In small quantities the best bet is sheet metal. You can take a design down to your local shop and they can cut and bend it. Ask them what colors they'll be powder coating that week and if you could slip your batch in with it (much cheaper than shutting down the line for your small volume)
It helps, of course, to know how to make the 3D drawings. But if you find the right shop, and make friends with them, you might get away with sketching it or paying a small fee for them to design it in CAD.
This is much more cost effective for small quantities compared to dealing with plastic. It also gives you more flexibility in your design since you don't have an expensive mold to change or re-machine when you want to make a change. And, at the end of it's use, it can be melted down and reused more efficiently than plastic.
If money is tight I'll get an extruded aluminum chassis and just make custom end caps for it.
In small quantities, your best bet is either to get the tools to make your own sheetmetal parts or make your design fit into an off the shelf enclosure. Just getting a single panel of aluminum with a few holes punched in it can run you $100 in set up costs at a sheet metal shop.
The same $100 will buy a few square feet of aluminum and tools to make holes yourself.
I'd find one of the online hobby machinist forums and ask someone there to make you what you need. As long as you're intelligent about it (learn to make your own drawings or to clearly explain what you need), you'll find plenty of hobbyists with the proper tools who don't mind helping you out at much less than professional shop rates.
Electronic, and by sources I mean forums or blogs. Somewhere with interesting people like HN, but with an electronics focus.
It was 4 or 5 years ago that I first heard of Stripe Snoop http://stripesnoop.sourceforge.net/ I thought it sounded like an interesting project, I'm not sure if it's dead now, but certainly interested me at the time. I was also intrigued by Zed's rant about programmable peddles.
The best one I know is the Sparkfun forum. It's heavily weighted towards newbies, so it's not as interesting as HN, but it seems to be growing fast. There are quite a few fun projects being discussed there at any given time.
It's interesting how software people congregate. It is really hard to find a good electronics blog or forum that isn't populated primarily by professionals talking about work-related topics. Electronic or Mechanical engineering versions of HN just don't seem to exist, unfortunately.
[edit] I know there are hobbyist electronics and machinist blogs out there; I'm saying that people with electronics & mechanical skills aren't discussing their startup ideas online.
Better yet, be the middleman! Implement a marketplace where people needing a part can hook up with people willing to fabricate it. Outsource the actual work and the fulfillment and the risk, and just take a small cut of each transaction.
Well, that's what I was thinking... If you have the 3D design knowledge, you could use these services, spec the part, then offer this it up for people that have broken plastic pieces around the house.
Hell, most of it is probably already spec'd in a manual somewhere, and just needs to be obtained.
Yes, but you'd have to outsource it to someplace really cheap. The 3D CAD work to draw up that part for your $300 lawnmower can cost $300 just for the drawing alone.
Same reason nobody repairs TVs for a living any more.
It helps, of course, to know how to make the 3D drawings. But if you find the right shop, and make friends with them, you might get away with sketching it or paying a small fee for them to design it in CAD.
This is much more cost effective for small quantities compared to dealing with plastic. It also gives you more flexibility in your design since you don't have an expensive mold to change or re-machine when you want to make a change. And, at the end of it's use, it can be melted down and reused more efficiently than plastic.
If money is tight I'll get an extruded aluminum chassis and just make custom end caps for it.