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Building Tips and technical articles. => Building techniques => Topic started by: Jeffrey Olijar on September 23, 2008, 01:53:27 AM
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I have a very shakey hand and whenever i try to cut out curved surfaces (such as ribs) I always end up with a huge difference between my ribs. I use a sharp exacto knife and a cardboard template tracing with a pencil. so whats the secret to doing this?
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I use 1/32" ply. templates, seems to guide the blade a little better than cardboard. Also you can nail a stack of blanks together, trace the pattern on the top piece, and cut it out on your bandsaw or jigsaw. Guaranteed to be identical pieces!
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Yea, more rigid templates helps.
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Before Pat got his laser cutter, I cut up a set of plans that I got copied (make sure th ecopier does not distort it.) then I used a glue stick to adhere the drawing to the part. Cut it big, say 1/16 oversize and sand it to shape. the paper template line is what you sand to. perfect parts.
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Many of the inexpensive CAD programs will print out on a cheap dot matrix printer. Stick the printout to the wood and stack cut some parts. If you use a jig saw and just nick the inkline you can cut parts to within .005 in. easily as good as a laser. I usually cut at least 4 layers at a time, either to have parts to repair with, or have parts to build another with quickly. A decent jigsaw will cut up to 1 in. thick with no problems, as long as the blade is sharp and you don't force it through the wood.
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I'm no expert but I'll share what I've learned or seen. From his lost foam video, Bob Hunt uses polystyrene foam as a cutting pad for cutting ribs by hand. It is supposed to help with blade control. I have better luck with using my band or scroll saw and sanding like mentioned above. I pin the template to the balsa stack and wearing safety glasses trim the pins flush on the bottom of the stack. This wastes pins but I can get a bunch at the $1 dollar store. Also using a fine tooth blade helps. I then sand by hand or power depending on part.
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I've cut ribs in about every way that can be done, except laser. I think my favorite for a constant chord, is to make a 1/32" ply template, poke some pins through the plywood, then install pins that are pre-bent at 90 degrees, with a bit of a horseshoe made out of the 'tag end' (knot term). Epoxy will hold that in place, but so will CA and baking soda. Get the pins eyeballed straight before or after you glue with a pair of needlenosed pliers. Since there will always be a slight difference between top & bottom, I put a ballpoint or Sharpie mark in the bottom of one of the spar notches, or on top of the TE relief. Marked for 'up', all the ribs will be identical, almost no sanding will be required, and the wing will be straight. I like a single edge razor blade to do most the work, then switch to a #11 Mator blade (German duplicate of Exacto #11, from Solengin Steel...good chit!) for the notches as needed.
Stack sanding is fine for tapered wings. Adjust the ends for the distorted angle in one of several ways. Cap strips cover the angular error on the top & bottom edges. Kewl... H^^ Steve
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Jeffrey
If your hand is shaky as you say, I sympathise but I would use laser cut ribs.
The choice of models that are available as CAD plans these days is astonishing so there are plenty of choices.
Having worked with laser cut ribs, I found them so easy to use that I would only consider cutting my own for a parallel-chord wing.
Whatever the model you want to build, ask around. There should be somebody who can supply you with a set of ribs.
Cheers
Geoff
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how much on average do you think it would cost to have a set cut. I have my eyes set on a 1/2a fierce arrow still... but it needs to be very light as It will be electric powered. VD~ i hope. still planning.
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My favorite method for constant cord wing ribs is to cut a 1/32" or 1/16" ply template, tack glue it to a block of balsa, cut it out on the band saw, use a piece of angle iron clamped to my band saw table, turn the block on its side, and slice the ribs off like balogna.
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Three methods. First cut out a paper template, 'gluestick" it to the wood, cut, sand to final shape. Second, a hard pattern, cut individual or stack of ribs, sand to final shape. Third and best, send off pattern to a laser cutter, get three sets of ribs, build planes. H^^
Hi Ty,
I use the paper method, most prints have each rib and most plane I build each rib is different. I cut the ribs from the print about a 1/16 from line than I tape the rib on to the wood with the clear box tape ( can get a roll of tape for a dollar) I use a single edge razor blade. Works for me, a lot of work but it just for fun. If you shake get your grandchild to cut them for you. It will give you time with the grandchild and you get the love of the child from all of it. My grandkids like to make drawing for me. Just a suggestion, good luck Gary
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Hi Ty,
I use the paper method, most prints have each rib and most plane I build each rib is different. I cut the ribs from the print about a 1/16 from line than I tape the rib on to the wood with the clear box tape ( can get a roll of tape for a dollar) I use a single edge razor blade. Works for me, a lot of work but it just for fun. If you shake get your grandchild to cut them for you. It will give you time with the grandchild and you get the love of the child from all of it. My grandkids like to make drawing for me. Just a suggestion, good luck Gary
dont have any grand children and my son is 7 months old ;D
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Jeffrey, On the 1/2a Fierce Arrow I'd contact Eric Rule at RSM. He kits the full size plane, ask him about a 1/2 a size kit. Worth a try.
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i am modifying the plane so i will have to have custom cut ribs. Ill try to do it myself first and then I will have them laser cut if I cant manage to get it right...
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Somebody say "1/2A Fierce Arrow"? This is one Frank Carlisle and I collaborated on, .061-powered, called the "Frankenstone Arrow".
--Ray (Stone)
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thats a nice looking arrow. what did the final weight (without tank & engine) come to?