire workpiece moving would be one explanation. But I am saying the shape of the wood changed. It bowed up or down during the cut. It may have even expanded as the rest of the wood was removed.
I may be wrong (happens a lot).
Wouldn’t it flex closer to the knot? Why would it be higher before and after the knot?
It does look very good. The design is great and the project is a perfect match for a CNC machine.
Early on with my lowrider2 I tried engraving a large-ish pine panel I glued up. It was all jacked up, which confused me because I’d surfaced it.
So I went back and surfaced it again, same problem.
Surfaced it a 3rd time (panel was already trash at this point), then went back to surface at the same depth, identical pass…still found wood to cut, about 10thou of it. Repeat again…more cut. Repeat again, yep, even more.
Definitely potato-chipped.
Committed to not making anything with pine that depended on staying dead flat unless it’s REALLY thick.
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Just a guess, for the full size one maybe you hit a depth limit or something that stopped it from removing more from the interior, causing the pattern not to show up. I assume the bowl bottom is below the parting line between top and bottom. Maybe you can measure the depth of the bowl and see if it agrees with the design or if it is a bit shallow.
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Cool Design,
Would love to see how you have designed and use the “Four Steel Pins”.
That would be really interesting to learn, for a newbi like me.
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Hey Chris,
I ordered 1/4 x 3/4" steel dowel pins. Found wood dowels were inconsistent in diameter. Plus, steel ones can be reused many times. I use estlcam two sided block machining. Then make seperate drill program to bore through material into spoilboard. So, when the top side is done being cut, take the material out, put pins into spoilboard holes you made earlier. Place the material with the bottom up and press down onto the pins. Normally need a scrap block of wood and a few taps of a hammer. The front to back alignment has been dead on ever since.
Hope this helps.
The four holes in the spoilboard are actually a perfect rectangle, the angle makes them look wonky… lol
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You’re probably right! You got me thinking about it. The knot is probably just a coincidence. The test cut went well, so next try again with oak or maple.
You were correct about the wood moving. Ran another test cut with additional tab at the tail and no issues this time.
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Thanks matt,
Yes it does. Now that study is done (for the moment) and work is quite till i change jobs i might have some motivation to try this.