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.