Hi Group
With regard to getting a good fit of pins on my quick build tailplanes
that had a lot of play at the tip of the stabilators from the get go (at
least 1"), I machined my own pins.
What I found was that even while taking extreme care using slightly
undersized drill, then reaming to size using plenty of cutting fluid (10
mm), the hole although it was close to proper size (using precision guage
pins in .0001 steps to measure), it was a pretty poor finish on the hole
if you look with a microscope. In other words half of the metal was only
making contact with the pin! After a bit of head scratching, I machined a
number of pins with .0001" tolerance in incremental size. I was able
to tap these in using lubricant until I could see and feel that there was
good contact. Then measuring with my precision pins, I made the
"real deal" pins between .0007 to m.0009" interference fit
of this "sized" hole. I cheated a little bit where I made the
first hole the pin would go in a few tenths larger at least than the
second hole, and made the pin a dog bone shape, where the center was a
few thousands smaller in diameter so it would not drag and oversize the
first hole. The only interference fit on the pin was ~ 1/8" longer
than needed. Machining to .0001" takes a bit of practice, but what I
did was laid out all my holes and machined the first pin the largest
size. This way if I went under, I was able to use this now undersized pin
for the smaller holes. Anyway about 33% scrap, not too bad. End result
was a really nice fit during final assembly. You can't use a
lath tool bit to work within .0001", you need to lap your size. If
you're lucky you may get within less than a thousand, if not two or
three thousands. In other words, wet and dry sandpaper glued to a
tongue depressor. Using a precision micrometer, use sandpaper on any over
sized areas to keep uniform diameter. net is you can work within amazing
tolerances! I made out of free machining 410 stainless purchased from
www.mcmaster.com
To make dogbone was easy. Tape over area of interference fit and using
tongue depressor with sandpaper go after what you want to make
undersized. Perhaps takes 5 or 10 minutes each pin.
If you want to see some pics, look under Torque Tube fit:
http://www.europaowners.org/main.php?g2_itemId=86924
Ron Parigoris
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