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Comment by fieldforceapp | Hacker News Reader

Just ordered my first AeroPress, wondering what type of grind works best?

> With his plans mapped out, Adler went to Westec Plastics in Livermore, California, > ordered $100,000 worth of molds, and put the invention into production.

Just how does one go about stepping up from something like 3D printing (manifold meshes [0] are easy) to something like injection molding?

[0] http://www.shapeways.com/tutorials/prepping_blender_files_fo...

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"Just how does one go about stepping up from something like 3D printing (manifold meshes [0] are easy) to something like injection molding?"

Pretty straight forward actually. If you have the solid shape you want and can find a line of symmetry that does not result in any over hangs, a good CAD package will let you slice the shape and create two halves. You use boolean subtraction from a solid block to create the mold profile, now you will add alignment pins (at least 3) and add sprue paths (this will depend on the injector you are using) then send that to a suitably equipped milling machine to mill out of a couple of blocks of alumninum. Assemble to two halves and hold them together (you can use a press or bracket for that) take your thermo plastic under modest pressure and heat, and squirt it into one sprue hold until it squirts out the other. That has to happen reasonably quickly as the plastic starts to harden as soon as it hits the Alumninum.

Pull apart the mold, pop out the part. if you get a machine like this one: http://www.ebay.com/itm/like/140895101602?lpid=82 you can pop out a hundred copies pretty quickly.

$12k??? is there no way to prototype an injection mold for less money? I'm trying to make something like the Xbox Kinect housing, for example.

Its possible to 3D print something as a prototype (a number of shops use stereo lithography for that) for a couple of hundred dollars. But that doesn't insure that it can actually be injection molded. You need a shape you can represent as a convex hull.

The process of developing the molds (aka putting them into a CAD system, slicing them, and then cutting the mold itself. Is called 'tooling.' Any tool and die shop can give you a quote. Back in '99 when the company I was with got quotes for tooling for a desktop gateway, a tool and die shop in Milpitas quoted us $36,000 out the door, and then $4,800 for each additional set of dies. A set of dies was good for between 100,000 and 500,000 uses. I don't doubt they were not the cheapest way to go, shops in China were willing to spread the tooling cost across an order of 100,000 units.

So are you trying to see if your design "fits"? If so get a stereo lithography shop to print one for you. If you are trying to see what it will cost to make take your printed part to a tool and die shop and ask for a quote. You will probably specify which type of machine you are going to use for the molding (dies are specific to machine models).

Toolmaking is not cheap. You're starting with a large block of steel or aluminum, and that's usually a custom alloy with extra hardness if you plan to make more than a few thousand. The molds wear out over time. So that's money right there.

Then it's a couple of weeks of milling, drilling, polishing, welding on support channels, etc. There's a lot of CNC time involved, and that's runtime on million-dollar machines with high maintenance and deprecation costs. If you want it done by hand by experienced machinists, that's even more money.

The Aeropress has some pretty tight tolerances on it's design, so there's more money right there. Size also kills. You want something the size of an Xbox housing? That's gonna be even more.

Protomold[1] are probably that niche, although I'd treat it more as proof of concept than as scalable as proper production molds. If you've validated your prototype that way, you'll probably end up with DFM[2] changes you want to make before dropping 10's of K (or more) on full production stuff.

[1] http://www.protolabs.com/protomold

[2] https://en.wikipedia.org/wiki/Design_for_manufacturability

Yes, that is the reason why 3D printing is a big deal :)

I use a fairly fine grind, although not as fine as I use for espresso. According to the stock AeroPress instructions it should take about 20s to depress the plunger, if it's too hard to press it's too fine, and conversely if it presses with little to no resistance then it's too coarse.

20s with 'average' pressure... good guidance, thanks!

I use a very fine grind (actually I cheat and use Cafe Bustelo right out of the bag). I've noticed using the inverted method makes the plunge step a lot easier, probably because the grounds are mostly still suspended in the water and not sitting on the filter right away.

I go with the finest possible while not impossible to push down the plunger. I bought an AeroPress about 18 months ago and haven't made coffee different way since.

Around a medium grind, finer if you prefer richer coffee (closer to espresso). Since you're using a filter, it doesn't need to be nearly as large as a french press grind.

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