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moTthediesel
11-21-2006, 11:12 AM
Just thinking: (U-oh!)
As a way of eliminating a time consuming step for planking larger boats (not canoes or kayaks) - assuming strip planking with crown and cove faying surfaces, molded 5/8" to 3/4" thick.
Rather than taking the time to scarf and glue up hull length strips prior to planking, how about finger jointing them together in-situ? Of course, the joints would best be made in areas of the hull with not too much shape, in order to keep the planking fair.
Lots of surface area in a finger joint, so strong, super quick to cut, and largely self-aligning.
Yes? No? Maybe?
moT

"Out! damn knot!" (apologies - W.S.)

Thorne
11-21-2006, 11:28 AM
This is sometimes done with ply, never heard of it used for solid wood planks. Might depend on the grain orientation...

Bob Smalser
11-21-2006, 11:51 AM
There's generally a minimum thickness of 5/8" for these joints, which also weren't engineered to bend except as part of large laminations of 2X stock. Plus the thinner the stock, the fewer fingers, which means a higher percentage of end-grain gluing and attendant less strength. I doubt a 5/8" finger joint when bent around a mold is anywhere near as strong as a traditional long scarf. But in a glued stripper like in a bent lammed beam, they may be strong enough.

But long scarfs bend fairly. Short finger joints may not. Try a few before committing yourself and let us know.

George Roberts
11-21-2006, 03:14 PM
butt joints.

2-3 days to do a hull that size using epoxy as glue.

paladin
11-21-2006, 03:19 PM
T'ain't nuthin' gonna replace the long scarph......if you don't have the time to do it right, when are ya gonna have time to do it again...

gert
11-21-2006, 03:31 PM
I was wondering this myself for 1/2" plywood, using a finger joint on the edges of a "face" scarf (terminology?), but the router bits arn't realy suitable for 1/2" material. I agree it wouldn't work on a joint streight across the plank but what is the joint ran diagonaly, say 18" long on a 4" wide plank (capiche?):confused:

Todd Bradshaw
11-21-2006, 04:11 PM
Baltek Duracore strips (balsa core sandwiched between layers of veneer) were sold in short lengths and finger-jointed on their ends. Construction was generally a fairly hefty fiberglass sandwich using the strips as a core, but they were used on a fair number of high-performance miltihulls.

Dan McCosh
11-21-2006, 04:22 PM
I used finger joints on a mahogany toerail, which worked fine. I would think they would work well strip planking, particularly if well staggered and in areas where the run is relatively flat.

Ken Hutchins
11-21-2006, 05:18 PM
I've used quite a number of finger joints cut on an angle, the plank bends in nice and fair, is as strong or stronger than a solid piece of wood, does not have to be put on a flat area, it will bend and twist just like the rest of the plank.
I put a finger joint made this way through an major torture test , bent the blank repeatedly back a forth both directions to more than twice the amount of bend the plank would get on the boat without a failure.
The joint in the photo is mid way between 2 double sawn frames that are 3 feet apart, the plank is nice and fair.
http://www.imagestation.com/picture/sraid81/p0a86206838a1833cc24385a518ebe544/fafd4aba.jpg

paladin
11-21-2006, 09:35 PM
yes, Todd...but the balsa is being used as a core, not the prime structural member....and it was never intended to be....
We used that technique in Thailand before it was "engineered" by Baltek, by a few years. Originally it was laced on a frame and thin veneers laminated over it, then vaccuum bagged inside.....eventually we went to Klegecell for the same purpose.

moTthediesel
11-21-2006, 10:57 PM
I've used quite a number of finger joints cut on an angle, the plank bends in nice and fair, is as strong or stronger than a solid piece of wood, does not have to be put on a flat area, it will bend and twist just like the rest of the plank.

Ken --
A finger/scarf hybred! That's a wrinkle I hadn't thought of -- BRILLIANT!

moT

Todd Bradshaw
11-21-2006, 11:12 PM
"yes, Todd...but the balsa is being used as a core, not the prime structural member"

......uhhhh, I think that's what I said......

paladin
11-22-2006, 06:40 AM
sorry....sorta misread it...had just taken the meds....

Boatmik
11-22-2006, 08:41 PM
Just thinking: (U-oh!)

Rather than taking the time to scarf and glue up hull length strips prior to planking, how about finger jointing them together in-situ? Of course, the joints would best be made in areas of the hull with not too much shape, in order to keep the planking fair.

"Out! damn knot!" (apologies - W.S.)

If the hull is being glassed inside and out (or cold moulded veneer on the outside and your timber is reasonable length so there are not too many joins it is quite safe just to butt the cedar strips.

Some of the boats I've built are now getting on and there have been no problems at all but I did take care not to get clusters of butts in the same area.

I think the finger jointing is a good strategy to make sure the planking runs fair at the joins in the plank. Using butts I sometimes had to clamp or screw a bit of timber temporarily across the join to hold things in line.

You might have problems with the structural strength of the fingerjointing in areas where the strip is going through a big bend or twist, but elswhere it will work well.

I wouldn't bother prejoining the strips to length it just adds another process. I'd do it on the boat as it is planked up. After all I've been doing the butt joins that way for years.

Michael Storer