Drawing Types (e.g. casting vs. machined vs. assembly....
Drawing Types (e.g. casting vs. machined vs. assembly....
(OP)
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
Phil





RE: Drawing Types (e.g. casting vs. machined vs. assembly....
Peter Stockhausen ://www.lin kedin.com/ profile/vi ew?id=3006 4526&t rk=tab_pro
Senior Design Analyst (Checker)
Infotech Aerospace Services
www.infotechpr.net
http
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
Regards,
Phil Martin
Oxford, MI
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
Peter Stockhausen ://www.lin kedin.com/ profile/vi ew?id=3006 4526&t rk=tab_pro
Senior Design Analyst (Checker)
Infotech Aerospace Services
www.infotechpr.net
http
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
However, there could be reasons to have separate cast and machining drawings - if nothing else in case of a vendor change in the future. In this case make extra sure and work closely with the vendor.
As Peter says, it may well be appropriate to develop machined datums from your cast datums.
I'd take a look at ASME Y14.8 Casting, Forgings, and Molded Parts which covers this type of thing in detail. It was a great help to me when I had to redesign a casting a couple years back.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
I agree with Peter, 3 drawings, with the machined-assembled datums the same and referenced from the cast surface datums.
"Wildfires are dangerous, hard to control, and economically catastrophic."
Ben Loosli
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
The machining drawing can have the material using the casting P/N.
Chris
SolidWorks 10 SP4.0
ctopher's home
SolidWorks Legion
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
An additional advantage was sort of noted above. Your casting reprents several thousand dollars (euros, yen, roubles?) worth of tooling. It would be nice to leverage this investment, and use the same casting for other stuff. This results in yet another machining drawing that calls up the casting by part number.
Your other option is to have two drawings showing the casting and machining. You can swear up and down to your foundry that the two castings are identical. Not a good idea.
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
Peter Truitt
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
Matt Lorono, CSWP
Lorono's SolidWorks Resources & SolidWorks Legion
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RE: Drawing Types (e.g. casting vs. machined vs. assembly....
That is what I was referring to.
Chris
SolidWorks 10 SP4.0
ctopher's home
SolidWorks Legion
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
I'd like to take it to the next level that I'm facing and that's I have a machined drawing, a casting drawing and 4 purchased component drawings. Now there's the need for the assembly drawing showing all of those pieces put together. I want to dimension the assembly drawing such that the supplier knows what to check for a capability study and ongoing SPC checks. I'll end up using new dimensions but also dimensions from the casting and/or the machined drawings so do I have to show them in parentheses as a reference dimension or with no parentheses? My understanding is a reference dimension does not get measured but I want it measured. On top of that, what's the best way to determine what dimensions should be measured on an assembly?
Regards,
Phil Martin
Oxford, MI
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
Note that in the CAD system of my choice, when you show a dimension from a part in the assembly instead of creating it in the assembly, if you modify it to display differently that it was in the part drawing, you have just changed the part drawing without intending to. I suggest creating most dimension in assembly drawings instead of showing them.
Peter Stockhausen ://www.lin kedin.com/ profile/vi ew?id=3006 4526&t rk=tab_pro
Senior Design Analyst (Checker)
Infotech Aerospace Services
www.infotechpr.net
http
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
"Wildfires are dangerous, hard to control, and economically catastrophic."
Ben Loosli
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
Let us assume you are on 3D CAD of some sort. You have a 3D model of your casting. You have attached a casting drawing to it. You have also attached your casting to an assembly, and at this assembly level, you are making cuts as per your machining requirements. Your machining drawing is attached to this. Perhaps you are attaching thread inserts as well.
The first thing you need is a common set of datums. The casting manuals I have read recommend casting in datum target features. If you have a consistent set of datum targets, the foundry and machine shops can fixture to the same points. Don't forget that casting is not as accurate as machining.
Your casting drawing must be a fully dimensioned and toleranced fabrication drawing.
Your machining drawing shows modifications to an existing part. It does not hurt to provide a few reference dimensions of the casting. Only your machined features require properly toleranced dimensions.
Critical specifications should be shown in one place only. At inspection time, a critical cast-in, unmachined feature should be inspected from the casting drawing. This is completely feasible if you specify datum targets as I noted above.
All of this is easily done with SolidWorks. I would be surprised if the other 3D CAD packages could not do it.
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
Peter Truitt
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
Why would casting and machining be different from any other fabrication process?
The main problem I can see is that the OP can produce crappy fabrication drawings for the casting. If the tolerances all are ±.005", then the foundry cannot achieve them.
It appears that the OP has not done castings before. He will need to establish a relationship with a reliable foundry.
Specify castable tolerances. Make sure the design works with them. Give the fabrication job to someone competent.
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
(I don't mean to say I am sure that Phil will be running into trouble, but I get suspicious whenever I hear of folks measuring parts at the assembly level.)
Peter Truitt
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
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.
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
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
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
RE: Drawing Types (e.g. casting vs. machined vs. assembly....
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.
RE: Drawing Types (e.g. casting vs. machined vs. assembly....