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

[AdamCord]

I was talking with @Horton and I told him that this winter I'm going to try and build some skis with a new technique in my garage. He suggested I post about it and that lead to me doing an entire How To / DIY ski build thread. So what I'm going to do is try and document the process here as I do it.

 

For all the people who don't know who I am I'm an engineer that used to be in the watersports industry designing / building skis. I started really skiing competitively in college at Purdue in 2002, and have been obsessed ever since. My tourney PB is into 39 @ 36mph so I'm by no means a "pro" skier, but I try and get after it. After getting a real job I tried to just "ski" but I've found that I can't stop playing with ski shapes, fins, bindings, etc.

 

I find it surprising that more people aren't experimenting with their own slalom skis. With all the DIY / Maker / 3D printing type stuff going on more and more people are building complicated products at home. There's even an entire forum dedicated to DIY snow ski building.(skibuilders.com) The only other "home" slalom ski builders I know of are @eleeski and @adamhcaldwell. I'm hoping that by showing in detail how to build a high quality and high performance scratch built ski at home I can inspire more people to get into the hobby. If nothing else this might take some of the mystery out of what goes into designing and building a slalom ski.

 

It's turning to winter up here in NY so I'll hopefully have time to get this project done fairly quickly. My wife is about a week away from popping out our first kid so that might slow me down a bit but I'll do my best!

[AdamCord]

So the entire process will look like this:

Build a "plug". A plug is basically the opposite of a mold and is used to build the mold from.

Build the mold. I'll build this in a similar way to how a boat is built, by using gel coat and fiberglass.

Build a foam core. The method I plan to try is a bit experimental so it may take a few tries to get right.

Layup and "press" the ski. I plan to use a resin infusion method that I've been thinking about for a while. This is VERY experimental so there's a chance I'll ruin a few skis before I get this right.

Ski finishing. This is pretty straight forward and involves cleaning off the flash edge of the ski, cutting a fin slot, and installing metal inserts to mount the bindings.

[AdamCord]

Right now I'm in the middle of building the plug. You could try and build this from scratch but I never would. It would take way too much work to try and shape it by hand and the chances of ending up with a decent ski shape are pretty low. By far the easiest way is to build a plug using an existing ski. You could copy an existing ski shape if you wanted, or you could modify the shape of an existing ski. Modifying an existing ski is what I do. This allows you to test your modifications on the water before spending all the money/effort of building a mold and ski.

 

What I usually do is take a shape that I like and start modifying it. That could mean splitting the ski to adjust the width, adding bondo and sanding, filing/sanding the bevels, heating it and changing the rocker, etc. Obviously you're going to ruin a ski or two doing this so it's not for the faint of heart, and I don't suggest you go out and buy a brand new ski to test with. What most manufacturers probably don't want you to know is there really isn't that much of a difference from skis built 5 or even 10 years ago vs. skis today. So use an old ski.

 

The ski I'm using for this project was actually built by @adamhcaldwell. His shop is basically a mini ski factory with a pneumatic press and every tool you need to build skis. It's a sweet setup and I am very jealous of him. The shape itself is something he and I worked on together and then we had a plug cut on a cnc machine. So this shape isn't based on any production ski. I rode this ski for most of the summer and made some modifications to it, and now I will turn it into my plug.

 

This ski was never intended to be "production quality" so it had some pin holes and blemishes, not to mention the cuts and other imperfections that I added by making changes to it. So what you can see below is the process of filling/sanding/painting that went in to getting a good surface finish. It's important to try and get the best surface possible now on the plug since any imperfections will get transferred to the mold. I will wet sand the plug and polish it to a shine before getting it ready to build the mold.

 

 

 

 

[thager]

Ahhh! So that is where @Horton got the email pic!! I might have to give this a go this winter. Been a long time since I built Indy car wings but the process sounds very similar.

[lcarnes]

I'm going to have fun watching this process over the winter!

 

[rq0013]

This is awesome. I love it! I would think making the plug would be the hardest job. I've been wanting to build a slalom ski but it seems so complicated with all the variables. So I built 2 trick skis out of pvc foam and carbon, uni and bi directional. Rides great, but a slalom ski is a different story.

