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Author Topic: Convert from hand-cutting balsa to laser-cutting?  (Read 1111 times)
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Pou Pou
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« on: July 24, 2014, 12:01:27 AM »

I started to build an old Comet kit, Sparky. It's a rubber powered free flight model with about a 30 inch wing span. I think it will be a nice plane and a good flyer...if I finish it.  The parts (ribs, formers, etc.) are defined by sticky-paper stuck onto balsa...not printed, not die-cut, and not laser cut!  I started working and doing OK but now have tendinitis of the right elbow, which hurts.

I have two questions (at least).

1. Are there some techniques, experience to make the hand-cutting go easier.  There are many notches on the formers and ribs which are small, 1/16x1/16, and these are quite difficult to do.

2. Are there places where I can go (send) to get he parts laser cut?

Thanks,
Pou Pou
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mjmccarron
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« Reply #1 on: July 24, 2014, 01:08:54 AM »

I can relate to painful building. Sorry to hear of your tendonitis. I recently (7 months ago) broke my back and collar bone. I'm healing slowly but still ßßhave trouble sitting for any length of time and have suffered some nerve damage in my right arm and hand. I'm building more to work as a kind of rehab. It's painful but patience and learning when to take a break helps.

As far as technique for cutting, I use an assortment of needle files for small slots and good sharp knives for the rest. Also, my scroll saw for notching plywood parts.

I have never used a laser cutting service but quite a few exist. Depending on where you are, there are a bunch listed on google. I typed in "model airplane custom laser cutting". National Balsa offers cutting and I have used them as a source for wood.

Good luck. I hope you get to feeling better!
Mike
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Bargle
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« Reply #2 on: July 24, 2014, 06:38:02 AM »

1. Are there some techniques, experience to make the hand-cutting go easier.  There are many notches on the formers and ribs which are small, 1/16x1/16, and these are quite difficult to do.

Thanks,
Pou Pou

I make the notches using a piece of balsa the thickness of the notch with a strip of sandpaper glued to it. I don't know if that method would be any better for your tendonitus, but the notches do come out better.
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Maxout
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« Reply #3 on: July 24, 2014, 10:24:42 AM »

If you've got tendonitis from cutting this stuff, perhaps your wood is too hard? I can relate...some of the wood in kits is a disaster in terms of density and will wear you out trying to cut it.

Specifically for the sparky, there are laser cut short kits already available (basically rib, tip, and former sets) from Bob Hollman and Jim O'Reilly. Jim actually makes kits for the Sparky's sister ships, the Pepper and Phantom Fury, as well. You'll want the plans as well, as he made some structural mods to further improve them.
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Pou Pou
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« Reply #4 on: July 24, 2014, 01:31:53 PM »

Many thanks.

I went to their site (Bob Hollman and Jim O'Reilly), spoke with Bob and placed plans and a short kit on order.  I will definitely try the other suggestions for cutting, but have to wait until my elbow stops hurting.  It didn't used to hurt, but then I didn't used to be old.

Pou Pou
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Starduster
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« Reply #5 on: July 24, 2014, 01:36:58 PM »

Pou Pou

If you've never built a laser kit (or short kit) prepare to be amazed. The parts are amazingly accurate and they fit.

Some people make a little extra effort and (lightly) sand off the burned edges. I don't, unless they are very noticable.

You might get spoiled...
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lincoln
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« Reply #6 on: July 24, 2014, 06:59:37 PM »

Seems to me if you get a scroll saw, use a fine tooth blade, and are patient you can do a pretty good job of cutting, and finish off with a sander. You can even get spiral blades which don't care which direction you're cutting, but they have a wider kerf. If you keep your eyes open, old ones are cheap.

Alternatively, if you have good ventilation in your building area, it's possible to hot wire wood. Picked this up from a column by Herk Stokely in an old Flying Models. It does smoke, but for a thin piece of balsa my guess is that it would be bearable with good ventilation. Particularly if you drew off the smoke into a tube, a la vacuum cleaner but slower and quieter. Maybe use nichrome wire? I've used picture hanging wire, some long leads, and 24 volts to hot wire a live tree branch that was in an inconvenient place. Much easier, safer, and slower than hanging upside down with a chain saw! I know there are commercially made foam cutters like this, but you might have to change the material for the cutting wire. You might also need a different voltage or current, which might require a different power supply. (perhaps from an obsolete computer??) These commercial ones are more or less like a fixed scroll saw.

You might try cutting the ribs slightly oversized and sanding to the correct profile. A disk sander might be good for this. A flat disk mounted on a motor with a table at right angles to it. Probably pretty easy to set up yourself. I have a homemade one (built by someone else) that's quite handy. The following picture, though it shows something fancier and more expensive than you need, shows the general idea:
http://www.micromark.com/RS/SR/Product/82889_R.jpg
I bet you could make something like this with an obsolete 05 ferrite motor. Or any number of other motors.

I was at a model engineering show a couple of years ago, and a guy showed me his rib cutting setup. The idea was to rough cut the wood and then attach it to a template which had a guide for a router bit. All the ribs would come out exactly the same. Not so great for a Sparky, I guess.

One thing that helps with tendinitis is ice. Try freezing water in a Dixie cup and peeling back the edge. Rub the effected area for a couple of minutes, two or more times a day, and you may see some progress. Especially if you are using an NSAID like naproxen. And there may be exercises you can do to help things along. If you haven't seen a doc about it, it might be a good thing to do. Physical therapists can sometimes do wonders.
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Pou Pou
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« Reply #7 on: August 18, 2014, 06:54:07 PM »

Thanks again,

I did get laser-cut parts and I will never, repeat never, go back!  The tendonitis is gone too!

I put up a post...I believe in was the General Forum (not sure)... on the amount of rubber for my Sparky.  Maybe you have some thoughts?

Pou Pou
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Art356A
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« Reply #8 on: August 18, 2014, 08:59:53 PM »

I was just converted 2 days ago with my first laser cut kit ever. Do you think it can cure arthritis, too?

a.
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My arms are so weak, it's like that pushup I did last year was a total waste.
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