Thanks, Dick!
I have been looking all morning for that printout of the epoxy mixing ratio circles, and just saw this thread.
No problem - after posting I realized the old forum “GALLEY of PHOTOS” feature was removed, and that’s where it had been posted.
Hi Angus, yes that is the way to use it. I am using ‘Z-Poxy’ simply because it is available in smaller quantities in model shops. Thinned a little with rubbing alcohol it does soak into balsa well.
So far though I only use it inside a hull. Like everything you soak into wood it does raise the grain but unlike dope, varnish or sanding sealer, it does not sand easily. The epoxy soaked grain is hard and of course the thin balsa skin is quite flexible so making sanding to a smooth surface pretty difficult. Has anyone found a solution to this? Would wet sanding with wet-or-dry be better I wonder?
Maybe one thin coat of epoxy (for hardenning) sanded as best as possible then switch to a varnish would work.
Just thinking aloud…
Graham
I wonder if you could prepare a sheet of balsa in advance by wiping epoxy on both sides then sandwiching it between two sheets of polypropelene, which I am pretty sure cannot stick to epoxy. If that works you would have a slick surface on both sides. You would have to do both sides to prevent warpage if the wood got wet.
Just a thought.
Pete
Alternately if you want ultra smooth epoxy finish sanwich the wood to be finished between mylar film, I have ued cheap space blankets, or waxed paper. I haven’t tried the mylar drafting film I use for sails, if I get time I’ll try today and report back tomorrow.
If it is a waterproofing agent that you are sourcing then you may wish to research “EVERDURE” which is designed to do just that, water proof by saturation which in turn hardens the wooden structure.
Here is a link to the product description…
http://www.boatbits.co.nz/shop/Paints+Resins+Cleaners/Resins+-+Epoxy+Polyester/International+Resin,+Glue,+Fillers/Everdure+A+B.html
Sorry I didn’t read this thread earlier. As Fotties are not my thing, I just didn’t get to it.
A couple of points:
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As usual Dick is on the money. I can vouch that, in my experience, the West stuff will still be fine despite the discoloration. I have used old stuff (older than 10 years) on my models which I had figured might be pass its “best by” date for my big boats. No problem at all.
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I used Everdure to seal the inside of my balsa/glass IOM (again - left over from the big boat supply). I added way too much weight in the process. On a subsequent model I’ve just used diluted single-pot varnish as a sealer.
(Incidentally Ian - I haven’t seen Everdure here in the US. It’s one product I miss from home. I gave away a couple of hundred bucks worth of epoxy product when we moved up here - a mix of West and Epiglass)
Just my 2 cents.
I don’t remember for sure, but I think Everdure in the US referred to a particular bronze that was used in marine applications.
Right now, for convenience I think I will just dig out my old West System stuff and use it.
BTW. I just bought an electric scissor for cutting glass. Nothing seems to work as well as one of these things. Looking forward to trying it after watching my flying buddy trim glass for an airplane fuse with his.
Pete
I bought a pair of these lightweight GINGHER (#536-a) scissors about 15 years ago for cutting Kevlar glass cloth. They work excellent for cutting the Kevlar but, do get get dull after a bit of cutting. When they won’t cut Kevlar anymore, they still slice thru fiberglass cloth with no problem. Might be worth looking into.
Fiberglast website
I’ve got a ton of various shears around here, (well, at least five or six) everything from high quality dressmaker shears, long paper shears, inexpensive but very nice ones from Fiskar. I also have rolling razor cutters that work really well if you can find a flat surface around here, but my flying buddy tried an old electric scissor that he got his wife years ago and that she never used. From the first it was excellent. He works with a roll of 0.7 oz fiberglass overhead, and the ease with which he zips off a piece has to be seen.
He introduced Dave Platt to electric scissors for glass work and reportedly Platt is showing them off in his next video with a credit to my flying buddy.
A lot of things work, the rolling razor would be great except for the flat surface requirement. The only flat surface is usually occupied by my boat!
Anyway, I am trying these after watching my friend glass a quarter scale aircraft using an electric scissor.
I got the $20 Black and Decker’s at Home Depot.
Pete
One would think that a scissors would need to be sharpened with the smoothest edge possible. That is the preferred result when sharpening a plane or chisel with Japanese water stones. Not so with scissors. To cut tough stuff, like glass, the blades need to have some tooth. A common bench grinder will impart a toothed edge. A sharp file will work on cheap scissors but will not quite get it on good quality ones because the blades are hardened. Good scissors have a warp in one of the blades. The warp is very small but necessary to do the job smoothly. Electric scissors usually have no blade warp but use a spring at the pivot pin to exert pressure between the blades.When cutting straight or near straight lines use only the tip of the scissors. That will work a lot better than when using the cutting edges nearer the pivot pin. When doing this tip method, do not open and close the blades, just slide the scissor along the cut line. Examine the cutting edges of your scissors. Really good scissors have different angles on the opposing blades. In fact some of them have one blade beveled at the cutting edge and the other is almost square to the sides. Keep that in mind when you sharpen them.
Epoxy component measuring is important, nay critical. Modelers often use small quantities, so measuring is more problematic. It is said that a measuring tolerance of 5% is the maximum for reliable result. Many of you have triple beam balance scales. That is the best tool around for getting the quantities of the components spot on. I sometimes mix as little as 2 or 3 grams using the scales. The hardener is usually lighter in weight than the resin, so you have to determine what the ratio of weights are. Once you know the weight ratio you can mix any quantity you need. The stuff I use has a resin weight of 31.2 grams per fluid ounce and the activator has a weight of 28.4 grams per fluid ounce. Yours may have a slightly different weight ratio so you have to make your own determination.
For a balsa covering coat. First sand the balsa with very fine grit sandpaper. Something on the order of 240 or 320 grit. Wet the balsa with water, let it dry, now sand it again. Apply epoxy and the tufts of soft grain will not surface to make a rough finish. Apply the epoxy with whatever tool you choose. I usually just pour it on in a generous streak, then spread it around with a stick or whatever is handy. Let it soak in for a few minutes and then squeegee off the excess with a plastic scraper. That makes a smooth surface and you can control the total deposit, thus the weight, with pretty fair accuracy. Good plastic scrapers can be had at automotive paint stores. It is essential that the scraper have a very smooth and flexible tip.
I find it convenient to epoxy coat the whole sheet of balsa, on both sides, before I ever cut it to shape. Assembly, using epoxy or CA, then has good faying surfaces that does not absorb a lot of adhesive but has plenty of strength.
Picked up some nice brushes at a craft store on the way home, and checked out the price of scissors while I was there. I don’t need scissors, having several good ones by Fiskar and Heinkel (or at least by whoever’s brand is on the scissors sold at Heinkel’s outlet) but I looked out of curiosity.
The $20 Black and Decker electric scissors look like a bargain since most of the manually operated ones were more expensive, even some that didn’t look like they were of particularly high quality.
My mother was a dressmaker most of her life so I always had good scissors at home and frequently got yelled at for mistreating them. I really have to wonder what she would think of electric scissors. After all, she used electric sewing machines though she started with a foot treadle when she was a kid.
I also got yelled at for making “bullet holes” in my Jack Armstrong paper airplanes. The sewing machine was perfect for the job!
Anyway, the price of the scissors I bought yesterday is really low compared to their utility. I have no idea how long they will last, but I’m not worried. By the time they need to be replaced there will be something better and probably less expensive.
Pete
Pre-raise the grain, now that I had not thought of. Thank you for the tip I will try it out.
Graham