Originally Posted by thkoutsidthebox  ....the fixture is actually more complicated than the parts its used to make!!! ?? At least to my untraind eye  . |
Yes, once you get past using a vise or just clamping things to a table your fixtures are often more involved than the part. Although if you look at things correctly a vise is often more complicated than the parts it holds when you get down to it; Kurt duoLock vises are very complicated internally.
I served my apprenticeship a bit earlier than CNC came into relatively common use in a place that did small scale production volumes of things like firefighting equipment, domestic water pumps, valves and fittings for dairy farms.
Pre CNC one emphasis was on maximizing efficiency by making multi-point tooling to complete a number of dimensions in one operation; also to have the tooling define sizes rather than rely on machine graduations. Another emphasis was on fixture design that was easy to load and which located the part on previously machine surfaces or which held the part through two or more operations with the fixture locating by reference surfaces in bases in one or more machines.
With CNC the need for multipoint tooling disappeared because the machines are so precise and can change tools. I also think to some extent the emphasis on effective fixturing also was downgraded to some extent. It still does exist in truly high volume work with pallet changers and things like that but it seems to me a lot of small volume shops still fumble around with vises and clamps when a little ingenuity could improve things. Even on non-repeat jobs sometimes it might be possible to have a net saving in time by using some time upfront to make fixtures that increase throughput. Even if the fixture building time plus shorter production time only equals what it would have been without building a fixture it is worth it. And....if it happens that the job does come back then the second time through and everything following has a lot of gravy in it.