paipo/kitesurfboard build - wood springback

bwd · June 29, 2013, 4:47am

I’m bulding a quasi-paipo-alaia thing, basically a short, modified
alaia outline with normal nose rocker and just touch of tail rocker.

The use will be as a kiteboard, occasional wakesurfer and paipo.

The blank is from ~7/16 western red cedar strips, aim is to bend to rocker and apply deck glass to hold the rocker.

Have
used this to rocker kiteboards, with a ton of springback, due to
shorter length of kiteboards and epoxy rails that somewhat fight the
rocker.

Springback after cure (RR cured on table several days) has been 60-75%.

For this one there are no epoxy rails to worry about, which wi!ll help, but am trying to figure out springback in advance.

Anybody with parallel experience care to share a datapoint?

I
have some strips to use for testing, and I will definitely test first,
but only a few, so I’m trying to figure out where to start, with the
table set up for 2.5X desired rocker, 2X, ???

Plan on 3 layers 6oz on deck, fairly standard for this type of deck…

bwd · July 4, 2013, 4:33pm

So, testing core strips to see how it goes…

7/16" thick, tapering at ends, bent to a 2X rocker jig, laminated on top onlywith 3x6oz eglass in Resin Research CE.

Lammed last night and sitting in sun under black plastic to post for a few hours today, plan to take off jig and check springback.

Will then tune taper to try to fit rocker, repeat until out of extra strips and go for it…

Question, anyboady know how long it should stay on jig to reduce “creep” springback?

Have had issues with this technique in past, giving ~30% springback at first, but after a week or so it becomes 50% +…

Mr Loehr?

Compsand/wood geniuses?

Will give results, regardless…

trent · July 4, 2013, 6:32pm

If you laminate 3 or more thin layers on a rocker table, the spring back will be close to zero.

I believe this would be the approach that most " wood geniuses" would take. You will not have to make multiple test laminates to guess the spring back. You will not have to worry about variations in the wood confounding your estimates.

Also since your are not relying on the glass to force the shape into the wood, you probably use a little less glass.

Trent

bwd · July 4, 2013, 9:44pm

True, but wood is much lighter than glue, and using vg strips all cut

from the same plank takes care of the variability pretty well.

cutting half inch strips the waste is about 18%, if I did 3 layers it would be almost 60%.

so I’m trying to figure out a recipe…

btw off the jig it lost 40% right away, as usual.

will leave it and check in a few days to see where it settles…

Have found in the past even 2 layers does make it easier, but I’m going for one.

thanks for your advice though!

dlock · July 4, 2013, 10:27pm

If you are planning 3 layers of 6oz. lay up a test board with a layer of cloth over and under. You’ll get your rocker.

bwd · July 10, 2013, 5:40am

Thanks dlock and trent

Results:

pretty good on nose and tail rocker, BUT

the 2’ from nose rocker is more than a hair too much,

luckily have more test planks.

Next one will go for keeping nose and tail in the right neighborhood while making sure the 2’ rocker does not create a nautical snowplow.

Or I will try to “relax” it over another day or so and then glass the bottom…

bwd · August 9, 2013, 2:51pm

still slowly coming along,

back in the lab, screwed to the slab…

kiter · August 9, 2013, 10:56pm

hello ,

I think we “met” in kiteforum .com ,my board started with 2 cm thick pawlonia planks , I taperd the last 30 cm down to

8 mm and then steam bent the strips that were about 6 cm wide,there was some spring beck but the curve that stayed was more then enough

I first soake the wood for 48 hours ,just the last half meter, and then steamed it for about 1/2 an hour each strip.

forgive me for the size of the photos I all most gave up ,dont get the system here yet

BarrySnyder · August 10, 2013, 1:45am

I would try a rocker table or a form of some sort.

Use an adjustable rocker bar.

Make some rocker templates.

An adjustable rocker form would be more versatile.

Make both a deck and bottom form.

Glue then press two forms together.

Much like how skateboard decks are made.

bwd · August 11, 2013, 12:43am

Thanks for the info kiter. 2cm is some serious thickness… I have been thinking of starting to use paulownia myself. I have some practice with cedar but it is not always as easy to make it behave, and it doesn’t respond to steam well.

I am most curious about the channels…/

bwd · August 15, 2013, 3:11am

bwd · August 23, 2013, 2:52am

Done, rocker came out pretty well, just needing wax and water…