Thanks for thinking it through about “ovality” vs reversal spikes. I was thinking if you say used a tool large tool in a large hole it must be better.
Oh well, I’ll put my theoretical question in context
I have a 4.5” bearing bore I need to hold 2 thou on. I get 1 thou difference measuring across the hole at various points just in diameter. So without knowing what it actually looks like in circularity it may impinge on a truly circular bearing race. Plus factoring in the 1 thou of error it only leaves 1 thou of tolerance. Needless to say I finished bored the first two parts and they passed inspection ok. But The boring head sucked btw. The other 6 I don’t want to bore if I can help it. Was thinking of trying a single point fly cutter set at about 4” and programming a tight boring cycle. Was thinking that would be a compromise between the cnc and boring strategies...
LOL that's cool,
I didn't know how theoretical you wanted to go with this so I actually stopped short for me.
Literally one could build formulae and equations for your question, with Brent's / Yardbird's point in mind it almost a calculus problem as one of the limits i.e. a tool that has the same diameter as the bore and makes an interpolated circle that tends to 'Zero" versus cutting tools of various smaller diameters with their respective interpolated circle radii + shifting from backlash + phase angle shifts...
I'm actually having to look at similar problems at higher tolerances so I will try to put a better thinking cap on maybe over the next few days.
Right now it's cool enough (temperature wise) for me to muck the barn out (rather than earlier)… To the barn !
Meanwhile I was thinking also some kind of epi-cyclic or trochoidal tool path that
processes (like as in procession) might cancel out some of what you are talking about (quadrant) errors on the machine here to deliver a smooth and round and circular bore (probably for a smaller diameter tool). Caveat being depth of bore + surface finish considerations, but for "bearings" . The motion a bit like spirograph (just a left of field idea).
Could look terrible but actually seat your bearing perfectly well with multiple good contact points and surfaces ?
^^^ kinda like a "spirograph" that but with less pointy tool path (broader smoother arcs) and maybe a larger endmill than 1/2" depends what the repeatability of your backlash is ?
What depth are you boring ?
'Circularity" how is your inspection department defining that / determining what they consider criteria for circularity i.e. procedures ?
Flycutter 4" down into a bore ? You grind your own tools and are completely 'Chill" with that ?
I don't know your set up and safety considerations blah blah blah…
Was wondering whether the single insert on a shell mill idea works for bores but I'm not the guy to ask whether the angles and geometry on the insert are 100% appropriate for that ???? Versus an actual boring tool.