Edge damage and repair; one example (aka my first edge replacement)

Discussion in 'Tuning Techniques and Tool Information' started by Doug Briggs, Jan 18, 2018.

  1. cantunamunch

    cantunamunch Meh Skier

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    It's stiffer and lighter than Titanal when set in epoxy, and you get mad on-axis tearout strength. So if you're concerned about lateral tearout say from another rock hit, you just put strips running towards the center of the ski and pin the edge to that. Upside: stiff, light repair with gobs of tensile and flexing strength, you're using epoxy anyway. Downside: Cost, annoying habit of CF to static cling to everything, and weak in off-axis loads.

    Another option would be to use a fiber-filled epoxy - cost there is just whatever 0000 steel wool costs in the hardware store. Upside: cheap, formable in any direction. Downside: not as good a tearout resistance for direct hits, random fibers contaminate work area.
     
    Last edited: Jan 18, 2018
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    Doug Briggs

    Doug Briggs Skiing the powder Industry Insider Pugski Ski Tester

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    Ah, cf = carbon fiber. Can you get it less than a mm thick? And where?
     
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    Doug Briggs

    Doug Briggs Skiing the powder Industry Insider Pugski Ski Tester

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    And tow = ?
     
  4. mdf

    mdf entering the Big Couloir Skier

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  5. James

    James Skiing the powder Instructor

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    I suppose the shop doesn't have a vaccuum bag. And the Fishcer boot is pressure.... Could use that pressure.
     
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  6. John O

    John O Getting on the lift Skier

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    Off topic, but is this a real concern or just bias? I skied my first pair of Armadas at a demo day last spring and loved them (tracer 98). Been thinking of picking up a pair, perhaps. So just curious.

    Back on topic, as an average joe with no shop experience, this looks like a great fix to what I would have been concerned was a total loss. Nice job.
     
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  7. cantunamunch

    cantunamunch Meh Skier

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    Because they resemble flax fibers?
     
  8. Eleeski

    Eleeski Out on the slopes Skier

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    For a repair like that, I like to get some carbon fiber cloth and tear it apart, smoosh it around with some epoxy and apply the matted up mess to the part needing reinforcement. On that edge, a little below and a little above might work best. Use a heat gun to thin out the epoxy resin and get it to soak in. Clean cloth or unitdirectional doesn't give the needed all direction support. Disclaimer, I haven't bonded metal edges to a snow ski but I can't count how many waterski repairs I've done.

    My repair resin of choice is JB Weld - the slow setting variety. It is a bit thick so the heat gun is critical.

    Steel wool epoxy works well on binding holes. Not so much elsewhere compared to the carbon fiber epoxy mix.

    Sandbags are an easy way to add some pressure. I've also used ace bandages over visqueen (or saran wrap) and some pliable foam. When I build my waterskis I use airbag pressure at about 5psi. For that edge repair, I would have just clamped it under some stiff but pliable foam.

    Nice repair!

    Eric
     
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  9. Dakine

    Dakine Out on the slopes Skier

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    Roger Eleeski...JB weld thinned with heat and carbon tow or cloth.
    I'd put some peel ply over the repair and a couple of layers of shop towel for padding than weight or clamp it until cured.
    Peel ply lets excess resin through and then peels clean for a very high fiber content composite.
    http://www.cstsales.com/peel-plies.html
     
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  10. crgildart

    crgildart Gravity Slave Skier

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    How sensitive to heat is the repaired area? Would folks doing future tuning and waxing want to be extra careful when grinding, filing, hot waxing?? Would it be prudent to avoid hot boxing a ski with that kind of damage and repair? I would think that the gorilla glue epoxy, metal grip. and p-tex would hold up pretty well to those things. Other contact cement variations, not so much..
     
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    Doug Briggs

    Doug Briggs Skiing the powder Industry Insider Pugski Ski Tester

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    This is all great info, guys. I have some skis I can play with at the shop.
     
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  12. Monique

    Monique bounceswoosh Skier

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    Would the CF stuff up the repair cost much?
     
