Drawn Into a Corner

摘要

Q: We are currently laying out a rnnew flex design, any thoughtsrnon how we can "design"ourrncosts lower?rnA: You have already begun to lowerrn costs as you realize cost controlrnis born with the very first CADrncommand! Your question is also timely, asrnrecently I have seen a rash of what I wouldrndescribe as "intolerant tolerance." Draftersrnand designers are an exacting bunch, a veryrngood trait to have for the job. The problemrnbegins when we set up tolerance blocksrnon a flex-circuit like we would use on arnpiece of tool steel. Flex materials are inher-rnently unstable, changes in temperature andrnhumidity can have a big impact on finishedrndimensions. Our experience has shown thernpotential for a mil or better of stretch orrnshrink per inch. I see many drawings withrnoutside trim dimensions (edge to edge) held rnto +/- .005". While this may be acceptablernfor aluminum, it is far beyond the ability ofrncommon flex materials.