Scarf joint question

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harry curzon
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Scarf joint question

Post by harry curzon » 23 May 2019, 08:27

I am about to make the wing spars for the Charlesworth K-18, 4 metre. I need to scarf join the spruce spars, what is the recommended length of the joint? 5 x width? More?

john greenfield
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Re: Scarf joint question

Post by john greenfield » 23 May 2019, 09:07

Harry

A structural scarf joint should be 15 x the thickness of the pieces being joined.

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harry curzon
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Re: Scarf joint question

Post by harry curzon » 23 May 2019, 09:16

Thanks John,
the spars are 10mm wide x 3 mm thick, so the joint should be 15 x 3?

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RobbieB
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Re: Scarf joint question

Post by RobbieB » 23 May 2019, 10:28

.................and Harry, make sure they are perfect. Check both down their length and across the width with your straight edge and clamp really tight.

John Vella
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Re: Scarf joint question

Post by John Vella » 23 May 2019, 15:54

Harry , what glue are you using on such a critical joint ?

john greenfield
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Re: Scarf joint question

Post by john greenfield » 24 May 2019, 08:42

harry curzon wrote:
23 May 2019, 09:16
Thanks John,
the spars are 10mm wide x 3 mm thick, so the joint should be 15 x 3?
Yes Harry. 45mm.

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harry curzon
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Re: Scarf joint question

Post by harry curzon » 24 May 2019, 12:37

Thanks John

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VinceC
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Re: Scarf joint question

Post by VinceC » 25 May 2019, 10:35

This information from the old site
Attachments
Scarf Joints.png

John Vella
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Re: Scarf joint question

Post by John Vella » 26 May 2019, 09:19

Vince, the splice angle recommended from the table is 15 to 1 for ply and 20 to 1 for wood. This is what we were working on with K13s and K8s. What I can't understand is the diagram below ? Surely the joint is stronger in bending load than shear load ? Regards John.

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chris williams
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Re: Scarf joint question

Post by chris williams » 26 May 2019, 11:28

What about the scaling factor...? Surely, a 1/4 scale spar would only need 1/4 of those dimensions? 8-) :lol: :lol:

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