[AdamCord]

So in order to make a mold from this ski I have to add a flange to it. The flange will create the geometry for the flat areas around the mold cavity. You can probably use a lot of different materials like plastic or sign board, but I had some 1/4" plywood so that's what I'm using. I'm not sure what type the wood is but it's got a very smoothe surface on one side so it should work well.

 

Before attaching it to the ski I sealed the surface with some cheap home depot polyester resin. I just used a standard foam paint roller. Once it was cured I spent about 10 minutes with a palm sander getting it smoothed down, and now I have a nice flat surface.

 

Here's the wood right after applying the resin:

 

After sanding down the board I centered the ski on it upside down so that I could attach the board to the ski's top. I drilled ~20 holes in the board and ski and used wood screws to attach it.

 

 

I want the new ski to be stiffer in the tail than the original. I could do this by adding layers of carbon to the layup when I build the ski, but it's better to make the ski thicker if possible. Stiffness increases with the cube of thickness so adding a little thickness goes a long way. I added some washers to the screws in the tail area to add the thickess:

 

In order to make a clean edge at the ski parting line and to fill the void left by the shimming I did in the tail, I filled the seam between the ski and board with some bondo type body filler. This part is tedious but it's important to get this right, otherwise it'll screw up the mold or I could end up with an undercut, which would make the mold mechanically lock to the plug. That would not be cool.

 

Next I'll sand that body filler down and *hopefully* be left with a nice clean edge.

[Horton]

I am surprised that you are using thickness to tune stiffness. I would have thought that thickness needs to be tuned for ride height.

[AdamCord]

@Horton that's true, but I'm normally a believer in thicker is better in that regard. Skis that are too thin tend to shut down pretty hard at apex, which is where you need it to carry speed. Obviously there's a limit there because with carbon the ski can get way too stiff very quickly. That's why modern carbon skis tend to be thinner than old fiberglass skis.

 

For this ski it was a bit too thin so I had to add extra carbon in the tail to get the numbers up. I'd rather avoid that.

[JAS]

Maybe an unspoken topic but what keeps a ski company from building a plug off of a successful ski made by another company? A change to top skin cosmetics and most of us would never know difference.

 

 

 

[Chef23]

@JAS there are rumors that other companies have used other ski designs as the foundation for their skis. Other people may know better than I do.

[Horton]

@JAS all good ski designers look at other designs. There is more to a ski than pure shape. Two skis of the same shape but built by different factorys will generally ski nothing alike.

[Mateo_Vargas]

DIY skis are cool but how about a DIY gasoline thread for the winter?

[skier2788]

@Mateo_Vargas did that in college. Not hard to get 48 octane but to go further than that gets difficult. We ran an old ford van on it. Ran like a diesel. This DIY ski project is cool have tried a couple different times to no success played with bondo and old skis some.

[Mateo_Vargas]

Well I guess I'll keep watching Moonshiners on Discovery Channel for tips or throw a diesel in the old MasterCraft like this guy in Turkey.

 

http://www.mastercraft.com/teamtalk/showthread.php?t=33716

[eleeski]

Adam, very cool!

 

One advantage of homebuilding is freedom from marketing driven finish. You can finish as a work of art without regard to cost. On the other hand, you can ignore the finish and its weight. You can use sawzalls, grinders and rough bondo to experiment. There's a good chance you'll end up doing a LOT of post molding work. Don't stress too much on the finish of the plug. Pick up some Superfil from Aircraft Spruce and lots of sandpaper to finish the ski to taste.

 

@Horton‌ Cap molding techniques can control flex control thickness without affecting the edge profile. Plus an edge built up with Superfil will not add too much stiffness. Thickness is a very useful tool to adjust stiffness.

 

@Mateo Vargas Homebrew fuel might be more fun in other applications than in your gas tank.

 

Eric

 

[AdamCord]

@JAS there's nothing stopping a manufacturer from copying someone else's ski. That's how a lot of startups get going. I know of at least one popular ski on the market that's a blatant rip off of another company's ski...

 

@eleeski I think we have two different ideas on this. I could build something ski shaped and then spend time tuning the shape in. Or in this case I can tune the shape first using an existing ski and then build a plug/mold from that shape. There are advantages/disadvantages to either way but I already spent the summer playing with this shape and I know it's really good. If I spend time now getting the plug perfect then I won't have to spend much time at all working on the ski after it's molded.

