OT: custom fab of cases/containers

If you have to do just one, you could paint/spray your clay model with an oily film. Then, just cover your model with clay to get a clay negative of your piece. Remove (or scrub out) your original one. Then, paint epoxy resin over it. You can even reinforce it with glass fibers and it becomes very robust. This smells, but depends on the size of your model. A mouse-sized object would be ok to at home, but his depends on your nose :) You may look up how modelists build stuff more or less this way. They sometimes make the negative with latex or silicone rubber. This allows reusing it.

Pere

Look for a 3D printer.

You could dip the model in wax. At the right temperature, you can use wax to build up even layers. Let the wax cool fully. Cut it all the way around to separate the wax into halves and remove them (assuming you have a roughly shell-like form now, minding concavities). Carve the wax pieces until they're in just the right shape. The wax pieces can be molded in silicone and resin parts made, or more wax parts made for metal casting (investment / lost wax casting).

Tim

-- Deep Friar: a very philosophical monk. Website:

If you don't have or don't want a 3D printer (should be around $3000) then check around. Here in Tulsa, Oklahoma, USA we now have a Fab Lab that is for this type of thing. They have a 3D printer, a minimill and what have you that are available for public use. This is becoming a type of thing that lot of places are starting to implement.

Bill

Why don't you just whip up a 3D CAD model and send an .stl file off to a service bureau? Your proposed technique is so last millenium. Google Sketchup is apparently ok for this purpose (and free), if you don't have access to something like Solidworks.

Tap Plastics (a chain of plastics stores, one near here, great fun) sells silicone mold-making stuff, and then resins and cloth fillers. The silicone mold stuff is fabulous... incredible fine-detail resolution.

They have videos and stuff.

I love their scrap bin, full of all sizes and shapes and colors of stuff left over from custom fab jobs. Great for test fixtures, cutting boards, like that.

casting_products

Search on "rotary molding" (I think that's the right term).

IIRC it uses a thermoplastic, not a thermoset, but the idea is that you make a negative mold, squirt in the right amount of hot goo, then tumble the mold to distribute the goo as it cools. Wall thickness is somewhat uncontrolled, and you can't have corners that are too sharp, but it may work for you.

Vacuum forming is fun, too. You need a rigid mold, often made of hardwood. Place a sheet of plastic over the inverted mold, with negative air pressure in the mold cavity. Heat it all up, and the plastic sheet is sucked into the mold. Trim the edges. There's a neat little book somewhere on how to do it yourself.

I've heard that 3D printers are down to about $500 now. One of the CAD guys at work was going to buy one and start a side business making models.

I have been keeping an eye on 3D printers for a while. The low cost ones usually have several severe problems. So in the end you'll need to spend somewhere around $3000 for something usefull.

We built a 3D printer here and have been using Sketchup and the very simple free add-on that translates it to STL along with the new ReplicatorG 40 and the Sailfish 4.1 firmware. (I'm still not entirely certain of the Sketchup add-on's behavior but it's pretty decent just the same from experience using it. Also, Sketchup can keep inside interesting artifacts that result from the process of making something there that, if not closely attended to, can physically show up after getting translated to STL.)

The problems may come in the drillability of the result, depending on how the drill holes line up with the layers, thickness of perimeter chosen, and so on. But I think for the most part it should be modestly acceptable.

Jon

Nico, Keep me posted on what you ultimately choose. Sounds like a really fun toy! ...Jim Thompson

I keep being tempted even though I have no idea what I would do with one. The software to make the designs to run it is a free download so it sure is tempting.

Bill

There is a comprehensive list with 3D printers:

Vacuum forming would be the best way. Lindsay Publications sells a book of plans, or lots of small systems on ebay. You put your mandrel (a hard block covered with felt, for example, with some gas passages drilled here and there) on a base sheet with lots of holes (think pegboard) mounted on a sealed box with a valve leading to a big vacuum pump with a heater box a foot above the base and a frame to hold a plastic sheet (1/16" polystyrene, for example) against the heater box. Let the plastic soften the right amount, drop the frame to the pegboard level so the plastic bulges up over the mandrel, and open the vacuum valve to suck all the air out through the pegboard and make the plastic conform to your mandrel. Lots of people make rc car bodies that way so they can go tear them up :-). Best is to carve the mandrel from wood but if you used clay you could probably freeze it and get a few formed sheets out of it, and then you can cast one of the sheets full of something like plaster of paris to get a durable mandrel. Or look in the phone book for plastics suppliers like Sabic Polymers or Total Plastics, they often do vacuum forming, bending, cutting, whatever. If you want to pull a mold go to

----- Regards, Carl Ijames "John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

On Wed, 14 Nov 2012 11:37:31 -0600, Tim Wescott wrote:

Vacuum forming is fun, too. You need a rigid mold, often made of hardwood. Place a sheet of plastic over the inverted mold, with negative air pressure in the mold cavity. Heat it all up, and the plastic sheet is sucked into the mold. Trim the edges. There's a neat little book somewhere on how to do it yourself.

I neither have nor can afford the thousands of dollars for that.and it makes no sense to $pend so much for what essentially is a $2 mouse.. And nobody will make one mouse-like item with a 3-D printer for under (say) $25..

Yeah, i know - used to visit them when i lived in Portland; a resource better than most hobby/model stores. They do not exist here in WA and shipping added to material costs tend to be a killer (used that scheme on 2 other projects that were "must do").

That is exactly how the Osbourne computer cases were originally made.

• Thanks!