The 'How to Build a Water Ski at Home' Thread

[Horton]

@AdamCord‌ is this @tap person the Mega Geek you told me about?

[Horton]

@tap‌

"The physics are sound" that sounds very Wile E. Coyote

[AdamCord]

@Horton if you read his posts about accelerometer data capture then you would know the answer to that question. @tap and I were roommates at Purdue. He's the guy who probably should have gone to MIT but he liked waterskiing and the waterski "lifestyle" a bit too much for that ;)

 

 

@tap fair enough

[AdamCord]

I plan to cast the urethane foam core in the mold I've built. This will leave me with a part that is exactly the right shape. But the carbon fiber has thickness and the core surface must be offset to make room for that thickness. If I don't account for it, the core and carbon won't fit in the mold. It's important to have a very consistent offset because I need a consistent pressure on the carbon laminate when it's being infused under vacuum. There are a few ways to do the offset. I could just cast the foam and then try to sand the surface back, but it would be very tough to do that consistently and also sanding sucks.

 

What I did was make an "insert" that drops into the mold and has the thickness I need built in. This way I can drop the insert into the mold before making any cores and I'll have a consistent offset. I know that my carbon laminate will be somewhere around .040" thick depending on the layup. I used 4 layers of ~.008" thick fiberglass and some cheap polyester resin to make a quick, cheap insert.

 

Here is the fiberglass sitting next to the mold

 

I didn't get any pics of the layup process because this stuff kicks off fast and also I had sticky resin all over my gloves. But to give you an idea I wet out the first layer on my table, then put the next layer on top of that, wet it out, and so on until I had 4 layers stacked up and fully saturated. Then I put the entire stack in the mold at once, and carefully pushed it down into the bevels. I used my fiberglass roller to get all the air pockets out between the fiberglass and the mold. On top of that I put down some perforated release film, then breather fabric. Lastly I put a vacuum bag over the top of that using vacuum tape. I pulled vacuum until it was cured. This is what it looked like while under vacuum

 

I then popped it into my awesome $10 oven ($30 if you include the cost of the space heater, which I already had) to let it cure. This little oven will get the whole part up to 150 or 160F.

 

Then after removing the bagging material it looked like this

 

I then spent some time trimming off the flash and sanding down any high spots. There were a few areas where the fiberglass didn't lay down perfectly so I needed to sand those to get a consistent thickness. Here's the finished insert

 

This came out to right at .035" thick, which should be perfect. When I make the core I will put this in the mold first, then I'll put a layer of .005" visqueen over it. The foam won't stick to the visqueen. Also later if I decide I need more offset I can just add another layer of visqueen or use different thicknesses.

 

 

 

[AdamCord]

Also as a side note - I used the same wax on the mold that I had used on the plug. This time however I brought the mold into the warm house to apply the wax instead of doing it out in the cold. I also did about 8 coats, where as I think I did 4 or 5 on the plug. The wax performed perfectly this time and the insert basically fell out of the mold, which is exactly what it's supposed to do.

 

So the lesson here is apply the wax at normal temps and use more coats than you think you need!

[oldjeep]

@AdamCord‌ curious how much it matters to your process to keep your oven at an even temp? Might want to look into some of the various homemade hotbox setups that folks make for downhill skis. This one is an excellent example with some pretty crazy accurate temp control

 

http://minneapolis.craigslist.org/hnp/spo/4777775947.html

 

While I would never consider making my own ski, this thread is an awesome read.

[AdamCord]

@oldjeep if I were building for mass production it would matter a lot. I would want to bring the ski up to a very high temperature so it cures more quickly. With short cure times and high temps I would need to keep the temps very consistent so I don't undercure anything and so I don't overheat anything.

 

But for this operation I have all the time in the world, which simplifies things a lot. I can cure at lower temps for a long time and never have to worry about getting too hot or undercuring, even if one end is hotter than the other.

[skiray]

Where do you purchase a vacuum bag?

[AdamCord]

@skiray I buy most of my bagging materials from ACP here in the US.