 

Also my motivation for this project is more about trying a new manufacturing technique that as far as I know hasn't been done. We did RTM at Obrien but that was a faster process that uses highly specialized equipment. The way I plan to do this ski (Resin Infusion) is a slower process that uses almost no specialized equipment (vacuum pump), but can theoretically make a better part.

[Stevie Boy]

Kewl, I watched a video on resin infusion, looks very good way of doing it.

 

I appreciate you are going to go through various stages, but these are some of the areas of the process, where people could come unstuck.

 

Question # 1 I take it there will be some sort of core material, that you wrap the carbon fibre around

 

Question # 2 is it going to be difficult, drawing resin, through the mould evenly.

 

Question # 3 the product of resin infusion, comes out pretty slick with a high gloss finish, surely that is not what you want on the underside of a ski.

 

Question # 4 regards flex, how do you know where and how much extra carbon, to place, to get your desired flex, I take it you use extra carbon and not some other material.

 

 

[AdamCord]

@Stevie Boy all good questions, I'll try and answer them as clearly as I can:

 

1. For this ski I am going to "cast" the core from 2 part polyurethane (PU) foam. This is the same type of foam that is used on lower end skis and that Connelly used for years in the F1/Prophecy. Now all high end skis on the market use a PVC or similar foam but that can't be cast, it has to be machined on a CNC. Since this is the DIY/at home version I won't be using a CNC. To get the same strength properties as the PVC I'll have to run a higher density PU, which means this ski will be about ~1/2 pound heavier than it would be with a PVC core. Not a big deal in my opinion. Some of the best skis I've ever ridden barely floated.

 

2. I've never used resin infusion to build a ski but I have some ideas on how to do it. I think I can figure out a way to make it work consistently, it just might take a few goes. @tap is a composites engineer that I went to Purdue with and he's been very helpful in determining the best way to do it.

 

3. Not necessarily. Take Horton's beloved Warp as an example. Your wife could do her makeup using that ski as a mirror it's so glossy. Surface finish definitely changes the way the ski rides, but I don't think one is better than the other, it's just different. Also it's easy to change. A few minutes with some sand paper and I can put a "textured" bottom on this ski.

 

4. Honestly this is just a combination of trial and error and experience. I've tried several times in the past to come up with a way to calculate the stiffness of a ski based on layup, but the geometry on the bottom of the ski is so complex that it just never really works. (If someone thinks they might know how to do this accurately please do share!) What I normally do is take a guess based on past experience but aim for the ski to come out a bit soft. Then I can add carbon to the top of the ski to bring the stiffness up to the desired level. Then I can base the layup of the next ski off of what I learned from the last ski.

[gsm_peter]

In case this helps anybody

2 cents for DIY on how to vacuum a laminate.

 

Have a friend that made model plans.

Wing was 2 m wide (6,7 feet) at 250 g weight (half lbs).

Did break at 50 kg load (+100 lbs) on the middle.

Carbon fiber, epoxy, foam. Laminated with use of vacuum and later high temp.

 

Vacuum was created by

- Putting the mold with wet laminate on a piece of window glass (very flat)

- Create a ‘plastic bag’ around it using thick plastic and tape (towards the glass)

- Put in a thin metal pipe with many small holes parallel to the object.

- Use a water hose connected vacuum pump to gradually create the vacuum.

- Use a soft rubber piece to ‘massage out’ un-needed resin (poor down outside of the mold)

- The water driven pump only need some gallons per hour and will create a pressure of almost 10 000 kg / sqr meter. (type 2 000 lbs / sqr feet)

 

Best luck!

[Chef23]

Very cool thread. I have read it a couple of times now and I will be interested to see the results. It is way beyond my abilities but interesting to follow.

[eleeski]

Adam, I completely understand your motivations and unique methods. And I commend them. And I'm really interested in the home resin infusion!

 

Also your plan to control variables is spot on. If you have evaluated the basic plug, that is an excellent baseline. Little changes in flex, weight, weight distribution, finish and many other variables can radically alter the feel of a ski. Control what you can.

