:: View topic - Foam Mold for use with Vacuum

I spent quite a while doing research and reading around the forum for a looong time and I hope that by the mid of September I will be able to gather everything and start building my first pair of skis

. I want to go with a vacuum setup because a pneumatic press is much too expensive and complicated to build.

Regarding the mold, I was thinking about using extruded polystyrene, covered up with fiberglass. After covering the whole mold with fiberglass I want to put a thin aluminum/plastic sheet on top that can be covered with mold release wax so I can get the skis out of the mold.

I have a friend who does CNC commercial signs out of the stuff, and I could get cheap access to make 10-15 mold shapes out of 30mm thick polystyrene. I was thinking about it since the material itself would be much cheaper than using MDF boards, and having access to a CNC router would mean a lot more precise results than just cutting MDF with a jig saw.

Considering I am only intending to use the mold for vacuum bagging and curing at room temperature, I don't think there would be any structural problems.

I am also considering building each plate of the mold out of 2 parts since I can't seem to find any 2m long extruded polystyrene sheets; largest I have found are someting like 1.25m long. I was thinking about drilling 2 holes in eacch 1/2 finsihed plate and then joining them with 2 round internal wood spars, so I could have a finsihed plate; after this would be done, I could glue all 20 or so (depending on thickness) finished plates and finally cover the whole thing withh fiberglass.

Do you guys think this could work?

Hi tomcat!

I am sure this will work out just fine with a vacuum setup!

Good luck and please let us know how it works out!

Why not use the pink insulation foam stuff from the home supply store? It comes in 8ft long, 2" thick sheets.

If you have any concerns about the foam crushing under vacuum, just tape the bag to the mold surface itself (rather than wrapping the entire thing in a bag). That way the foam won't have any pressure applied to it.

Thanks for the reply!

The stuff I was thinking about is actually green :P. I live in Romania, and only did some research on the internet regarding insulation foam, as right now I am doing a 3 month internship in Ireland; that's why I only predict starting the project in September.

Anyway, it's a nice idea to only tape the vacuum bag only to the mold surface; I'll have to keep that in mind.

Another thing I had in mind and I'm not sure will work: would it be possible to heat the edges red hot and bend them along a template at the tips and tail, while they are still hot? I know this will anneal the steel, but I was thinking about reheating the edges after they cool down and quenching them in water to regain some of the strength; they might change their shape a little after I quench them, but I guess it will be far easier to adjust them by hand afterwards, rather than just do the whole bending by hand with the edges annealed. I was thinking about this solution as a way to get around building an edge bender as I don't have access to the necessary machinery to mill the parts.

@twizzstyle: I will definitely have to build a tip bender like the one you did; I saw the video you posted; that tool is sick! And more importantly, it seems quite easy and inexpensive to build

.

Will keep you guys up to date and once I complete and I am happy with my design for the shape and core profile I will open a new topic for critique :P

There's no need to heat the edges for bending. You saw Twizz's edge bender. That's really all that is necessary. Even if you don't have an edge bender you can still accomplish bending the edges w/o heat. Also pre-bend the edges to form the tip. You don't need to be exact in the bending, just want to give it a head start.

If you do a 3/4 edge wrap, instead of a full wrap, that will make bending a lot easier. Lots of guys are using modified tile nippers for bending edges by hand, if you don't want to build a bender.

@skidesomnd: I was talking about bending the edges at the tips and tails with the base flat, before bending them for the tip and tail radius. I was just thinking about bending them around a flat MDF template while hot and then trying to restore the temper by quenching them.

@twizzstyle: I'll give it a thought, regarding the 3/4 edge wrap. Where I ski, I tend to come down hard on rocks and there is a lot of ice/ sasturgi (really nasty stuff to ski on, I know...) so I thought a full wrap would give better durability and a better finish.; but you may be right and I might just be thinking too far ahead for the first pair.

Did you have any problems when bending tips and tails for radius, with the superglue bond failing or any stuff like that? Your video seems almost too god to be true

@Tomcat - I get what you're saying, but you really don't need to heat the edges. It just takes a little bit of time to bend a tight fit. Modified nippers work well as Twizz mentioned.

I do a 3/4 wrap. I ski New England and we have plenty of hardpack and ice to choose from :-) . A full wrap does look better but as for durability, assuming a good bond of materials, a 3/4 wrap works fine and simplifies the edge bending process.

Yeah especially for your first pair, you've got enough other potential issues to worry about, keep the edges simple!

Sometimes the edges will pop off the super glue in a few places using my tip bender, but if the edges were bent properly (with the edge bender) in the first place it doesn't really matter. Just needs to hold the edge in place long enough to make it into the mold for layup.

For my very first pair I heated the edges until red hot and tried to bend them. I ended up over-bending, and then unbending, and repeating and they ended up looking terrible. Cold-bending seems to be the more preferred method nowadays.

I'll do more research on the modified nippers; I think I remember seeing something around here that involved cutting a small trench with a dremel so the tang of the edges would fit.

Glad to hear I'm not the only one who isn't so blessed that offpiste skiing automatically means powder. I actually enjoy hardpack, ice and corn snow. It's the breakable crust and sasturgi that gets me.

But imagine how it feels when you actually get powder, if you get to the point where you can say you had a good day on breakable crust :P.

Careful when selecting a resin system for the tool - polyesters will dissolve polystyrene. Also, most tooling foams are polyurethane, as they are more dimensionally stable. But if you're looking to get a part or two from the mold, you shouldn't have a problem. Machining that is gonna get messy...

Damon

I know about the issue of polyester dissolving polystyrene; I will go with epoxy and I think it will be a nice opportunity to test the resin system I will use for building the skis (though a little expensive maybe). I used to build model aircraft wings with some friends by using the same technique a few years ago and that's where the idea came from.

Regarding the part with cutting the mold shapes out of polystyrene, the guy I know that does the commercial signs out of the stuff has a hot wire cnc cutter, so in theory there should be no mess(or at least nasty polystyrene dust) at all.

Thanks for the input about dimensional stability. I have to admit that I haven't thought how differences in temperature/humidity could affect the mold. I'll have to do more research on that...

Personally I'd use mdf because by the time you cut and glass the foam you could have made a form with mdf which is a WAY better material to use. Mdf is just very heavy to move around.

Here you go: http://www.happymonkeysnowboards.com/MonkeyWiki/Edge_Benders I avoided making a nipper tool for a long time, but I found I really needed them the first time I bent edges for a pair of skis.

I used this pink insulation foam (I believe it is polystyrene as well) to make a CF longboard a few years ago. I sealed the bag to the table and didn't have any issues with crushing the foam.

I don't really see any reason why skis would be any different, so I'm thinking covering it with fiberglass is overkill. I just used plastic packaging tape and some mold release and had a decent surface finish on the board.

hmmm, that seems very interesting interesting.

It would save a lot of work and fiberglass/epoxy. Nice idea with the plastic packing tape and mold release; will have to remember that one; I also guess it's very easy to just replace the tape once you pull the skis form the mold and you end up with a nice, clean mold all over again.

With the skateboard, I had epoxy-laden fiber right on the packaging tape, and I definitely "lost" (ie - broke off) some of the mold when I was removing the board. It wasn't a big deal for me as I was only making one.

I guess it depends on how tightly you control your epoxy. If you're going to have alot of overspill, I would assume you run the risk of breaking off some of the mold.

Perhaps a thin sheet of AL or melamanine (something that will flex to the contours) over the top of the mold would be a better option if you're planning on reusing the mold.

There's no way you'll get even remotely flat bases if you're just laying a ski straight onto foam. You absolutely need to sheet it with something (sheet metal, some kind of stiff-ish plastic sheet, or formica might work)

You're absolutely right about it twizzstyle; I think I just got too excited in the moment thinking I could make things even more simple.

I'll have to think about what material to use so it can easily take the contour of the mold, but still offer enough support to get the bases flat.

I guess it's a lot easier to just use screws if one has wood underneath...

Maybe the initial idea about using fiberglass wasn't that bad as it seems that way there isn't a problem to get it to the shape of the mold.

Do you think that it would be enough just to cover the fiberglass surface with a plastic sheath that doesn't bond to epoxy, or is that just asking to get the skis glued to the mold?

Also, would there be any problem with base flatness from the texture of the fiberglass?

Whatever the surface of your mold looks like, will transfer to your base. If you have a tiny speck of dust, you'll get a big dimple in your base. If it's a rough fiberglass texture, that will show up on your base too. It can all be sanded out, but it's not ideal.

It'd be cheaper to just get some formica and glue that to the foam, it will form to the shape no problem. As for how to prevent things from sticking, that's what mold release wax and parchment paper are for!

I'll try to look for some formica; never worked with it yet.

At first I was thinking about using some 0.3mm aluminum sheet, but I don't really think I can bend it precisely enough to the mold shape.

Good to know that the mold surface has to be as close to perfect as I can get it; since you said that even some dust can cause base flatness problems...

Thanks for the advice again

Foam works great as a mold for vacuum bagging, I have some photos showing a part I made entirely out of styrofoam molds (not skis) it worked great. What has been mentioned about surface finish is absolutely true. There is an amazing polyester based surfacing primer called duratec that will produce a perfect mirror finish on the mold after a bit of buffing. They sell a styrofoam safe version that works great but requires a spray gun with a large nozzle.

I'll post some photos of the process tomorrow

I've been thinking about possibly making skis this way, I'd use 2 pieces of MDF with pink insulation foam set in-between for the mold profile, rough cut with a hot-wire and finish with a large sanding block, not too different from how core profiling with a router works. Then Duratec and bag the skis, here in Colorado I can pull about 20" Hg of vacuum which should fine.

Agreed, that sounds like the easiest/cheapest method.