gluing sheet balsa

[Ed Carlaw]

What's the best way to glue sheets lengthwise and keep everything straight and flat? Ed.

[Ed Carlaw]

I forgot to mention why. I am attempting to make profile fuselage wider than four inches and want to keep things as warp free as possible. Thanks, Ed.

[Tim Wescott]

Get the two pieces of wood so that the edges match.  Best is if you can make them dead straight.  I use my longest sanding board to get part way there, then hand-tune by holding the joint up to the light and sanding down the high spots.  Note that you can't trust them to be straight from the box: it's balsa wood, and wood changes shape over time.

If I had a joiner I'd use that, but I have a typical model shop.

Glue it up on your flattest surface (I scored some 1/2" thick glass, but whatever you use for a building board will do).  I typically use Titebond for this, but you have lots of options.

If you really want to do a good job, use four pieces of 1/4" wood (assuming a 1/2" thick fuselage) and laminate them, with the fore-aft parting lines in different spots between the top and the bottom.  You'll spend more time joining, but you'll get a stronger, stiffer fuselage.  Again, I'd use Titebond (in a really thin layer between the laminations), but if you do you want to give the fuselage a lot of time to dry -- I give it at least a week before paint, and I'm happier if it takes two or three.  If you build the fuselage first then set it aside that would be good.

Or if it fits the competition category you're building for, and you don't mind spending an inordinate amount of time building a flat slab of fuselage, build it up and make it thicker than 1/2, like I did in this thread.

[Ed Carlaw]

Thanks Tim. How do you keep the laminations from sliding when you weight the pieces? Ed.

[FLOYD CARTER]

Easy.  The glue has sufficient "grab" such that the pieces don't move when weighted down. 

[Ed Carlaw]

Does the amount of weight matter as I have some tank vent weights that are pretty robust. Ed.

[Tim Wescott]

First, I make everything oversize to allow for some sliding. 

Second, if things really slide then you're using too much glue.  Remember that balsa is weak in splitting, so there's no sense in trying to make a super-strong joint in that direction.  If you use a thin layer of glue then sliding will be minimized and so will added weight.  I make glue spreaders out of used gift cards.  For Titebond and balsa I like to make the notches about 1/32" deep; that seems to make a strong, light bond.

I suppose if I'd cut everything to size first I'd either pile on the weights and then peer into the side of the pile and try to get everything upright, or I'd pin straight down into my building board before putting on the weights -- I much prefer making things a bit over, and then trimming afterward (that built-up fuselage I showed you was made of 1/2" square sticks, sheeted with 3/32" moderately heavy balsa.  By design it was supposed to have 1/8" overhang all around for later trimming; it ended up being 1/16" in places, but all I needed was no less than zero, so it worked out OK.)

[Tim Wescott]

Does the amount of weight matter as I have some tank vent weights that are pretty robust. Ed.

If you put 1/2" worth of balsa into the press and come out with 1/8", it was too much weight.

I use all the flat pieces that I can find, or a flat thing like a board or metal plate with heavy stuff piled on top.  You do want to enforce flatness, and you don't want to dent the wood.  But you don't have to feel like you need to be refined in what you choose for weights.

[Ed Carlaw]

Thanks Tim, I'll re-evaluate my weight situation with the vent weights, they are a foot in diameter, 1 1/4 think steel. I'm thinking that's going to be way more than I need. I have some smaller plate steel pieces that I think I will use. Any thoughts on a thin plywood sandwich between the two laminations. I weight will be a concern but I'm not building for competition.

[Tim Wescott]

If you're going to use plywood, put it on the outside -- that'll give you the most stiffness for the weight.  But if you laminate plywood directly onto an open structure, you'll end up with something impossible to repair.  At least, when someone gifted me with a really nice plane whose fuselage was made of 1/64" plywood and I crashed it, I couldn't figure out how to repair it short of replacing the fuse.

If you had something to spread that weight out over the whole fuselage, like a really flat 2x8 or some thick plywood, then one of your vent weights may work.  Otherwise, I'd suggest something else.  You don't want weight concentrated in one spot -- either use a spreader like I showed, or use a bunch of weights that you can put along the length of the fuselage.

[Ed Carlaw]

Thanks, I"ll skip the plywood sandwich and I've got enough lumber around that I should be able to use my vent weights. Thanks again for all of the help. Ed.

[john e. holliday]

Instead of glue like Tim says, I use Gorilla Glue.   The Gorilla Glue expands and will find every worm hole or pin hole in the 1/4 inch sheets.  I also don't weight the wood as the few times I did it came out bowed.  I use lots of clamps and lots of eye balling.  Then hang it vertically for a day(24 hours) and it is ready to start shaping.  The laminated sheet done this way can be used for a ball bat or an attitude adjuster it is so stiff.

[FLOYD CARTER]

Can't understand any need for excessive weights.  I glue ply doublers onto fuselage sides with 15 min epoxy.  For weight, a few large cans of tomatoes is enough.  Too much weight, you will squash the balsa!

[Tim Wescott]

Instead of glue like Tim says, I use Gorilla Glue.   The Gorilla Glue expands and will find every worm hole or pin hole in the 1/4 inch sheets.  I also don't weight the wood as the few times I did it came out bowed.  I use lots of clamps and lots of eye balling.  Then hang it vertically for a day(24 hours) and it is ready to start shaping.  The laminated sheet done this way can be used for a ball bat or an attitude adjuster it is so stiff.

Yes on the Gorilla Glue, if you want to use it.  Interesting that you had problems with warping -- I had exactly one fuse come out warped, and that was because it faithfully mold itself to my warped building board.  I was able to fix it by intentionally warping it backwards and leaving it on my bench for a week (my build process gets interrupted a lot by things like work).  That was for my Fancherized Twister, which has done pretty well.

[Fred Cronenwett]

I have been building profile fuselages much like Tim is doing with the following

1) 1/16 side skins, glued together with titebond, then sanded and they are oversize
2) build the fuselage from 1/2 x  3/4 sticks or in my current build they are 7/8 wide so I can end up with a 1" wide fuselage
3) take the fuselage off the building board and then glue the skins to the fuse
4) trim the skin to match the outline of the fuselage
5) glue the other skin on and then trim it to match the outline of the fuselage

Even my glow powered profiles have the 1/16" skins, hardwood beams for the motors and the internal sticks but I DO NOT put doublers on the plane, it's strong enough the way it is. Then I fiberglass my airplanes so they are really strong enough. On my 6' long B-29 profile fuselage I have a carbon fibre cloth glued to the inside of the skins so they are really strong enough. that the black looking material on the inside of the fuselage skin.

I have not built a a traditional 1/2" balsa profile in a very long time, all of my profiles have the thin balsa skins with stick structure on the inside, lighter and stiffer than the 1/2" balsa.

Fred