I Missed My Precision Measurement

Without precision measurement tools the plastic injection mold making industry would never be able to produce the high quality products that we have all come to expect and rely on; read on..

How small is small?

She is hard at work on the lathe
She is hard at work on the lathe

The average consumer has no idea at all just how precise the mold making process must be in order to manufacture our cell phones, computers, automobiles and thousands of other products.

Imagine for a moment that you split a hair, then split one of the pieces, then split one of those pieces, and then finally split one of those pieces. This is how precisely mold makers work on a daily basis. For the curious, this equals approximately .00015 in.

Even if you loosen things up and work in the .0003 in. range, this is still quite small.
For reference, a cigarette paper is .0008 in. thick, or 4 times thicker than what a mold maker deals with everyday! This is actually quite easy to measure with a precision micrometer.

The amazing thing is that the molten plastic that is injected in a steel mold will find the tiniest opening and fill it. If there are imperfections in the fit of the mold components or if the dimensions are wrong, the plastic will reveal this upon cooling.

Everyone has seen what is called “flash” on plastic parts. Flash is the scratchy, mismatched plastic that you find on low quality toys or cheap electronics. Flash can occur with as little as .0005 in. opening in a mold, so it is a wonder you do not find it more often.

The Metrology Handbook, Second Edition

An authoritative book, “The Metrology Handbook, Second Edition” provides a foundation for understanding basic metrology and calibration principles and practices.

Mold Makers are masters at precision measuring

Precision Digital Bore Gage
Precision Digital Bore Gage

A qualified toolmaker is competent with many tools. Years of experience are required to learn the proper use and maintenance of these precision instruments. Small deviations can occur due to temperature variations, dusty work areas and improper technique. The apparent measurement may turn out to be quite different than would appear in the hands of an inexperienced craftsman.

Precision Measuring Tools

Outside MicrometerInside MicrometerDial Test Indicator
Surface GaugeSurface PlateHeight Gauge
Gauge BlocksPin GaugesOptical Comparator
Vision SystemCMMA Good Eye!

Don’t buy cheap measuring tools

Management would do well to invest in the highest quality precision measurement tools, rather than cut costs by purchasing low quality tools. It makes no sense to expect a high level of accuracy from an inferior measuring tools, yet this happens all the time.

Just because the micrometer reads a certain number does not mean the mold component is actually that size. Proper calibration is required, as is the testing of the micrometer over the range of tool. Cheap tools give unreliable results, despite the appearance of working just fine.

Basic Metrology for ISO 9000 Certification

An authoritative book, “Basic Metrology for ISO 9000 Certification” gives a nice introduction to ISO 9001 requirements for calibration of test and measuring instruments.

Think of your friendly toolmaker

Precision Swiss Watches Don’t Just Happen
Precision Swiss Watches Don’t Just Happen

The next time you pick up a cell phone, for example, consider just how much skill has gone into making the molds that produce all those intricate plastic parts. Each one required a molding area that was produced using precision measurement tools in the hands of skilled mold makers.

Precision Tool Manufacturers

StarrettBrowne and SharpeMitutoyo

These are just a few of the more common brands that are reliable, year in and year out. You, of course, pay more initially, but save money in the long run. For example: an Etalon micrometer can easily give reliable results even after 20 years of regular use. A cheap micrometer will possibly last a few years and never give good results.

Just because one precision measuring tools resembles another doesn’t mean that they function equally. Not even close! Some companies make their living by copying the real thing, and the unwary bargain hunter soon becomes the victim.

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