 

I'm not sure that my crazy shapes intended to be that way. OK, some did but I'm not sure any of those ever getting seriously used. Most of the unusual features ended up as a result of tuning. Not fin dialing but grinder tuning. Skis are expensive and time consuming. Grinders, Bondo and a Surform not so much. I'm cheap and lazy so I might work too hard to salvage a sketchy ski. And yes, I did originally start with a factory ski and now I copy the skis of my own that I like. There is a lot of post molding finish that I end up doing.

 

My motivation was (and is) to push the limits of how light a ski could be. Perhaps if I had invested the time and money in more practice rather than building I'd have gained a couple of buoys or picked up another trick. But my recreational engineering has sure been fun. And maybe I'm actually a better skier because of my skis. At least I need to believe.

 

And Adam by sharing his experience here is entertaining us. Thanks and keep it coming!

 

Eric

[skiray]

@AdamCord thank you for this post. I've always wanted to build a ski just for fun.

 

Are you going to add any suggestions on where to get the materials needed? (Later in the process)

[tap]

@gsm_peter‌ , if I read your post correctly I think what you are describing is a "wet bag" technique. A similar process to what @AdamCord‌ is getting after, but different. Wet bagging generally implies wetting out the fiber during the layup process then using ambient pressure, via use of a vacuum bag and consumable stack, to consolidate the layup and press out air and excess resin. @AdamCord‌ is hinting at using more of a vacuum assisted resin transfer process whereby the layup would be constructed dry, then the resin would be forced through the laminate using ambient pressure, via use of a vacuum bag or vacuum cavity.

[Mateo_Vargas]

Am I the only one that thinks @eleeski builds his own skis just for the fumes?

[Drago]

On # 2: there is a fabric you can run down the entire length that will distribute the vacuum (would pull the epoxy up around the edges to the top)

[bishop8950]

Great thread, thanks Adam! I remember Jamie talking about how he wished there were more home grown garage operations like the snow ski industry. If Adam gets it working without CNCs and presses it will be interesting. Looking forward to the rest!

[gsm_peter]

@tap‌

Yes you a correct. Some difference.

 

It was a looong time ago when I assisted him building epoxy (type 1983 or so).

First vacuum machine came from an old fridge. Did not last so long.

The water driven vacuum pump was expensive then (type 30 USD or so ;)

 

The important hints are

- Water driven vacuum pump are rather cheap and creates almost 'space vacuum'

- Window glass is very flat and creates an excellent building surface.

- Regular tape (example for use for 'moving paper boxes') can be used to seal plastic

 

=0)

 

 

[AdamCord]

@eleeski that's interesting that you've focused on making the ski light. I notice very little difference between light and heavy skis and I would much prefer a ski that will never break/break down. I could also be a bit jaded though because I seem to have the unique ability to break skis at will. It's not as much fun as it sounds.

 

@skiray good suggestion I'll definitely list the materials used for each step and where I got them.

 

@Drago yes that's called flow mesh or flow media and it's very commonly used in large parts like boat hulls and wind turbine blades for infusion. I may use some of it around the edges of the ski but I don't want to use any on the part. A big part of the challenge of what I'm hoping to do is end up with a smooth surface on the top and bottom of the ski. That means using no peel ply or flow media on the ski itself. I will use a piece of 1/4" thick acrylic as the top half of the mold, which will give a nice smooth/flat surface finish.

 

@bishop8950 what I REALLY want to do is build on of these! http://www.cncmogul.com/. Then I could cut the mold, cut the core from PVC, possibly even do the finishing on CNC.

[dbski]

@AdamCord , have you checked out Shopbot CNC machines? I use one of their smaller machines to cut the graphics and smaller parts of my wood decorative skis. They are fairly reasonably priced. I find this thread really interesting as building things yourself whether its skis, boats, cars or houses is incrediably rewarding. Seems like this is common trait to alot of skiers.

[jimbrake]

@AdamCord‌ - there are a lot of surfboard shapers who use CNC machines to shape their blanks. I wonder if one of them would cut a water ski core if you provided the specs for their program. Hmmm. This has me thinking now.

[AdamCord]

@dbski I've seen shopbot but they're still pretty expensive for a garage shop. The cnc mogul type kit allows you to build it to exactly what size you want and it's about 1/10th the price of a shop bot. It isn't nearly as fast/powerful as a shopbot but in a non commercial application I don't see why you would need it to be. I hope to build a cnc that's just big enough to do ski related stuff. and still allow me to park the car in the garage.

