Reducing rejects at Pennsylvania machine shop

Modern Machine Shop, May, 1995

The Tri-Kris Company decided last year to enhance its position as a reliable machine shop supplying fine-tolerance parts for helicopters, the petrochemical industry, the Navy and other machine shops unable to perform the delicate milling and boring operations in which it specializes. Older height gages with set-up blocks could not meet current standards.

"Some of our parts are quite intricate," says Inspector Ron Treat, "for example, parts with triple leads, Acme threads, and double-ended studs. Measurements of thread pitches, the finish of an inside thread, and the distance from starting and stopping points above center where the thread stops - the ability to make these and many other complex measurements is critical to the integrity of our output."

As a result, it became necessary to have more precise gaging capability at Tri-Kris. The company was going into ISO 9000 certification and they wanted a better way to inspect their parts, Mr. Treat said. "We made an assessment of all our gaging equipment and concluded by taking two remedial actions: we replaced all of our old micrometers with new equipment and purchased some new high-precision instruments."

One of the key acquisitions was a Fowler/Trimos 24[inches] "Vertical 3" measuring system (Fred V. Fowler Co., Inc., Newtown, Massachusetts), which was carefully evaluated against directly competitive systems of both US and Japanese manufacture.

"We found out we could do things with it," he adds, "that even Fowler is amazed at - pitch thread angles and so forth. With a special adapter, we can use it horizontally. The only thing that limits me with this kind of instrument is my own imagination. It measures depth and vertical parameters simultaneously."

Tri-Kris works with part tolerances as tight as 0.0002[inches] all the way to less critical tolerances of [ or -]0.010[inches] T.I.R.

The Fowler/Trimos "Vertical 3" instrument, manufactured in Switzerland, is available in three ranges: 0-12[inches] (0-300 mm), 0-23.6[inches] (0-600 mm) and 0-39.37[inches] (0-1000 mm). It uses solid state capacitive measuring scales insensitive to both electrical and magnetic interference as well as to dust, oil or dirt. Using offset values and rotation, the instrument gives 2D calculations for X and Y coordinates and angles. Rotational errors are corrected while part measurement is in process.

A typical example of how the new gaging instrumentation is helping Tri-Kris to maintain and expand its position as a high-precision machine shop is a Navy aircraft carrier part with 200 holes. "It used to take 4 1/2 hours to inspect this piece," Mr. Treat says. "Now we can do it in 17 minutes. In addition, we've improved dimensional accuracies, and, as a consequence, have reduced our rejects on complex parts like this by 93%."

Customers of the company seem to be pleased with the results, particularly with the appearance of the manufactured parts - no burrs, the hole chamfers (where angle accuracy is critical), finish (No. 16 or No. 8) and the overall time factor between ordering and delivery.

"The only irony in the whole upgrading of our inspection capability is that old, old story," Tri-Kris says, "customers want more quality for the same price."