Short-Run, High-Complexity Job


This series of photos describes how the shop machined the part shown in Get Better Before You Get Bigger and even why the shop took on this work. Click here to view the full case study.

 

For a small and relatively new job shop to win attention, it sometimes has to demonstrate its competence by excelling at parts that more established shops would have difficulty machining cost-effectively. This aluminum arm, part of a proprietary product prototype, is an example. It needed to be produced in a quantity of just two.
The part could be machined in two setups out of a solid block. For the first setup, cutting time was long, but at least the part was relatively straightforward to hold. The block could simply be secured with a vise.
Here is the first operation, with the shape of the part beginning to emerge from the solid block. Note how the shop uses all of the table space of the machine, keeping the fixturing for its bread-and-butter spinal plate work in place, but well off to one side so there is room to set up less predictable work such as this.
How to hold the part for the second operation was the challenge. The highly fluid shape of the arm does not offer any good holding features for clamping. Therefore, between operation 1 and operation 2, a custom fixture had to be produced. This fixture was much like a mold cavity, a negative version of the shape of the part. The same CAM software that programmed tool paths for the part itself was used to create and generate the tool paths for this fixture. Shop co-owner Paul Gombar says the shop’s CAM software, FeatureCAM, is quite effective at 3D work. About 80 percent of the shop’s work is 3D. In the screen capture above, the line of the fixture can be seen—it looks much like the parting line of a mold.

Jobs like this are challenging because the shop can easily bid wrong and fail to make money. However, the work is exciting, and that excitement does have indirect rewards that help compensate for the risk. This shop competes with others to find and retain the best employees—people with both a talent and love for machining. By being a shop willing to take on parts such as this, and by engaging employees in the challenge of producing them efficiently, the shop reinforces employees’ opinions that they have chosen the right place to work.

Article by Peter Zelinski, MMS Online