 

Anyone who wants to learn the basics for all this stuff should watch the Easy Composites videos on Youtube. The one about the car hood is probably the closest to the process I'm using. Those guys do a really good job of explaining and I wish their videos had been around back when I got into this hobby.

[AdamCord]

Ok so we're ready to make a core. Now as I said before I have never tried to make a Polyurethane core this way. Normally I've done it either with a dedicated core mold and press (the way it's done in a ski factory), or in a mold like mine in a ski press. The reason you need a press is that when the foam starts to expand, there is a LOT of pressure. Also you need the closed mold to force the foam to expand into the tip and tail, working against gravity. I could try and clamp a top to my mold, but the pressures would probably cause the mold and/or top to deform.

 

So for this method I am taking a new approach. I want to let the foam expand freely in the mold and also up and out of the mold cavity. Then after it is cured I can cut/sand the excess foam away. There are a few problems with this approach. First the poured foam is a liquid, so gravity is a problem. I solve this by doing multiple pours with the mold tilted at different angles instead of doing the whole core in one shot. The second issue is that by freely letting the foam expand from the mold it may not fill out the top edge well, and also I have no reference for where the top of the core should end. I solve this by using plywood to make a small overhang around the edge of the mold cavity. See the pics below and it will make more sense.

 

Here is the offset insert I made sitting in the mold

 

I then used spray adhesive to put the 5mil visqueen into the mold

 

Here is my top that will overhang the mold cavity by about 1/2" but still leave the center open to allow the foam to flow freely

 

And here's that board also wrapped in visqueen and clamped to the top of the mold.

 

I poured the tail section first. This stuff expands very quickly so this was hard to the touch in maybe 5 minutes

 

Within 5 minutes I poured the tip section. This is quick enough that the first and second sections should get a good chemical bond

 

 

I then put my "oven" box over the top and let it cure for a few hours. The foam fell right out of the mold because it doesn't bond at all to visqueen

 

But this is where we can see where it all went wrong. When I've done this before in a press, the closed mold and pressure from the expanding foam didn't allow the visqueen to wrinkle at all. This time the foam was just freely expanding and there was no positive pressure. I am not sure if it's because of a chemical softening caused by solvents in the foam or from the exothermic heat, but the visqueen wrinkled a LOT. Those wrinkles were transferred to the foam. So my nicely formed core looks like a raisin on the bottom, which just won't work

 

Luckily once it's all set up it only takes about 15 minutes to make a core and this is maybe $10 of foam, so not a huge loss. My new plan is to use packing tape instead of visqueen. I did a really quick test and the packing tape seems like it will work. The lines you see are just cosmetic from where I poured the foam, and not wrinkles in the surface.

 

I'm planning to try this again with the packing tape instead of visqueen and I'll report back!

[DanE]

Am I the only one who think this thread is making me appreciate an off the shelve ready to buy high end ski even more?

[Jordan]

@AdamCord‌ ....in your method does the foam's final density differ as a result of it being allowed to freely expand, as opposed to doing it with a closed mold and having it cure under lots of pressure?

[AdamCord]

@Jordan yes it makes a big difference. This is part of why I like the free expansion method better than forming the foam under pressure. Expanding freely like this I will have a more consistent density. This foam I use will be 8lb/ft^3 when left to expand free. If I had it under pressure it might be 10 or 12 lbs. To compensate I would have to use a lighter foam to begin with.

[Horton]

Waiting for @eleeski‌ to see wrinkles and claim "Eureka! That is the future!"

[AdamCord]

@Horton they are "speed wrinkles", and the help turbulate the water flow. Worth 3 buoys at least.

[mwetskier]

my concern would be the strength of the bond you can get between the outer composite layer and the top of the core with the much more porous foam due to the free expansion aspect. it will be lighter but could it also negatively impact the transition area between the skin and the core?

[AdamCord]

@mwetskier that is definitely a concern when choosing core density, as is tensile strength, compressive strength, modulus, etc. In this case I chose the density based on those metrics after free expansion. When forming the core in a closed mold you would choose a different foam.

