I have never oiled my air tools, Lancair's advice.  My favorite sanding tool is the 5" Dynabrade I bought from Lancair while I was at the workshop.  I converted the pad to Velcro so I could quickly change from 80 to 40 or even 120 for some sanding tasks.  I bought some die grinders at Harbor Freight when they were on sale, somewhere around $8.99 a piece.  I put my favorite bits in the grinders so I wouldn't have to change bits.  The grinders were cheaper than the bits!

 

After sanding, a good wipe down with acetone, let it dry and catch the light off the surface and check for any shiny spots.  I agree with the "light pressure" and "change the paper often" comments.  The prepreg is definitely a challenge to rough up, you gotta get the shine off of it, but not dig into the weave.  I also used liberal amounts of acetone, changed the paper towel very often.  I wet the surface with acetone, and followed up with a fresh, dry paper towel.

 

I think I read somewhere about sanding just prior to bonding, something about exciting the molecules.  I had sanded everything for my left side vert stab closeout.  I got delayed a day so I resanded everything just prior to bonding.

 

Another thing I found that could really mess up your bonds, the pump getting out of calibration.  I'm working on my interior panels, not nearly as critical as a wing skin.  A small interior panel seemed "soft" after it was cured.  The bolt that holds the arm had loosened enough so the hardener wasn't pumping 100%.  The bolt had worked loose in about 1/2 gallon of epoxy.  I had checked my pump ratio before my big bonds, the fuselage top and the tail feathers.

 

Another thing about using Jeffco/flox, I installed some small "L" brackets in my fuselage to attach my interior panels to.  I did a quick rough up on the fuselage floor, didn't wet out the surfaces, just put a glob of flox on the "L" bracket and squished it in place.  I bumped it with my foot and it popped right off!  The sanding is critical, but so is a good wet out of pure epoxy.  I redid all my brackets with a little more care, they are all solid now.

 

After reading the description again of the Legacy skin, it seems like the layups might have contributed to the failure.  Jeffco/flox is weakest in peel.  That's one of the reasons for the additional layups.  A failure of a layup could allow the flox bond to "get started".  Once it starts to peel, it has very little strength.

 

Dan, I might have been the one you referred to as saying Jeffco was the same as Hysol.  I was told that by Lancair.  I think I also said that either is totally adequate under the expected loads IF we do the proper prep and follow the bonding procedures.  You were 100% right by saying Hysol is better, and gives you a larger margin of safety.  Bottom line after reading this account, if you use Jeffco, you better get it right, do good layups over the seams, and you'll be fine, don't cut corners!

 

Mike Easley

Colorado Springs