Fiberglass...

[Jidis]

I had a post at the tail end of Sasa’s DIY illuminated buttons thread the other day about some fiberglass enclosures.

I did a small WinampLCD box as a test, which turned out surprisingly well and have some pictures and info which may be of help to someone here.

This is most of the photos, but the whole batch is at http://photobucket.com/albums/y193/Jidis/

Some of them aren’t that clear, but should get the idea across. To summarize, I started with a CAD sketch of the dimensions I would require

I laminated two pieces of soft (easy to work) 3/4" pine and a piece of 1/8" hardboard to get the 1&5/8" that I wanted for the height. This was glued to an oversize piece of hardboard to serve as a stop and guide, while it was in the form. I marked guide lines on the block of glued together pine and chopped away at it to get the shape I wanted. (This was actually done on a radial arm saw, but it probably could be hand cut) The corners were rounded over where need be, some with a small belt sander, and some by hand. You could also probably just smear putty or plaster into the inside corners of the female plaster mold after it dries and get the same result.

I hotmelt glued a rough plywood box together to the overall outer dimensions I needed, filled it with wet plaster, greased up the wood model with petroleum jelly and lowered it into the box. After it set, I removed the wood model, cleaned and touched up the inside mold with putty and sprayed it with clear lacquer (I had read of this, but I don’t like it. I think there’s something which would adhere to the plaster better).

The original model would also be used for the male (inside) half of the mold. It could be shimmed upward to the target thickness for the enclosure, but the sides would need to be trimmed down to create gaps in those directions. I drew lines 1/8" from all sides and sliced that off (again with the radial saw). The corners of the male mold were also chopped around 45 degrees to allow a build up of fiberglass in the corners, which might be used to secure the bottom with screws.

Shims were glued to the box edges to create the upward gap

Now the promising part- I made paper templates of the holes I would need for my buttons and LCD, and stuck them to the wood model. I then glued pieces of 1/8" hardboard, cut to the required sizes onto the layout. The excess paper was cut away afterward.

I thoroughly greased both molds, took a couple big globs of the filler (in the round quart can), and liquefied it with resin (the big square can), mixed it with some of each hardener, and poured it into the boxed form. I think I smeared a bunch of filler on the LCD and button part of the inside form beforehand, to make sure it got everywhere.

I then lowered the inside form into the boxed outer part and squashed it down until it oozed out the sides.

After this cured, I pried the male half out and got this.

I trimmed the excess on the radial saw out of laziness (I’ve done this with a belt sander before).

After a bit of sanding, I had this.

And after some black plastic spray paint, this

The holes are cleaner than they look in my pictures. They took nothing more than a few light strokes with a file, though I had been quite sloppy with the hardboard pieces I cut. I chopped them about 90% through with the radial saw and broke them off the rest of the way (radial saws will shoot you with small cut offs). The edges were sort of “fuzzy” and the dimensions weren’t perfect. I think some thick mat board (for picture framing) might be a better choice, and it can be cut with a sharp utility knife and a metal ruler. Gluing them to the model after it had been greased was also a bad idea. It needed to be cleaned with paint thinner and sanded a bit and it still didn’t hold well. Covering the area with scotch tape and removing it after the female mold was done would probably have been easier.

More good stuff-

With as easy as the square and rectangular cutouts were, I had some ideas for some others. I believe if you were to cut a series of parallel slots across a piece of plywood or something, you could insert some strips of mat board or hardboard (the width of the saw kerf) and get some nice clean fader slots. The knob/pot holes are even easier, and could be done with dowels tapped into holes. You could also produce threaded protrusions for securing the body to the bottom or PCB simply by drilling stopped holes into the model or panel. A cross sectional view of this shows a form for- (left to right) A pre-drilled standoff, two round (pot) holes and two fader slots

A side view of the result should be this-

The face of it would look about like this

I have not done this yet, but I don’t see any reason that it wouldn’t work. There’s a nail in the center of the counterbored standoff hole, which would create a screw hole in the final piece. The head is just there so you can tell what it is. If anyone tries that, make sure you chop or file the head off, so it won’t lock everything together.