[gmut]

@AdamCord I think that you might really be on to something with that textured core. Many great inventions came about as a result of a mistake(just another word for a result that wasn't expected or intended).

[eleeski]

Are you making fun of my wrinkles? It took years to get this wrinkly.

Are you talking about my ski?

 

I'm very interested in the foaming process. Spot reinforcing the core with some wood or honeycomb might be very interesting. Thanks Adam for sharing this.

 

I don't feel so bad about all my failures now. Maybe it's not just me.

 

Eric

 

 

[AdamCord]

@eleeski if it were easy it would be called 'building wakeboards'...

 

Ok so round 2 of core building went much better as I was able to make a core that didn't look like a raisin. This time I covered the mold with packing tape, and used a heat gun to remove any wrinkles before starting. I'm still not sure this is the best way, as putting on the tape is tedious and it actually stuck to my foam in one very small spot, which is strange. If I end up deciding I need to make a lot of cores I may paint/polish/wax my mold insert. If I only ever make one ski then I won't bother.

 

Anyway this new core looked a lot like the last core minus surface wrinkles. After removing it from the mold I was able to cut off the excess. My mold overhang idea worked perfectly as it gave me a reference of exactly where to cut and sand to.

 

 

 

This foam cuts pretty easily so after maybe 15 minutes of work I had the core ready to go. You can see some imperfections on the edges where the different pours met eachother. I'll fill those areas with some filled epoxy, no big deal.

 

 

My only problem was that it was COLD when I made this core, so the foam didn't expand as much as it normally would. Because of that the weight came out to about 1lb 5oz, instead of the ~1lb 1oz that it should be. That's not enough weight to bother me, but if I were building this ski for someone else I would probably go buy a bigger space heater and get my garage up to temp.

 

Now we're almost ready to make a ski! I haven't even ordered the materials yet for it so I need to get on that...

[skiray]

@AdamCord‌ do you think your first try would have worked if you would have pulled a vacuum on it to eliminate the wrinkles?

[mwetskier]

@skiray -i work with 2-part foam some times when i am brought in on prothetics projects and i can tell you if @AdamCord pulled a vacuum on the core it would have probably blown up to the size of a volkswagon.

[AdamCord]

@skiray interesting idea. I don't think it could ever work because the foam starts to expand in under a minute. There would never be time to get the bag on and sealed.

[thager]

@AdamCord Probably a dumb question but ever try the expanding foam in a can?

[AdamCord]

@thager the stuff in the can is basically the same thing, but it expands to a much lower density so it wouldn't have the needed structural properties.

[skiray]

@AdamCord‌ - I was asking if you could vacuum the plastic in place prior to adding foam. That way you could work out the wrinkles. Vacuum would be used to "suck" the plastic to the insert.

[eleeski]

@thager‌ I have used canned expanding foam a lot. But not for skis. It's very inconsistent in density and strength. It is fairly flexible as well. Structurally it has very little strength. Also epoxy doesn't bond terribly well to it.

 

It is however wonderful to make interesting shapes. The Focus/Ranchita car project was welded wire covered with canned foam sculpted to make the base shape for the epoxy glass skin. Added a bit of strength and allowed the moldless custom shape.

 

I did have a small issue with the canned foam. My desert was hot and dry when I used it. The canned foam wouldn't kick off. I ended up squirting a spray of water on the foam to get the foam to cure. A bit counterintuitive but when I realized that the canned foam is isocyanurate based (like crazy glue) it made sense. Now I have a spray bottle of water whenever I foam from a can.

 

@AdamCord‌ , I've built wakeboards. Still a challenge. Now skateboards are easy....

 

Eric

[thager]

@eleeski @AdamCord Thx for the responses. I was thinking more along the line of shooting it into a closed mold on one end until it started to come out the other end then closing it off and allowing it to cure. Would probably be trial and error to get proper amount without blowing up the mold. Otherwise, have also wondered if one could do ribs, stringers, etc. then fill with foam before laminating a top sheet. Now you've done it. I am going to have to try this now!