 

@jimbrake That's basically what we did with this last ski shape. Custom kitchen/panel shops have cncs that work perfectly for this sort of thing and the price isn't crazy. The hard part is doing the CAD. CAD for skis is really difficult and you can't expect a machine shop to look at a ski and put it into digital easily. 3D scanning is an option but it's expensive for something as big as a ski. I was lucky enough to learn how to do ski CAD when I was at Obrien :smile:

[AdamCord]

So back to work...

 

I was a bit too liberal in my application of body filler around the edge of the ski so it was a PITA to get it all sanded down, but I did it. Next time I'll mask the board AND the ski and try to only put down as much as I need. You can see in one of the pics previously posted how much I used.

 

It's important to get the sidewall flat AND make sure there is still a draft/taper. If the sidewall is concave at all, the ski will have a lip on the top edge and it will do all sorts of weird things on the water. If the sidewall is convex, the mold will lock to the plug. Here's where I was once I got the body filler mostly sanded down:

 

I used a file to remove material until the body filler and ski were flush all the way around the ski:

 

Then some light sanding to get rid of any ridges or high spots before applying a coat of primer over the whole plug. This is just cheap Rustoleum automotive spray primer from a rattle can. I'll be able to wet sand this down to a nice surface, and then it'll be time to build a mold!

 

 

 

 

 

[eleeski]

CNC cores? Old school uses the skil saw set on the TLAR angle and depth then pulls sideways to cut the tunnel. A jig gets the silhouette and a router makes the edges.

 

Or even lower tech just slits the core longitudinally to make the bottom of the core conform to the mold's tunnel. Shape the silhouette by stuffing it in the mold and filing it until it fits.

 

Finish with Superfil and block sand to make things straight. Very low tech.

 

It's really hard to exactly copy or reproduce a ski that way.

 

Eric

[AdamCord]

Just so you guys can see what I'm working with, I uploaded a video of one of my passes on the prototype of this ski. I'm not generally known as the smoothest skier on the lake, so for me this is decent. It's only 32off but it gives you an idea of what I'm going for. This ski was too stiff and had some other issues but the shape itself is great IMO :D

 

[DW]

@Adam: we could scan a ski for ~$500 and capture the ski surface.

[GOODESkier]

Where is your lake? @AdamCord‌

[AdamCord]

@DW That's not too bad

 

@GOODESkier that's Twin Lakes just outside of NYC

[gginco]

@adamcord Any update on the ski build project?

[Horton]

@gginco‌

@AdamCord‌ might be a little distracted at the moment. Not only has he been building skis but he just popped a baby out of the press last week.

[MattP]

@Horton‌ I think his wife did most of that work.

[AdamCord]

@gginco I was all ready to get started on the mold last weekend when the contractions started. Mini me popped out Sunday night! I'm hoping to get some work done on the mold tomorrow. I wonder if sleep deprivation will effect my ability to do a good job...

[eleeski]

Congratulations! In a few years you will have another ski tester. Certain to improve your ski and skiing.

I'm not sure the sleep deprivation ever ends.

Eric

[ToddL]

@AdamCord I hope your wife didn't need too much mold release when "mini me" popped out of the mold. Those latest generation "mini me"s are really cute, but they need a lot of post production tuning. It takes several years to get them setup just right for optimal performance. Then, sometime around 13, the fin seems to get a little loose and you have to work a lot harder to keep 'em tuned up. Have fun, because the best years are going to be coming at you quickly now!

[skiray]

Congratulations @AdamCord‌

[gginco]

@AdamCord‌ Congratulations Adam! Good to hear you're doing your part to keep the sport alive! haha. Enjoy! It flies by!

[AdamCord]

Thanks for the kind words and also the advice guys! When do kids learn to slalom? I have a few different ideas on how a kid's ski should be designed...

[TylerR]

@AdamCord‌ depends on how addicted the parents are.. My siblings and I learned at like 6 or 7.

[DW]

@Adam: congrats to you and mostly your better half, I think she did most of the work...

[Stevie Boy]

@Adam congrats, by the way your thread has inspired me, I am thinking of doing something with my sixam 2 that I loved, until it went too soft, I was thinking keeping the shape but create a tunnel on the underside through to the back of the ski, does that sound like a good thing or is it a case of suck and see.