Pietenpol-List: No more clamps (well, for some things.....)

[matronics]

Original Posted By: "Alex Sloan"
Well, basically, after slopping on the epoxy where you want to join theparts, you stick them into a plastic bag, suck all the air out and voila!Perfectly uniform pressure over the ENTIRE area (as long as you maintain thevacuum). No voids or air bubbles or delamination or excess epoxy...theresult is a perfectly even, easily controlled pressure. And useless excessair and epoxy gets sucked out (into a thin line along the edge that is assharp as a razor blade....)A number of years ago I bought a $400 "professional" bagging system withpump, etc so I could build foam core and hollow core wings for mycompetition radio controlled sailplanes. I got tired of trying to stackbricks on top of the epoxy/foam/carbon fiber/kevlar/whatever sandwich andjust hoping for even pressure throughout. (It was a teeny bit frustratingto check it the next day and find some carbon fiber delamination where oneof the bricks moved a bit....) Even though the materials used in mysailplanes was different, the benefit of applying a perfectly even (andeasily controlled) pressure to the parts being joined is the same for woodconstruction.It's perfect for laminated pieces like wing tip bows.....just build arectangular box with a curved top, stack some epoxied strips on top of eachother and lay them on top of the curve, put everything (the box with theepoxied strips on top) in a bag and draw a vacuum. Let it sit overnite andyou're done.....And being much more of a scrounger now than I was then, I've actually builtan even better setup using a (free) freon pump from a discarded refrigeratorand some pvc/plastic tubing/plastic sheets/window sealer goop from HomeDepot. MUCH cheaper! You could probably put the whole setup together forunder $20.It's a pretty worthless process for things like attaching ribs to spars butit would work very nicely for a number of other homebuilding processes.I'll bet the composite homebuilders use vacuum bagging on a regular basis.There's really no other way to so easily control the epoxy to cloth ratioswhich optimizes the weight to strength ratio. And that same benefit wouldsurely apply to epoxy/wood/ply construction.Yes, you can draw too much vacuum and starve the joints of epoxy. But witha bit of patience you quickly figure out how much pressure to use. Andmaking one adjustment to the vacuum pressure is MUCH easier than runningaround adjusting a bunch of clamps....If anyone's interested in pursuing this, let me know (offline please) andI'll put some pictures and a little more detail together.Jim in Plano,----- Original Message -----

[matronics]

Original Posted By: "Jim Markle"
Jim,It sounds as if you need to write an article for To Fly! or Experimenter onthis subject.chris bobka----- Original Message -----