Is casting this my only option?

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Risu

Master Member
RPF PREMIUM MEMBER
I'm about half way done with this helmet I'm working on and I've hit a wall. The base helmet has gaps where the ears are, and in the finished piece they've been covered with these plugs. I'm attempting to scratch build the plugs, and not having much luck. I was planning to stack three 1/2" foam exercise mats, cut off the beveled edge, and curve the back part around the helmet, then coat it with fiberglass resin. Unfortunately, in my tests the resin does nothing to harden the foam, even with fiberglass cloth added in. My original plan was to figure out a way to create a "pep file" drawn by hand on some card stock that I could fold into the shape, but I can't figure out how to do that. I've also got some pink insulation foam that I could carve into the shape, but EVERYTHING melts that foam, even regular Krylon primer. Anything I sculpt out of it will be incredibly fragile and will melt in short order. I've got sheet styrene, but not enough to stack up to the 1.5" thickness of the plug. Normally I would just bite the bullet and flush $50 worth of silicone down the drain to mold the foam and do a resin cast of each ear, but I don't know if I have the time for that whole process and the curved section in the back might make that plan impossible. I'm open to suggestions right now, can anybody recommend a way for me to do this?

Oh, and I'm just talking about the basic shape of it, all those little details and greeblies will be added later.

Photos thanks to Primrodo.


 

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Ozymandius

Sr Member
RPF PREMIUM MEMBER
Fortunately there is a very cheap and simple solution.

You had the right idea with the foam, but just used the wrong kind. Go to a craft store and pick up some green floral foam. It's rigid, carves easily, and doesn't melt when coated with fiberglass resin. Best part is that it you can get it for just a few bucks.

One note though. Most places will carry two different kinds of green foam. One has big open pours, and the other looks like packed blocks of sand. You want the sand like blocks as the resin will adhere to the surface better.
 

clonesix

Sr Member
Let me see if I understand your question after reading all that. You want to make an ear piece for the above helmet? Is that the same as the audio pick up, or the black hemi-sphere next to it? You want to make to fit into or onto the base helmet?

Polystyrene foam (pink foam) will melt if you use any type of solvent based paint, and you don't want to use sheet stock.

Can you get some polyurethane foam? It will not melt

Can you use 1/4" acrylic and stack it? I get scraps for free.
 

Risu

Master Member
RPF PREMIUM MEMBER
I have some "1/4" thick" acrylic (its actually more like 1/8", great honest marketing there) that I was considering using. I might possibly stack 3 sheets of it, carve the bevels, and then glue some card stock around the edge of it, fiberglass, and maybe rondo it for added strength. That was the last resort though as that 2' by 4' sheet of acrylic cost me close to $100 and I've been meaning to make stands for my blasters and whatnot with it.

The green floral foam won't melt!? That's news to me. How's the surface after it's coated with fiberglass resin? Is it smooth? What about rigidity? Since it is a helmet, I want it to be able to withstand the kind of abuse caused by taking it on and off, putting it down on tables, bumping into stuff, and possibly even getting smacked over the head, some con-goers can't be trusted to behave like adults. As for which section I'm talking about, I mean the big chunk there. Here's a picture of the original base helmet that I'm modifying. The big section missing at the side there is what I need to fill in.

 

robstyle

Master Member
Risu, how about using MDF as the base. If your handy with a dremel you can avoid the hot shards of doom acrylic will nuke at you when trying to shape it.
 

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Risu

Master Member
RPF PREMIUM MEMBER
Does MDF cut easier than wood? I tried shaping some wood grips for my Mal gun a while back and didn't get very far. I went through about one cutoff wheel per inch of material.

I'm going to try to find the floral foam today, I've never seen the dense kind before, but I've never actually looked. That feels like my best bet right now. If that fails I'll move on to the next option.
 

Nwerke

Master Member
The florist's foam is phenolic resin IIRC. It definitely won't melt from paint or resin. It can be a bit soft sometimes so take care not to crush it, or buy a harder grade if there is a choice. A slab of urethane foam would be the perfect solution if you have any suppliers (signwriters use a lot of it and may have scraps for free). Get some of that stuff in stock and it will change your life.
 

robstyle

Master Member
MDF is basically saw dust mixed with glue. Ive seen both amazing things created with it and utterly mind numbingly horrible things done with it as well. You dont want Ikea press board but actual MDF. Its sold is small sections at Home Labyrinth.
 

Ozymandius

Sr Member
RPF PREMIUM MEMBER
...
The green floral foam won't melt!? That's news to me. How's the surface after it's coated with fiberglass resin? Is it smooth? What about rigidity? Since it is a helmet, I want it to be able to withstand the kind of abuse caused by taking it on and off, putting it down on tables, bumping into stuff, and possibly even getting smacked over the head, ...

