Drawing Types (e.g. casting vs. machined vs. assembly.... 1

[philipdmartin]

I saw on another thread some discussion about having a casting drawing and a machined drawing if you're using different vendors. In my case I have one vendor doing it all, cast-machine-assemble, and I was wondering can I still have seperate drawings? It seems a lot cleaner if I break the two/three apart. The casting department of the vendor can focus on the casting drawing, the machining department the machining drawing and the assembly area the assembly drawing. Can the casting drawing have datums ABC or should it only have XYZ? I'm assuming the machining and assembly drawing should share the same datums unless functionality comes into play but I'm not sure. I know there's a lot packed in this thread but any thoughts would be extremely helpful. Thank you.

Phil

 

[drawoh]

ptruitt,

If you are nervous about your foundry and you prepared separate drawings for casting and machining, you have the option of shipping the castings directly to you. You can then inspect them, and ship them to your machinist. Regardless, your machinist has an interest in receiving good castings. His inspections should be valid.

JHG

 

[ptruitt]

drawoh,

I do not distrust foundries. Most of my career has been in either medical or aviation product design, documentation, and quality, so I was referring to situations where a high degree of formality and documentation is required. Philip is apparently with the military and I am no expert in that area, but perhaps some of my comments are useful.

Peter Truitt

 

[SDETERS]

One thing I would double check is to make sure your tolerance stacks are taken into consideration when you specify your final assembly drawing dimension tolerances.

 

[drawoh]

SDETERS,

That is a given for any design drawing package.

The problem with casting is that foundries claim that they can hold tolerances of ±.005"/inch. On a 10" casting, the length is ±.050". Your tolerance stack must account for this. If you apply your drawing default tolerance of ±.005" to everything, the foundy simply cannot do it. When they quote, they will state that they are making a best effort.

Your inspection problem is that the vendor did not promise to meet any tolerances. You have no grounds to reject stuff other than keeping a good relationship between vendor and customer. At some point, you are not worth their trouble.

I am convinced that most problems with non-accurate manufacturing processes are caused by bad drawings. The bad drawings camouflage bad design, and they provide un-meetable requirements to the vendor. Everything else follows.

JHG

 

[SDETERS]

We usually use the Nadaca Standards for Die cast. They have different type of tolerances for over split lines and different type of tolerances precision and or normal. We use this as good guidlines. I have experience with prints where Tolerance stacks are ignored and a +/-.005 dimension was put on the print. The foundary should have in process checking that check most parts that come off each run.