Building a prototype is a multi-stage process that can involve unexpected changes along the way and the construction of multiple copies, so its important that time be allowed to correct for substituting materials used and to correct design errors that inevitably arise. The first step in prototype construction is to mentally determine what the function of the invention will be, and then to begin making crude drawings of the prototype, which can be followed up afterwards by more precisely-measured designs that are often easiest to produce with computer-aided design (CAD) software. Once a detailed design has been produced, the next most practical step in building a prototype is to create a non-functional model of the device out of an easy-to-work-with material like plastic foam, cardboard, or clay. This will present a more thorough visual image of the functioning of the device so a parts list can be created for making a fully-functional model.
As more detailed knowledge of what's involved in constructing a prototype is understood and what prototype materials will be required to complete it, a cost list can be generated. This list should be finalized before a working model is built, as it may include unexpected costs not seen in building a mock-up. One of the often-overlooked costs in prototype production is the cost of tools and specialized machinery necessary to make it. Some parts also may not be possible to conveniently create from scratch, such as electronic components, motors, and custom-molded plastic body parts. In these cases, building a prototype may require consultation with a professional engineering firm or designer with access to small-scale manufacturing resources.
Several important tips exist for building a prototype out of general materials without the aid of outside professional help. Of primary importance is that the parts of a prototype are fastened together in a way that makes the device easy to take apart in order to explain how it works, so pins or fasteners should be used to give each significant part freedom of movement. To provide texture to surfaces and to draw the eye to certain key areas of a prototype over that of others, soft-touch paint can be used as an inexpensive substitute for rubber or urethane plastic parts that must be carefully molded to fit properly and look appealing. Prototype design is also easier for functional models if each individual part is completed separately of the whole unit. If the parts are then discovered to be too large in the final assembly process, they can be reshaped or replaced before assembly so that every moving part has sufficient clearance to operate properly.
What's important to remember with building a prototype is that it will naturally have something of a crude appearance and function to it as compared to a version produced in a factory setting. Accepting this fact allows for low-cost construction of initial prototypes using common household materials. Once a prototype has been shown to a patent attorney or has gained the interest of commercial manufacturers, it can be refined and redesigned to improve its marketing value overall.