One of the main things we builders have to do when kit building is laminate pieces of balsa wood or plywood together. The manufacturers have us do this to be cost effective with the different thicknesses of balsa and plywood they purchase. If they only need a few pieces of 1/4-inch thick wood, then they laminate two pieces of 1/8-inch wood to produce a part rather than buy the 1/-inch stock for that purpose. There are additional reasons to laminate wood, and I will go into that later on. I will also explain how to do it, what glues to use, and when it will be most beneficial.
Most kit manufacturers only want to make wood thicker and don’t laminate to get added strength, but to get the most benefit out of laminating. The grain on each piece of wood should be cross-grain (run in opposite directions) to add strength. Of course, on really small parts, this does not matter.
You might say that laminated parts are heavier because of the added glue. This is true, but you can use thinner laminated parts in place of heavier single-sheet parts because the laminations make them just as strong.
Here are the most common glues used for laminating. Apply a thin even coat on one side. No need to put it on both surfaces; one even, thin coat will do it.
WHAT GLUE TO USE
Laminating can be done with all types of glue. I use Mercury Adhesives M300 Medium CA, but you have to work fast to align the layers. You can use white glue for all your general laminating. It’s cheap and will give you plenty of time to align the parts. Spread it thin and evenly to keep weight down and clamp it until cured. For extra strength in high-stress places, use 30 minute epoxy—especially when laminating firewalls or other places where higher strength is required. Again, don’t overdo it with the epoxy but make sure you mix enough.
After you’ve applied the glue, make sure the layers are aligned. Then clamp or weight down the layers until the glue cures. If using small clamps, place a piece of protective wood on each side to help spread the load and prevent the clamp from marring the part.
HOW TO LAMINATE
When you laminate a part of any size, first consider the wood grain direction to get the most strength benefit. On smaller pieces this won’t matter but it will on larger parts. Have a flat surface to lay the part on. Spread the glue thin and evenly over the mating surface, align the layers and apply weights or clamps to hold them together until cured.
If you use white glue, as I do most of the time (especially with balsa), it is a good idea to dampen the outer surfaces with a wet cloth. If you don’t, the moisture from the glue will expand the cells in the wood, causing the edges to lift up toward the dry side. The moisture will stabilize the wood cells and help to retain the part’s form.
It is always a good idea to weight down or clamp the layers together to ensure good contact and adhesion. A large piece of wood works well to cover the part(s) with weights placed for even distribution of weight. You might even consider placing wax paper on either side of the pieces in case glue spills over and glues them in place.
I always do my laminating ahead of time, letting the parts cure overnight so they are ready when needed. Generally 3 to 4 hours is adequate. I can remember when building a laser-cut kit I had to apply sheet balsa on both sides over a balsa core on a stab and elevator. Looking at the parts, I noticed the grain running the same direction. To make it stronger, I removed the ribs in the stab and elevator core and replaced them with ones that had the wood grain running the opposite direction. After laminating the sheet on both sides, I was amazed by how stiff it was.
TAIL FEATHERS IMPROVED
When building a laser cut kit, I had to apply sheet balsa over a balsa core on a stab and elevator. Looking at the parts I noticed the grain running all in the same direction. Knowing from past experience that this was not good, and how to make it stronger, I removed the ribs in the stab and elevator core. I replaced the ribs with wood grain running the opposite direction. After laminating the sheet on both sides I was amazed by how stiff it was.
Laminating is most beneficial when extra strength is required, such as a firewall or landing gear mount that experiences greater stress. Laminate layers of balsa to the size required and then, after the layers have cured, you can carve and sand the part to shape. You can also laminate fiberglass or carbon-fiber cloth between wood layers for super strength.
BY JERRY SMITH