[GTA04] When is the next and more powerful openmoko releasing

Al Johnson openmoko at mazikeen.demon.co.uk
Mon Oct 25 23:00:32 CEST 2010

On Monday 25 October 2010, Dr. H. Nikolaus Schaller wrote:
> >> Well, we have anlysed approx. 5 or 6 different methods and none was
> >> inexpensive for low volumes. The only one that came down below 50 EUR
> >> per case is injection moulding.
> >> 
> >> But I would be happy if you can guide the GTA04 to a different approach.
> > 
> > It would be good if you could share the results of your research so other
> > open hardware projects can get an idea of what a custom case might cost,
> > and see how different manufacturing methods compare. It might also stop
> > us suggesting things you've already investigated an rejected! Also
> > exactly how low is low volume? Given the differences in setup costs for
> > different manufacturing methods it could make a huge difference to the
> > unit cost.
> All methods have setup cost (once) and cost per unit. Some methods have to
> repeat setup cost avery n units (e.g. silicon moulds made from
> Stereolitography).
> Our results so far (I can't share all of them):
> STL + Silicone moulds: 2000 EUR setup + 50 EUR each every 100 units
> Injection Moulds: 25000 EUR setup + 20 EUR per unit
> 3D-Printing: no setup, 400 EUR every unit (quality doubtful)
> Milling from ABS block: no setup, 500 EUR every unit
> So 1-10 units does not come below 250 EUR. 100 units may come to 70 EUR.
> 1000 units to 45 EUR. 10k to 22.50 EUR. You see the volume effect and
> clear preference of injection moulds. Which also give best quality...
> All these are lower estimates on industrial (not hobbyist) quality and
> based on 3D CAD files from Openmoko and does not include control of the
> process (someone must spend time to initiate and keep it running).
> Experience shows that real project cost is twice as high as the
> estimate...

Thanks. I'm surprised milling comes with no setup cost. Automated tool paths 
must have come on somewhat since I last looked, but that was probably longer 
ago than it seems. 

> Laser cutting was not yet amongst the production methods. Please try to get
> an estimate for setup cost (e.g. converting CAD data) and unit cost
> (material plus machine operation time).

Laser cutting isn't suitable for making the existing case design, so 
converting the cad data wouldn't be an issue. This would be a new design 
tailored to the production method. It's a fast and accurate way to cut shapes 
from (usually) sheet materials. Edge quality is good with the right materials, 
including ABS and especially acrylic. Setup costs are low to zero, 
particularly if you can supply a DXF with the outlines already offset for the 
cut width and set out on the sheet. You can get a rough idea of the 
capabilities at:
Prices from that site for one offs are low enough to be worth further 
investigation, at least for small numbers of cases. It may be time to try 
prototyping some ideas in cardboard...

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