The Latest in Our Series on Prototyping Explores Two Common Techniques for Creating Professional Models.

In this issue, let's explore other techniques for presenting your new product to prospective manufacturers or licensees.

CAST MODELS

If your product idea is very sculptural with lots of ins and outs and is just impossible to make from flat sheets and cylindrical tube shapes, you'll need to basically sculpt your final shape. You can use a variety of materials for sculpture.

1. Plastileen--This is a clay that never hardens. As it gets warmer, its gets easier to work with. After you have sculpted the clay into the shape you want, you can put it in the refrigerator, harden it up and then cast that piece in plaster.

Once you have the female plaster mold, you can cast it in a variety of materials. If you want to get a shell piece rather than a solid piece, there are various Urethane mixtures that you can mix and brush into the plaster mold. The Urethane hardens and forms a thin plastic shell which you can then pop out of the mold. Be sure to avoid undercuts in your design, otherwise the part won't come out of the mold. You must use mold-release material like Vaseline to make sure that the Urethane ( or whatever you're putting in the plaster mold) doesn't stick.

2. Clear Resins--For clear parts, you can use clear casting resins. These you can buy at the plastics store. You can get them in clear or you can put colored tints in to produce different colors. It comes as a hardener and a resin which you mix up and pour into the mold. They take about a day to harden.

3. RTV Silicone--Another great mold-making material is RTV silicone rubber which is available in a good plastics store. This silicone mold material is rubber-like, so when you cast into it, it's easy to get the part out because the mold flexes a bit.

In conclusion, you'll use a sculpting and casting technique when your design is an irregular sculpted shape. I don't use it that often because it's amazing what I can accomplish with flat plastic sheets, cylindrical tubes and Bondo blending techniques. Sometimes, if I need a special shape, I'll go to a department store or a toy store and I will look for a shape that's very close to what I want. I'll buy that product and, using the cut-off wheel on the Dremmel (discussed in the last Dream Merchant issue), I will cut the actual piece or shape that I want out of an already existing product and put it into my product. Just splice it in! All is fair in love and model-making.

You can use whatever techniques work. What you want to do is be as efficient with your time as possible and do as much of the work yourself so that you don't have to spend lots of money for a professional model maker to construct your prototype.

METAL MODELS

Unless you have the right equipment, it's somewhat difficult to make metal models in your own home. So I usually recommend that you make your parts out of other materials, but if you need a particular part made out of metal, you can get thin metal at any hobby store. You can also get metal tubes, strips and plates at any hobby store. These are thin enough that you can bend them pretty easily in a small vise and they can be cut with the cut-off wheel on your Dremmel.

If you need thicker metals you can look in your Yellow Pages under "Metal Fabricators" or "Metal Suppliers" and you can have your metal cut to size.

If you have to work in metal, I recommend using aluminum if at all possible, because it's lighter weight and it's easier to work. It's softer than steel, so it's not so hard to cut and drill. The supplier of the metal should be able to cut it exactly to your size so that if you have to do minor work, such as drilling holes or shaping, you can do that with hand tools at home.

In the worst case, if you've got some slots and other more elaborate shapes to make, you'll have to look under "Metal Fabricators" in your Yellow Pages, make a call, and tell them what you're trying to do and see what it will cost to have them do it.

One good rule in making phone calls is to present yourself as a company, not as an individual. They take you more seriously that way. Also, if the one person you contact can't do what you want, always ask them if they know of someone who can. This is the Sherlock Holmes method of finding just the right person to fill your needs.

Metal pieces that need to be put together can be screwed together. This isn't as difficult as it sounds. You drill holes in the metal and then create an internal thread with a tap that you can buy in any hardware store. Once you have the one piece of metal with the threaded hole, the other piece of metal has a larger clearance hole and you can drive a screw through it and turn and lock those pieces together.

You can also use the five-minute epoxy or special metal epoxies to hold metal together. If you need a really solid bond, and the metal is going to be taking a lot of stress, you'll probably have to get the metal welded together and unless you have welding equipment, you'll have to locate a welder. Look in your Yellow Pages, either under "Metal Fabricators" or "Welders."

In the next issue, I'll discuss how to find outside help for developing your prototype.

Ken Tarlow is president of Tarlow Design, a full-service product development company that helps independent inventors design, prototype, patent and license consumer product ideas. He has developed more than 300 consumer products worth over one billion dollars in retail sales. Tarlow's office is in San Rafael, CA. He may be reached at (415) 457-6428.

The above article was excerpted from Tarlow's MIND TO MONEY, a cassette tape/workbook package that can help you develop a new product from the idea stage to the marketplace. MIND TO MONEY may be ordered from the Dream Merchant at $59.95 plus $4.95 CA sales tax and$5 shipping and handling ($69.90 total). Send orders to the Dream Merchant, 2309 Torrance Blvd., Suite 104, Torrance, CA 90501.