Hello everybody,
I have been playing with my little printer and dreaming of constructing a truly life-sized 3D printer. Something with a build space of some 2.6x12.0x3m high – basically the largest size that can be transported by a lorry in Europe, and equivalent to the size of a large shipping container.
This would enable the prototyping and printing of full-size boats, car bodies, micro-homes/cabins, elements of buildings, large and complex formwork and moulds, etc.
Shape and form of the printer: I think the only sensible way of constructing this printer is to take inspiration from the construction printers like this good example: [
www.betabram.com] and there have been a few articles about small houses being 3D printed in China. Overall, the idea of a rolling gantry is certainly the most cost-effective and practical at this scale.
Material: Although I am huge fan of concrete, I think that its weight, lack of ductility and poor finish have their drawbacks. Printing in ABS seems to make more sense, and when purchased in bulk the cost can dip below 1$/kg. Obviously, this means that buying pre-rolled filament is out of the question and rolling your own filament is the only option. Other materials may also be feasible – any suggestions? Polyurethanes, perhaps?
Capacity: The printer has to be capable of printing at least 20kg/hour to make it viable. 50kg/hour would be even better. Anything below 20kg/hr would make little sense at this scale resulting in prints taking days or weeks.
A typical 3D printer outputs about 0.01kg/hr, with estimate based on printing about 2mm3/s through a 0.4mm diameter nozzle running at around 20-40mm/s at around 80% efficiency (since the printer is not outputting filament 100% of the time, etc etc). These are only meant to be ballpark figures based on only a few examples.
Obviously, something significantly more capacious is required. To achieve capacity a larger nozzle is required, and ideally the extruder should be moving faster (I am oversimplifying things, I know!). I have found a few links with people printing with a 1mm nozzle [
www.tridimake.com] (excellent article, BTW), and a guy successfully printing with a 2.8mm nozzle [
www.youtube.com] . They seem to be printing at around 100mm/s which is pretty much the max for garden variety 3d printers these days. However, the guys in Amsterdam printing a 3D house appear to be printing at 240mm/s!
I have absolutely no idea what would be the max feasible print speed, so if we fix this to 100mm/s, and to achieve 20kg/hr capacity, I think I’d need to be printing with a 8-10mm nozzle. This would achieve flow volume of some 5000-8000 mm3/s. If the speed can be increased a slightly smaller nozzle can be used (which would be good). Obviously, this is only a ballpark figure assuming 80% printing time efficiency, disregarding material expansion and probably a million other factors! I have tried creating g-code using these parameters (7mm layer height, 8mm nozzle diameter, 100mm/s max travel speed) and it vaguely corresponds to these figures in terms of build weight over time. However, please advise if I am wildly off the mark for whatever reason.
I doubt that there are extruders on the market capable of achieving this capacity so one would need to be made. I presume that it should be possible to replicate and scale up a standard stepper motor-heating element-nozzle extruder used in today’s printers. People have built these from scratch, so it should be feasible, unless I am missing something.
Filament: Not sure what would be a good filament diameter to use. Given that 1.75mm filament is used with 0.35-0.6mm nozzles, I presume 20-30mm filament should be extruded and used. Or perhaps this is wrong? Any ideas?
There is a wide selection of filament extruders available on the market and at 10-20-30kg/hr capacity these should not be prohibitively expensive. Although I am not sure how much larger dye diameter affects the cost.
For printing, probably the easiest solution is to fix a spool of filament (say 50kg or so) at the top of the gantry to move with the extruder, or it can be fed from the bottom. This is better is it would reduce the inertia forces of the print head, but then the filament needs to be fed carefully and this may not be simple at this scale!
Finish: Printing with such a large nozzle and at that speed would not result in a great finish. For the purpose of prototyping it will have to do, but otherwise decent finish would need to be achieved through post-printing. Thankfully, epoxy fillers and paints are fairly cheap where I live, as is the labour.
Potential problems: Not sure if people have tried printing ABS filament at these flow rates and with nozzles of this size. Does filament coming out of a 8-10mm nozzle behave like the one coming out of a 0.5 or 1.0mm nozzle? Probably not! Has anyone tried this?
I note that the author of the text who tried printing with a 1mm nozzle has run into problems where it was impossible for the extruded filament to span any gaps horizontally due to its weight and high viscosity – basically all horizontal ‘bridges’ were sagging badly. I can only assume that at 8-10mm nozzle this problem would only be exacerbated!
Given the size of the model, there would be considerable delay between layers. Therefore the layer below would cool and it is uncertain that the new layer would fuse with the one below properly?
At this scale, and this printing flow-rates how would the model cool? Would there be big issues with warping? Again layer-to-layer time would be decent, so perhaps that would actually help with gradual cooling? Perhaps enclosing the print area would help, but what would be a good chamber temperature? How difficult would it be to maintain it at this scale?
My experience with 3d printers is that they are sensitive to imperfections and extruders tend to collide with poorly levelled build plates or with warping printed layers underneath. With small printers this is somewhat alleviated by comfortably oversizing the enclosure, frames, runners, gears etc. At the proposed scale ‘comfortably sizing’ anything would have significant cost implications and is not really an option. Hence mechanical factors such as sagging of the gantry, lateral inertia forces, etc all come into play and are very significant.
Software and controllers – would it be possible to use standard RepRap tools? Perhaps! I sure hope so!
Cost - I seem to think that this can be done on a shoe-string budget (in relative terms, of course). However, fabricating a sturdy gantry with decent runners will not be easy. A perfectly level (and heated) build platform of this size would also be a bit of a challenge. Finally, purchasing an industrial extruder capable of producing large diameter filament is not a small investment.
Conclusions: I think most of the latter issues can be overcome one way or another. However, if ABS ‘doesn’t like’ being deposited through a 8-10mm nozzle at 100mm/s to achieve the required build speed then this will not work.
What do you guys think about it? Is there an elephant in the room that I am missing here? I haven’t read that people have done this? Why is that? If printing ABS at this capacity is not possible, what other materials would be feasible?
If it is feasible, then the first step would presumably be to build a smaller printer (or modify the one I’ve got) to test the feasibility of extruding ABS at these speeds, flow rates, nozzle and filament diameters? Then scour the internet for a few kg of large diameter filament for testing purposes.
Or is this whole thing a non-starter?