Carbon strip responsible for convex bases ?

[ben_mtl]

Hi there !

Yesterday I went to the ski shop to have my bases ground, just before that I inspected the bases and noticed they're slightly convex, hopefully the sanding will take care of it.. but still they're not flat !.. it's always something :p !
On the few last pairs I made I added a 1" (sometimes 1.5") , 9Oz carbon strip top and bottom in the center to add some stiffness and I just realized it matches the beginning of getting slightly convex bases...
Could this be one of my problem ? When I inspect the bases I can clearly see the weave of the fabric only on a 1" strip running in the middle of the ski.
I press @40PSI and don't feel confident going ways higher but I dont think it will eliminate the problem.

Should I rabbet the cores to account for the carbon strip ? like I do for edges ?
What weight of carbon tape do you guys use (if you use any...) ?

I was thinking if i get a lower weight carbon (4.1Oz is available) It would be an improvement. And as I would need twice the width I could split it in (2) 1" strips top and bottom, spacing the 2 strips so all the carbon is not in the middle...
Or maybe switch to (15Oz or so) biax fiberglass + a full layer of 4.1Oz uni carbon... but it will get quite more expensive and I'll have to tweak my core thickness to achieve the same flex I have right now... but I'll shave some weight too....

Well if someone has a solution with only the 1" carbon strip, please let me know.

Maybe it also has nothing to do with the carbon strip...

Thanks !

[twizzstyle]

I, too, was getting convex bases, and have been using a strip of cf in the middle. For the last two pairs I did, I didn't do the edge rabbit at all. Now granted, I changed a few other things during pressing (lower pressure, and lower heat), but my bases came out of the press nearly perfectly flat.

[ben_mtl]

great idea ! I thought about another groove in the core but I didn't even thought about not doing the edge rabbet (or at least less pronounced)

[doughboyshredder]

I would bet that the CF is definitely causing it.

Interesting that not doing a rabbet took care of it for twizz.

[ben_mtl]

I just took some measurements and the edge teeth are something like .50mm thick. The CF, in 9 Oz weight is about 0.36mm thick if I trust the data sheet.
Not doing the rabbet should definitively help ! but then the fiberglass between the edges and the CF would not be as "compressed" as usual...

[twizzstyle]

Yep, absolutely true. I remember seeing one snowboard manufacturer on here that was CNC'ing channels in their cores anywhere they had added strips of CF or kevlar, for just the reason you say.

When I build my CNC router, I'll probably try the channel that you're talking about, but when I'm still doing things by hand I just don't think the lack of accuracy is worth it. Also you've got to somehow ensure that the CF stays exactly in the channel, etc.

I also don't think that this was the only thing causing my convexity - as you said, the CF is only so thick (I don't remember the thickness, or weight, of my CF but it was on the same order as yours), but my bases were horribly convex, more than I could grind.