Random questions

[agiocochook]

A couple questions for y'all....

Is anyone using metal as the base in the tip and tail? I’d like to get away from full wrap edges, but wanted to make the skis look a little more finished. Also, I wonder if having the base at the very tip and tail be a separate piece than the rest of the base would alleviate the shear stress between the base and core (when the ski is flexed) where it’s the worst.

I’m curious as to how much epoxy others use for a pair of skis (180 length, say). I use about 1400-1500 g.

Looking for something better than what I’m using to protect the bases during pressing. Currently, I’m using GXF-101 from signwarehouse.com and I’ve also tried the GXF-100. The 101 is “high tack” and the 100 is “medium tack”. The 100 doesn’t stick very well to the base (especially Isospeed 7500) and tears easily when peeling it off after pressing, but it does leave the base clean. The 101 sticks better (but not great) and I can usually peel it off in one piece, but it leaves most of the adhesive on the base which means some quality acetone time….. I’ve also tried painter’s tape, but found it a real pain to get off.

The printed topsheets I'm using have had chipping issues (see below). I bevel the corner between the topsheet and sidewalls but still have fairly large chips come off where I would otherwise expect the damage to be a smaller gouge. Is it the material, or should I be doing something I’m not?


Thanks!
Scott

[skimann20]

I only do a 3/4 wrap and have had very good results and no failures. I haven't seen anyone use metal as the base, I would think this would add a lot of weight in the tip and tail and increase your swing weight.

epoxy: It really depends on what is in the "sandwich". FB weight, CF weight, how many layers, 180 by how wide? I would say you are using A LOT of epoxy. someone about 3-4 years ago did a writeup on fiber weight to epoxy weight. do a search on that one.

I use to protect the base when I first started out but I found it was just easier to grind the epoxy off instead of dealing with the glue and potential imprint of tape on the base.

stop crossing your tips. ;-) what material is the top sheet?

[twizzstyle]

Nylon is a good topsheet material if you're having chipping issues. It gouges/tears rather than chipping.

There have been a small handful of folks that have done metal tip/tail protectors. 3/4 wrap is way easier.

I don't quite understand your idea about separate base pieces at the tip and tail. Are you having delam issues there? Unless you're doing cutouts for different colors of base material, it should all be once piece.

I don't protect my bases at all. Whatever tiny amount of epoxy ends up on there comes off on the sander easy.

[mikic1]

I can comment on epoxy, it does sound a lot, but it depends very much on the physical size of the ski and the layup.

A good rule for me when I was pressing skis was I would weigh all the fabric that is going in the layup, and mix the same amount of epoxy + 10% or so. After pressing at 30psi, some of epoxy would escape, leaving the ration close to the same weight of the effective fabric.

At the time I was using around 700g of fabric and also ~700g of epoxy on a 150-112-144 and 1780mm long ski.

As for topsheet, I had good success with TPU/ABS and PA/nylon topsheet. PBT sublimated might chip as from what I have heard, but then again I am sure it depends on the supplier quality.

Hope it helps.

[rnordell]

You can see the metal tip and tail section in the ski with the snowflakes I made for my fiancé

[amidnightproject]

Don't smash your skis together when you ski is the easy solution

I've been fighting that for years. I'm hard on my skis as far as that is concerned and when I look at other peoples skis (ones i've made) it's a non issue for them. Therefore it's my riding style. I will say I prefer the durability of PBT over nylon. Nylon tears and pulls and PBT just chips off leaving the composite layers alone.

[agiocochook]

Appreciate the input, and sorry for the delayed response – been skiing & ski making. As for the epoxy amount, I’m using about 1400-1500g for a pair of 181 138/98/123 skis with 2 layers of triax, an extra layer of triax in the tip and tail and a 2” strip of carbon per ski (I also thinly wet out all other surfaces, like the core and topsheet). The squeeze out doesn’t seem super excessive, but then I’m using a vacuum press so something less than 14psi….I also generally delegate the wetting out of the glass to whoever I can trick into helping me, so mostly first timers and usually they seem to go a little overboard…..

