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Author Topic: Flaps  (Read 3476 times)

Offline James Mills

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Flaps
« on: March 14, 2018, 10:23:57 PM »
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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Offline Brett Buck

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Re: Flaps
« Reply #1 on: March 14, 2018, 11:11:48 PM »
Quote from: James Mills on March 14, 2018, 10:23:57 PM
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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Offline Allan Perret

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Re: Flaps
« Reply #2 on: March 15, 2018, 05:26:15 AM »
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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Offline Perry Rose

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Re: Flaps
« Reply #3 on: March 15, 2018, 06:40:03 AM »
I cut my sense of humor once and it warped pretty bad.
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Offline Phil Krankowski

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Re: Flaps
« Reply #4 on: March 15, 2018, 07:04:48 AM »
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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Offline Gerald Arana

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Re: Flaps
« Reply #5 on: March 15, 2018, 09:21:39 AM »
Quote from: Perry Rose on March 15, 2018, 06:40:03 AM
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!


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Offline Avaiojet

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Re: Flaps
« Reply #6 on: March 15, 2018, 10:08:36 AM »
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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Offline Brett Buck

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Re: Flaps
« Reply #7 on: March 15, 2018, 11:17:18 AM »
Quote from: Avaiojet on March 15, 2018, 10:08:36 AM
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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Offline Brett Buck

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Re: Flaps
« Reply #8 on: March 15, 2018, 11:23:19 AM »
Quote from: Phil Krankowski on March 15, 2018, 07:04:48 AM
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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Online Ken Culbertson

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Re: Flaps
« Reply #9 on: March 15, 2018, 12:57:19 PM »
Quote from: Avaiojet on March 15, 2018, 10:08:36 AM
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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Offline RandySmith

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Re: Flaps
« Reply #10 on: March 15, 2018, 02:40:30 PM »
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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Offline James Mills

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Re: Flaps
« Reply #11 on: March 15, 2018, 05:54:54 PM »
Thanks for all the reply's.

James
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Offline Randy Powell

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Re: Flaps
« Reply #12 on: March 22, 2018, 08:54:27 PM »
I prefer a band saw, but whatever.
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Offline Chris Fretz

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Re: Flaps
« Reply #13 on: March 23, 2018, 03:35:31 AM »
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Offline Howard Rush

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Re: Flaps
« Reply #14 on: March 23, 2018, 02:13:27 PM »
Quote from: Brett Buck on March 15, 2018, 11:23:19 AM
  ... 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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Offline Target

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Re: Flaps
« Reply #15 on: March 23, 2018, 03:43:00 PM »
Quote from: Brett Buck on March 15, 2018, 11:17:18 AM
   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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Offline Brett Buck

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Re: Flaps
« Reply #16 on: March 23, 2018, 05:24:38 PM »
Quote from: Target on March 23, 2018, 03:43:00 PM
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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Offline Target

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Re: Flaps
« Reply #17 on: March 24, 2018, 01:46:35 AM »
Alrighty then!
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Chris
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Offline RandySmith

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Re: Flaps
« Reply #18 on: March 24, 2018, 01:59:38 PM »
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
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