b'Getting Defensive say my transition was challengingflaws that could not be detected would be an understatement. with micrometers and calipers.Adapting to GD&T was part ofAggravatingthedimensional the challenge. At the family shop,challenges was the rigidity of our 0.0127 mm (0.0005") range. We didwe had old-fashioned drawings thatprocess controls. At the small shop, not know anything about geomet- specified a dimension with a toler- manufacturing process control did ric dimensioning and tolerancing.ance that was not dependent onnot exist outside the mindset of If So the dimensional requirementsthe correctness of any other fea- it aint broke, dont fix it. Aerospace of work at the shop were not veryture. At the new shop, I was facedmanufacturing uses very deliber-challenging. with dimensions that alone wouldate, complex and thorough proce-At the new company, we madebe correct but when included in adures to demonstrate the ability of high-performance hydraulic pumpsGD&T structure were out of toler- a process to deliver the required and motors for military aircraft. Op-erating pressures of 5,000 psi wereThe transition from a small shop to a Department common in many of these units, andof Defense contractor was difficult.the entire pump was sealed by me-chanical fit. There were no O-rings, rubber seals or gaskets used in theance. In one case, I had to deal withengineering specifications.assembly process. Seals were madebored holes that had correct diame- Part of that process is first-arti-by machining the mating compo- ters and correct locations in a singlecle inspection. Once programs are nents so flat that high-pressure oilplane that would be out of tolerancewritten and tools are made, it is time could not find a gap. Flatness re- when included in the GD&T dimen- to run the first part. At completion, quirements were below 0.001016sioning scheme. I learned to hatethere is a 100% dimensional veri-mm (0.00004") and had to be mea- coordinate measuring machinesfication of the component. Every sured with light-emitting optics. Tobecause of their ability to uncoverdiameter, step, hole position, ra-dius and chamfer is inspected for correctness. Completing the FAI can take several attempts and con-sume many hours. Prior to aero-space work, I never really worried about stuff like a chamfer on the edge of a hole. But I quickly real-ized that every dimensionand there could be hundredshad to meet the drawing requirement or else I never would get through the FAI process.Once the component has passed FAI and the processes have been with buyers in print and online validated, the part can be released for production, which is when you ALL YEAR LONG may find out that a process that works on one or two FAI parts is notabout the author BUYERS GUIDE Christopher Tate is facilities operation director at Ethos-Reserve your ad space and Stay Connected! Energy in Houston. www.ctemag.com/advertise Contact him at [email protected] online listing links all your CTE-published videos, products, news and articles. com.44SEPTEMBER 2021DefenseMaterials.indd 44 8/17/21 3:57 PM'