Machining and Mechanical Design for EEs? - Page 1
Forum section: electronics / beginners

author: krivx
author_rank: Frequent Contributor
timestamp: May 14, 2013, 01:40:24 pm
content: A little while ago I had to draw up some custom parts for machining. My background is in EE and most of this was completely new to me. I had a lot of help and things went quite well but if I was to do this again I would like to be more comfortable with the process. I don't mean to be insulting and assume that I can teach myself a discipline of engineering to a professional level in a few hours, but even grasping basic concepts and being aware of standard real-world practices would be a huge help. Are there any books or other resources to bring me up to speed a little bit? I do have access to a University library.

author: robrenz
author_rank: Super Contributor
timestamp: May 14, 2013, 02:08:57 pm
content: Tough to beat "Manufacturing Engineering and Technology" by Kalpakjian and Schmid. I have the 5th edition, I don't know if there is a newer edition. ISBN 0-13-148965-8Extremely good coverage from making the raw materials to mems devices.

author: krivx
author_rank: Frequent Contributor
timestamp: May 14, 2013, 02:16:26 pm
content: That looks like exactly the sort of thing I was looking for, thanks very much. It looks like the 7th edition was published in April but the length of the book doesn't seem to change much between editions, I would guess these are incremental updates.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: May 14, 2013, 08:46:58 pm
content: Having some familiarity with the processes used can be very helpful. If you have time have a look at the MIT machine shop teaching videos:http://techtv.mit.edu/search?q=machine+shopI suspect it'll mostly be the milling machine one that would be helpful to you. If you can picture what the shop is going to do while you're drawing the part, you can spot what's going to be the hard parts.I was trying to find a really good article I read that was something like the "don'ts" of mechanical drawing. If I find it I'll post it. Basically it gives a few tips, like inside square corners are really expensive (end-mills have a radius, and generally the bigger the end-mill you can use the faster it goes.) Deep, narrow slots are expensive (start getting a little squeemish around a 3:1 length to depth.) There are ways of doing deep slots in certain circumstances very easily though, like using a slitting saw. Intelligent tolerancing can save you a fortune; for example I'll usually indicate a drilled hole as with so-and-so size drill rather than a hole size, like "DRILL 6mm" rather than "6mm +0.01/-0.01". The latter is a lot more work. Thru-tapped holes are a lot easier than bottom tapped ones. Nuts & bolts are even cheaper if they can be used. Only tap to a depth you really need if not going though, and give a good wide tolerance on it's depth if you suspect they'll be doing it by hand. If you can, give some thought about how the material will be setup on the machine, and if they can't grip it in a vice say, try to give them something on the part to work with.If the parts are to be CNC machined rather than manual, the ball-game changes a bit. Basically what you strive for there is a minimum of tools used to do the job, and the absolute minimum number of setups (setting the material up on the CNC machine).If you can, swing your early drawings by a machine shop for a critique. The smaller the shop, the better. They'll tell you what they hate on your drawings. They are often very good at understanding the function of your part as well and can give you some advice there.

author: Smokey
author_rank: Super Contributor
timestamp: May 14, 2013, 09:06:12 pm
content: I've been in your position, starting out as an EE and ending up as the guy that does a little bit of everything including all the sheet metal. The best resource I've found for getting help designing metalwork stuff is the guy that will end up making the parts. We work with some small local shops and they are always more than welcome to do a quick design review and recommend changes that will make the manufacturing process easier for everyone. It's in their best interest for the parts to be easy to manufacture. The less time and processes it takes for them to make the parts the less time their machines are tied up on your job and the more money they make, and that translates into cheaper prices for you the customer which makes you happy and coming back for more parts.Our metal shops have all kinds stories of customers sending them design files of parts that are impossible to actually make because the customer didn't understand the actual manufacturing processes. Sometimes the parts are just very difficult to manufacture because they need special tooling or a TON of processes and the price will reflect that.I can't recommend enough finding a small local shop at least to do prototype work and that has someone you can go over the designs with before you release them for quote.

author: krivx
author_rank: Frequent Contributor
timestamp: May 14, 2013, 09:54:45 pm
content: Thanks for the suggestions, the MIT video looks quite good. I'll keep an eye on any open CourseWare series that are related, I'm sure there are universities that offer rapid-prototyping or manufacturing classes.Quote from: Paul Moir on May 14, 2013, 08:46:58 pmI'm almost certain I've read that article but I can't find it right now. They also had an example where every dimension had a ridiculous tolerance and one where all annotation where in yellow (!).

author: KJDS
author_rank: Super Contributor
timestamp: May 14, 2013, 10:05:11 pm
content: This bloke has a good series of machine shop tips. Doesn't cover much drawing but does on the use of lathe and mill.https://www.youtube.com/user/mrpete222/videos?view=0&flow=gridI'd love to have a place big enough to put some decent machine tools in.

author: krivx
author_rank: Frequent Contributor
timestamp: May 14, 2013, 10:56:14 pm
content: Quote from: KJDS on May 14, 2013, 10:05:11 pmWow, a lot of great material there. Thanks.

author: mc
author_rank: Regular Contributor
timestamp: May 15, 2013, 11:47:36 am
content: As others have said, try and get an understanding of the processes involved.Also find someone knowledgeable to look over your drawings and highlight any features/areas that could be a problem.

author: eKretz
author_rank: Frequent Contributor
timestamp: May 16, 2013, 02:06:53 am
content: You can easily learn some basics from those videos and learn the major no-nos. But like with any other discipline, the more complex the parts, the more knowledge you need to make them. (I was a machinist for nearly 20 years until my back gave out).QuoteThe above is very good advice, and so is the suggestion to look for something along the lines of "Dos and Don'ts of Mechanical Drawing." It will be easier to get the info you're looking for faster from something like that. The reason inside square corners can be expensive, BTW, is not only that endmills come with radiused corners. They are available just as easily with square corners unless you use carbide. However, another important reason is that sharp corners require slower feeds to prevent corner/edge damage to the tooling. Sharp tooling corners are fragile. Slower is more $$, like with everything else. With a square corner spec, you also have to worry about whether the mating part has a square corner, since any tiny obstruction will prevent the parts sitting aligned and flat to each other. As noted above, in some instances, square corners are easier (shell milling, slitting saws, etc. but then you have to have the OK to have a radiused runout area since the tooling is radiused in a different orientation to an endmill.

author: Fuse_Burner
author_rank: Contributor
timestamp: May 16, 2013, 02:07:18 am
content: Being a machinist for 20 years, I can tell you countless stories of recently graduated engineers producing drawings of parts that were impossible to make. It's important to have a firm grip on being able to get your vision on a piece of paper correctly. Unless you're solely concerned with fits, finishes, tolerances and strength of materials, get a little study in on drafting as well.