Thanks for the pics rnordell, they look great! What type/thickness metal are you using and are you sandblasting to help with bonding, if you don’t mind my asking? Regarding tip and tail base pieces independent from the rest of the base to alleviate shear stress, I’m just sort of thinking out loud….Given that the shifting between layers progressively increases from the center of a ski towards the ends as it’s being flexed (and, consequently, so does the stress on the bond keeping the layers from shifting, right?), my thought is that making the tip and tail independent would result in the shear stress between the base and the rest of the ski being reduced or eliminated in those areas. When a skis is flexed, it’s just the running length part of the ski that is bent, not the tip and tail, but any layer that’s one continuous piece from tip to tail is going to want to shift even where it’s not being bent. The couple time I’ve had delaminations, they’ve been at the ends of the ski and though there are probably other factors involved that either increase the internal stress (bases not being properly pre-bent) or weaken the bond (plastic tip-fill vs. wood core), I’m guessing it’s the shear stress (at its maximum in the tip and tail) that ultimately causes the delams. Does that make any kind of sense, or am I just smoking crack?....

Recently, I’ve been getting topsheets from Miller Studio, but I’m not sure what the material is. My partner handles the graphics and topsheet orders and I’m still waiting for her to get back to me with info. But, based on the comments and what Miller offers, I’m guessing it’s PBT. And in my efforts to keep up with my school ski program kids in the park, I’m afraid my skis are always going to suffer….:)

Since I end up with a little epoxy on the bases that needs to be sanded off even when I protect them, it sounds like I might as well leave them unprotected.

[rnordell]

I use either 2024 or 6061 aluminum, thickness usually 0.080" but this sometimes changes depending on what I'm doing with it. I made matched dies to stamp the tip curvature in so that it matches my layup tooling. I heat treat the aluminum and stamp it in the water quenched condition to minimize springback while forming. For 6061 I will heat treat back to T6, 2024 I just leave in the T4 condition. I will sandblast the surface for bonding, but then within 24-48 hours of bonding I will chromate conversion coat (Alodine) the parts. See http://www.eaa1000.av.org/technicl/corr ... lodine.htm for a decent description of the process.

[rnordell]

I use either 2024 or 6061 aluminum, thickness usually 0.080" but this sometimes changes depending on what I'm doing with it. I made matched dies to stamp the tip curvature in so that it matches my layup tooling. I heat treat the aluminum and stamp it in the water quenched condition to minimize springback while forming. For 6061 I will heat treat back to T6, 2024 I just leave in the T4 condition. I will sandblast the surface for bonding, but then within 24-48 hours of bonding I will chromate conversion coat (Alodine) the parts. See http://www.eaa1000.av.org/technicl/corr ... lodine.htm for a decent description of the process.

[agiocochook]

Thanks for the beta! I wasn't sure whether to use .080, or .063 and add a layer of fiberglass.

[rnordell]

I guess I should have clarified. I use 0.080" because I usually machine out a pocket on the aluminum part. The pocket is the depth of the base material + 0.005" to control the bond line thickness. This makes the remaining flange that overlaps the abraded inner surface of the base material about 0.020" thick. Having a thin flange of metal sandwiched inside the laminate increases the bond area, and keeps the spacer from pulling out of the ski. If the tip piece was only about 1/4-1/2" wide and 3-4" long, the bond area is only 0.75-2 sq inches. By having some internal flange, the surface area that is bonded can be increased 2-2.5 times (or more depending on your design). I hope this explanation of what I do makes sence.

[rnordell]

I guess I should have clarified. I use 0.080" because I usually machine out a pocket on the aluminum part. The pocket is the depth of the base material + 0.005" to control the bond line thickness. This makes the remaining flange that overlaps the abraded inner surface of the base material about 0.020" thick. Having a thin flange of metal sandwiched inside the laminate increases the bond area, and keeps the spacer from pulling out of the ski. If the tip piece was only about 1/4-1/2" wide and 3-4" long, the bond area is only 0.75-2 sq inches. By having some internal flange, the surface area that is bonded can be increased 2-2.5 times (or more depending on your design). I hope this explanation of what I do makes sence.

[agiocochook]

Thanks -- it does make sense. Did you try without the overlap and have problems?

[falls]

On a 180cm ski I'm using 4 x 250g pots of epoxy to wet out 22oz glass that is 165mm wide. Then 3-4 more pots of 125g for the rest of the layup. So about 1.375-1.5kg epoxy in a 135-97-125 180cm ski.

[agiocochook]

Hi Falls, I'm assuming the epoxy amounts you use are for a pair of skis, not just for a single ski, right?