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I want to injection-mold several thousand of a part that fits in a 6" x 6" x 2" bed.

I would like to be able to use only tooling that I can make myself, so I can rapidly iterate on the tooling as production problems are discovered.

I know that typical injection-mold "hard tooling" is created using electrical discharge machining, which requires first CNCing a carbon positive and then using that as an electrode to spark-burn out a negative mold from hard steel.

However, I do not have the equipment for EDM. Instead, I would prefer to directly CNC the negative mold. I know that a soft enough steel to be CNCed will not last very long as an injection mold, but like I said, my run size is tiny, and I am ok with making a new mold every 500 units or so if necessary.

I am open to buying an endmill that is diamond-tipped, to work with harder steel, but then the limitation will probably be how much torque the CNC can produce on the endmill.

What are some recommendations or links to helpful resources? In particular, what is a good CNC with enough torque, and what blend of steel should I use? Thanks!

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  • $\begingroup$ Interesting question but I don't believe there is yet a relevant site to ask it on. This is probably off topic here, maybe it should be migrated to the proposed Digital Fabrication should it reach beta? $\endgroup$ – Joe Baker Jan 26 '13 at 5:51
  • $\begingroup$ The long list of CNC mills at reprap.org/wiki/MillStrap surely has at least a few suitable machines. $\endgroup$ – David Cary Jan 26 '13 at 7:55
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    $\begingroup$ @Andrew: (a) people who make robots often use CNC machines to make robots, and more importantly, (b) CNC machines themselves are a kind of robot. $\endgroup$ – David Cary Jan 26 '13 at 20:02
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    $\begingroup$ CNC related questions are not directly on- or off-topic... but this question appears related to tooling rather than any robotics aspect. My comment was more of a hint to make it better - if I was decided I'd have closed it. I didn't (yet) but there are Votes... $\endgroup$ – Andrew♦ Jan 27 '13 at 8:06
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    $\begingroup$ Having said that, this question would be better if it weren't summarised at the end as if it were a shopping question however. $\endgroup$ – Mark Booth♦ Jan 28 '13 at 11:50
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Answer from my MechE friend Sam who doesn't have an account:

First, I don't think you're going to have trouble with any CNC not having enough torque

Second I don't think you'll need diamond tipped. Tungsten carbide max.

I would look into using aluminum I believe it is viable for some molding.

And mild steel should definitely hold up. Easier to machine as well.

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