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Building Tips and technical articles. => Building techniques => Topic started by: Dennis Toth on February 14, 2022, 07:55:45 AM
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Guys,
I'm getting ready to start a new ship that will use a component that is going to be assembled then pressed between two sheets of glass to cure/dry hopefully straight. The issue is what can be used that is light but slow to cure/dry that will allow time to assemble/position the various components then get the press top glass sheet in place. I'm thinking 2 hours would be great.
Was thinking slow CA or 2 hour epoxy or Titebond III. Problem I see with the 2 hour epoxy is to get it on light you need to be very careful to spread it thin, could take a lot more time. The slow CA is a question of how long do you have before it kicks or if you get it on and pressed does it kick? Regular Sigment or white glue dries too quick to get it done a really good joint but looking at the Titbond III specs says has 10 minute work time maybe? What have you used?
Best, DennisT
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Show us a picture?
I'd either find a way to position the parts so that they go right where they belong, or if possible, find a way to glue them up so they don't have to be super precise.
If you can live with Titebond's 10 minute working time you could just use that, although "pressed thin between glass" means that, first, you'll need to give it a lot of dry time, and second, it'll never fully dry while it's pressed between sheets of glass. I have, contrary to many dire warnings, laminated large sheets of balsa and/or plywood onto fuselages using SigBond, and have not had problems with them drying out -- but I build with awesome and ponderous slowness, so if I get my fuselage all laminated up today, then chances are it'll have weeks or months to dry before it sees paint.
Epoxy pot life assumes some self-heating in the pot (epoxy cure is exothermic). If you're paranoid about it kicking off too soon, mix it up then put it on ice. Or remember that when you spread it out thin it won't heat up, so you'll have a longer working time. For spreading thin layers of glue, I make up spreaders out of plastic fake credit cards with notches cut in the edge. To make a thin (on average) layer of epoxy you just sweep that over the balsa; what's left is little ridges of epoxy to match the notches in the card. You'll spend time making the sweeper, but not using it. Or, if a really thin layer is enough, just sweeping balsa with card will leave epoxy in the grain of the wood -- doing both sides of a piece should be enough for a laminated bond.
This thread (https://stunthanger.com/smf/building-techniques/fancherized-twister-build/msg277642/#msg277642) and this thread (https://stunthanger.com/smf/scale-models/ercoupe-build-(slow)/msg534318/#msg534318) have profile fuselages that I built up with inner balsa framing, sheet on the outside, and plywood doublers (even triplers in one case) on the nose.
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Dennis,
Epoxy can be thinned with denatured alcohol. It’s been used for fiberglassing over balsa.
When parts are sandwiched and pressed between glass with slow curing glue they slip away. If work table is not on level. It’s good to have extra material for slip adjustment , level the surface, block perimeter, or use some CA to secure final position. Thinned epoxy usually cures slower, and become not so brittle.
Titebond can be thinned too. But epoxy is more forgiving for repositioning.
Jerry.
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Gorrillla Glue. I have sheets that I laminated and are really stiff. The glue will sand easy and find all the worm holes in the wood. The draw back is the glue has a short shelf life. D>K
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The way we used to do this on the FF models is to first spray the balsa with a coat of nitrate dope. That stops the epoxy from soaking too deeply in the balsa. The epoxy can be spread with a scraper or a roller which is my preferred method. I'd use West Systems for this job as it has the pot life you need.
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Don't be coy--tell us what your application is, otherwise, most of the advice will be (far) less than optimal, and unlikely targeted to your situation.
You are all over the map in the original post when you suggest you are considering, among your other choices, two-hour epoxy and slow CyA. That gives us range that you might think is useful of nearly two hours....
Dave
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The way we used to do this on the FF models is to first spray the balsa with a coat of nitrate dope.
Bob Hunt recommends hair spray -- which is basically lacquer. Charcoal drawing fixitive or other stuff from the craft store, car parts store, or art store may work, too.
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Bob Hunt recommends hair spray -- which is basically lacquer. Charcoal drawing fixitive or other stuff from the craft store, car parts store, or art store may work, too.
I know for certain nitrate dope works. and us full scale airplane guys have it around.
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I know for certain nitrate dope works. and us full scale airplane guys have it around.
And more power to you. But if I can do the job with a rattle can and save myself setting up my compressor, setting up my paint gun, mixing paint, then cleaning my paint gun and putting everything away, any extra expense involved with using the rattle can is acceptable to me.
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For laminating balsa sheeting onto profile fuselage cores, I have had no problems using 30-minute epoxy and credit cards to squeegee the epoxy (ultra thin layers) onto both mating surfaces (I do one pair of plies at a time. The core is shaped, and the outer plies are oversized. However, I have managed the same operation on a short kit with 1/4"-thick laser-cut halves, without mismatching and/or having the epoxy set up too quickly. Just work diligently, and don't mix the epoxy in a container. Just running out equal-length streams of the two parts makes quite enough epoxy for that thin an application for those sized parts. You can also apply a thinned coat of dope to seal pours, and sand, but I haven't had weight problems with this construction technique. Alignment pins aren't difficult, if you want them.
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z-poxy finish resin is great for the task. its string as epoxy but very thin and easy to spread. great penetrating capability, light and good working time.
i have build a lot od 1/3d scale r/c models with HUGE foam wings fully sheeted with the material. they endure a lot of flight stress and sun exposure with no delamination and weight was always bellow the target
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What ever happened to that blue and yellow 3 hour epoxy.
Hobbypoxy Formula 2, long gone, but plenty of equal or superior are available. I still have about 3/4" in the later plastic bottles (not the original toothpaste tube). Forget about it, get the "30 minute" EZ-LAM, 30 minutes is the pot life with A LOT of margin, cure is 24ish hours.
Brett
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z-poxy finish resin is great for the task. its string as epoxy but very thin and easy to spread. great penetrating capability, light and good working time.
i have build a lot od 1/3d scale r/c models with HUGE foam wings fully sheeted with the material. they endure a lot of flight stress and sun exposure with no delamination and weight was always bellow the target
This is what I use as well Fred.
Mike