By Randy Hough
One time I was looking through a career book that featured tool and die making. I was hoping it might actually accurately describe what it is like to be a toolmaker, but, as usual, I was disappointed. One of the pictures showed a man holding a precision micrometer while he measured a workpiece.
The caption described the man as holding a tiny component in a miniature vise! And this was a book about jobs and careers.
Unless you have some kind of personal experience with these tools, it is nearly impossible to grasp what actually goes on in a typical tool shop. So, here are some things that these tools do, and what they are used for.
- Granite surface plates are really just big, flat rocks. However, they are very flat, as in .0001 variation in the flatness of the surface. How flat is that? Imagine a cigarette paper that you split 3 times in the thickness; that equals .0001 in..
The reason the surface plate must be so flat is because it is the table that is used to hold the workpiece being inspected, as well as the inspection tools. If the surface was irregular, none of the measurements could be reliable.
- Precision micrometers are perhaps the most common tools used to measure workpieces. These are rather amazing in that they have not changed at all since they were invented about 200 years ago! These simple tools are quite capable of measuring less than one-eighth of a hair.
- Dial indicators look like watches with a needle sticking out one side. This needle is connected to the hands on the dial and show how much the needle moves when passed over a surface. These tools are used all day long in any tools shop, inspection area and in thousands of manufacturing plants everywhere.
Like many of these devices, the Starrett and Brown and Sharpe company manufacture all of the commonly used measuring tools. There are many other excellent companies, such as Mitutoyo and Tesa as well.
- Optical comparators are a little like a film projector that you can put your hand in front of and see your shadow on the wall. The difference is that the shadow is magnified an exact amount and cast onto a calibrated screen. This shadow is a very accurate representation of the workpiece being inspected.
- Gage blocks are small steel or carbide blocks that are exactly a certain size. These are also extremely simple, they are just blocks! Yet they form the foundation for all measurement in a mold making or tool and die shop.
These little blocks can be stacked up together to make any size you want, then you can use it as a standard to compare your workpiece with. This reveals differences in size, so adjustments can be made.
- Pin gages are similar to gage blocks, except they are round. They are used for a variety of reasons, mainly to check holes for size. You can take a pin of a known diameter and test it in a hole until you determine the hole size.
- The coordinate measuring machine is a newer instrument that uses a probe to check parts. The probe touches the workpiece in various locations and averages the numbers to determine the size or location of the details. All this information can be stored and compared to a data base or CAD file to find variances in the dimensions.
- Why are these tools important? Because, in manufacturing, things need to fit very precisely in order to function. In an injection mold, if the parts do not match exactly, you get flash, or the little bumps or fins that you can see on cheap plastic parts. In metal stamping, you get burrs, or the scratchy rough edges that can rip cloth or skin.
- Who uses these precision measurement tools? Tool and die makers, precision aerospace machinists, injection mold makers, CNC machinists, automotive machinists, and anyone associated with manufacturing.
- What does the future hold for precision? If the past in an indication of the future, tolerances are only going to get smaller. What is acceptable today will be unacceptable tomorrow. As technology advances, sizes are getting smaller. Nano-technology is all about this miniature world that is almost beyond belief.
Randy Hough writes about precision measurement tools at precisionmeasurementtools.com.
About the Author
|Randy Hough||Randy Hough lived, traveled, and studied in Europe for 3 years after college at Colorado State University, where he was an art major. After marrying in Denmark, he and his wife settled in Wisconsin, and he graduated from the Winona Technical Institute in Minnesota in 1978. Randy then became a mold making apprentice with the state of Wisconsin. After the 4 year apprenticeship, he worked at several shops to broaden his experience and finally settled in the beautiful Upper Valley of Vermont, where he lives and works. His main emphasis has been CNC EDM and the hand work side of mold making. At present Randy is involved in web site work regarding plastic injection molding/mold making as a means to make use of some of his accumulated knowledge.|
The views, opinions and technical analyses presented here are those of the author, and are not necessarily those of UL, ULProspector.com or Knowledge.ULProspector.com. While the editors of this site make every effort to verify the accuracy of its content, we assume no responsibility for errors made by the author, editorial staff or any other contributor. All content is subject to copyright and may not be reproduced without prior authorization from Prospector.