Problem solving help

vinman · Post by **vinman** » Fri Aug 10, 2012 2:30 pm

So I have a problem I need to solve. One sidewall have somehow come out to thin., measuring 10.8mm at the waist of the core. I was shooting for more like 12 mm. But it is only 1 out of 4 sidewalls that is too thin. This pair of skis was meant to be on the stiff side for a powerful skier. A 10.8mm core will just not cut it. Rebuilding the core is not an option at this point.

Do I....
1. Add some VDS and glass to the one sidewall during lay up to just sort of fill the area that is too thin?

2. Go and head and profile the cores to 10.8mm and beef the layup up with extra carbon and basalt fiber and maybe an extra mat of glass under the bindings?

3. Some other idea one of you have?

I may have answered my own question but I want to hear what everyone else thinks?

Thanks

vinman · Post by **vinman** » Fri Aug 10, 2012 3:00 pm

After it thinking about this more here is my idea.

Using 22oz glass.

1. Profile the core down to 2.3 in the tip using the planer and jig.

2. Profile the waist to max possible thickness without the sled.

3 add an extra glass mat about 6-8 inches longer than the flat spot created by the second step of profiling creates.

3a. Should I just add a full extra layer of 19 oz glass on the top or bottom?

4. Use 6 stings of carbon tow on each side of the core to beef the longitudinal stiffness

4a. Should I add more carbon and forget the extra glass. 8-10 strings per side?

5. Use 2-4 strings of basalt fiber on each side running on an angle between the contact points to beef up the torsional stiffness.

This should hopefully restore some of the stiffness lost by the thinner core.

What do you guys think?

MontuckyMadman · Post by **MontuckyMadman** » Fri Aug 10, 2012 6:51 pm

The prob with extra composite is extra weight. If you are fine with that, then hey do it. What you are really loosing will be the underfoot or longitudinal flex at those areas. The torsional will be minimally effected in this area cause the core is so thick there.
Extra carbon has a tendency to dramatically change the camber, at least as a full layer. Extra tows will be minimal stiffness increase i thnk.
How bout a section of 1/16" veneer either maple or ash underfoot or two maybe?
Perhaps you could diamond the shape of the veneer to feather out the transition.
I am making a ski from 1/16" veneers kinda skateboard style so I have no idea how the transitions will pan out.
If you can wait a week or 2 I will tell you.

vinman · Post by **vinman** » Fri Aug 10, 2012 7:02 pm

I like the diamond idea with the extra glass underfoot to make a better transition in the flex. I think I'll go with that and some extra carbon longitudinally and the basalt on the angles. The tow definitely has some effect on stiffness. I used his in my last layup with 19 oz glass and it felt equal to or stiffer than a similar core with 22oz glass.

I'm not too concerned with weight. The core will be lighter because it is thinner and it is an all poplar core with only a mounting zone of maple. I was shooting for 8-8.5 lbs or the pair as it will be a touring ski.

Thanks MM

Keep the ideas coming.

skidesmond · Post by **skidesmond** » Sat Aug 11, 2012 3:52 am

Not to hijack the thread but .....
MM - I'd be interested in how your layered veneer ski comes out, aka like Line Afterbang. I helped make one like that with another guy but never had a chance to flex it after wards. I think we used 7 layers of ash. He used a belt sander to flare out the transition points. We used 2 full veneer layers on the bottom and then started layering the veneer with shorter and shorter pieces. I may have some details on the build if you want them.

twizzstyle · Post by **twizzstyle** » Sun Aug 12, 2012 8:25 am

I'd probably just mix up some epoxy and pigment it to match the sidewall, fill it in where you need extra, then plane it.

vinman · Post by **vinman** » Sun Aug 12, 2012 11:57 am

The issue is not so much the sidewall as it is the thickness of the ski itself.

I think I'm going to add a diamond of 19 oz glass under foot and run that out 6 inches in front and in back of the thin spot. With extra carbon to beef things up

twizzstyle · Post by **twizzstyle** » Sun Aug 12, 2012 5:30 pm

Right, by adding some epoxy just to fill the void where you need more sidewall, you can keep the core the exact thickness you want without adding more glass. At least this would give you known results.

vinman · Post by **vinman** » Sun Aug 12, 2012 5:58 pm

Right, I see what you are saying. I did buy some black liquid Rit dye today. Maybe I'll experiment with it a little before pulling the trigger.

twizzstyle · Post by **twizzstyle** » Mon Aug 13, 2012 6:49 am

I guess one consideration would be getting a good bond between the sidewall and epoxy. Would be frustrating if it cracked right there after trimming up the ski.

vinman · Post by **vinman** » Mon Aug 13, 2012 7:42 am

That is maybe my biggest concern... Leaning toward thinner core and adding composite.

barnboy · Post by **barnboy** » Mon Aug 13, 2012 4:58 pm

I've dealt with this in the past myself, it's a bummer for sure. I ended up building a matching "mini-core", about 10cm longer than the deck on each end, take about a 4mm slice off with a table/uni saw, plane and sand out your taper and there you go. It's not the quickest solution, but it'll probably help you sleep easier. As mentioned above, you're for sure going to want to diamond end, or round off the taper to prevent adding a hinge.

Granted, this was a wooden sidewall set-up, and it sounds like you're using ABS on this one, but it's still an option. If you were real classy you could even use your router to take a mm of material off the bottom of the mini-core, inside the sidewalls, to allow for whatever composite material you decide to put in there to "hide" from view on the sidewall.

Best of luck whichever way you go with it.

vinman · Post by **vinman** » Mon Aug 13, 2012 5:12 pm

I have to talk with my friend to see what he wants to do. My gut says go with the thinner core and beef it up with some carbon or I may call another local builder to see if he has some full width carbon we can try instead of the glass. There is a local outfit that make a lot of carbon fiber stuff also. I may call them to see if they have some leftovers we can get to play with.

I am also going to profile the rest of the core thicker in the transition zones, so leave the tip and tail at like 2.5-2.6mm before flat planing the waist. I'll hand sand the transition to the tip spacers out to 2.2 to give me a good transition. I think between the thicker core in the tip and tail and extra composite it will come out to be close enough

Thanks for the ideas everyone. Keep them coming if you think of anything else. I'd love to hear it.

vinman · Post by **vinman** » Sat Sep 01, 2012 2:20 pm

So I still have not built this ski, but here is my latest possible solution let me know what you think.

Wood core profiled to 3-10.6-3, hand sanded in the tip spacer area to 2.2 to get the interlock style spacer to sit flat.

22 oz glass to start.

Full width 11 oz carbon fiber diamond shaped patch over the binding mount and running 8 inches beyond the heel and toe piece to feather the flex and stiff area as well as preventing a stress riser on top.

6-8 strands of carbon tow full length under the diamond on top.

20 strands of carbon tow on bottom.

I think this should beef up this ski well enough,

Is this too much carbon? Will I make it an I beam? Should I go with less carbon in the bottom?

I don't think the top carbon will have a ton of effect on the stiffness but thought it would beef up the mount and keep things from getting too asymmetrical.

Brazen · Post by **Brazen** » Sat Sep 01, 2012 5:26 pm

Actually, when you press it epoxy and glass will fill the 1mm area above the sidewall automatically. It won't look quite exact, but it'll be just fine.

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Problem solving help

Problem solving help