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Building Tips and technical articles. => Building techniques => Topic started by: James Mills on March 14, 2018, 10:23:57 PM
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I'm ready to cut out my flaps from quarter grain 3/8". I plan to use a scroll saw but was wondering if an Xacto knife would be better to prevent any warping.
Thanks,
James
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I'm ready to cut out my flaps from quarter grain 3/8". I plan to use a scroll saw but was wondering if an Xacto knife would be better to prevent any warping.
I would cut it with a scroll saw, a little oversize, then plane/sand to the final shape. That way, if it does happen to warp, you can still cut the edges to the final shape with most of the stress relieved.
The scrolls saw/jig saw seems to cause less warping, generally, than any other method.
Brett
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Cutting by any method relieves stresses [if present] and wood will move..
Not seeing how method of cut affects degree of warping ?
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I cut my sense of humor once and it warped pretty bad.
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Saws remove a kerf, a quantity of wood that is now sawdust. Saws tend to not push wood out of shape, but that doesn't mean the wood won't move.
Knives push through the wood without removing space for the blade. Some deformation always occurs.
Cutting oversize by any method and planing or sanding to fit should be just as good. With 3/8 wood sawing will also be safer as less chance of slipping.
Phil
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I cut my sense of humor once and it warped pretty bad.
LL~ LL~ LL~ LL~ LL~ LL~ LL~ LL~ LL~ LL~ Good one Perry!
Jerry
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That's a good deal of flap material at 3/8" thick?
Plans don't call for built up?
Save some weight.
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That's a good deal of flap material at 3/8" thick?
Plans don't call for built up?
Save some weight.
Oy Vey!
Brett
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Saws remove a kerf, a quantity of wood that is now sawdust. Saws tend to not push wood out of shape, but that doesn't mean the wood won't move.
... as much. But otherwise, that is the mechanism. Knives push the wood on either side. A jigsaw seems to work better than, say, a table saw, because the table saw also heats it up as it cuts.
Allan is right, if you cut it in any way, you change the stress, and it will usually change it's shape. But some methods definitely add new stress when you are cutting it, which makes it even more unpredictable. As and aside, not much you can do about it, but it seems to be a bigger effect in humid environments.
Brett
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That's a good deal of flap material at 3/8" thick?
Plans don't call for built up?
Save some weight.
I know I am going to get smacked down but I have to agree. At 3/8 and up you can build a fully sheeted structure that is considerably more warp resistant and more than stiff enough. Maybe it is all the years flying free flight and sailplanes.
Ken
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Brett is correct about the Saw, I have cut many 1000s or 10,000 pieces of Balsa, I can tell you it will warp more curl more, act up more with using a knife instead of a saw
Randy
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Thanks for all the reply's.
James
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I prefer a band saw, but whatever.
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Oy Vey!
Brett
LL~
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... A jigsaw seems to work better than, say, a table saw, because the table saw also heats it up as it cuts.
That’s why my laser cutter has sat idle for the last year. (No, that’s not the reason.)
I’d use a saw because if I tried to cut something that thick with a knife, I’d hurt myself.
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Oy Vey!
Brett
So the message implied here is that flap torsional stiffness is far more important than weight savings, Brett?
Flaps are close to the cg relatively also, compared to the tail surfaces. And they are longer, so the torsion from flight loads i would assume have more leverage.
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So the message implied here is that flap torsional stiffness is far more important than weight savings, Brett?
Flaps are close to the cg relatively also, compared to the tail surfaces. And they are longer, so the torsion from flight loads i would assume have more leverage.
Yes, we have people leaving the flaps untapered in thickness with square cross-sections to maintain as much stiffness as possible (Paul Walker) and we have people trying to put together built-up flaps from balsa to save weight (Aviaojet).
I think we should probably do it more like Paul than like Charles.
Brett
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Alrighty then!
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In some of my new laser cut kits we are using 2 pieces of light 3/16 , laminated together, to make the 3/8 instead of using a single 3/8 in piece, this makes for a very stiffer flap. I have a flat glass piece that keeps what ever I am gluing flat and straight while the glue cures, For items like this, i use a very thin layer of SLOW cure epoxy. I have not tried Gorilla type glues, but they may work well too
Randy