Bigger table and frame with I3 parts?

Im looking for a 3D printer and found many from the wiki list, but the table sizes of these printers are quite small, only 200x200 or similar to that, and the larger ones naturally come at a much higher cost and since I'm not gonna use it for commercial purposes I wouldn't like to pay thousands off it. I need a table size of 400mm minimum, and found that my local shop sells hardened glass plates 400x480mm in size, so very suitable for my need. Therefore I thought could I just simply take the Prusa I3 and increase the size? I quickly made the following illustration on what I was after (ATTACHMENT).

So my idea is to take the Prusa parts kit with required stuff, and fabricate the frame. Originally I planned to plasma cut the frame from steel and weld it, but it would have too high cost and weight and it would literally be too rigid, it could house a CNC mill. I would use 20x50 for the box frame, and use 20 or 25mm plywood for the center. I might add sound insulation on the frame and line it up with thin plywood. The guide rods and other parts may need to be scaled up in order to avoid warping, something like 8, 10 or 12mm threaded rods and stainless round bars for linear bearings. I'll find something lightweight but rigid to carry the table, probably wood or aluminium.

My concern is that are the servos strong enough to move the increased weight of the table, and are the parts reasonably easy to fabricate for the increased size schema? Can the software be adjusted to adapt the larger table size, and are the stoppers only ones that restrict the movement of XYZ axis?

Another issue comes with the heated bed. I saw someone just coiled some nichrome wire under the table and installed a thermal sensor underneath it. I'm mostly planning on PLA, so would it be enough if I just put the standard 180x200mm prusa heater under the bigger table and print non-PLA items only on the center? I heard that printing PLA warpless can be done without the heated bed with proper cooling, and if I add sound insulation and plywood around the frame, I need to make line fan to the box anyways, so these could be combined for results?

Would this kind of design work, has anyone tried it? In there would be 4 servos to drive the up-down axis, and there be two servos driving the longitudial axis and one servo to drive the left-right axis. The table would be stationary. With long rod lengths there may be need for increased stiffness, like 12 or 16mm threaded and smooth rods to avoid warping.

i was actually looking in building a larger 3d printer with my current printer

the only problem that was mentioned to me when i brought the idea up was the printing might get sloppy after a while

and the 3d printer that i wanted a larger one of is the prusa mendel v2 off of reprap.org wikipedia

and the larger size would be able to print out a decent size computer case or an object of similar size

Edited 1 time(s). Last edit at 08/29/2014 11:04AM by pspuria81.

Most of the problems with scaling up printers has to do with the flexibility of the X and Y rods. When you get much longer than 2 feet there is a significant bow in the smooth rods. Even going with larger diameter rods you are adding extra weight to the system causing more bowing/binding. A solution is to use rails/channels instead of rods for your X and y I think the Prusa i3 Vslot variant is a example of this.

Another option might be to have a Stationary lead screws mounted in a solid box frame with a stepper motor driven carriage on one side of the Y and a smooth rail on the other. The X carriage as I am seeing it is a lead screw on a vertical mounted rail/channel. In your design it looks like you have four Stepper motors to run the Z You might be able to get away with two placed diagonally across from each other and smooth stabilizer rods/rails in the off corners.
Thanks Mike

I redesigned the concept a little bit as attached pic shows. It's essentially the same concept, but I though that two X-axis motors should be sufficient. They're mounted on the upside so they pull, and I have concepted axial bearings on them so no axial load would be applied on the servos. So there's 2 motors on X axis, 2 motors on Y axis and one on Z axis moving the extruder head. The print table would be acrylic sheet 500x500 in size. The threaded rods and smooth rods are all 12mm, except for the extruder slide which I'm gonna test 8mm bars to see if they warp too much, they're substantially more lightweight. In future I could also look for aluminium profile wether it is more lightweight or not.