Torsion box

COsurfer · Post by **COsurfer** » Sun Dec 12, 2010 2:02 pm

On my last board I created a torsion box with carbon fiber. I slit my core approx. 1.5" off the edge from one binding to the other. I threaded triax carbon fiber through the slits so I have a complete wrap. My reasoning for this is to provide better energy transfer from the bindings to the core. I have only tested the board once and it rode well. I wanted to get feedback from the forum on the idea in general and do you believe I weakened the core by cutting through it? I did run full triax fiberglass along the top and bottom and made sure the epoxy filled any gaps in the core. Here are some pics:

vinman · Post by **vinman** » Sun Dec 12, 2010 2:32 pm

I like your idea. How did it work?

I had an idea about taking some biax 0/90 or 45/45 glass and wrapping the edges of the core with it before laminating the rest of the core as usual. My though was this C channel would enhance stiffness as the fibers would wrap the core in 2 dimensions.

COsurfer · Post by **COsurfer** » Sun Dec 12, 2010 3:26 pm

It rode great! The problem is I did a lot of things to the board from changing to a rocker/camber/rocker, adding uni carbon up the edges and then doing this torsion box idea. I dont know if the board rode well because of all of the above or a combo of the items. I may need to do a board without the torsion box and just lay CF in the same areas to see if it makes any difference. My biggest concern is that I weakened the core but I think with all of the epoxy and running fiberglass over it I should be fine. I guess only riding the board a lot will tell.

I like your idea as well but won't you end up cutting into the fabric when you finish the edges?

vinman · Post by **vinman** » Sun Dec 12, 2010 4:49 pm

no the glass C cap would be between the core and sidewall. Not sure how well sidewall would bond to that but wood side walls might work out ok. This idea may very well be crap.

doughboyshredder · Post by **doughboyshredder** » Sun Dec 12, 2010 5:06 pm

you're really doing some cool stuff. I like it.

The only concern would be that the epoxy may break down in the small gap created by the slits in the core, but I doubt that would be an issue.

twizzstyle · Post by **twizzstyle** » Tue Dec 14, 2010 7:17 am

I'm loving the outside-the-box thinking from a lot of people these days, experimenting is the best part of DIY building I think.

What you've made isn't really a torsion box if it's not wrapping all the way around. I'm not sure if the vertical sides of the CF are really doing much.

Have you thought about getting some CF sleeving material? You could sleeve the entire core, or if you wanted it "inside" the core like this one - you could made the core minus ~1" of the outside, sleeve it in CF, then add on some sidewalls (or more core wood). It would have to be profiled first of course, but that's an idea.

You shouldn't have to worry about weakening the core with this, unless you slit the entire length, and even then unless the gap is big, the epoxy won't break down. If it's big, like doughboy said, it will break down as the board is flexed.

COsurfer · Post by **COsurfer** » Tue Dec 14, 2010 7:42 am

Hey Twizz, Thanks for the input! I am wrapping the entire board. The CF fabric overlaps on the other side at the bindings. My concern with incorporating the CF fabric in the core layup is I dont think the CF will wet out if its sandwiched between two pieces of wood. My design allows for a full box shape and the vert sides will be coated in epoxy. Here is a pic I posted on my website:

twizzstyle · Post by **twizzstyle** » Tue Dec 14, 2010 9:52 am

Ah ok, I get it now. I thought your picture above on the right had the CF in it and it only stuck barely through the slits without wrapping. Nice work!

Richuk · Post by **Richuk** » Tue Dec 14, 2010 2:46 pm

Co - perhaps you could leave sections of relevant stringers without glue, so you could pry them open when treading through the CF. Drill a hole at each end of the section without the glue, say 2mm and it would be easier to open. Maybe this would work? I would certainly reduce the amount of epoxy used to fill the gap.

Great work btw!!!

COsurfer · Post by **COsurfer** » Tue Dec 14, 2010 3:20 pm

Good idea richuk!

gketcham · Post by **gketcham** » Thu Jan 06, 2011 9:55 pm

Hey COsurfer, I also live in denver, and can't find a carbon supplier, who are you using? Also I think that the vertical pieces of carbon could be eliminated. But if it works, why screw with a good product

Jekul · Post by **Jekul** » Fri Jan 07, 2011 8:23 am

Gketcham-I just ordered some UNI CF from fiberglass supply. I ordered a 50" wide roll (2cents/in^2 vs. 6cents/in^2 for the 'tape'). I'm planning to cut it to width with a saw (band or table). If you only need a small amount I could probably sell some (I also live near Denver), but it's easiest just to order what you'll be using.

SHIF · Post by **SHIF** » Fri Jan 07, 2011 9:47 am

I found the best on-line source for uni-carbon fiber materials is:

http://www.solarcomposites.com/

FiberglassSupply is also a reliable vendor, I use their 19 oz. knitted triaxial glass.
Hey Jekul, you better check that recent order, I don't think they offer uni carbon wider than 24 inches.

-S

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