Drawing Standard Practices
Hello, just found the forum, I've been looking for a community like this recently so I'm hoping that I can get some advice I need while also offering assistance when I can based on my own experience.
A little background about myself, I have been a CAD Designer/Engineer for close to 15 years, working on a multitude of different types of products and tooling from automotive, aerospace, furniture **********. Before getting into design I worked under my father's tutilage from a young age in his fabrication shop, building conveyors and other material handling systems, cutting, welding, painting, we did it all as it was a small shop. I also worked in maintenance and as a machinist for a few years. So I have a pretty diverse background from both sides.
I recently started a new position as a design reviewer & drawing checker for a large material handling company in their R&D department. They have a long history and outdated standards. They also are very set in their ways and while the managers are fairly young and wish update the standards at some point we aren't there yet. With all that said, I have some issues with how they like to do things because I've never seen it done in the ways they are doing it. Now I'm not saying I'm right, I'm trying to find clarification because they have tasked me with bringing a fresh perspective and trying to steer them towards better manufacturability of their parts and yet I'm meeting incredible resistance, which I expected.
First issue, they like to do what I call "chaining" their dimensions together when it comes to holes. Being tasked with trying to find and eliminate tolerance stack-ups this strikes a nerve with me because I have never seen it done this way. I've worked in many tool and die shops as well as other types of places and this is the first place I have ran into where they dimension to the first hole, then dimension all the other holes in a pattern, and sometimes even other holes that are different all off of that first hole location. Most of them claim that they are controlling the pattern by doing that, which I contend is not true because you are stacking the tolerance of the dimension to the first hole with the tolerance of the dimension from the first to the second hole. Is this a common practice that I have just not ran into somehow over the years?
Something else, there is not one control point on the part, they will dimension from 2-3, even sometimes more edges to dimension something, which also does not make sense to me.
Another issue that came up today again is dimensioning to a centerline, then dimensioning from the centerline to a hole or slot or to locate a part in an assembly. The problem I have with this is, when you are building it you have no centerlines. Today it was a rectangular part, with 2 angled slots, the centerline was dimensioned then the slot end centerpoints were dimensioned from the centerline. If I were going to make that part I would want to know the location of the slots from one of the edges. Yet the response I get is "I've been dimensioning to centerlines for 40 years". To top it off its a charted drawing as it has multiple lengths and the slot locations change. So the reason I was given was he dimensioned it according to the "intent of the design". Which when I had him show me what he meant it was what the sketch in the model was drawn like, so he dimensioned it the way the sketch was made. While I understand it had to be made that way from a design perspective, to show it correctly on the drawing and make it "manufacturable" I need dimensions I can use. Because the length varies his centerline dimension was "L/2", then dim B goes back from the centerline to the slot location. While I realize that yes, you can make it from the information given, having to do the math to figure out what L/2 is introduces the possibility of human error in manufacturing which I am not comfortable with. There is no reason it cannot be dimensioned from the edge of the part, then that dimension tabled instead. Thus giving me a dimension I can build from and check to.
Anyway, sorry for the long post, but I could really use a gut check if anyone would like to chime in and see if I'm off my rocker or on the right track because this is getting a bit irritating.
Thanks,