Old vs. new- Model vs. Drawing
Old vs. new- Model vs. Drawing
(OP)
I work in the lighting industry- pedestrian scale light fixtures- and the majority of our manufactured parts are die and sand cast. Before I came to this company the process was to design the parts in 3d CAD, create a technical drawing with only critical fit and function dimensions (mostly for inspection purposes) and only qualify vendors who would make the part from the model. The main reason for this was each part only has maybe 10-15 critical dimensions, but a
considerable amount of cosmetic surfaces that are difficult and timely to dimension.
Now, however, because of quality issues (hello outsourcing to China!), we are starting to go back to full dimensioning so that we have back-up when the vendor produces a sub-par part. I think that having a written clause in the purchase order as well as a note defining the part is to be made from the model and must be within given tolerances
should be enough.
So my Question: How does your company deal with this process? Are there any good solutions you have come up with? Do we really just have to go back to the days of full dimensioning because of Vendor quality? I feel like going backwards is a huge mistake- but I need a good argument as I will be a lone 23 year old female engineer launching this against an engineer who would rather computers didn't exist. I know ANSI Y14.41 is starting to make some inroads but I think it's usefulness is further down the road.
thank-you! and sorry for the novel.
considerable amount of cosmetic surfaces that are difficult and timely to dimension.
Now, however, because of quality issues (hello outsourcing to China!), we are starting to go back to full dimensioning so that we have back-up when the vendor produces a sub-par part. I think that having a written clause in the purchase order as well as a note defining the part is to be made from the model and must be within given tolerances
should be enough.
So my Question: How does your company deal with this process? Are there any good solutions you have come up with? Do we really just have to go back to the days of full dimensioning because of Vendor quality? I feel like going backwards is a huge mistake- but I need a good argument as I will be a lone 23 year old female engineer launching this against an engineer who would rather computers didn't exist. I know ANSI Y14.41 is starting to make some inroads but I think it's usefulness is further down the road.
thank-you! and sorry for the novel.





RE: Old vs. new- Model vs. Drawing
RE: Old vs. new- Model vs. Drawing
Being clear on the drawing is all one needs (the note you mentioned), but it helps to also mention it on the P.O. Warning about the note on the drawing: be cautious when using a generic note to define tolerance. Many industries have their own set of tolerances they will use based on the processes used. Be sure to be fully aware of these when creating the components and specifying a general model tolerance note. For example, it may be impossible to keep a tolerance of +/-.010 on a cast part over 12 inches; there may be a per-inch tolerance applied.
Best of luck!
Matt
CAD Engineer/ECN Analyst
Silicon Valley, CA
sw.fcsuper.com
Co-moderator of Solidworks Yahoo! Group
RE: Old vs. new- Model vs. Drawing
I can honestly tell you regardless if you have MDD or full dimensioned drawings you will fight this quality issue. Sand casting in China is even worse then injection molding or die casting. It's best to work through a broker who is located in the USA otherwise you will have a cultural fight on your hands. Trust me.....I'm in the fifth round and getting ready for a TKO
Heckler
Sr. Mechanical Engineer
SWx 2007 SP 3.0 & Pro/E 2001
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NVIDIA Quadro FX 1400
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RE: Old vs. new- Model vs. Drawing
RE: Old vs. new- Model vs. Drawing
Regards
RE: Old vs. new- Model vs. Drawing
I am headed into casting territory, although, I hope, not to outsourcing to China.
My first pass at a casting has been to use geometric forms I can apply tolerances to. I am assuming that I can create section views with GD&T profile tolerances, and that I can use these to create inspection tools. Even if the geometry is very weird, I should be able to insert a go gauge, and verify that there is not excessive clearance around it.
My problem at the moment is that all my design to date has been machined parts, sheet metal and some weldments, where drawings are used and are straightforward to generate. Our foundry guy used our 3D model to create rapid prototypes. I am not sure I am speaking their language yet.
Definitely, I am in favour of 2D drawings. The problems all look solvable to me.
JHG