Draft angles are fundamental to part design. If you want to make physical things, you gotsta’ master draft. In his inaugural post, the great Vince “Skill Coach” Haley shows you how.
There’s nothing like the musty aroma of carefully crafted paper mache popping free of its surrogate mold. And to my daughter’s delight, that’s exactly what happened! Seizing the moment, I said “You know why it works like that don’t you? Well It’s because of something called draft angle.” She raised a brow as if to say “Do tell”. I pointed out that the opening was larger in size than the base, making the sidewalls tilt at an angle. I said, “‘The more tilt the easier to separate the piece from the mold that makes them. Also the angle helps you stack a bunch together using less space.” I was thrilled to share such a teachable moment!
Draft angle has the power to make or break a design!
“Draft” just means tilting a part’s walls one way or the other–usually outward. A perfectly vertical 90deg wall is called “zero degree” draft. If the wall is tilted one way or the other, the draft is measured in degrees-from-vertical.
Image: source.
First of all, draft is mandatory for most manufacturing processes. Whether your parts are molded, cast, stamped, slumped, or drawn, draft is crucial. Without it, the part can’t be made. (There’s a great overview of injection molding here, and the same basic concepts apply to most other common manufacturing methods.)
Draft is also critical for space efficiency. If you want to ship a few million bowls across an ocean, you need to maximize every inch of available space. The same is true at retail: the more you can optimize the physical space the more effective the Point of Purchase (POP) presence.
The more stuff you can fit on a retail shelf, the more you can sell. Efficient stacking is critical.
Let me explain. I designed products at Rubbermaid Home Products Division circa ‘96. We were known for cranking out one new product per day! Industrial Design, Engineering, and Manufacturing were all under one roof. We were a well-oiled PDev. machine.
At the time we had a saying “Stack’m high and let’em fly!” And it was none other than the mighty draft angle that allowed for tight nesting and dense product placement. Our marketing folks would smile with glee at the news of an end cap POP placement. We all knew our sells chances would be much greater when our products were front-and-center.
So from the start of a new project, no matter what the discipline, one of our first questions was the draft requirement. From my very first sketch I’m think’n how to harmonize the products aesthetics and change the game from a product architecture standpoint, knowing I’ve got to deal with 7 whopping degrees of draft. Moldability was king and cycle-time was queen, and all the other gentry were in their service.
Time and time again, whether we had the luxury of designing for zero degree draft or the dreaded 15 degrees, we found the ‘sweet spot’ where looks, features, and functions came together in highly desirable product solutions.
If you want to up your game and garner some new knowledge around draft angle and the whole injection-molding process, check out the Engineering Guy overview or visit Protolabs for a quick draft angle tidbit.
