I really need some free advice from one M.E. to another, or draftsman…
Please give me a crash course in drawings, esp. fabrication (assembly?) drawings.
Also, are there any good references…Creating Good Dwgs for Dummies?
My forte is in analysis and sizing equipment, not in fabrication. But, I’ve been tasked to review a package of drawings which must shown enough detail so a shop can assemble the item. So, I need some good rules of thumb as what makes for a good fabrication drawing vs. what should go into the related spec I have to review. For starters, what notes belong on the drawing, and what belongs in the spec? Think of all the details that go into a drawing, and it’s overwhelming! Materials, welds, protective coatings, minimium thicknesses, etc. What about deburring drilled holes, etc? I know usually there’s statements citing ANSI and ASTM stds, but I don’t know these off the top of my head.
Also, what about finer details? For example, suppose a hinged surface is lined with a gasket to create a good seal, should there be a detail dwg (or section dwg? i.e. a “cut away” showing section A-A, for example…) calling out the gasket?
In the few drafting electives I took, I always felt so “illiterate”. Good drafting procedure is like its own microchasm within my field, and now I must know what to look for in such a drawing package.
ANSI actually has a drafting standards handbook. I’m not sure how good it is - I’ve been using CAD since I started studying engineering since I’m so bad at manual drafting, but it does exist.
Machinery’s Handbook has a lot of good information on this. However, it’s spread over 2500 pages. Not great.
If you want holes deburred and sharp edges broken, write in the lower left corner “Debur All Holes. Break All Sharp Edges”.
You only need a sectioned drawing when it’s unclear what surfaces will be sealing up against each other. They’re difficult to create, easy to make mistakes on, and usually no clearer than the other drawings were.
I’d suggest you use a computer and a solid-modeling program (Pro/ENGINEER or similar) anyway. It makes things a lot easier to visualize and gets rid of stupid stuff-ups in drawings.
Your component fabrication detail drawing could contain a bill of materials. Special standards can be notated in a block of text on the drawing. As for the assembly, an exploded view isometric is a good way to show how the components fit togehter and are assembled.
Are you doing this work for a large company, or will these drawings eventually be seen by a large company? If so, you should ask for a copy of the company’s drafting standards. They should give the guidelines you need. Plus, it’ll make you look diligent.
You raise a good point. Ideally, we should have an understanding of what the manufacturer will require…but I doubt we’ll ever see it because of the chain of command, etc., etc., etc… - Jinx
Jinx, I feel your pain. My first job after getting my BSME was in a manufacturing plant where I was expected to know a lot of things that were never taught to me in school. I got a lot of good advice from the people on the shop floor, especially the old tool and die makers (they are always old guys!) and I managed to get a practical machine shop education after a few months. I was eventually able to call myself a “manufacturing engineer”.
If you have access to the shop where the parts are to be fabricated, you might ask the shop foreman for advice. He can point you to some knowledgeable people. You might have to swallow your pride and endure some snickers. They might send you to the supply room for a “long weight”. But this is something you really should do.
The best book I have seen on this subject is the ‘Handbook of Product Design for Manufacturing’ (McGraw-Hill). It contains most of the stuff you need to know.
If you have specific questions, such as the tolerances involved in drilled vs. reamed holes, or grinding vs. cutting, etc., I’m sure I or someone else on this message board will be able to help you, so feel free to post!
Well, I do structural drafting, not mechanical stuff but my best piece of advice (along with all the helpful stuff above) would be to get a go-by, a set of plans similar to what you’re trying to review that have already been approved by someone knowledgable. Go-bys helped me immensely when I started making drawings.
Try not to fall for “sparks for the grinder (you’ll need a damp paper bag for those, son)”, or “a square bubble for the spirit level (don’t let the storeman palm you off with one of those obsolete round ones)”.
Go get yourself a handbook on manual drafting. Because it was so time intensive, strict rules were created to ensure that a drawing had the information it needed to convey. It took far too much time to redo a drawing by hand to screw it up the first time around. Those older books tell you how to lay out drawings, in which instances you will need detail drawings, and how to go about specifying common features such as tolerances, finishes, radii, and chamfers.
Use a CAD program to do the drawings, but use the old rules to lay it out. CAD makes it too easy to quickly put together bad drawings.
