What is the main constraint for building large objects

I was wondering, what limits the size of a build object? I see that the tallest part built so far is only around 11". I have a ton of rails, slides, and was wondering what would prevent me from building large object such as a human size object?

I think the answer is temperature. You have to pretty much run your printer inside an oven that can go a little above 100C and also heat the build platform or the parts warp. This is how the commercial printers run and they have some pretty big ones that can print up to about 4 feet and probably bigger. I suppose if you limit yourself to PLA, then you don't to go above 100C. Maybe 50C is enough.

Edited 1 time(s). Last edit at 03/06/2011 02:11PM by brnrd.

Warping is the biggest barrier, second is time. The bigger/taller a print is, the more warping affects it. This isn't as big an issue with PLA, but is a huge issue with ABS. Heated beds get around this, but they wouldn't work for something really big. The only real option would be to have a heated build chamber.

As for time, a human size object would take forever to print, even commercial FDM machines don't print real big.

The best way to do large prints is to cut it up and print pieces to be assembled later.

How long does the part need to be heated? Say I build a 6ft tall object, does the entire object need to be at 50'C or 100'C? or can the bottom parts be allowed to return to room temperature as the build goes up? I figure I can build a heat ring using coil heater parts. This ring would be around 1' high and ride up with the nozzle. But that assumes that the bottom part will be ok to cool down.

Lots of restrictions:

-Material restrictions. 5lb of plastic is $60. If you print something big it's going to have a lot of plastic in it. hello 50 dollar print

-If you want fine detail you ened a small nozzle. large prints with a small nozzle might have a 2-3 day print time.

-Also if your printing larger by it's very nature the carrages are going to be heavier, byebye cheap nema 17 hello nema 23 at the least (if not much higher

-Granular extruders have worked, but your then heating a HUGE mass of plastic, no more 110 plug, or true indoor printing (that much plastic melting is going to be unfriendly for the office/home".


I think it's only a matter of time before we are doing large format prints, but I think the large format prints will be in ceramic, not plastic.

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@hereincs - I just realized that you're probably unaware that this technology - fused deposition modeling - has been around for many years and there are already mature companies that make printers that can print large parts. I think that the patent is held by stratasys. They have come up with solutions to address these issues. Their largest build volume is 3'x2'x3'. Of course, they also come at a very high price.

At first I thought that idea won't work. After thinking about it some more, it might work. Parts warp when the previous layers cool down below the glass transition temperature at different times. Extruded plastic shrinks when cooled below this temperature. As parts are laid down, the oldest layers cool down first followed by the ones laid down later. Since we're laying down hot plastic over ones that have cooled down and have already shrunk, the lower levels get pulled upwards as the upper layers cool down and shrink. The obvious solution is to keep the whole part above this temperature until the whole part is done. Thus, you need an oven. But perhaps if you heat a large enough height of the part below the extruder, it might be enough. So, not a ring but a heated chamber that moves up with the extruder as you build.

@specxula -All very good points but I thought that the question was the main constraint to building large objects. Interesting point about ceramics.

Edited 2 time(s). Last edit at 03/06/2011 08:11PM by brnrd.

Quote
NewPerfection
The best way to do large prints is to cut it up and print pieces to be assembled later.

Yes. Then you can print all the pieces at the same time on different printers.