Jim Yurchenco on Model-Building

Source: Interview with Jim Yurchenco, 25 May 2000.

Pang: Once you passed this on to Bud to build the model, it took him about six weeks, as he recalled--

Yurchenco: I don't remember the time frame--

Pang: Did the design change in the course of building the model, as a result of finding something that was too difficult to machine?

Yurchenco: Well, making a machined model is a very different process that making a molded part. Designing and building a tool is a very different process from designing and building a plastic model: in one case you're working in the negative, in the other case you're working in the positive. Bud was working in the positive, and making it out of a piece of plastic. So he had to be able to get into areas to machine that would be very different than you do when you're building a tool. When you're building a tool, you're working in steel, but you're also working in the negative: even though the tools may be similar, the processes are extremely different.

So the problems that Bud faced were very different than the problems the tool-maker faced. Bud, for instance, was able to make individual little pieces and glue them together; the tool-maker could make individual inserts for the mold, and screw them all together. But Bud could work with tools to cut plastic fairly quickly, while the tool-maker was working with steel, which is much harder to cut; but he could work with something called an EDM machine, with which you can create carbon positives, and burn holes in the steel. So in Bud's case it's very difficult to measure what you're doing, particularly with the kinds of tools you have; so it's almost got to be an act of faith that once you've started you're going to get it right.

But no, there weren't any significant design changes that occurred based on the model.

Pang: So it sounds like in this process all the hard work is at the front end: once you get the tool made, turning the parts out doesn't require nearly as much skilled labor.

Yurchenco: It doesn't require any skilled labor at all. Injection molding those parts is done automatically: the machine sits there and spits out parts. There's a molding cycle, the press closes, fills with plastic, cools for a period, the press opens, the part falls out onto a conveyor belt, conveyor belt carries it to a box, and every now and then someone comes around and takes the box away. It's as simple as that.

I'm oversimplifying the problems of injection molding, but basically there's very little skill once you've got the press set up and it's producing parts.

Pang: There was one other thing you and Rickson had talked about, which was keeping an eye on how these parts could be assembled.

Yurchenco: Yeah, you always have to think about how you're going to put these parts together, so that's part of the design: can the person who's going to assemble this get the parts together, can they physically get their fingers in, can you pass part B past part A once it's in there? You have to think about the assembly sequence when you're doing this. But that's just part of the basic design process: no matter what you design, you're going to have that problem. In a way, I probably should bring it up, but it's intrinsic: being able to assemble a product makes a big difference in whether it's successful or not. If it assembles easily that means there are fewer errors, it costs less money, and it's more reliable. So you take that into account.

Obviously, you're dealing in this case with rather small parts, so you need to have assemblers who have some dexterity and good eyesight and small fingers and so forth. You still try to make it as simple as possible from their point of view. You also try to make it difficult to assemble things in the wrong way. So you key parts, you put features on parts whose only purpose is to aid in assembly or aid in orientation, or you make parts so you can assemble them both ways and they still work. You can't always succeed, but designers do their best to prevent those kinds of errors from occurring.

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Document created on 28 November 2000;