Floral foam is actually quite fragile and will break and crumble easily. So don't think of it as a structural material, but as a form to build something structural on. In other words, it's only going to be as strong as the material you put on top of it.

Polyester resin alone is going to be brittle. But layer in a little fiberglass and you've got a very strong piece.

Ideally, you could lay a single layer of fiberglass on top. Then remove the foam from underneath and reinforce the underside so that you don't add extra mass to the surface.



The best way to use it for this application would be as a buck to build your panel on top of, and then remove the foam when it's done. This way you would have access to the underside so that you can reinforce it.
 

NormanF

Master Member
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...I'm going to try to find the floral foam today, I've never seen the dense kind before, but I've never actually looked. That feels like my best bet right now. If that fails I'll move on to the next option.
There are two densities of floral foam that I am familiar with: one that will dent while you just look at it on the shelf and another that is more rigid. The stuff I used as a core for the Mini-Nuke I am working on is "Desert Foam" made by FloraCraft. It's not as rigid as styrene foam or the pink stuff so you still need to be a little careful with it. I used one layer of resin on top of that and it was a bit rough. I would think you could use two or three coats and then sand the final coat. Or do like I am and cover it with body filler and sand that smooth with 320 grit paper.

I like the idea of using the foam as just a form and removing the foam later. Hope I remember it when I need it.
 

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Risu

Master Member
RPF PREMIUM MEMBER
Thanks for the advice everybody. I'm about to head out to get some stuff at Home Depot and Michael's, so I'll check out the foam and MDF.
 

Risu

Master Member
RPF PREMIUM MEMBER
I did a test with the resin on the sand-like floral foam and the results were excellent. I'm not sure yet if I'll just put several coats of resin on or if I'll hollow it out and fill it with some rondo. I'll play it by ear. Fiberglassing the outside probably won't happen though, because getting the cloth to stick to the surface and not get bubbles underneath seems impossible. It would just mess up the shape. I'll do the carving tomorrow. The bricks are kind of small though, can anybody tell me what type of glue works best to hold two bricks together long enough to resin them? I've got Elmer's, 2-part epoxy, E6000, 3M 77, Super glue, JB Weld, hot glue, and Barge.
 

Ozymandius

Sr Member
RPF PREMIUM MEMBER
The surface of the green foam is so crumbly that glue is next to useless. Best bet is to pin the pieces together with some skewers. Popsicle sticks or something similar.

And you can always put the fiberglass on the inside to reinforce your part so you don't mess up your surface. I like to lay the glass out on a pallete and wet it down with resin before applying it to the part.
 

NormanF

Master Member
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I did a test with the resin on the sand-like floral foam and the results were excellent. I'm not sure yet if I'll just put several coats of resin on or if I'll hollow it out and fill it with some rondo. I'll play it by ear. Fiberglassing the outside probably won't happen though, because getting the cloth to stick to the surface and not get bubbles underneath seems impossible. It would just mess up the shape. I'll do the carving tomorrow. The bricks are kind of small though, can anybody tell me what type of glue works best to hold two bricks together long enough to resin them? I've got Elmer's, 2-part epoxy, E6000, 3M 77, Super glue, JB Weld, hot glue, and Barge.
If you got the super soft stuff, I don't know what to tell you. The desert foam you can use Elmers, but it takes at least over night to dry.
 

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Risu

Master Member
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I got the dry sand, not the wet stuff. I'll do a test with Elmer's, but I don't really have that long. Maybe I'll coat a popsicle sick in 2-part and stick it in to pin them together.
 

Risu

Master Member
RPF PREMIUM MEMBER
This stuff is incredibly frustrating to work with and I'm doubting it's durability. Tomorrow I'm going to pick up a sheet of MDF and try my hand at that. So long as I can finish the job with a dremel tool and I don't need any kind of fancy saws, I should be fine. Way less work to get it paint ready, too.
 

robstyle

Master Member
be easy with the dremel on MDF as it will sand like nothing with that high speed and paper grit. You can bondo MDF to repair the surface or coat it if need be. You will need to seal it if your after a usable part and not a master for molding. If so you want a filler primer. Ive cheated around that before and used gloss coat but again, only when molding MDF and not as a usable part.
 

Risu

Master Member
RPF PREMIUM MEMBER
What kind of negative effects would I expect if I only primed the MDF with regular Krylon primer? Would multiple coats of that still get the job done? Basically I just don't want to go out and buy an $8 can of primer if I don't have to. $8 is a pretty large percentage of my monthly budget right now.
 

NormanF

Master Member
RPF PREMIUM MEMBER
I was afraid that soft foam would not hold up. Even the stuff I use is mostly there as a base for resin and body filler.

Make sure you wear a respirator while you work on the mdf.
 

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