Ok, cut my first partin the new fangled solutions spiral circle wizard. It cuts a Perfect circle... But I tried to cut a .862" dia with a 3/4" endmill. Circle ended up being .838".

Why would this be?

Spindle flex, cutter size?

Hood

no, i was cutting wood. i'll measure cutter.. ( i just did, hard to measure, seems like atleast .720" (supposed to be .725") but that wouldn't explain difference).

it cuts beautifully... less than .00025" out of round. and multiple steps down to achieve depth.

no, i was cutting wood. i'll measure cutter.. ( i just did, hard to measure, seems like atleast .720" (supposed to be .725") but that wouldn't explain difference).

it cuts beautifully... less than .00025" out of round. and multiple steps down to achieve depth.

0.720? thats 0.030 under a 3/4 cutter is it not?
Hood

see this is what happens when you have a new machine and learning curve, plus you've been working on it for 12 hours straight. for some reason my mind was looking for .725"

you're absolutely correct and thank you for not calling me an idiot. I thought that was a brand new carbide endmill. it was obviously a newly sharpened end mill!

so nice to know i'm the one making the mistakes, not the mill or software!

Ha ha been there done that and likely will do something like that again, probably today
Hood