What is the maximum tolerance for a DIY Machine ?!

[Neale]

Anyway, what kind of machine? Over what working area? While the figures quoted might be achievable on a milling machine with the rigidity that goes with it, put those ballscrews on a large working area router and they will hit performance and travel speeds, unless you pair them with massive motors. But that kind of machine is typically cutting wood, and there ain't much point in cutting that to micron accuracy.

So out of context, talking about achievable accuracy/resolution/repeatability and so on is interesting but not very useful. I think my 1500x750 cutting area router can theoretically achieve something like 3 micron resolution, based on step size and ballscrew pitch, but there is no way I would claim that it is accurate to that degree - and neither does it need to be for its intended purpose, cutting wood. Working to 3 thou, 25 times that theoretical resolution, is probably better than required. Good engineering is about trade-offs and compromise, not throwing money at the problem. Of course, a toolroom lathe or mill is a different question, with different criteria and different priorities - like accuracy over speed.

[Clive S]

Well said Neal. Timber with also change with moisture content from day to day. Plus the fact like a router built out of ali with change dimension as it warms up and cools down.

[Fancy]

I had the accuracy of a mill in mind of course not a large router.