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Scarf joint question

Posted: 23 May 2019, 08:27
by harry curzon
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?

Re: Scarf joint question

Posted: 23 May 2019, 09:07
by john greenfield
Harry

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

AEB

Re: Scarf joint question

Posted: 23 May 2019, 09:16
by harry curzon
Thanks John,
the spars are 10mm wide x 3 mm thick, so the joint should be 15 x 3?

Re: Scarf joint question

Posted: 23 May 2019, 10:28
by RobbieB
.................and Harry, make sure they are perfect. Check both down their length and across the width with your straight edge and clamp really tight.

Re: Scarf joint question

Posted: 23 May 2019, 15:54
by John Vella
Harry , what glue are you using on such a critical joint ?

Re: Scarf joint question

Posted: 24 May 2019, 08:42
by john greenfield
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.

AEB

Re: Scarf joint question

Posted: 24 May 2019, 12:37
by harry curzon
Thanks John

Re: Scarf joint question

Posted: 25 May 2019, 10:35
by VinceC
This information from the old site

Re: Scarf joint question

Posted: 26 May 2019, 09:19
by John Vella
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.

Re: Scarf joint question

Posted: 26 May 2019, 11:28
by chris williams
What about the scaling factor...? Surely, a 1/4 scale spar would only need 1/4 of those dimensions? 8-) :lol: :lol: