Tips for building with wood.

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skeeter_ca

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When building a wing rib jig, overlay a thin piece (1/8") of acrylic on the jig and glue acrylic blocks to hold the wood pieces. Epoxy doesn't stick to acrylic so the rib is easily remove after to epoxy dries.
skeeter
 

BJC

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Question driven from Aerowerx's J-1B build thread, which I am following with great interest:

Why not laminate the longerons from strips of 3/16 " +/- wood? It seems as if it would be relatively easy to accomplish with the gap-filling properties of T-88, and it would produce a part without as much induced fiber stresses that come with steam bending.

Thanks,


BJC
 

Aerowerx

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Question driven from Aerowerx's J-1B build thread, which I am following with great interest:

Why not laminate the longerons from strips of 3/16 " +/- wood? It seems as if it would be relatively easy to accomplish with the gap-filling properties of T-88, and it would produce a part without as much induced fiber stresses that come with steam bending.

Thanks,


BJC
I have thought of that, and it is a possibility. But remember that when you rip a wider piece of wood into a thin one, you are throwing away material. How much is all that sawdust worth? I try to get as much as possible out of a board with a little waste as possible.

Lets say you want 3 laminations 7.0 mm thick, to make the 20 mm longeron. You will need to make 3 cuts on the table saw. My saw blade is about 1/8th inch wide, so in a 20 mm by 15 ft (yes, mixing units!) you would be throwing away about 53 cubic inches per longeron.

There is also the problem of maintaining alignment of all those pieces while clamping them in the fuselage jig.
 

mcrae0104

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...it would produce a part without as much induced fiber stresses that come with steam bending.
Does steam bending produce induced stresses? I thought the point of it is that you relax/plasticize the lignin so that there are no induced stresses once the lignin re-hardens.
 

rbrochey

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This is how we laminate guitar sides when not bending solid wood... laminated sides are just as good tonally as say solid maple... so basically you build a jig setup... there's a company out there I can't remember their name, who makes a bendable jig that put several together would be long enough for a longeron. I think laminated longerons is a great idea. I'm building a Russian seven string guitar and will be laminating the sides instead of heating up my bending iron. Laminated longerons would be every bit, if not more, strong as solid wood. My only question would be would they be heavier...

laminate sides.jpeg
 

BJC

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Does steam bending produce induced stresses? I thought the point of it is that you relax/plasticize the lignin so that there are no induced stresses once the lignin re-hardens.
My understand, which may well be incorrect, is that properly steamed wood can be compressed without significant loss of strength, but not stretched. Free-bending, as depicted in the thread, which seems to be the standard way of doing it, stretches some of the longeron wood. The strength degredation may be small enough not to be a problem. I've never designed a wooden structure that required steam bending.


BJC
 

rbrochey

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My understand, which may well be incorrect, is that properly steamed wood can be compressed without significant loss of strength, but not stretched. Free-bending, as depicted in the thread, which seems to be the standard way of doing it, stretches some of the longeron wood. The strength degredation may be small enough not to be a problem. I've never designed a wooden structure that required steam bending.


BJC
I steam bend hard woods at 400 degrees...what I discovered was if you spend too much time one the bend the strength in that area can be compromised... the fibers can actually separate. The trick is to know when to stop and then let the spring back relax.
 

Aerowerx

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I steam bend hard woods at 400 degrees...
Steam bending wood at 400 degrees would require a high-pressure enclosed steam system. The only way you can get steam that hot is to increase the pressure significantly over ambient. Not something I would want in my garage.

"Normal" low pressure steam can not be over 212 degrees---that's basic physics.
 

rbrochey

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Steam bending wood at 400 degrees would require a high-pressure enclosed steam system. The only way you can get steam that hot is to increase the pressure significantly over ambient. Not something I would want in my garage.


"Normal" low pressure steam can not be over 212 degrees---that's basic physics.
The wood is soaked in water or sprayed on... the steam is crated when the wood is laid on the iron... the steam surfaces through the wood which is about 2mm thick and relaxes the fibers... lots of steam.... lots... you move the wood continuously.. when all the water is gone you spritz the wood (lots of steam and wood smells) and that's how it's been donefor hundreds of years... I teach people to do this... come on by my shop...

350 degrees works best with walnut... 400 with mahogany

This is the iron I use

bend.jpeg
 

Aerowerx

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...wood which is about 2mm thick...
How will this work with thicker wood? Say 3/4 inch or so?

I would think there would be a big difference for the techniques for bending thin plys and thicker longerons. And I am talking about something 16 feet long, too.
 

Aerowerx

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Two different techniques for two different needs.
From what I have been reading, 1 hour of steaming for each inch of thickness. So 3/4 inch would take 45 minutes, and 2 mm would take less than 5 minutes. But this is for low pressure steam at 212 degrees.
 

rbrochey

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How will this work with thicker wood? Say 3/4 inch or so?

I would think there would be a big difference for the techniques for bending thin plys and thicker longerons. And I am talking about something 16 feet long, too.
I'm sure that's true... the bends can be very tight in the instrument world. :)
 

rbrochey

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A book I would highly recommend to the wood builders in here would be "Understanding Wood, A craftsman guide to wood technology" by R. Bruce Hoadley a really great resource. There's a section on Bending theory and Bending wood including ammonia plasticizing, green wood and steam bending. My wife picked it up for me several years ago, about $40.00 and worth every cent. :)


Just checked AMAZON has it for $27.16 BUY IT!!!
 
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don january

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On building my Taylor-m I came across a very good challenge on sheeting the sides of the Fuselage because it taper's in both directions. I did find a way that worked real good to hold shape but was very time consuming. It's amazing what a wet wash cloth will do and a heat gun.;)
 

fly2kads

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A book I would highly recommend to the wood builders in here would be "Understanding Wood, A craftsman guide to wood technology" by R. Bruce Hoadley a really great resource.
I'll second that recommendation!
 

Aerowerx

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...Why not laminate the longerons from strips...
Another answer to this question...

My bottom longeron has a compound curve. How would you laminate that? Out of a bunch of 1/4x1/4 strips?

When you consider that, steam bending looks better, doesn't it?
 
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