Basically only holes bored on lathes or bored via boring heads or boring tools on mills are "straight" and "true".
hi hanermo, yup, and also those delivered by coordinate grinding machines, especially because they grind, thus cutting force is low, and remanent tension, inside the part, is really low : this helps to deliver consistent dimensions in soft materials, that, otherwise, because of heavy cutting, may deform in time, at least at micron level; there are cases when parts are ok right after machining, but after a few days, if they are checked again, they are out of tolerances

there are cases when the client is not accepting a process that is finishing a part with high cutting forces; so far, this had no been discused in this thread, but, whatever

about this "straight & true", i needed to deliver some parts with non-standard tolerated holes, with length between 6-9D, that were checked with a go-gauge as long as the hole; it was a bit tricky, because :
... at that length, all drills would bend, so, after drilling, the hole was not cilindrical, and this was breaking the reamers like crazy; i managed it but using plungers ( some custom tools that would improve cilindricity after driling ), and reamers inside floating chucks; also, i had shorten the active length of the reamer ( thus shorter flutes, but overall tool length remained the same ), to make it a bit more flexible
... also, each part had at least 2 such holes, with tolerated reciprocal positioning : imagine a few H7 holes, that are not paralel, required to be at H7 coordinates, something like a " tolerated swiss cheese "; it was a bit hard, because, if the hole diameter was near the minimal value, then there was a chance to miss the reciprocal positioning; to manage this, i had delivered all the holes near the maximal diameter, i had crafted my own go-gauges ( with bigger diameter then the original ), and i was working in a tolerance that was much smaller then the original tolerance of the technical drawing; in the end, it worked, but it took me a while to figure it out

It is perfectly possible to make ball-burnishing tools.
Sub-micron incremental sizes are reportedly easy to do
i don't have experience with such tools; i know that they can deliver smooth surface and increase the cilindricity specs, but i don't know what tolerances they can deliver, and, for the adjustable ones, i don't know what is the finess/accuracy of the adjusting system

i believe that they should somehow have a radial play, so to be able to copy the hole ...

i have seen that there are some burnishing tools that may turn, and other types doing some things; i shared the videos at the end of this post

The hole is finished with a single rigid hone coated by diamond abrasives.
Take about 20 secs or less.
in automotive, it won't be long until they will finish all the engine with a single tool, just like a snake, going from one hole to the other

i have seen a documentary about engines, and it said that, if you wish to increase the power, you have to craft the engine with less play between the pistons and the holes, so to lose less power during combustion; when tolerances are tight, it is recomended to heat-up the engine before starting it, because, otherwise, if it would start cold, the pistons may damage the engine; motorsport / kindly


https://www.youtube.com/watch?v=eAwqtMtzNYs

https://cogsdill.com/videos/burnishing-tools/

https://www.youtube.com/watch?v=B6YxFxMCKkQ