Introduction: Poor Man's (not So Rapid) Prototyping Method for the Fabber-less

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About: I'm an electrical engineer specializing in software. My hobbies consist of software, hardware, and design. I dabble with industrial design.

Many have wished to be able to fabricate plastic models of their 3D designs, and many do not have access to rapid prototyping machines or cnc millers. And many do not want to pay 10 dollars a cubic inch of plastic prototyped.

This instructable will introduce my method of fairly rapid prototyping with sheets of abs plastic, no special machines required.

Step 1: Precursor

Many people who design 3D models on their computer would probably like to fabricate them in some sorta material. Other's design solely for the purpose of creating a part and getting it casted. I am part of the later.

This instructable started from my need to create a custom case for my tablet pc. I wanted to house certain components with the tablet and thus, I could not have used any typical case made for my tablet model.

Like many people, I resorted to finding places where I can get the parts milled or printed. And like most people, I was disturbed about the high costs for materials and production. And thus, I sought out an easy way to prototype parts cheaply without the need to produce my own fabber machine.

I have came up with a slue of methods, all of which I summarize by calling it the Origami Prototyping Method.

The key points of this method is to use plastic sheets as if paper, and produce papercraft equivalents of the 3D models.

This instructable goes over the basics and certain key points about this method.

Step 2: Materials and Tools

Materials:
- ABS plastic sheets
- Acetone
- Bottle
- Clay (optional)

Tools:
- Dremel (rotary saw, miller, etc)
- Popsicle sticks (or other stick like spreading tool)
- Grinder
- A BOX (the Z.O.E box if possible)
- Plastic Heat Strip (or Poor Man's Plastic Heat Strip https://www.instructables.com/id/E6CUQ8MF2H0OWHU/)

Step 3: The Design

Use AutoCAD, SolidWorks, 3D studio Max, or Maya, etc to design the 3D model.

When designing on AutoCAD or SolidWorks, a note of advice is to keep the model "low res". What I mean when I say low res is that there shouldn't be any fillets, or at least keep them to a minimal (more on this later).

When designing on Maya or 3Dsm, design however you want, but lower the resolution for the final product.

Why make it low res? Because we're going to use the Pepakura Designer software to "unfold" the 3D model. Low res or else there's going to be millions of small polygons. Pepakura is used for papercraft making, and it will serve its purpose for this instructable.

Step 4: The Cut

If the unfolded model is large, either print it out with a plotter, or (pepakura does it naturally) separate it into pages.

Align the pieces and tape or glue it to the abs plastic sheet. I suggest using some fabric spray adhesive (perhaps those used to adhere the felt to a pool table).

Cut out the plastic with the dremel as if it's a paper craft model, noting not to cut the attached edges. However, cut away any tabs Pepakura has created for the model. We do not need tabs to glue the plastic together. (Do the cutting over the box so the plastic scraps are collected.)

Note: this step is totally unnecessary if you have a CNC milling machine, but then again, this instructable might seem unnecessary since you can mill out the 3D model.

Step 5: The Fold

Warm up that heat strip. Place the the edge of each fold parallel to the heat strip. Once the plastic around the folding edge is soft enough, bend it. (Perhaps one would want some sort of jig to help the fold. Refer to my other instructable: Poor Man's heat strip for the tip. It can work with non-square folds as well, just don't apply too much pressure or apply the design at an angle.)

Repeat and treat the plastic as a papercraft. Make sure the edges where the tabs use to be line up.

Step 6: Preparation of ABS Glue

Place the grinder in the box. Take scraps of plastic from cutting out your design and grind them down into powder or smaller bits of plastic. You might want to use pliers instead of your hands to hold the plastic when the plastic gets really small.

Collect the granulated plastic and place it in a bottle. Add a small amount of acetone to the bottle, close the lid and shake. Every now and then, pour out or stick a stick into the bottle and draw out a small amount of goop to check for consistency. It should be more like maple syrup or honey rather than elmer's glue. I like to keep it that consistency because it has a greater ratio of plastic to acetone.

ABS breaks down upon contact with acetone. It becomes goopy and can be used to glue pieces of abs together. This is ideal because as the goop comes in contact with more abs, the acetone in the goop prepares the surface of the abs for gluing by decomposing a little bit of the abs. As the acetone dries, the abs restructures itself. The strength of reformed ABS after being decomposed by acetone is about 75% of the original abs.

Step 7: The Gluing

Now that the plastic is bent and the tabbed edges are facing each other, they can be glued together. Pour out a small amount of plastic goop on a flat, discard-able surface. Take a Popsicle stick and scoop some goop. Apply it on the tabbed edges. Do no worry about overflow; it is expected. The joints can be sanded down later.

Leave it to dry for a day (two days, to be safe).

Step 8: Notes and Tips

With the gluing, make sure not to make it too thick. Because the glue dries from the outside in, the dried coat outside slows down the drying process for the glue inside. This is one reason I keep a greater plastic to acetone ratio for the glue.

Another reason for the ratio is because acetone is not plastic, thus, making the glue liquidy means the bulk of the glue is acetone, and not plastic (which we'd want). Another thing about adding too much acetone is the the glue bubbles. If you're laying the glue on thick, the acetone might bubble out and expand the glue as well as making the plastic that reconstitute porous.

You can lay thick glops of plastic goop, but it's not recommended. If you have too much acetone, the extra acetone bleeds through to the hard plastic you're applying the goop to. If you want thicker reconstituted plastic, try applying multiple layers.

As for the 3D model's resolution, the reason why I suggested low resolution is because this method might require a bit of sculpting. Bending thick plastic is prone to inaccurate bends; and it's almost impossible to bend thousands of tiny polygons of plastic. However, sanding is always an option. Thus, making the plastic model low res is not bad. From a sculpting standpoint, more than half the task is over. Just reinforce the insides of the plastic with layers of plastic glue and sand down the outside. Make points which needs to be curved curvier, sand down the edges if it's a fillet, etc.

Which leads to my last tip. When using Pepakura, you can decide where the model can be broken up. Keep fillets as one flap, this way, the fillet can be bent easily with the heat strip.