It was seen that the works of founders of States, law-givers, tyrant-destroyers, and heroes cover
but narrow spaces and endure but for a time; while the work of the inventor, though of less pomp,
is felt everywhere and lasts forever.          - Francis Bacon Preface to a Treatise on Interpreting Nature

The Design of Everyday Things

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How to Design Breakthrough Inventions

A CBS interview of IDEO founder David Kelley

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Tuesday, August 4, 2009

August 2009

A prototype can help you to see whether your invention works, to identify ways to improve its appearance and function, and to communicate it to the world of business and law. A prototype made of plastic is attractive and affordable, and can be made quickly. Mr. Andrew Nehrt (812-522-4433, of Pro-Form Plastics, Inc. (manufacturer of heavy-gauge [.03-.5" thick] molded plastics, non-metallic material [foam, felt, plastic, etc.] cut by steel-rule die, and customized wood shipping containers) spoke to us about the different designs, methods, plastics, and tools he uses to build prototypes. The method of thermoforming uses a vacuum to fit a rectangular sheet of heated plastic (3x4' to 5x9') to a mold of a product part (remember the Vac-u-form toy from years ago?). Before being fit to a deep mold, the plastic is stretched with a felt-covered plug. Plastic shrinks while cooling on the mold, so designing the mold with at least 2 degrees of draft angle makes separation of the plastic from the mold easier and less expensive. Several kinds of plastic, each with its own advantages and disadvantages, can be thermoformed.
  • HDPE/LDPE/PP (high density polyethylene/low density polyethylene/polypropylene) can be used to make things like a gasoline tank. It is tough, resists chemicals and weather, and is relatively inexpensive. However it is dull and pliable.
  • ABS (acetonitrile butadiene styrene) is durable, stiff, glossy, and can be used for detailed parts However it cracks under stress, does not resist chemicals, and is expensive.
  • HIPS (high impact polystyrene) provides good detail, stiffness, and formability, and is the least expensive of these plastics. However it is brittle, unsuited for stress, and does not resist chemicals.
  • Polycarbonate (Lexan) is clear, stiff, tough, and resists scratching. However it is amorphous (needs to dry), hard to form, and expensive.
  • Acrylic (Plexiglass) is easy to form, somewhat clear, and relatively inexpensive (half the cost of polycarbonate). However it is brittle, scratches easily, and can't be used for detail.
The mold can be made from different materials, each with its own advantages and disadvantages.
  • Wood (especially mahogany, which lasts and doesn't leave an imprint of its grain in the plastic product) is good for prototypes and small production runs of products made of ABS/styrene.
  • Aluminum (machined or cast) allows temperature control during cooling, is an inexpensive (~ 30% the cost of an injection mold) way to make a long-lasting tool, and is good for making prototypes out of any of the listed plastics.
  • Epoxy/Ren/Gypsum performs a little better than wood, is significantly more expensive than wood, and is good for limited production using ABS/styrene.
Mr. Nehrt generously offered to act as a resource for inventors. So don't hesitate to contact him about your planned prototypes. Thank you for all of this useful information, Mr. Nehrt!

Patent Drawings by Richard McVicker

Some inventions patented by our members:

Bob Brand
3,179,907 Tuning system for television receivers
3,219,933 Television tuner switching system
3,241,072 Tuning control system
3,538,466 Television tuner cast housing with integrally cast transmission lines
4,503,740 Optical cutting edge locator for a cutting apparatus
4,503,896 Dog system for veneer slicer
4,601,317 Veneer slicing system
5,511,598 Veneer-slicer with remotely controllable blade angle adjustment
5,562,137 Method and apparatus for retaining a flitch for cutting
5,590,700 Vacuum flitch table with self-cleaning vacuum valve
5,678,619 Method and apparatus for cutting veneer from a tapered flitch
5,680,887 Veneer slicer with timing belt
5,694,995 Method and apparatus for preparing a flitch for cutting
5,701,938 Method and apparatus for retaining a flitch for cutting
5,819,828 Method and apparatus for preparing a flitch for cutting
5,868,187 Method and apparatus for retaining a flitch for cutting
7,395,843 Method and apparatus for retaining a flitch for cutting
7,552,750 Method and apparatus for cutting veneer sheets from a flitch

Rick Hanson
6,240,579 Unitary pedal control of brake and fifth wheel deployment via side and end articulation with additional unitary pedal control of height of patient support
6,253,397 Deployable siderails for a wheeled carriage
6,256,812 Wheeled carriage having auxiliary wheel spaced from center of gravity of wheeled base and cam apparatus controlling deployment of auxiliary wheel and deployable side rails for the wheeled carriage
6,264,006 Brake for castered wheels
6,507,964 Surgical table
D474,446 Sterilizable battery component

Bob Humbert
4,281,368 Keyhole illuminating apparatus

Ron Jackson
4,886,110 HVAC zone control system
4,943,039 Adjustable clamp
4,987,409 Level sensor and alarm
5,132,669 Level sensor with alarm
5,381,989 Adjustable spring clamp
5,944,098 Zone control for HVAC system
6,145,752 Temperature monitoring and control system
6,322,443 Duct supported booster fan
D347,596 Audible security alarm
D376,747 Door security device

Jerry McQuinn
D689,343 Universal Nutcracker

Richard McVicker
3,261,937 Three position snap switch utilizing interference blade means
3,319,477 Timer Escapement
3,332,704 Manually propelled treadmill vehicle
4,625,616 Thumb pick
6,309,076 Light barrier, screen or reflector
D240,237 Sculpture or the like
D356,653 Yard light
8389839 Thumb pick

Bill Pangburn
5,943,831 Device for Hauling Objects

Al Robbins

3,882,960 Ride quality control for surface effects craft
3,946,689 Air dynamo pressure regulation and modulation device for surface effect ships and air cushion vehicles
6,588,702 Lighter-than-air device having a flexible usable surface

Matt Thie
4,844,446 Multiple-compartment currency stacker-sorter
4,940,162 Rolled coin dispenser
7,298,280 Lighted fluid flow indication apparatus
7,617,826 Conserver

Richard Tucker
5,833,751 Powder coating booth having smooth internal surfaces
6,840,367 Material handling and manufacturing system and method
6,976,835 Manufacturing system and process
7,018,579 Manufacturing system and process

Don Walls
D707090 Torque key lever
RE36209 Door lock apparatus

Dave Zedonis
5,637,926 Battery powered electronic assembly for wheel attachment

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