How to mesure down to micron range?

[blue_luke]

One of the goal I have with my machines is to fabricate my own capsules for building microphones.

Some of the tolerances are in the few microns range.
For example, I need to make a shoulder .0015 high (in brass) +/- 5um.

In microphone capsules, exact dimensions are not that critical, +/- half a thou is perfectly viable,
but the spacing of the membrane ( 6um mylar with gold sputering) to the face of the backplate is EVERYTHING!

So how do I measure such small amounts, and how do I machine these.
In my projects, a 'skim cut' may very well be only a few micron thick!

Actually I doubt that I will succeed with the machines I am getting, but still, the questions remains valid and informative.

 

[Tony Wells]

That's going to be tough in an average home shop. That's tough in an average commercial shop. First, let's define what a micron is:

1 micron = 1 000 000th of a meter or, approximately, 0.00003937 inches, roughly 40/1,000,000 of an inch. We can look at it as a "half-tenth".

One major problem with accurate measurements at that level is temperature. Your instruments, whatever they are, must be first of all capable of that resolution, and accurate enough to yield meaningful results at the required tolerance, and stabilized for long enough at a standardized temperature (usually 68f or 20c) and 50% RH. The parts to be measured must also be stabilized at that temperature. Most QC labs would allow a 24 hour soak, but the mass of the part can be taken into consideration.

There are times that the manufacturing approach can be adjusted to achieve the desired results. Is the configuration one that requires actual machining, or will electrochemical etching accomplish the controlled removal, or will controlled electroplating do the job better. In any case, you must be able to measure the product, but repeatable methods can often yield a higher percentage of acceptable pieces,

Without seeing a print, I can't give you much in the way of specific methods, but in general, when working in the micron range, you use one of the above mentioned methods, or lapping/grinding. Whatever method you use, measurement will be key. Work out a reliable way to measure to the accuracy you need, then see how to get there.