Jet engines, power generators and other large parts present a challenge when measuring diameter because of their size. Bar gages and periphery tapes are two ways to measure the part. A third way is a product that counts the revolutions of a wheel as it rolls across the outside or inside diameter of a large part.

The product is the MIC 360 diameter gage from Gagemaker Inc. (Houston). The in-process measurement tool works on grinders and lathes and mounts on the machine's tool changer with a standard 11/4 inch shank or a custom quick-change tool shank. It measures diameters as small as 4 inches, but it is better suited for measuring larger diameters, said John Wolfe, Gagemaker's vice president of special projects.

The MIC 360 measures interior diameters that are up to 360 inches. The outside diameter measuring range is virtually unlimited, constrained only by the grinder or lathe's capacity. The gage's measurement accuracy, which is traceable to NIST, is + or - 0.0002 inch on diameters less than 12 inches, + or - 0.001 inch on diameters up to 200 inches and + or - 0.002 on diameters up to 360 inches, said Wolfe.

The hands-off measurement device means that workers do not have to climb on ladders or scramble on parts to take a measurement. It helps reduce measurement discrepancies from one worker to the next. "There is no operator involvement and so there are no variations in measurements because of inconsistent gaging techniques," said Wolfe. "Once you get above 12 inches, two people measuring the same part aren't going to get the same reading."

In a sense, the part measures itself. After machining, but while the part is still fixtured to the tool, the part is measured as it turns at speeds of 360 surface feet per minute (SFM). The recommended speed is 150 SFM, which is the speed at which Gagemaker calibrates the gage. As the part rotates, it turns a 33/4-inch hardened steel precision gage wheel that is held against the part by a spring-loaded bearing slide with 8 pounds of tension.

A high-resolution optical encoder counts the revolutions of the gage wheel as it rotates around the workpiece. An optical target mounts on the machine chuck and an optical light switch mounts on the machine base. Each time the target passes the light switch, the gage head notes the revolution and saves the measurement value.

From there, the data is transmitted by infrared communication link to the MIC 360's CPU, which can be mounted as far as 14 feet away but must be within the gage's line of sight. The processor's LCD continually updates the measurement data and an operator can track the readout and adjust the machining tool as needed.

"We can connect with CNC controls and do automated updating of offsets," said Wolfe. "If they program the next-to-the-final cut in a lathe to leave a 0.01 stock and we determine that it has 0.0101 stock, then the operator adjusts the machine to 0.0101 and not 0.01."

The MIC 360, priced at $9,700 for the basic package, can inspect multiple sized diameters. "The gage doesn't care about what size the diameter is, or if it has 6 or 7 diameters on it," said Wolfe. "An airplane engine would take 100 different gages to make all the needed measurements. With the MIC 360, the machine tool is positioned to measure the inside or outside no matter the size of the diameter."

The system can be used in a completely automated production line where the gage head output is wired to the machine controller and machining offsets are automatically reset. Automatic tool changers can exchange a cutting tool for the MIC 360.

The tool can also be used in a manual production setting or in a variety of other configurations. For instance, some older vertical lathes have cutting tool holders on opposite sides of the component. The gage can be fixed to the second tool changer so that the operator can cut and then measure the part without having to change tools.

"We have a customer who uses air-bearing tables on his grinder and we mounted the gage to that," said Jim Douglas, vice president of marketing. "We used a robotic welding arm to hold the MIC 360 against the part. The customer grinds the part and then takes the measurements. He won't run the grinder without it."

Whether used in a high-volume, through feed line or in a one-part-at-a-time production setting, the gage is subject to the environmental conditions of the plant including temperature fluctuations and environmental contaminants. Gagemaker offers an optional handheld temperature probe. The operator takes temperature readings at 20 locations on the part and one reading on the gage wheel. The computer averages those readings and compensates for any thermal changes.

The environmentally sealed gage also is waterproof, an important consideration considering the amount of coolants used in grinding and other machining operations. "The MIC will run right through any coolant on the part," said Wolfe.


  • Base unit mounts in a machine's tool holder and tracks the precision diameter wheel around the part as it rotates. This direct interface with any machine gives it repeatability.
  • An infrared signal sends diameter measurements to the MIC 360's computer, as far as 14 feet away.
  • Measures internal diameters as small as 4 inches and as large as 360 inches, even as the part is rotating at 360 SFM. The measurement range of outside diameters is unlimited.
  • Eliminates variations in critical measurements because of different operators and inconsistent gaging techniques. No operator involvement during the measurements is required.
  • Inspects tapers and grooves.
  • A comprehensive instruction manual that includes installation and usage photos.

    Technology Contact
    For more information on the MIC 360, contact:
    Gagemaker Inc.
    710 E. Southmore Ave.
    Pasadena, TX 77502
    (713) 472-7360
    Fax: (713) 472-7241
    E-Mail: [email protected]