Cutting out these holes on a CNC is not that complicated, but I do agree you need to add a tolerance spec to the diameter callout for circles on your drawing. The tolerance should read 20mm -0.000" / +0.010" (assuming the exact diameter of the MFT dogs is 20mm). If you put a spec like that on the drawing and they ask what that is, go to someone else. Anyone with Biesse, CR Onsrud, Thermwood or another of the industrial machines can produce a ridiculously simple piece like this to a tolerance of 0.005". If you need better than that you are working with the wrong media. If you start talking to someone with a hobby machine you will need to make sure they understand the capability of their machine. I could produce this on my 4'x8' machine to within 0.010", but that takes time and the interest in setting up your machine to do so when you buy an entry level machine (grid squares in image below all within 0.010" so I can use vacuum pods).
I think Ted means an oblong hole. That will be largely the result of a sloppy operator that never checks the X/Y accuracy of his machine. So long as they use a 3/8" diameter bit, and the machine is not a cheap pile, using a pocket tool path is fine. If you spec that you want them to use a special bit they do not own, they will charge for that. A 20mm bit will be in the realm of $100 and they may need a $30 collet as well. Keep in mind you will be begging for someone to do this. Someone that owns a $100k machine could care less about your $100. The less annoying you are the more likely they will do it.
If you could live with a reduction in the length that will make the operators setup a bit quicker. To utilize the full 60" length without much extra setup time they would need popup pins. Most cab shops have that, but some of the smaller machines do not. Also, you can probably get two for very little cost. If it were me, I would charge you for the full sheet of Baltic Birch unless I had a piece kicking around.
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