I’m a electrical engineer but an amateur in mechanics. I’ve been checking some tools and machines in the market for small works which would allow me to manufacture small but precise pieces, such as a 5mm H6 tolerance shaft to fit a bearing bore under interference. The thing is this shaft should have a tolerance of +-4um, maximum. Ok, so usual lathe setups allow you to position the cutting tool in a scale of 50um marks, with god knows which accuracy. I’d guess no less than +- 50um. But even if it was perfectly match, 50um is rather large near H6 tolerances for my shaft. Ok, let’s assume I could iteratively remove material using a lathe and use a top precision micrometer to check if my shaft is within required dimension. Still it seems to be a very non-professional way to do it, basically a try-and-error approach, moreover I could accidentally remove more material than I should and end up losing all the work and also money. Could anyone tell me if there’s a more efficient method to produce such precise pieces?
If you truly need that type of tolerance and repeatability, then you are way out of the hobby equipment territory. You’ll need high precision calibrated measuring equipment, temperature stability, and specialty manufacturing equipment.
Likely an O.D. cylindrical grinding machine will get you there. If the bars are long, they need to be supported while being processed.
If you want to get close at the hobby scale, patience, scrap material and some decent micrometers will get you close. You can turn(machine) your diameter oversize and then you could use some abrasives(Emory cloth and scotch bright to polish the diameter to size. You could also make a homemade toolpost grinder. Essentially mount a grinding wheel and motor to your carriage. Trial and error. Cut and measure. Adjust, re-cut. Possible, but seems like an academic effort.
To start, I suggest you purchase pre-made shafts to that tolerance and focus on the lower precision items you can actually produce.