[AdamCord]

@thager what you're describing is basically how the ski factories do it. Imagine a big heated machine with hoses that go to an injection head, and 10 or more presses with heated core molds. An operator goes to each mold and injects the urethane foam. There are vent holes so the excess can escape. The foam cures very quickly. They can make a LOT of cores in a day with a setup like that!

[MattP]

@AdamCord‌ how are things with the ski coming?

[AdamCord]

@MattP I've done a little work but not much since my last update. It's way too cold in my garage so I spent a few hours this weekend clearing out some space in my basement and moving all my equipment down there. Now I've got it almost all set up to build a ski. The only thing I have left to do is finish prepping the core and build a vacuum pot so that I can degas the resin before infusion. I have all the materials it's just a matter of finding the time!

[AdamCord]

Ok I've made some progress on this project after transporting my shop to my basement. It's amazing how temperatures in the teens will kill your motivation to work outside...

 

So first off I spent some time getting my core thickness dialed in. This basically consisted of putting it in the mold, marking the high spots, removing it from the mold, sanding, repeat, repeat until the core top sits just below the flash line. Too low and there won't be enough pressure on the carbon to consolidate the fibers, too high and I'll end up with a really thick flash line, which I just don't want. Also the ski will be thick in those spots which is just amateur.

After getting the core shape all right it was time to drill some holes. First I drilled a lot of tiny holes in the core. This is to help with pressure distribution when I do the vacuum infusion. I also drilled out pockets where the inserts will go. I poured filled epoxy resin into each pocket, and I'll install inserts in them after the ski is made.

 

Drilling tiny holes

 

 

Marking for insert blocks

 

Insert pockets

 

Insert blocks poured

 

Hmm needs carbon

 

Hey look carbon!

 

So I put uni carbon on the top and bottom of the core (with the bottom sheet wrapping up the sidewalls) and trimmed the sheets so that the go right to the top edge of the ski. Then I cut a bigger fabric weave piece that I put on the bottom and wrapped up and over the top edge. Wrapping over the top edge like that adds a lot of strength/durability to the ski. Some manufacturers do this, some don't. As you might guess the ones who do have a better durability track record. I used 3m 77 spray to adhere the carbon so it stays in place. You can also use staples, but then you'll have to tell people you have staples in your ski.

 

This is what it looks like without the top layer of carbon

 

On the top goes an over sized weave piece. This runs out into the flash. You can see my acrylic mold "top" as well. The acrylic is how I plan to get a smooth flat top on the ski. I could build the ski without it but the top would not be smooth/flat, and it would look like something @eleeski would ride. The top carbon sheet runs out beyond the acrylic and it will essentially be used as a "path" for the resin to get to the ski. I'll get more into the details of that when I set up the vacuum bag.

 

 

 

[kstateskier]

wow this is getting serious!

[gt2003]

Love the progress. Been missing this thread!

[mack]

hmm. starting to see how you plan to get the resin to flow throughout to wet out both top and bottom with one infusion.

[mack]

@ AdamCord what diameter were the holes you drilled into to the core? how far apart did you place them? those holes will be filled with resin once infusion is completed? Also what diameter hole for insert? and did those hole run thru core or did they stop short of full penetratation

[AdamCord]

@mack the core holes were I think 3/32", but you could go a little bigger or smaller. I spaced them every 3" down the length of the ski and 1.5" apart across the width. I chose those numbers at random. Just as long as there is a good distribution it should work. The holes will get filled with resin but it's such a small amount it won't add a noticeable amount of weight to the ski, and it will actually help with strength.

 

The insert holes were cut with a 3/4" spade bit. You only need to cut down about ~5/16" to give the insert something to sink into. The tip of the blade did pierce the bottom of the core on some of the holes. I just taped over the back side when I poured the resin.

[mack]

@AdamCord a question about your carbon. you stated in an earlier post that you'd be using 12 oz. carbon. how many yarns /strand? 3K,6K,12K? also a general question about carbon weight. could I, for example, use 2- 6 oz. weight pieces of cloth to equal 1-12 oz piece of carbon. could i expect equal strength properties in both layups??

