scarf strength?

[JoeT]

For my 21' hollow box mast I have 12 footers of Sitka spruce to work with. Scarfing 2 together for the length will leave all 4 sides with the joint around the same area. Should I cut 2 of the sides into 3 pieces to stagger the joints or the 4 joints glued with epoxy near one another will be strong enough?
Thank you.

[TimH]

Would probably be strong enough without staggering, but I personaly would stagger. Just to be safe. :D

[mmd]

Stagger the joints.

[Bob Smalser]

In any construction, it is good practice to plan for every glue joint to fail, allowing a graceful recovery, if not full function.

Dovetails, M/T's, staggered scarfs...all the same principle...plus staggering those scarfs makes sure you have an even modulus of bending.

[NormMessinger]

Rats. If mmd hadn't answered I would have said what Tim said. Now, just for discussion, what do we mean by stagger? I've always put severa inches and much more if possible between the beginning of one scarf and the end of another whether on hollow mast staves or hull strips. However, if one had to choose between two scarfs in a stave to avoid adjacent scarfs and slanting adjacent scarf opposite each other, what would one chose?

[George Roberts]

JoeT ---

If this was a clothespin scarf or a single board with a scarf in the center, there would be no discussion - there scarfed areas would be in the same place.

Since most people agree that a 12:1 scarf is full strength and 8:1 scarf is (I sure wish I had my scarfing reference with me but ...), there is no reason to stagger the scarfs.

If you have engineered the mast based on the loading, perhaps you might have some reason to stagger the scarfs, but you did not engineer the mast.

Now it might look nicer with the scarfs staggered but it does not matter.

[whb]

Just a thought for the forum to consider.

Given a 21' total length wouldn't simply alternating the end at which the full 12' piece is at provide an adequate stagger.

It would be close to 3' even taking into account the scarf.

Howard

[TimH]

I would definately stagger the joints.Its the proper way to go. Even though I have seen tests where they have broken scarf joints glued with WEST and the wood will break near the joint, but I never saw the joint itself break.

[ 09-17-2003, 12:24 PM: Message edited by: TimH ]

[Venchka]

Originally posted by whb:
Just a thought for the forum to consider.

Given a 21' total length wouldn't simply alternating the end at which the full 12' piece is at provide an adequate stagger.

It would be close to 3' even taking into account the scarf.

HowardThat is what I was thinking also. Join the 12' pieces full length. Stagger the joints during assembly.

I wish this Forum allowed drawing a picture.

------------------/---------------
-------------/---------------- (both ends like this)

Assemble so that the cut offs leave you with the 21' you need in the middle. Assuming 12" scarphs and the ends offset 18" leaves you with 21'-6" of spar stock and 6" of wood between the glue lines of the scarphs (sp?). Or so says the picture on my computer.

It's amazing what you can do on a slow day at work. I trimed off the ends so it would fit on the screen.

http://www.imagestation.com/picture/sraid79/p9a830fd666f1ce85e57fee9e4e380b5d/fb103a46.jpg

[ 09-17-2003, 03:02 PM: Message edited by: Venchka ]

[Dave Williams]

Stagger the joints! Why not?

[Venchka]

Originally posted by Dave Williams:
Stagger the joints! Why not?Agreed! Fortunately there is enough length so that extra cuts and extra scarfs aren't needed.

[JoeT]

Ok thanks. It's a 12:1 scarf (9" for 3/4 thickness).
I was thinking like Norm, "How much stagger is stagger?"Flipping the boards over end to end offsets 2 sides but puts all the joints within 3' of each other. Is that acceptable?

[Venchka]

Originally posted by JoeT:
...puts all the joints within 3' of each other. Is that acceptable?Perfectly acceptable.

[Mrleft8]

I don't care how strong my scarfs are, as long as they keep my neck warm while I stagger my joints home... :D