12-10-2014, 09:39 AM
(12-10-2014, 08:29 AM)DaveH Wrote: Tolerances have two main purpose's
One is so the bits and pieces fit together where ever they are made and secondary the machinist making the part doesn't have to "nail it" - it is time consuming and hence expensive.
I (and I suspect many hobby machinists) don't work too much about tolerances. I make a cylinder to roughly the right bore, and then make the piston to fit. If it's .50 or .55 doesn't really matter. It's the fit that's important.
In production shops it's different. You may not even know what the mating part is. So, tolerances make it fit when you don't have the time to custom fit each part, and it's also what makes interchangable parts possible. Time is money in a shop.
Tolerances, knowing how tight to make them, and knowing where and when to use them is the mark of an experienced designer. I wouldn't have known how to use them properly 20 years ago. Now, it's second nature.
BTW, I work at a place that does diamond machining for optical tooling. Those guys work to insane tolerances. Minutes of angle and tenths of an inch are pretty common around here. I have actually seen specifications that list tolerances in microns. That's 40 millionths of an inch.
Full of ideas, but slow to produce parts