Some long-winded thoughts:

I have been periodically checking my feeler guage thicknesses with my 
digital calipers.  I try to check them in the region used during 
facing work.  I have not ben real satisfied with doing this since the 
numbers vary by 0 to +/-.001" each time I do this.  I do not think 
the feelers are changing, just my ability to measure them was not 
good.  The problem is, for my work, this inconsistency can be enough 
effect what I do to a piece.

I have some gage blocks I use to check my calipers.  It checks out 
good at small readings but reads low by .001" at at higher readings 
(~.100).

Another area of concern is wear on the caliper jaws.  When you close 
them and electronically zero them, the measurement edges may not be 
completly touching due to wear.  I've pulled some strips of fine 
sandpaper though the jaws to help correct some of this wear effect.

So, I decided it was time to grab another common tool that is right 
for the job.  I just got a micrometer!  It zeros nice and checks out 
good on the gage blocks.  It should be more linear than the digital 
calipers I had been using since the micrometer uses a precision 
screw.  The calipers probably have a LVDT in them that may not be 
real linear.  Plus it rounds to .0005".  The micrometer at least 
shows you where you fall between the lines.

Another difference is that the standard micrometer contact area is a 
~3/16" diameter flat end.  The calipers have a ~1/32" wide edge.  The 
edge may find low spots on the feelers that the micrometer misses.  I 
dont think this is a big deal, but it could be going on.

This micrometer also has a ratchet on the screw so you apply the same 
force when making a measurement.  On the calipers, you can get 
different readings depending on how hard you clamp on the feelers.

So I finally measured all my feelers again with the micrometer.  I 
did it a couple of times and I got much more consistent results than 
with my calipers.  I'll check them again a week or so, but I expect 
the readings to stay the same.

This level of detail is not real important to do good facing work.  
I've been getting good playing results for a couple years now.  But 
there are enough variables that we can not measure real well (like 
baffle shapes) that I think it is a good practice to nail down the 
ones we can.  Several little errors can add up to a significant 
problem.

So I recommend you at least borrow a micrometer to check out your own 
feeler gauge set.  Then mark on the feelers what the actual sizes 
are.  Also enter the actual numbers into your calculations if you are 
making/plotting your own facing curves.  I found that some small 
bumps and low spots went away...

I am new of this list and I hope to offer a present to
every body suggesting a completely free source of very

thin feeler guage: .02mm .05mm (.001" .002")
It is possible to find these thin permalloy ribbon
inside the bar code target put on goods of stores that
are used in order of electromagnetically detecting
theft.
After selling, store attendant people procede to
demagnetisation of the code target attached to the
purchased goods and the demagnetized target still
remain attached.
It is not easy open the plastic case of the code
target but using a good knife you can extract the
feeler without damaging them.
I have found it very usefull in determining the first
point in the profile curve and in calibrating calipers
or micrometers.
My name is Manfredo Cavallini I am from Rome Italy.
My web site is www.clarinet.it
Best regards




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