I noticed on the PT-40 build thread in the beginners forum that some of the guys had trouble placing the fuselage doublers in the correct position when using CA medium as per the Great Planes instruction book. I have several volumes of the old RCM "For What It's Worth" books and I ran across an article in volume IV for attaching doublers by drilling a series of holes in the doublers and it works great with lite ply.

For hole spacing I went down 3/8" from the edges and 3/8" for the vertical rows. I spaced the holes 3/4" apart horizontally. Some of the holes can be randomly placed as needed. The spacing is not that critical. Use a soft lead pencil to layout the hole spacing. After laying out the holes, take a sharp center punch and make indentations by hand in the doublers where the holes are to be drilled. Clamp the like doublers together with clothes pins or whatever, back up the doublers with a block of wood and drill through the punch marks with a 3/32 drill bit. If you have a drill press then it's a piece of cake. After drilling all the holes, lightly sand the doublers to remove the drill fuzz.

Now position a doubler as per the instruction book. Starting at one end, apply CA THIN with an applicator to the first hole. You can actually watch it wick into the wood. Work your way to the other end of the doubler pressing it down to the fuse side as you go. You can make slight adjustments as you go for a perfect alignment. I usually do about six holes at a time. I kept a paper towel handy and wiped off the excess CA as I went. After all the holes have been CA'd, I went along the edges and wicked in thin CA.

My fuselage doublers are perfectly aligned (as well as can be expected for die cutting) and it took maybe 30-45 minutes extra. I hope this will help anyone planning on building the PT-40 or any other kit for that matter.

great method!, Thank you
Evaristo

The PT-60 doublers have "punch marks" and the instructions have you drill 1/16 holes for the CA to wick in. It does work well.

Or you could just use 30 minute epoxy and spread it with a credit card to a very thin layer. Put the doublers on and line them up. Wipe off excess expoy. Put about 100 pounds of weight on it and, again, wipe off any that squeezes out. Keep the weights on for about 2hrs minimum. Done.

I wouldn't use CA to put my fuselage doublers in. Thats an area for epoxy. Maybe I'm doing it overkill, but I don't think epoxy is going to weigh that much more than CA if you spread it paper thin. The joint will end up 10 times stronger with epoxy.

Actually you should use alphatic resin glue for attaching doublers. It's cheaper, lighter and gives you more time to work. In case you are not familar with the name it is carpenters glue.

Rcpilet - your method is actually the best one to use. I go one step farther and use masking tape around where the doubler will go. I spread a thin layer of epoxy as you do on both pieces and remove as much as possible. It doesn't take much. I line up the doubler, press it in place firmly and allow any excess epoxy to ooze out. Then I remove the tape and stack as much weight as I can on top. Let it cure 24 hours and you have a very little glue holding the piece firmly in place. And it will be as flat as the work surface.

CA is fine to use but it makes a really ugly mess, you don't get second chances and the fumes are horrible. Plus it's more brittle than epoxy but I doubt his doublers are going to ever let go.