Gents: some time back someone imported a bunch of PU blanks from China. They turned out to be mostly crap and he sold 'em off for $15 for a nine footer, $10 for shorties. I went through quite a stack and picked up three, now have one left.
However, the plug these long blanks were molded from has very little rocker. I'm thinking to make about a 7-4 double wing swallow, but will need to add rocker.
I can think of several ways this might happen. One, remove the existing 1/4" thick stringer and glue in a new one with more rocker. Will it hold? I'd do this at the rough shaped stage, so the foam wouldn't still be full thickness.
Two, stringerless with some sort of rocker table during lamination. Guess I'd have to construct the table (I kin do that) and borrow a vacuum pump, but the neighbor has an auto a/c vacuum pump that will pull much more than I'd ever need. Concerned about the amount of effort, though, and potential springback.
Three, laying some sort of band with weights over the deck immediately after wetting out the lam. Springback again an issue, and surely the band would leave some sort of marks.
Four.... well it's up to you. Suggestions? (Yeah for $15 I can stuff it, but I kinda hate to waste it. I've done a good many reshapes in my day, and I'm not over that yet)
The problem with first glassing the blank and when wet bending the rocker is that the fibres on the deck will be pushed together and the fibres won’t be taut anymore, or even worse bubbles will appear.
If you have to bend in a lot of rocker, try to use a rocker table and multiple (3) stringers.
Remember to bend the rocker to the deck profile, this gives you denser foam under the feet.
Same as Hans and Ambrose, but do not rough shape BEFORE glueing. If your new rocker is not perfectly smooth, you’ll need all the thickness to plane it down to a natural curve.
I concur, remove stringer, by cutting carefully along side of old stringer as others have stated and run over jointer if you can, and re-glue with your favorite adhesive. While the blank is stringer-less it will be pliant and you can trace a new rocker template by sitting on the rail and bending the nose and tail up or down and tracing with a pencil. go through the stacks of lumber at your local yard, and plane your choice to desired thickness. I have stringered countless blanks in this manner and have turned long board blanks into gun blanks when not readily available. You will be surprised on how much you can add or subtract on rockers. After that do not buy any more china POS blanks.
Okay thanks gents. The process will somewhat depend on the blank flex after I rough shape and then remove the present stringer. I expect to make a short hotwire on a deep U shape to accomplish this, seems more likely to produce a good result, than trying to keep the saw blade just "so". Yes I have a good respirator and will perform this little bit of stuff in a nice tradewind. My neighbors are pretty nice, and with luck they won't be home when this happens ;)
I'm attracted to the triple stringer idea, they could be made quite thin and still work IF I can bed things right for the glue-up.
As for POS blanks from anywhere, these are the perfect thing to try out new ideas. If no workie, slash 'em and stuff in the trash can, little loss, and the education is a big gain. Remember it is said "Pay attention to the mistakes of others. You won't have time to make them all yourself"
I have an old wind surfer blank that I am working on. Great rocker in the nose but no rocker in the tail. Since this was a wind board in its ealier life the blank is plenty thick about 4(+) inches. I am going to attempt to plane in a rocker in the tail. I hope it works.
I expect to make a short hotwire on a deep U shape to accomplish this, seems more likely to produce a good result, than trying to keep the saw blade just "so". Yes I have a good respirator and will perform this little bit of stuff in a nice tradewind.
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You're way better off using a saw held vertically than trying to drag a hotwire through PU foam. It's not just toxic, it's very likely to catch fire. Try a sample first before you commit.
Hi Charlie, I agree about those blanks. I scored a bunch myself. Rich was very up front about the quality, and told me to look carefully before buying. He was put of the longboards, but he was selling 3 PU short boards for $25 when I saw him. My friend got a longboard and when he started shaping it, he had issues, so Rich just gave him another one.
I learned a lot about PU foam from those blanks, and I still have 2 of those boards. I gave one board away at a fund raising event last year.
Hey I think Cliffs and Right Hand will be epic on Thursday. It was pretty good on Sunday.
As noted by Sharkcountry, the seller was indeed upfront about quality. I have no idea what wood is used in the stringer, but some of them were really crooked. I picked three blanks that seemed straight. The two I've already shaped didn't give my any particular problem with the stringer,they cut evenly with planer, surform and finger plane.
But I do have the idea the wood is something heavy, and that's part of my deal here, to reduce weight. I like durable glassing too.
I've done a very little hotwiring through some lightweight EPS rubbish can scraps. Though the wire would smoke a bit, it didn't get red; I also hotwired some PU foam scraps just to see, and there seemed no evidence of impending flame. I'll certainly be doing the stringer-ectomy outside so as to minimize respiratory issues, and if the whole thing goes up in flames, I've lost what - $15? I can't stress too much about that.