[AdamCord]

@mack,

 

I prefer to use the lower K carbon because it tends to be easier to work with. You can use 2 layers of 6oz in place of one layer of 12oz. I had actually planned to use multiple layers of 6oz on this ski but I was sent the wrong material by mistake. But because they sent me way more than I paid for I didn't bother replacing it :smile: . So on this ski I actually ended up using one layer of 20oz (not what I ordered) and one layer of 6oz (I had some of this left over). So my total weight is 26oz, which is below what I think the ski will actually need. It's much better to build the ski a bit too soft and stiffen it than the other way around. Stiffening is just a matter of adding carbon to the top. This is also a good way to know what layup the next ski needs. Softening a ski is a sketchy practice that I do at my own risk and I don't ever recommend to anyone else!

 

I also prefer very stiff skis. Soft skis and big people don't mix when the rope gets very short. If you're smaller and not into short line you may prefer a softer ski, and you may want to consider using a softer layup than I did for your first ski.

[eleeski]

@mack Consider using some unitdirectional. Most of the load is down the length of the ski. Unitdirectional runs its fibers along that load. Fibers running across the width of the ski are just bulk that adds strength that is not needed. A layup on a 45 degree bias is better but still a bit inefficient. Obviously you will need something to keep the ski from splitting down the middle but one ply (with maybe a second in the high stress binding areas) should do the trick. A few plies of unitdirectional down the length of the ski can carry most of the load.

 

Unitdirectional is easy to wet out and not terribly expensive. Carbon isn't that strong in compression so use plenty on the top skin (or use Boron). Maybe mix in some glass unitdirectional on top as well to get compressive strength.

 

I use fairly light woven cloth (not sure of the weight - a baller was cleaning up his shop and gave a roll to me! Cool!). One ply on the bottom with reinforcements under the feet and 4 plies of unitdirectional. Layup on top is 2 plies of cloth plus reinforcement on the back of the ski, then one ply on the front, 4 plies of unitdirectional boron and buried patches of kevlar cloth for binding mounting. I also add some glass matte on the edges to give me something to sand (doesn't always work as often I grind more or add lots of material. Who needs fine tuning?) I try not to use material that isn't structurally needed. My skis end up pretty light.

 

Eric

[mack]

@ADAMCORD@eleeski my plan is to use 2 plies of uni directional 9.4 0z. 12K prox. .03" thick each and 1 plie of woven fabric 5.5 oz. 3k carbon prox. .009 thick on both the top and bottom skins. It may be a little soft, I don't know. My skill level is, I get into 35 all the time make it sometimes, my PB last season-got outside of no. 4 ball at 38. Am getting close to owning 35. I am 5'-10" prox. 190 lbs. I'm skiing on {chuckle at Adam} a 2012 67 Elite that was {supposedly} skied on and doctored by a very well known water skier in Fl. I don't know if that is true, but that is what i was told. I plan on using some tape and adding a little epoxy to the edges and sand the bevels in an attempt to create some very sharp edges and feathering them into a transition zone to a more rounded bevel from around mid-rear foot thru the tail, similar to the way the surfboard guys make their sharp edges. Eric, I'm not sure if your suggesting i use only Uni in the construction of this ski?gheeze I don't know if i can afford Boran. If i'm reading right you have 5 plies of carbon on the bottom and some additional reinforcement under the foot bed? On the top skin you have 2 plies of 0-90 cloth plus 4 plies of uni Boron with more reinforcement on both the tail and the tip?

 

my main concern is that I don't build it so light that it breaks up on me

[mack]

@ADAMCORD

@eleeski Typo- 2 plies 9.4 oz. 12K unidirectional prox. .020 thick

[eleeski]

@mack I do use 4 plies of boron unitdirectional on top. But the finished boron strips are about 2cm wide with one strip on each side of the ski. I actually taper the plies so it is only full 4 ply thickness from a ways behind the rear heel to the toes of the front foot. So not a prohibitive amount of boron (still not cheap). The carbon unitdirectional on the bottom are similar strips (maybe a bit wider ~3cm) one on each side of the ski. Not that much unitdirectional carbon (and it is relatively inexpensive).

