[Coco] Sacrificial carts - opinions?

[Mark J. Blair]

On Jun 9, 2014, at 15:36 , Mark McDougall <msmcdoug at iinet.net.au> wrote:
> According to my colleague, who has had some molding done recently for a new product, it is the *engineering* costs that make the tooling process so expensive, rather than the actual production of the mold. So for the tooling process, you're paying the wages for an engineer to design the mold to your specifications; if you can do that yourself, it's a lot cheaper. Mind you, I think there's more to it than simply drawing up your case - the design has to be 'mold-ready' for the plastics and the injection process, so you need some knowledge of the job at hand.

Just to be clear, the $10k ballpark estimate that I quoted would be the tooling charge that I'd expect from ProtoMold for two molds, each for an item about the size of a CoCo cartridge case half. They require a solid model of the end product that is mold-ready, i.e., it already has the necessary drafts. So that $10k would include the engineering necessary to make the mold, such as ejector and gate placement, any side-actions or pick-outs if necessary (and the $10k guess assumes plain straight-pull molds with no side actions), compensation for shrinkage, part line definition, and so forth. But it doesn't include any engineering cost for designing the actual part in a moldable form (i.e., the industrial design part of the job, including all necessary draft angles).

In the projects I've done before, I did the industrial design of the parta myself. My background is in electrical engineering, but I was able to successfully design the parts I needed through a combination of hobbyist-level experience with mechanical design and machining, the excellent tutorials that ProtoMold provided to offer a crash course in injection molded part design, and their automated design rule checking system that provides a detailed design rule check within 24 hours after uploading a solid model to their site.

The CAD package I've used is Cobalt from Ashlar-Vellum. A "real" mechanical engineer would probably find it lacking because it doesn't include the sort of analysis features that they would need. I love it, though, because it has a really nice user interface, it runs natively on my Mac, and I don't know how to do any "real" mechanical engineering such as determining how fat of a person could stand on top of the finished part without crushing it, anyway. :)

So, if $10k or so magically appeared, I could design a mold-ready CoCo cartridge housing (my time would be free) and make a hundred of them appear in the mail a few weeks later as if by magic. Further runs would probably cost around $5 per part (per case-half, that is), plus $500 setup per mold per run (at least two molds per run, or three if a sliding shutter was desired). This is definitely something that's in the realm of possibility for a start-up class of endeavor, in that it wouldn't cost a hundred grand, require production of tens of thousands or parts, or require the effort of a major corporation... but I think it's still outside the practical realm for something as niche as the CoCo collector market. I don't think we could scare up ten grand in a Kickstarter campaign for a CoCo cartridge.

For the quantities that CoCo collectors might absorb, my gut feeling is that 3D printing would probably be the most practical approach. CNC machining out of blocks of plastic might also work, using something like that cool-looking Nomad CNC mill whose Kickstarter campaign recently finished. For best results, the design would be different for a machined part vs. a molded part; the molded part would need draft angles, while the machined version would be better off with straight walls to reduce machining time. I don't think it would make a difference for 3D printed parts, would it?

-- 
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/