I could use some clarification

I have been into CNC machining and 3d printing for years now and there are a few questions I can't seem to find answers to. I was hoping some of you guys could help me understand some things.

1. What are the limitations to making a big 3d printer? I can build a 4X8' CNC router table for a pretty reasonable price, using standardized parts. Is there some major problem stopping people from building something like a 4'X4'X4' reprap? What about a 10'X10'X10'? Is it only a matter of the cost of doing such a thing? Has some sort of limitation been reached that we need to engineer a solution for? I just can't seem to find any info at all on this.

2. Assuming you could just build a huge 3d printer, is there filament available that is thicker then 3mm? Would you have to switch to rods of material?

3. Has anyone experimented with a dual hot head, one using 1.7mm filament for finer detail and one 3mm for a faster fill rate? This seems pretty obvious as a way to speed up build speeds but I have not seen anyone try it.

1. Speed/runtime, warping of the part due to plastic shrinking as it cools, cost of plastic.

3. Input filament width has no bearing on extrusion width, other than needing to feed 1.7mm filament about 3x as fast for the same plastic volume.
I've seen others suggest using two not ends with different sized nozzles, I've never seen it done, and I don't know of any software that supports it.

Printing filament is just welding rod. Available in many sizes.

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It's perfectly possible to create large scale printers with large nozzles, see this: [vimeo.com]
However, extruding plastic at larger scales become increasingly complex and costly; the size and complexity of the delivery, the quantity of plastic, thermal shrinkage are all problems to overcome. In the end, it's better to choose the best manufacturing technique for a given product and quantity required, rather than creating a manufacturing technique and then decide what to make with it.

Thanks for the info and the video. I wonder where I can find info about his extruder, that would be a much more economical way of going big.

I have to disagree with your statement, "it's better to choose the best manufacturing technique for a given product and quantity required, rather than creating a manufacturing technique and then decide what to make with it." If that was true reprap would not have even been a concept. A reprap is a machine as well as a process/technique, it is not the best for making reprap parts however. Injection molding would be much faster and consistant, I strongly believe in creating new manufacturing techniques and then figuring out what you can make with it, that you couldn't before. In the video, 3d printing is not the "best" manufactuing technique to make a chair. That is unless you want to make a 3d printed chair.

I think you're kind of agreeing with my statement. If you want to make a 3D printed chair, you do it with a 3D printer, ie you choose the manufacturing technique that best suits your product. I was, however, thinking from a more production point of view; FDM and other 3D printing solutions are ideal for design, prototyping and short run production, but at the point you scale up to larger production, you look at what the most effective means of production is, balancing up cost, time, finish, quality etc. That's why repraps, though fun, are still struggling to come up with their 'killer app'. That's not to say that personal fabrication or distributed manufacturing isn't its own reason, but it doesn't scale well to the next step up - actually selling products, where the priorities are different.

Generally, I don't think manufacturing techniques advance through general experimentation; it's too open-ended and vaguely focused. Some companies can afford R&D departments, but most manufacturing advances through someone coming up with a new product, or improvement, that needs different techniques to produce it. It then gets repurposed for other markets. This is, of course my opinion, with no hard facts to back it up!

This is all part of a larger discussion about the future of reprap and personal 3D printing, of course. The beauty and power of reprap is that it makes manufacturing more accessible to ordinary people.

I see what you are saying, I guess I viewed your comment a little differently then you meant it.

My vote is that the Reprap is the killer app itself but one killer app does not take the place of a whole market place.

Although necessity is the mother of all invention I do think that there is a lot of room for open experimentation. I feel that size is a big limitation to the current generation of printers. By going bigger we open up the potential of what can be made. It also helps people open their minds a bit more to the possibilities. If you ask someone what they can print with a 6"X6"X6" print area, they are going to have a tougher time then if you ask them what they would build if they had 6'X6'X6'. I would also say that by being able to print larger, you make personal manufacturing a more valid option in the future. This is because large pieces are more expensive to make and ship. I believe that traditional methods start to lose their price advantage the larger you go.

Now if it was as easy to build a machine to do it as it is to talk about it

There are lots of large machines out there but they are not just larger RepRaps. Like D-shape is so large it prints buildings. But it went away from the biggest problem with printing large items with a RepRap and that was the plastic. It uses waste material from a quarry and binds it together with a special binder that makes it as strong as concrete.

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Hi, I'd like to order a 1000lb roll of 50mm ABS filament....what you say? $39000...damn, and I just gotta have it, cuz my last print failed at 90% because the Arduino I use to run my reprap Gigantica stopped communicating...It's like real super important too... a big plastic yoda head.

badumpbump.