:: View topic - Problem solving help

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

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?

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.

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.

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.

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.

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

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.

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.

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.

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

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.

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.

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.

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.

Thanks brazen, I am now more concerned with what type of flex I'm going to create here. This guy wanted a light-beefy BC ski. Kind of a tough combo.

A noodle won't do for this guy.

These cores only weight in at 1 lb 10 oz. so the weight will be on target but Im really trying to beef up the stiffness.

I guess there is really no way to know except just try.

I think the top layers are close I guess I just have to figure out how. Uh carbon to put in the bottom.

20 strands might be too much, maybe 12 each ski.....

I'm still hashing this out

What I'm now thinking about is the order of which I lay these composites out

We know that a reinforcement has a great effect the further away from the core that it is placed. Twizz wrote some good posts to this effect a while back.

So what I'm thinking is

Veneer top sheet (paperbacked birch) .7mm thick (this will help some)

11oz carbon fiber diamond with 8 strands of full lenght 3Kcarbon tow

22 oz glass with long fibers away from core

4 strands basalt fiber tow running at an angle between contact points

10.6mm core

4 basalt strands as above forming Xs underfoot (beef up torsion)

FG with long fibers down

16 strands of carbon

VDS

base

I think this is the best i can do for this guy, any ideas?

This might be a stupid idea.... But if the underlying problem is that the core is too thin, what about using a layer of veneer or two on top of the core, then proceeding as originally planned?

edit: ohhhhh. sidewall. ignore me.

I think you are right More, just add a veneer to the bottom. The veneer would be the size of the base, less the width of the edge set ... offset 8mm.

Usual layup ... fibre, veneer, core etc. It will raise the core up by about 0.6mm, without any evidence of the issue shown on the sidewall. Just need to make sure the veneer is saturated really well in this instance, otherwise it will upset the fibre.

Only problem with adding veneer to the base side of the core it that I've already rabbetted the sidewalls.

I could double up the top veneer though...

I'll have to think about it some. Thanks guys.

you'd want to do it under the fibre layers I think Vinman... Isn't the spacing of the fibre layers out from the laminate centre a pretty key contributor to stiffness?

Wouldn't adding anything that thick to the base side give me a convexity issue?

Yeah keep the materials under the core flat, you don't want to ruin the base flatness.

And yes, distance from the laminate center is a huge player in bending thickness, but if you're just trying to get back to your original design, you probably do want the extra layers under the composites (but on top of the core)

I think if I add any extra layers I'll add more carbon tow on the bottom. The cabon tape I have for the top is 12k strands/ 144k/ inch. The other tow I have is likely 3k. This fabric was carbon-basalt hybrid and the only cloth of this kind I can find on the net is 3k carbon.

So if I go with multiples of 4 I can come close to the weight of the carbon on top.without having a finite shape of stitched fabric creating base flatness issues for me. Thinking about it this way I'll need a lot more strands of carbon on the bottom.

What will the heavier carbon on the top do to my camber? Crap.... Likely a decrease in camber or increased camber? Crap...

Maybe I should just go with a diamond of glass on top with some carbon tow to back it up to not have unpredictable camber behavior?

I only have 12 feet of the heavier carbon tape. I could split it in half to get 24 feet of 1.5 inch material and just do a full lent carbon strip top and bottom with a diamond of glass under foot on top....crap

Pretty amazing you are still deciding what to do here.

Few things.

I did a layup like the afterbang all veneers and I did not rabbit as the materials were too thin and I had completely flat bases. so ymmv.

I used some 2.5 inch wide carbon uni 12oz for the length of the core on top only, in one pair with a standard glass and core layup that I knew how it would flex as I have built the same ski before and I am afraid it will almost be unridebly stiff.

The only reason I'm still deciding what to do is that the guy these are for isn't available to come help build them for a few weeks, so my brain goes into overdrive thinking about how to make these come out as good as possible.

I think I'm just going with a 1.5 inch strip of the 11oz carbon top and bottom with a diamond of glass on top and maybe some basalt to beef up the torsional component and hope for the best, it seems that is the best I can do.

Thanks for the help everyone.