One of the reasons I apply my own finishes is that I don't like to relinquish control of the finish's film thickness to someone else's hands. OK, so I am admittedly a control freak in this area of guitar building. There are some very talented finish subcontractors doing great work so please don't read into this post that I am putting someone else's work down. I'm merely trying to outline my process for the readers.
I closely monitor the number of coats of finish I apply and then measure the final thickness to confirm my application process is on schedule. My final finish target thickness range is .0025" to .0045". You may be surprised to learn that many factory guitar finishes are >.010" thick. The thicker the finish the more the finish [could] impede top movement. Applying too much finish has an effect of tossing a blanket over your guitar. Try that sometime ;(
I mentioned earlier that I use "Frisket Film" to mask off the bare wood below the bridge and fingerboard extension. The adhesive backed plastic film is a consistent .001" thick. So after I peel the film off, prior to gluing the bridge and fingerboard extension down, I measure the thickness of the finish and subtract .001" to tell me how thick the final finish is.
On this particular guitar, the measurement is .004" and then I subtract .001" for the Friskit Film which leaves a remainder of .003" or the finish's final thickness measured at the fingerboard extension area. I repeat the same measurement process at the bridge but did not bother to duplicate that identical measurement in this post.
For a reference analogy, the thickness of a sheet of notebook or printer paper measures .003" thick. This will give you a tactile example of how thick the finish is on this guitar.
*** Disclaimer ***
I'm not saying that I am right or the amount of finish others apply are wrong but I am merely showing the readers an example of our finish process and current ideals. Other builders may share similar ideals ... or not?