 

Top skin is 3 full width plies of cloth, 2 at 90 degrees and one at 45. This tapers at the front foot to 2 plies then to 1 ply not too far ahead of the boots. Bottom is 2 plies, one at 90 and one at 45 from the fin to halfway up the front foot and one ply of 90 for the rest.

 

I've not broken too many skis with this layup. One where I ground away one of the boron strips and that side cracked halfway between the fin and the rear boot but I did ski several runs with the crack and only one boron strip for strength and had no complete breakage. Another ski snapped just in front of the front binding. I was experimenting with a carbon unitdirectional/ABS strip reinforcement (where the boron is now). Structurally that mix didn't work...

 

Bindings ripping out cause most failures of my old skis. Or my grinder gets too aggressive. Or I just want to experiment with something new. That's fun.

 

Eric

[mack]

@eleeski thanks Eric. That explanation is much clearer to me. If I may ask, where does one buy boron? I'm curious how much it would add to the cost.

 

Joe

[eleeski]

Specialty Materials might be the only retail boron supplier. It's very expensive - but $1000 buys enough for several skis when used judiciously. So really not that expensive.

 

It is miserable to work with as you can get splinters too easily. They go in very deep and are hard to get out. Be careful.

 

Boron is just about as strong in compression as in tension. It is close in strength to weight to carbon in tension. Structurally it is fantastic.

 

Eric

[AdamCord]

Ok back on topic...

 

So let me start off right away with my list of excuses:

This is an experimental method that I have never done before (vacuum infusion)

I'm trying to achieve and also show you how to build a factory quality ski in a garage without specialized equipment

This is not the easiest way to make something ski-able

Um...boat driving? Oh wait wrong excuse list

 

Alright now that that's out of the way. I built the first ski!....sort of. I've now built skis using at least 5 completely different composites manufacturing methods, and so far none have been an amazing success on the first try. That's just part of it though. Hopefully you guys can learn from me and we can all build great skis.

 

So here's how it went. First I put my carbon wrapped core into the mold, and placed the over sized carbon sheet on top. Over that went my acrylic top piece. I used Frekote mold release on the mold and the acrylic and it worked beautifully BTW.

 

Then I started with the infusion/bagging materials. Here you can see the spiral wrap running around the tail and most of the way to the tip. This is how the resin gets into the part:

 

Then I put the vacuum bag on. Here was my first mistake. I have used this green bag before (called stretchlon) and I knew it was terrible, but I ordered this stuff by mistake. I was hoping it wasn't that bad, but it's awful. Don't use it. Also the folds are called pleats. Pleats are your friend. The more pleats the better.

 

Then I did a vacuum drop test. This is where you pull vacuum and see if there are any leaks. I had a few small leaks around the bagging tape. Once I found those I was able to hold vacuum overnight. If you don't have a perfect seal you will draw air into the part during the infusion, leaving surface porosity all over the part. After I knew I had a good seal it was time to prep the resin. Now for a word about vacuum chambers:

 

You can buy a vacuum pot online for a few hundred $. Or you can do what I did and build your own. I used a 2 gallon aluminum pot and a 5/8" thick piece of Acrylic. The seal is just RTV silicon. Then I attached a vacuum gauge, bleeder valve, and some hose fittings. It works great and the clear top makes it easy to see what you're doing. Here I'm pulling vacuum on the separate resin parts (A and B ) to pull out any entrapped air or moisture. You want to remove all the air/moisture before making the part so it doesn't bubble up when you're making the ski. I left these in the pot for about an hour.

