Balsa Wood Grain

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jinhusong
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Balsa Wood Grain

Post by jinhusong » April 7th, 2019, 12:18 pm

Hi,

This may be well known to expert, but I just found it now after using balsa wood for so many years.

The lines you see on the end grain of balsa wood is RAY not RING.

We ordered C-grain 1/4X1/8X48 balsa sticks for the compression member following Aia's Boomilever Guide. Before they arrived, I was wondering why. When you look at the end, c-grain, I assumed that stronger lines (ring) all parallel to the shorter edge of 1/4 X 1/8 rectangle. It should be bad, not good for boomilever.

I was happy to see the stronger lines are parallel to the longer edge after I received the sticks. Guessing they may have sent us the A-grain because our teacher told them there are for Boomilever. This is perfect. We got second place in NoCal State yesterday (weight 7.57g, holding 14.03 kg).

After search internet for a few hours, I finally found they are c-grain and for balsa wood, the lines you see are ray not ring.

Jinhu

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Re: Balsa Wood Grain

Post by sciencecat42 » April 10th, 2019, 7:53 pm

Sorry I'm a bit confused about your post. Did you end up using C grain or A grain? And how much does the grain actually matter? I tried making a design with 1/4x1/8 balsa sticks today and it barely held any sand before the whole compression structure began to bow upwards. I did put the 1/4" end vertically so I'm not sure what caused this.

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Re: Balsa Wood Grain

Post by MadCow2357 » April 10th, 2019, 8:44 pm

sciencecat42 wrote:Sorry I'm a bit confused about your post. Did you end up using C grain or A grain? And how much does the grain actually matter? I tried making a design with 1/4x1/8 balsa sticks today and it barely held any sand before the whole compression structure began to bow upwards. I did put the 1/4" end vertically so I'm not sure what caused this.
Did you use buckling members to decrease the unsupported length intervals?
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Re: Balsa Wood Grain

Post by sciencecat42 » April 10th, 2019, 9:34 pm

MadCow2357 wrote:
sciencecat42 wrote:Sorry I'm a bit confused about your post. Did you end up using C grain or A grain? And how much does the grain actually matter? I tried making a design with 1/4x1/8 balsa sticks today and it barely held any sand before the whole compression structure began to bow upwards. I did put the 1/4" end vertically so I'm not sure what caused this.
Did you use buckling members to decrease the unsupported length intervals?
What do you mean by buckling members? If you mean bracing, I did ladders on the top and bottom of the 1/4x1/8 members and then added zigzags on each side so overall they formed X's.

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Re: Balsa Wood Grain

Post by jinhusong » April 10th, 2019, 10:07 pm

We added 8-10 X bracing on top and bottom of the 2 compression members.

The bracing is 1/16X1/32, cutting from sheet 1/32 X 3 X 36, 8 gram.

We use C-grain.

You will also need some vertical bracing from the compression member to tension member. Without it, the compression member will bend around 3 kg.

For us, we add 3 or 4 vertical bracings. It hold 14 kg.

Our boomilever: 7.57g holding 14kg.

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Re: Balsa Wood Grain

Post by MadCow2357 » April 11th, 2019, 5:28 am

sciencecat42 wrote:
MadCow2357 wrote:
sciencecat42 wrote:Sorry I'm a bit confused about your post. Did you end up using C grain or A grain? And how much does the grain actually matter? I tried making a design with 1/4x1/8 balsa sticks today and it barely held any sand before the whole compression structure began to bow upwards. I did put the 1/4" end vertically so I'm not sure what caused this.
Did you use buckling members to decrease the unsupported length intervals?
What do you mean by buckling members? If you mean bracing, I did ladders on the top and bottom of the 1/4x1/8 members and then added zigzags on each side so overall they formed X's.
Vertical members? Not sure how else to explain it...
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Re: Balsa Wood Grain

Post by AlexDeKuang » April 11th, 2019, 7:34 am

sciencecat42 wrote:
MadCow2357 wrote:
sciencecat42 wrote:Sorry I'm a bit confused about your post. Did you end up using C grain or A grain? And how much does the grain actually matter? I tried making a design with 1/4x1/8 balsa sticks today and it barely held any sand before the whole compression structure began to bow upwards. I did put the 1/4" end vertically so I'm not sure what caused this.
Did you use buckling members to decrease the unsupported length intervals?
What do you mean by buckling members? If you mean bracing, I did ladders on the top and bottom of the 1/4x1/8 members and then added zigzags on each side so overall they formed X's.
Pretty sure it's bracing between the tension members and compression members.

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Re: Balsa Wood Grain

Post by jinhusong » April 11th, 2019, 2:29 pm

It is the vertical bending that will kill the boomilever and the bracing between compression and tension are better pulling than pushing.

When you range the stick, you will orient it so that it will bend down not up. To enforce it, the compression member ends, which touch the wall, have some small angle, not exactly normal to the sticks. These will force the stick to bend downward.

Because we more worry about vertical bending, the C-grain is better for compression members.

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