If you’re a product developer working with precision machine shops for the first time, you may notice the measurements that shops use aren’t what you might expect. While a shop’s system may seem a bit confusing initially, there’s a method to the madness—we promise!
While precision machine shops often manufacture parts for large-scale industrial applications, the measurements that the functionality of these parts depend on are incredibly small. The conventions we use are well-suited to the minuscule scale of our work.
Starting in the Thousandths Place
Standard precision machining dimensions are ± 0.005”— in total, about the width of three hairs. To make communicating about such small measurements easier, we collapse the first two places following the decimal so that the measurement begins in the thousandths place. This adjustment eliminates cumbersome strings of leading zeros and adapts our measurement system to the range that is relevant to our work.
Our base unit of measurement is one thousandth, also frequently called “one thou” in machinist lingo. Whereas a traditional measurement system notates this number as 0.001”, a precision machine shop records it as 1 thousands of an inch. We then apply this adjustment to all similar measurements, for example:
- 0.7” = 700 thousandths of an inch
- 0.25” = 250 thousandths of an inch
The Troublesome Tenth
The ten-thousandth place in the precision machine shop system is another common point of confusion for those new to our conventions. We refer to this place
as “tenths,” a shorthand for “ten thousandths.”
This naming convention is a bit idiosyncratic since machinists don’t shorten any other decimal place names. But we find that our customers quickly adapt to using the term “tenths” once they understand what it means in the context of their parts.
Here are a couple of examples of how machinists use the term “tenths”:
- 0.5001” = 500 thousandths one tenth of an inch
- 0.0232” = 23 thousandths two tenths of an inch
This illustration is a helpful resource for comparing the naming conventions that machinists use for measurements to the naming conventions used in traditional mathematics:
Why Imperial Instead of Metric?
Engineers often wonder why shops use the imperial (i.e., English) measurement system rather than the metric system—after all, many engineering schools use the metric system.
The simple answer is that the English system is easier to work with when doing business in America. Metric calculations aren’t as automatic, and converting measurements from one system to the other introduces the risk of error and takes longer than using the system that’s standard in the United States.
Although we can program our machines for either system of measurement, we’ve found that choosing one system and sticking with it helps us avoid mistakes, like forgetting that we set a machine for one system over the other. Entering a measurement in metrics rather than inches (or vice versa) could cause the machine to crash due to the significant measurement difference.
For example, consider that 1 inch equals exactly 25.4 millimeters. If a machine’s settings were changed to the English system but the machinist thought they were set to metric, programming an intended move of one millimeter would instead result in a move 25 times the intended movement!
The Reata Engineering Difference
We pride ourselves on being an engineer-friendly shop created by engineers for engineers. When we effectively communicate the reasoning behind our specialized systems, we empower our customers to better understand the services we provide.
Your precision machine shop should never keep you guessing about the meaning of terms or the conventions they use when manufacturing your parts. That’s why Reata Engineering takes the time to answer questions about our measurement system and anything else you’re curious about.
Request a quote to get started on your project today!