                               Hope someone can find some use for some of this

                                                                                                          -George

PS- The frozen piezo is in that batch of pictures too, complete with rubber coating. That one was done in a 1/2" deep round hole cut with a forstner bit and the bottom corners were rounded with putty before the fiberglass went in. I filled it about halfway, let the fiberglass get hard but “gummy” and stuck the piezo on top of it with the wires in the groove. I then filled it the rest of the way and squashed a piece of mouse pad to the bottom while it was wet (to see if it would stick). The whole top half, in it’s naked green color, was dipped in liquid latex to soften the feel. It triggers quite well and the mouse pad is secure enough that it will rip if I try to pull it off. If I do a batch, they will most likely be square and I may move the piezo closer to the surface. I’ll probably glue the bottom of all of them to a mouse pad for isolation and center them with wherever the holes are in the enclosure.

   

   

[Davo]

Very nice!  I’ve had some experience with theatrical makeup, and this looks very similar to how foamed latex prosthesis are made.  One thing puzzles me: what was the purpose of spraying the female mold with laquer?

Here’s an approach that’s closer to the foamed latex procedure:  This should allow for better control over the thickness of the box’s walls.

Make a negative of what will be the inside of the box.  Avoid undercuts for obvious reasons.  Cover this with wax and build it up to form what you want the outside of the box to be.  Ladle a thin plaster over the negative, making sure there are no bubbles against it.  Build up a layer of, say, 1cm.  Then stick it into a box filled with plaster, as you did.  Before you do this, bore at least three  holes equidistant around the edge of the negative.  Insert metal rods into these holes.  When you put the inside negative into the plaster, the rods will stick into the wet plaster.  These rods will remain in the plaster and slip out of the inside negative.  When the plaster is cured, remove the inner negative and as much wax  as you can.  Put the plaster mold and inner negative into an oven on low to melt out the remaining wax.  You will now have a pair of perfectly-fitted male and female molds.  The metal rods will make sure the molds stay properly aligned.

[Jidis]

what was the purpose of spraying the female mold with laquer?

Probably none

It’s been done to slicken up the mold so nothing can stick to it, and to hold the plaster together, but it’s probably the wrong thing for that surface. A spray primer or something might be better suited. The plaster is sort of chunky and crumbles easily. I may also be a bit impatient about how soon I try to use it. A lot of the stuff I’ve done has been “one off” molding, where I don’t really care, as long as I get the first piece out OK. For multiple uses, a nice solid top coat would help. I’ve been very lucky with not having things get glued to the molds. I’m thinking that a spray coating of PAM (cooking spray) or spray oil might work better for lube on intricate details and holes too. The petroleum jelly can get messy and globs or lines in it will transfer to the fiberglass. The fiberglass has the potential to exit the mold with a slick, smooth, paintable surface if the mold is well prepared.

I was going to mention that an “inside only” mold would probably work as well and you could still attach protrusions to create holes, etc. This would be similar to the first couple steps you mentioned, but you would build up layers of fiberglass. I *think* this is what Pierrot did with that gray box. It does seem it would involve some heavy sanding though (I think he mentioned that as well).

I’m reading over your post again. An easier means of getting a perfectly matching male/female set would definitely help. For the thing I just did, consistent thickness wasn’t that important, but it does get difficult dealing with angles. For horizontal surfaces the male can be shimmed upward by an exact amount to dictate the thickness and for vertical surfaces, the sides can be trimmed by this same amount, for angles - you’re left with something in between.

I only wish there was a way to label onto this crap!

         -Thanks!

[Davo]

Sounds like impatience.  Plaster should be cured for at least a day and kept slightly damp after it sets.  Mist it lightly, then put plastic over it.  It should be very difficult to scratch cured plaster with a fingernail.

Here’s another idea borrowed from makeup.  Foamed latex prosthetics are very realistic, but can be used only once, are costly, and it’s a difficult and long process.  A much cheaper and easier way is called shell latex.  It works well for stage, but looks funny for extreme closeups as in film or TV.  For this technique, you omit the inner piece and instead paint liquid latex around the inside of the mold.  For fiberglass, do the same thing.  Make your model from something that plaster won’t stick to.  Make a mold as described before.  Now paint the inside with resin, let it set, then add resin mixed with fiberglass.  You should be able to easily get walls of uniform thickness with no need for alignment.