5 Minute Stab

LAST EDITED ON Nov-28-04 AT 10:56 AM (CST)
 
Maybe 10 minutes...

The core is 1/4" balsa, and is made in two halves.

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The core is joined.

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The core is sheeted on both sides with 1/16" balsa.

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The stab shown has a 30" span and weighs 1 oz.

>Maybe 10 minutes...

Here again HOW MUCH A PUPPY WEIGH?

>>Maybe 10 minutes...
>
>Here again HOW MUCH A PUPPY WEIGH?

1 oz.

Same as flap question, would you share the file?

>Same as flap question, would you share the file?

I e-mailed you one of the files.

Access to a laser cutter is very cool.

WOW! 1oz!, what grade wood? obviously really light, but will the skins stiffen the core that much? I may try this myself, but with the dremel saw instead. Maybe a layer of carbon veil to help hold the wood togather?

Is there any advice as to the best way to make a surface like this without a laser cutter?

I say again, wow.

I build stabs like that with appropriate sticks and glue. I've gone to using 1/32 quarter-grain for covering. I put the bottom 1/32 down on the building board and glue the sticks to it. After it dries, I get out two plate glass sheets and put the stab down on one, with plastic for protection. I use tite bond on the sticks to glue the other sheet on top and put a sheet of plastic, then the other plate glass. I weight it down and come back tomorrow to finish it up. Not as fast as Brad's method, but I don't have a lazer cutter in my shop. It is surprising how much stiffer a stab like this is than a piece of sheet balsa of similar dimensions and weight. Cover with tissue and it gets even stiffer.

Does the 1/32 sheet ripple when tissued? is it strong enough - I assume is is but I have always used 1/16 and worried that it is too fragile - seems that I worry too much

Regards

Mike

http://www.mike-nelson.co.uk

To really stiffen it up, put strips of carbon fiber or glass on the surface, about half an inch wide and 12 in. span top and bottom along the hinge line. This makes the stab about twice as stiff spanwise.

Then, if you really want to save some weight, skip the sheeting and just cover with film. Then paint, 'ala Brad.

>WOW! 1oz!, what grade wood? obviously really light, but will
>the skins stiffen the core that much? I may try this myself,
>but with the dremel saw instead. Maybe a layer of carbon
>veil to help hold the wood togather?

The sheeting is 5 lbs c grain.

The core is 6 lbs A-grain (Kyle's off the shelf stuff).

>Is there any advice as to the best way to make a surface
>like this without a laser cutter?
>
>I say again, wow.

You can do the same thing without a laser. In fact the laser is not important. I have done EXACTLY the same procedure and made the core from scratch.

Take a piece of light 1/4" balsa. Draw your shape on the balsa. Offset the perimeter about 3/8" with another line. Leave a 1 1/2" center section solid. Cut out all the lines. You can use a real new Exacto blade or a scroll saw. Now add 1/8" x 1/4" former sticks (I use straight formers not geo) every two inches.

You are ready to sheet.

Since Ferocious said that PolyU glue was the lightest, I decided to test this fact. I used Gorilla glue dispensed from a Monoject 412 syringe for all the laminating, and it did appear to come out nice and light.

...and hey, anyone can get laser cutting. You do not need to live near one either. Just call Kyle.

http://www.tanks-hangar.com/

All of my designs can be cut by Kyle, if you want one.

Does the 1/32 sheet ripple? I would say no, except that on my last project I used 1/32 which was not quarter grain and it has sunk in between the strips. This is mildly irritating because I was reproducing sheet surfaces on an OTS model but making them stronger.

Godzilla,

Neat work, nice and light.

However, I'd be interested in knowing which the way the grain runs on those diagonal pieces. I don't think I'm gonna like the answer, but there it is...

You surely do nice work for a guy with an unmentionable position on an unmentionable topic.

LAST EDITED ON Nov-28-04 AT 06:18 PM (CST)
 
Dan,

The answer is that the grain is not running lengthwise, which would of course be ideal. However, with the laminated construction with top and bottom sheets, these areas are constrained quite well by a "box" construction.

Nevertheless, I think this would be a poor construction if you simply try to cover it with silkspan or (worse) plastic film.

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"The test of good manners is to be patient with the bad ones." -Ibn Gabirol

>However, I'd be interested in knowing which the way the
>grain runs on those diagonal pieces. I don't think I'm gonna
>like the answer, but there it is...

Ahah...

You know what? That grain means nothing. I have built cores with the grains all running the "correct" direction, there is absolutely no different than a core that is not "correct" (don't tell anyone...its a secret). In fact, the best core I have seen is Doug's foam core stab that was vaccuum bagged using West Systems epoxy and is sheeted on both sides with 1/16" balsa. The thing is a surfboard. You simply cannot bend it, and it weighs nothing. Foam has no "grain" at all.

The geo work is simply to keep the two sheets from crushing, and to maintain the seperation between the sheets without "slippage". Slippage in space between the two sheets is where the torque deflection comes from. This is a why a foam cored stab is the strongest of all, it has the least shear "slip", which results in the strongest plank in bending and twisting.

So much has been made of geo construction. Like it is some magic shape. this would be true if you turned a stab (for example) up on its side and put some weight on it. Geo works great for trusses in bridges, I do not see it has any engineering advantage at all in flat planks.

>You surely do nice work for a guy with an unmentionable
>position on an unmentionable topic.
>
>Dan

It appears to be quite "mentionable".

Thanks godzilla, I'll be trying it out next project. But I may have to order some lighter wood first. I like the core idea alot. Light and rigid, mostly rigid. Now, I need some time off work to get at it......

LAST EDITED ON Nov-28-04 AT 06:15 PM (CST)
 
Clever. I *knew* this was going to work well! Here is my latest rework of the Brodak Mo'Best (kit) stab:

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S2 is 1/4" balsa, S1 is 1/16" top and bottom sheets. E1-E4 is 1/4" elevator sheet. Notice that we are prenotching trailing and leading edges for hinge barrel and control horn clearance. Elevator has (partially) precut slots for using imbedded control horn wire boxes (so it can be sanded to taper to 1/8" trailing edge height)..

(BTW, I'm reworking the laminated spars to eliminate the 1/32" ply center, for simpler construction - back toward Morris' Lincoln Log.) The 1/32" ply center version is harder to build and easier to warp or misalign, which offsets the advantage of precut hinge pockets.)

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"Life's Tragedy is that we get old to soon and wise too late." -Benjamin Franklin