Brodhead Pietenpol Association

Original Posted By: Galen Hutcheson
Subject: Pietenpol-List: sanding glue jointsIn the advisory circular "acceptable methods.." section 1-6 "preparation of woodsurfaces for bonding" it states that sandpaper must never be used to smoothsoftwood surfaces that are to be bonded. I built my fuselage by cutting the braceson the table saw to a rough dimension and using a stationary disc sanderto get just the right fit. Does this mean that I'm building an expensive 2-seatpiece of firewood?I did the same with the ribs I've been building. Any thoughts on this?Tom BrantBrooklyn Park, MN________________________________________________________________________________Date: Sat, 12 Mar 2005 20:53:18 -0800 (PST)

Original Posted By: owner-pietenpol-list-server(at)matronics.com
As Doc says, the best thing to do is to make some test joints and then breakthem. IF you get a clean break at the glue line, the joint is no good. Ifyou get a messy break with lots of wood fibers broken, indicating the woodbroke before the glue did, you can't ask for a stronger joint.My Piet was built mostly with resorcinol, with T-88 in some places. A fewtips I learned along the way (through breaking test joints) are:When properly made, a resorcinol joint is incredibly strongWhen improperly made, a resorcinol joint is not very strongT-88 is more forgiving than resorcinol, but cleanup is messierT-88 is quite strong for butt joints. Resorcinol is not.When making plywood doublers for use with either type of glue, you get abetter joint if you roughen the surface of the plywood with coarsesandpaper. This is especially true for birch plywood, which has a verysmooth "sheen" that prevents good wetting by the glue.Good tight fitting joints are essential with resorcinol. T-88 can standsome (small) gap, but don't think it will let you get away with sloppyconstructionAs for what the advisory circular says, I wonder if they were talking aboutthe hard sheen you sometimes see after using a belt sander on softwood? Inmy experience, it is hard to get glue to penetrate such a sheen. I foundthat roughing parts up, particularly for butt joints like the uprights in arib, gives a better joint.Just my two cents, but after finishing up the structural repairs of myPietenpol from last fall's forced landing, I've had a lot of glue joints tohave to break. I've been very pleased with the results, and with theoverall structural integrity of the craft.Jack PhillipsRaleigh, NC -----Original Message-----

Original Posted By:
Hi Tom,Don't throw away anything you've already built. I did test samples on both sanded and unsanded joints, including some using birch ply with the "manufacturing glaze" still intact. Tests included both T-88 and Aerolite. I even made some intentionally bad joints that fit poorly and didn't have 100% glue coverage.Not one single glue joint broke.Just follow "acceptable methods" for the rest of the project.Greg CardinalMinneapolis----- Original Message -----

Original Posted By: Galen Hutcheson

Original Posted By: "DJ Vegh"
Jack wrote->T-88 can stand some (small) gap, but don't think it will let you get away>with sloppy construction.In fact, T-88 requires a small gap. If you over-clamp a joint made with T-88 you'll squeeze out too much of the glue and will not get a good joint. One of the big plusses of working with T-88 is that it is much more forgiving than resorcinol or some of the other glues. Joints should be nice, but even if you have slight discrepancies the T-88 will fill the gap and give you good strength.Although I haven't tried it myself, it is said that wood joints can be made with T-88 on wood that is moist (such as from steaming, to bend capstrips). It has also been said, and my experience bears it out, that T-88 will soften at elevated temperatures. Icarus would have had a problem with T-88, although we know that Piets would take an eternity to climb close enough to the sun to make a difference ;o)Oscar ZunigaSan Antonio, TXmailto: taildrags(at)hotmail.comwebsite at http://www.flysquirrel.net________________________________________________________________________________