The typical process for measuring mouthpiece facings is to buy a facing gauge from J.J. Babbitt (click on the link and request information on mouthpiece measuring tools) and then use a set of feeler gages to measure the distance from the tip where a particular set of facing curvature exists. To do this one needs a precision set of feeler gages (strips of metal of precise thickness). A variety of standards exist, but many folks use gage sizes from the following set (measured in inches):
0.0015 0.005 0.010 0.016 0.024 0.035 0.050 0.063 0.078 0.093 0.109 0.125
This set includes only the following seven sizes:
0.035 0.050 0.063 0.078 0.093 0.109 0.125
The sizes up to 0.024 are readily available in sets (available from any automotive supply shop), although you need to take care that you do not buy gages that have too much radius at the edges, as you are measuring the precise position of the edge. The sizes from 0.035 and up have been difficult to procure and various makeshift solutions have been tried. A set of these 7 sizes is now available in high carbon spring steel. They are labeled with the thickness and the edges and faces are precision ground.
You will have to do a little hand-finishing to 'soften' the corners...they are 'as machined'...the edges are crisp/sharp, but it only took me 15-20 minutes to do my set with a popsicle stick wrapped in 1000 grit wet-dry. I'm saving everyone a few dollars on this.
I'm sorry they are gone, but I can't afford to make any more...too much hand work to finish them.
P.S. if you are just getting into the art of mouthpiece refacing, you may
want to join the
Yahoo discussion group on mouthpiece work
Other tools that you need to get