Eyeballing the placement, no matter how well your red dot pointer or even a lightburn camera is aligned, will never be perfect / exact. There are, however, alternatives to making larger than bed cuts such as:
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Joinery - create two halves of the circle and join them such as this:
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Indexing the machine with positive stops and using absolute coordinates (or the move controls / preset coordinates). This is a very long explanation, but here is an example of the general idea:
