Foam Mold for use with Vacuum

tomcat · Post by **tomcat** » Sun Jul 08, 2012 6:27 am

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?

deepskis · Post by **deepskis** » Sun Jul 08, 2012 12:03 pm

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!

twizzstyle · Post by **twizzstyle** » Mon Jul 09, 2012 6:49 am

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.

tomcat · Post by **tomcat** » Mon Jul 09, 2012 8:24 am

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

skidesmond · Post by **skidesmond** » Mon Jul 09, 2012 10:37 am

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.

twizzstyle · Post by **twizzstyle** » Mon Jul 09, 2012 11:16 am

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.

tomcat · Post by **tomcat** » Mon Jul 09, 2012 11:50 am

@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

skidesmond · Post by **skidesmond** » Mon Jul 09, 2012 12:10 pm

@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.

twizzstyle · Post by **twizzstyle** » Mon Jul 09, 2012 12:36 pm

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.

tomcat · Post by **tomcat** » Mon Jul 09, 2012 12:47 pm

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.

Damon · Post by **Damon** » Tue Jul 10, 2012 7:36 pm

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

tomcat · Post by **tomcat** » Wed Jul 11, 2012 2:17 pm

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...

Huck Pitueee · Post by **Huck Pitueee** » Fri Jul 13, 2012 9:38 am

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.

Head Monkey · Post by **Head Monkey** » Sat Jul 14, 2012 10:02 am

tomcat wrote: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.

Here you go: http://www.happymonkeysnowboards.com/Mo ... ge_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.

nfaust · Post by **nfaust** » Wed Jul 18, 2012 8:30 am

twizzstyle wrote: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.

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.

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Foam Mold for use with Vacuum

Foam Mold for use with Vacuum