 

I then mixed the two parts together and put it back into the pot for an additional 2-3 minutes just to remove any air I may have mixed in. Oh and in case people ask, this is my vacuum pump. I've had it for years and as long as you keep it oiled it does it's job well: http://www.harborfreight.com/25-cfm-vacuum-pump-61245.html

 

Ok so now it's showtime. I am pulling vacuum at the tip of the ski so I raised the tip a bit higher than the tail. This helps any residual air stay ahead of the resin flow front. It feels good to finally get some use out of that workout bench I bought:

 

Then I pull full vacuum on the part, using the vacuum pot as a catch pot for resin overflow. To start the resin feed line at the tail is pinched off so I can evacuate all the air from the part. Then the feed line is placed into the resin bucket and the resin starts to flow. This is where the action is, and it all looks like it's going perfectly until.....DEVASTATION! The resin shoots up the spiral feed lines like it's supposed to and begins spreading across the ski like it's supposed to but then something horrible happens. The resin should slow down considerably when it reaches the end of the spiral feed lines, which is about 8" from the tip where the vacuum port is. This is what gives the resin time to also spread across the width of the ski.

 

But instead the resin shot directly to the vacuum port. WAY too soon. Resin began to flow out the vacuum port into the catch pot almost immediately. This is a nightmare for resin infusion. What this does is give the resin an easy path out of the part before it has had a chance to spread through the fibers. At this point there's not much one can do. So I let the infusion finish. The resin soaked into the fibers more than expected it would. First it looked like this:

 

Then like this:

 

Eventually the top was mostly wet out but I could see the porosity through the plastic. Also I was pretty sure that the bottom would look much worse than the top. After curing overnight under vacuum I pulled the part from the mold to assess the damage. The top actually isn't terrible:

 

But the bottom is beyond terrible. You can see all the dry patches:

 

Ok so analysis time. What went wrong? After looking more closely at how the resin moved to the tip (my slow curing resin gave me hours of agonizing time to watch it happen) and thinking some about what's really going on in the mold, I have come to the conclusion that my acrylic top was the problem. The way I built it the acrylic goes over the part and out into the flash. I had adjusted the core thickness so that the ski would stick up just a bit above the flash line, allowing the acrylic top to put pressure on the part and compress the fibers. But what this did was leave a gap around the edge of the ski between the acrylic and the mold. Any gap like that is basically a racetrack for resin. And in this case the resin used that racetrack to shoot right to the vacuum port.

 

So now I have a few options. I can try and make the core thinner, but then I won't get the pressure on the ski I'm looking for. I can forego the acrylic altogether. This is definitely the safest bet. The top will have some texture to it but who cares? It's not like these skis will end up on the showroom floor at Performance. The last option would be to cut my acrylic (or possibly a different, easier to work with piece of plastic) so it's just a hair smaller than the size of the top of the ski. That would allow it to put pressure on the ski and smooth out the top without creating any resin racetracks.

 

I'm undecided at this point about which way to go. I might go the safe route for the next one just to get a ride-able ski out..

 

 

[AdamCord]

Also for people who are wondering, I did go ahead and save this ski. I wet out the dry spots by hand and put it back into the mold. Then I pulled vacuum over the top to pull it down tightly into the mold. BTW you can do this from the beginning and skip the whole infusion thing if you want. You will be guaranteed to have some surface porosity and other cosmetic issues, but it will be ski-able and probably pretty good.

 

I popped my makeshift oven on top to speed up the cure time:

 

After pulling it out of the mold I cut off most of the flash with shears, then sanded the rest away with an orbital sander. I did have to do a decent amount of sanding on the bottom to get everything back to level but the final product is not the ugliest thing I've ever skied on believe it or not:

 

 

So I figure there are a couple good uses for this ski. First off I can use it as a reference for flex so I know how to adjust the layup for the next ski. Also I could use it as the base for some crazy prototype I might want to try. And who knows, maybe it skis amazing (although I doubt it...).

 

Some of the things I won't be doing with this ski:

Letting people I like try it

Using it as a show piece to display my amazing composites skills

Setting a new PB (probably)

 

[klindy]

Send it to @eleeski He'll like it...he skis on everything!! Oh wait that was "Mikey" from a cereal commercial long ago!

[mack]

@ADAMCORD ok so first infusion failed. If you do use a smaller piece of plastic and repeat the above infusion, will you post the process and results?? if one wished, could't one use sanding and a hot coat to remove the porosity and other cosmetic blems?

[Tyler_R]

@AdamCord I bet I can bribe @MattP into taking a set on it for you to test it.