So, since I have an exclusively draft FDM background, I forgot about how long it might take to print in SLA, especially with all the extra stuff happening during the print. 

Calculating print times

If I assume 35um layer heights (to make a cube voxel), there's over 285 layers in 1 single centimetre. That's already not sounding good. With a 2-screen print cross section and 5 colours per layer to expose, that's 2,850 exposures in 10mm. Assuming 2 second exposure per screen area (though, the 108W source probably could cut that in half) and a very optimistic sounding 8 seconds to clean up the layer and switch to the next material, for a 320mm model:

320/0.035 = 9,142.8571 
9143 * 2 * 5 * 2 = 182,860s exposing
9143 * 5 * 8     = 365,720s cleaning and swapping
182860 + 365720  = 548580s 
                 / 3600 = 152.3833 hours
                 / 24 = 6.3493 days

 And then, to see the maintenance costs:

182860 / 3600 = 50.7944 exposure hours
2000 screen hours / 50.8 = 39.3701 models
Assuming LED lasts 3 screens:
4/3 * (£43 screen / 39)  = 4/3 * £1.10
                         = £1.47

Now a 1s exposure could shave off over a day of printing, and printing 70um voxels could cut print time in half (as well as have a higher chance in the resin filling the voxel before photopolymerisation), but the real concern is the cleaning cycle. 

Cleaning

BCN3D was never all that clear about this, thus I assume they haven't quite got the science just yet, but they intend to clean the layer before switch to another material. I'm intending to do the same and will have to discover some kind of method. 

Before thinking of the print times, I was planning on doing a wash similar to a dishwasher, with the potential requirement of filling the entire chamber with cleaning fluid for the final wash before the cure.

Now I'm thinking that an adequete clean cycle per change could cut complexities like that out, such as plumbing, cleaning fluid filtration and storage, and internal voids where cleaning fluid could get trapped and be unable to evaporate. If possible, I'd like to do away with inserting holes into the part to get liquids out of it, bringing it closer to the benefits of FDM. 

Ideally, there may be an opportunity to cure the part as the cleaning cycle takes place, resulting in a mostly cured part by the time all the layers have been exposed. Researching around Google leads me to believe that this wouldn't be necessary as even large objects would cure in 20 minutes, with smaller objects being closer to 5.

The ease of cleaning is inversely porportinal to the thickness of the resin the cartridges are able to accurately coat onto the film. That is to say, the closer the max thickness can be to the layer height without the minimum thickness going under that, the more likely a cleaning pass will obtain any resin still around.

How would I clean features that are so small they'd probably get damaged? No idea. Then again, those same thin features plunge into a vat of liquid for standard resin printers so perhaps they're a bit more resilient.

Cleaning methods

I'm thinking of:

• Use the clear film to wipe the resin and collect it (like a purge bucket).
• Have a microfibre cloth or paper stuck to a section of the film and clean onto that.
• Laminate a cleaning liquid on the film to dissolve liquid resin, perhaps with combination with the above idea.
• A sponge/roller/squeegee pass over the part.