John Hayward

Electronic Measuring Devices, Inc

November, 1999

Upgrading an older Coordinate Measuring Machine (CMM) has many advantages. One of the most common advantages is the shear cost of trying to replace the existing CMM with a brand new one. It will cost far less money to breathe new life into the existing CMM than it would be to purchase a new system. You should ask yourself: How does someone get rid of a used CMM? How long do you have to wait for a brand new one? Does the new CMM have any great advantages over the one that is being replaced?

Let’s take a look at how the older CMMs were constructed. A definite advantage to upgrading the older CMM is the fact that the framework of older CMM’s were made to be mechanically accurate first. The materials used were all very similar in mass and expansion coefficients, unlike many of the newer machines today. Straightness, squareness, flatness, and linearity were all machined, scraped, lapped and tweaked into the CMM components to be as accurate as possible resulting in very highly repeatable machines before any compensation was introduced. These machines have had the opportunity to "settle out" over the years and are pretty much void of any initial stresses caused from assembly. These reasons make the older CMM’s much more precise mechanically than those found on new systems. After upgrading to the new Scanning Probe and Software, any repeatable errors found in the system after the initial calibration such as inaccuracies in straightness, squareness, flatness and linearity can be compensated out through the use of this new software.

The vast majority of the CMM’s out in the work environment are using the Touch Trigger Probe to collect data points along part features one point at a time. Touch Trigger technology requires that the probe come into contact with a part surface and when it does, a single data point is collected. This point is determined by the position of X, Y, and Z Axis at the moment of probe contact. The CMM will then move to another location where this process is repeated until the operator determines that enough data points have been collected for analysis.

By upgrading to a Scanning Probe, the CMM now has the ability to vector into the part surface, know or unknown, and then scan about the feature, much like a person feeling their way along a wall. As the probe scans along the surface, the software is collecting upwards of 300 data points per second. And depending upon how much data is required, an operator could collect up to 32,700 data points per scanned feature. Quite an improvement over a single data point! With all of these data points, the CMM is now capable of inspecting and analyzing not only dimensionally, but also surface profiles and contours! Scanning the part surface and collecting thousands of data points gives you many more details of the part. With all of these details taken from a single scan, look at all of the setup time and money that can be saved! Many of the part inspections can be combined to one inspection system. No resetting of the part for other types of inspections; no excess handling of components.

Electronic Measuring Devices, Inc, has a long and successful history of upgrading many makes of CMM’s from the Touch Trigger Probes to the very much faster and definitely more accurate Scanning Probes. Our history goes back to 1986 where we developed and manufacture the Sceptre Software and Scanning Probe. Since then we have installed this system on close to 100 CMM’s manufactured by Boise, Sheffield, Starrett, Brown & Sharp, Leitz, Wenzel, Moore, DEA, LK, Zeiss, Poli, Federal, SIP and Shelton. This successful integration has drastically improved the overall machine accuracy as well as breathe new life into an otherwise outdated machine.

I’ve touched upon upgrading vs. purchasing new. One more advantage for the upgrade is that there are plenty of pre-owned CMM’s around. These CMM’s can be purchased at a very reasonable and negotiable price. Anyone who needs a CMM or is looking to add a CMM should give this some serious thought. Important items to look for are the overall condition of the framework, working motorized axis, scales and limit switches. Once that it has been determine that these items are in decent condition, EMD, Inc could then upgrade the CMM with the Sceptre System which will include an analog contact probe, computer, controller, joystick assembly, monitor, keyboard and software to provide scanning capability. Once that is complete, you will easily and accurately be able to measure all of your components, whether complex or of unknown shapes that you thought only the big guys could measure with highly expensive equipment.