Building Lessons Learned

Building Lessons Learned

wing

The Allegro-Lite 2-meter glider I’ve just completed have taught me a number of things — some Allegro-specific, others model-building specific. I thought I’d share my thoughts here, in one place for the benefits of others.

The Allegro-Lite was a pretty advanced build for me (and I think for most folks!), so having only completed maybe a half dozen balsa kits beforehand, I still had a lot to learn. The Allegro is very exacting, and needs to be built as closely to plan as possible, so good tools and techniques (and patience) are demanded.

Read on for a listing of the tools and tips that I have amassed during my build…


Overall shop design and configuration

1. Good, flat tables are a necessity. Hollow- or solid-core doors (available at your local Home Depot for $20-$30) and some 2×4’s make excellent shop tables. I have a plane for some here: http://thelocust.org/gallery/20040830workbench

2. Plate glass is a gift from the gods. For the perfect working surface, find an old entertainment center for a decently-sized sheet of plate glass. Remember that glass is essentially a liquid-solid, and can bend and warp (slowly) so the thicker the better.

3. Wax paper and grocery bags (plastic). Wax paper is great to cover plans and resists adhesion from most adhesives. It’s fairly stiff, lays flat and is transparent. Plastic grocery bags (HDPE – high-density polyethylene) also resist adhesion by epoxy! This can be used to “pot” servos, or cover sensitive parts when “potting” a wing to a fuselage to make a perfect joint.

Cutting, sanding, etc.

1. Hard, smooth and “true” sanding blocks are a necessity, as is a good selection of different grits of sandpaper. See if you can get a sack of “balsa blocks” from your LHS — I bought a SIG sack of balsa with numerous sizes and shapes of balsa blocks and they have served me very well. I use some Titebond to adhere strips of sandpaper to the blocks. I also have a Great Planes “T-bar” sander.

2. There is nothing quite like a new blade. Either buy a lot of blades, or learn how to sharpen old ones! Whether you are cross-grain cuting a piece of balsa or cutting covering, you need a sharp blade! Otherwise, you’ll end up with a jagged, ragged. It is the first thing someone will notice when they see your model!

3. Razor saw. I used the razor saw and jig for every cut I could on my allegro-lite! Slow, soft strokes with the razor saw make excellent, smooth cuts every time. Even free-hand cuts w/o the jig were very accurate and smooth. It is my favorite tool!

4. Free-hand sanding is for the birds (most of the time). Always use a jig to keep your sanding perfectly flat, if that is what you need. Free-hand sanding a precise angle does not work, and will most likely cause a joint made with that angle to be weak, due to the preeminence of glue to fill out the gaps. Free-hand sanding works if you are sanding in a curve or the like. Otherwise, use a block and jig, or perhaps a belt/disc sander.

Measuring!

1. Straightedges/rulers. First off are some decent, heavy straightedges. Here in Louisville, we have a “Harbor Freight” tool store. Excellent source for such things. A thin, flexible straightedge is nice as well.

calipers

2. Calipers. While you are there (at Harbor Freight), pick up some 6″ digital calipers for $15 (when they are on sale). They are very precise, and appear to be the same tool that everyone else re-brands!

3. A multi-functional protractor. I got the Multipurpose Angle Finder from Harbor Freight. A fantastic tool for $4. Much better than a regular protractor.

4. A pocket gram scale! I bought a MyWeigh 200-Z pocket scale that can measure down to .01g. It can only handle up to 200g, but that is good enough for weighing those small parts and individual panels. They can be found online for ~$25.

Tape and Adhesives

1. Tape. That 3M blue masking tape is fantastic. It doesn’t rip as easily as normal masking tape, and the adhesive is superior. I use it for everything from jigging parts in place, to labeling, to holding plans or wax paper down to the glass, to masking parts when I’m using epoxy. The adhesive is strong, yet it leaves no residue and releases easily.

2. Epoxy. I used West Systems epoxy (205 hardener, 206 slow resin) from CST for my Allegro build — and I’m NOT GOING BACK! A little expensive, but I bought a quart of resin, and it will last me some time. Very thin compared to over-the-counter five minute epoxy, so you can thicken it as much as you’d like with something like Cabosil (fumed silica). Also, while it is is great stuff — be safe!. Most people don’t realize that you can build an allergy to epoxy! Never use epoxy w/o wearing vinyl or nitrile gloves. Latex is semi-permeable! It won’t kill you to get it on your skin, but eventually you can build an allergy to it, and then you won’t be able to go near the stuff until it hardens!

3. A small, plastic pipet is excellent for applying thin CA precisely. They sell them for a dime a piece at our local model shop. Since they are plastic, you can stretch the tips on them until the inner diameter of the tip is VERY small. Perfect for accurate gluing.

4. Eat some yogurt or pudding. Yogurt and pudding cups are excellent adhesive receptacles. Epoxy will not adhere to the plastic, and since most pudding/yogurt cups are “crushable”, after the adhesive hardens, you can just “crack” the hardened adhesive out, leaving a nice, clean recepticle again.

5. Titebond is good for wood. Titebond or Titebond II — an “aliphatic resin” is superior for wood adhesion. Thin CA is great and provides “instant” bonding, but it is also brittle! These “aliphatic resin” glues actually make a bond stronger than the wood itself. It has a fairly short pot-life, so it isn’t painfully slow to set up, unlike epoxy. It also is fairly thick, so you can easily make “fillets” out of it. Thin it to increase potlife. It is especially good for d-tube sheeting. A hard landing can “crack” a CA joint, and thereby reduce the strength of the wing. No good!

6. Syringes. They sell these at my LHS as “pinpoint glue applicators” and have low-gague (wide) needles on them. They are excellent for accurately measuring epoxy, and clean up easily with alcohol. You can also use them to squirt epoxy under wing-skins on bagged wings for delamination repairs.

Jigs and weights and such

1. A bag of shot. While lead shot is expensive, it is invaluable for curing epoxy under compression on a compound surface (like sheeting). I use some heavy-weight freezer bags and masking tape for large surfaces, and little sandwich bags for smaller surfaces.

2. Mylar! Mylar is fantastic stuff — and is needed to “shim” the spar on the Allegro-Lite during building. It is flexible and adhesive-resistant. Know someone who bags wings? They should have some mylar for you. X-Ray sheets are also made of mylar. Ask your dentist or doctor. While your at it, get some hemostats and syringes, too!

I probably learned WAAAY more than this, but my brain is now emptied. Perhaps more later!

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