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Old Mar 09, 2003, 12:20 AM
He wasn't always evil
AirVenture's Avatar
SW Wisconsin
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Lightening Holes

Anybody have good advice on how to make 1" diameter lightening holes in a sheet of 1/8" balsa? I've done a search and it didn't reveal too much. Any ideas?

Thanks a lot!
-Brett
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Old Mar 09, 2003, 05:23 AM
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Punta Gorda, FL
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It depends on how many holes you want to cut. If you just want to cut a few, use an Exacto knife and sand the holes smooth.

If you want to make a dozen or so, get a piece of one inch diameter brass tubing from Small Parts,
www.smallparts.com
and chamfer the inside of one end to a cutting edge. Mount the other end in a wood block for a handle. Just rotate the tool while pressing it into the balsa where you want the hole. This tool will need the edge to be resharpened frequently.

If you want to make a hundred holes or more, consider investing in a one inch diameter forstner bit. These bits are available from professionl wood working tool outlets like Garrett Wade. A forstner bit will set you back from about $6 to $20 depending on the quality of the tool. For soft balsa, the angle of the cutting edge of the spur on the drill needs to be reground and redressed to a small angle to prevent tearout. The softer the material, the smaller the cutting angle is the general rule.

A less expensive tool with a long lasting edge can be made from a short length of thin wall chrome vanadium steel tubing from Small Parts. The cutting edge is more work to form than the brass tubing but the edge will last much longer before needing to be resharpened. The steel tool can be pressed into the balsa with an arbor press, using the tool as a die cutter. This is what I would suggest for production work.

The best results for the least effort is to have the ribs laser cut by an outfit like Laser Arts.
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Old Mar 09, 2003, 08:35 AM
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I usually place the wood outside just prior to a storm and let nature do its thing.
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Old Mar 09, 2003, 10:12 AM
He wasn't always evil
AirVenture's Avatar
SW Wisconsin
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Hehe Al, I would concider your method except it's winter, and I'm not so sure how effective that would be!

Thanks Ollie. I have six holes to be cut in the horizontal stab of my Lazy Bee. I think I'll either go with the forstner bits (if I can find them) or just go to town with a sharp hobby nife. I have some 1/4" brass tubing that might work nicely for some smaller parts however. Thanks for the info!

-Brett
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Old Mar 09, 2003, 11:44 AM
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I would get a piece of contest balsa to replace the stab and forget the holes. The contest balsa stab will be lighter than a medium balsa stab with holes in it.

I would sand the stab to an airfoil that tapers to a trailing edge about1/64 of an inch thick. The airfoil should be a straight line taper from about 20% chord to the trailing edge and a long semi-ellipse from 20% chord forward. You will remove more weight by airfoiling the stab than by cutting holes in it.
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Old Mar 09, 2003, 01:16 PM
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Thanks again Ollie. I'll have think about modifying the horizontal stab. The only thing I'm conserned about is that I'm going to be doing a review. Plus, the stab is atached to the fuse with 1/8" opening so I'd have to change that as well. If I ever make another Bee, I'll definately follow your idea. I'd imagine that would save a lot of weight.

-Brett
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Old Mar 09, 2003, 01:23 PM
It's just PLANE silly!
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I use a cnc router....but you probably don't want to hear that....

Eric
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Old Mar 09, 2003, 05:29 PM
He wasn't always evil
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Yeah, I really didn't need to hear that
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Old Mar 10, 2003, 12:49 AM
Joined Nov 2001
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Laser

Well not to be outdone, i just go out to our shop and use the laser.

Sorry, could not resist

visit http://www.climatemodels.com
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Old Mar 11, 2003, 04:05 PM
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Hope that you have better luck with Forstner bits than I have...
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Old Mar 11, 2003, 08:13 PM
He wasn't always evil
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Quote:
Originally posted by Donk
Hope that you have better luck with Forstner bits than I have...
What kind of problems have you had?
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Old Mar 11, 2003, 10:53 PM
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Ripping and tearing...
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Old Mar 12, 2003, 04:15 AM
All under control, Grommit!
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The sharpened brass tube idea is one that I've used on rather smaller diameter holes (less than 1/2 inch) but there's no reason I can think of why it wouldn't work with a larger diameter. The hole saws that most places sell are too coarse-toothed and rip and tear balsa and having hunted down Forstner bits from a specialist tool supplier I also experienced the ripping and tearing mentioned above with balsa.

The Miniature Aircraft Factory used to sell a sheet of lightening holes for use in their models- really they did- it was always displayed next to their sheets of left-handed sandpaper. I'm sure Dereck remembers both of these items as I think he reviewed them in one of his magazine articles.

Brian
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Old Mar 12, 2003, 06:23 AM
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The reason Forstner bits tear balsa is that the spur of a stock bit is sharpened at too high an angle for soft material like balsa. The forstner bit spur can be reground on the inside to a lower cutting angle and then honed to a razor edge. If it is resharpened in this way, tearing can be greatly reduced or eliminated. I think it would be easier and less expensive to cut six holes by hand with with a #11 blade. If a good quality one inch forstner bit costs $18, that comes to $3 per hole plus the effort to regrind and hone the spur.

Cutting six, one inch diameter holes in 1/8 inch balsa sheet with a sharp hobby knife equipped with a new #11 blade seems like a trivial effort for an experienced modeler. Just draw the circles on the wood with a soft tip pen using a circle template for a guide and cut along the insides of the lines. No big deal.
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Old Mar 12, 2003, 06:18 PM
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SW Wisconsin
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The Answer?

Wood Spade Bits!

These seem to be working well. On a few tests on scrap balsa they worked great. I found that by using the drill at high speed and low pressure worked perfect. It also helps that if you are half way through one side, flip the piece over and start from the opposite side. This virtually elimates any unwanted tearing. Also the bit's center point makes it easy to find the center of the hole. I picked up six of these for $16. They range from 3/8" to 1" plus there were many other sizes available. Check them out!

-Brett
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