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    Doug Briggs

    Doug Briggs Skiing the powder Industry Insider Pugski Ski Tester

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    I don't expect any issues from heating this repair. The trickiest part is when using the soldering iron to apply the MetalGrip. You have to avoid overheating the epoxy. I just work quickly. You don't need the MG to be picture perfect, just a thin coating.

    Not much. A 25ft tow bundle would last years and costs under $10 sans shipping and tax. It would be a minor additional step if I understand how I would use it.

    @Eleeski, @cantunamunch and @Dakine. Your info on CF is priceless.

    For a small up front purchase and a slight additional step to the epoxy process, I can really beef up the repair. I envision cutting up CF tow into 1/2 or smaller lengths and mixing it into the epoxy. I presume it won't flow quite as well, but it will certainly enhance the strength of the epoxy and leave me with a material that could be screwed into and transfer the stresses further into the ski, away from the damaged core section. Or maybe two epoxy steps, one to saturate any cracks and another with the tow to create a structural layer tied into the ski.

    Does the tow fiber size remain the same regardless of the number of fibers per bundle? I couldn't quickly find clarification on the CST site.

    Thanks again to everyone. I love learning. :)
     
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    Doug Briggs

    Doug Briggs Skiing the powder Industry Insider Pugski Ski Tester

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    I forgot to ask, @Eleeski . Why cut up CF cloth instead of use tow? Do you simply have cloth on hand and it is more convenient than having cloth and tow?
     
  15. cantunamunch

    cantunamunch Meh Skier

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    tow breaks up into component fibers very easily - rub it once/twice between thumb and forefinger and it starts looking like that clump of flax I linked to. Cloth gives him neatness, multi-axis strength and greater control.
     
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    Doug Briggs

    Doug Briggs Skiing the powder Industry Insider Pugski Ski Tester

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    Understood. @Eleeski said

    "carbon fiber cloth and tear it apart, smoosh it around with some epoxy and apply the matted up mess"
    so I was wondering if it was just convenience or had some other benefit. It sounds like it doesn't matter, cloth is just woven tow so cutting it up just results in cut tow. The random, matted up mess is stronger for my application than fabric. It seems like cut up tow (or matted up mess ;-) ) would also allow for thinner layers than cloth.
     
  17. cantunamunch

    cantunamunch Meh Skier

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    Yes; tow fiber size is implicit in the modulus, figure anywhere from 5 microns to (extreme) 15 microns for the intermediate grades.
     
  18. Eleeski

    Eleeski Out on the slopes Skier

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    Doesn't everybody have some scrap carbonfiber cloth sitting around in their shop?

    @Doug Briggs I end up with lots of spare fiber (when I cut cloth, I pull out one fiber to make a line to follow). I like about 4" lengths to make up my repair goo. 1/2" lengths are the standard for chopped fiber filler but for a hand done repair, I've done better longer. I like the clump effect @cantunamunch describes for a repair as it gives multi axis strength. I have to engineer my cloth layout (some in line, some on the bias (45 degrees tilted) and unitdirectional for major loads) to carry the loads of my layup.

    Some unitdirectional (sometimes advertised as tow) is hard to pull apart for fibers. (Some styles are great.) Crow foot style cloth is more flexible and fits contours better (and pulls apart to yield nice fibers). Some of my cloths seem to have different fiber size. I like small diameter fibers for repairs and complex shaped layups. The heavy fibers are easier for unitdirectional applications. Heavy seems to be less expensive (but it's all cheap compared to boron fibers).

    Note that for this type of repair, fiberglass is pretty good also. Probably not a gram of weight difference and glass is quite strong. If you can find small strand flexible glass cloth to pull apart, that works really well. I use the carbon for repairs because I have it sitting around but I've done a lot of repairs with glass too.

    Note, glass is very strong in compression and it can be tougher than carbon. Arguably a better repair choice.

    Don't use Kevlar. It doesn't bond well to the resins and is impossible to sand for a finish. Not good for the home workshop.

    Eric
     

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