I am interested in building a 3D printer for producing objects bigger than the normal 200mm cube (initially in chocolate) without requiring a lot of mechanical engineering. The precision need not be up the standard of the conventional desktop printer but it will be interesting to see what are the limitations. I have a simple extruder which works with chocolate so my current thoughts are on positioning the extruder. The bed needs to be stationary as wobbling warm chocolate will cause a collapse. The current extruder weighs about 200g but will need an extra cooling pipe as my first attempt worked in 2D but not 3D.
My current thoughts are to suspend the extruder on 3 wires, with the same geometry as the delta printers, but with another 3 wires to the top of the extruder to hold it vertical. It avoids all the sliders and parallel bars of the conventional delta. Click to see my simple diagram. The diagram shows six stepper motors, each with a pulley. I have not yet thought a good way to use the fixed pitch of a toothed belt to pull the wires.
If this works, the printer could be made to almost any scale. A downside is that the printer will be much bigger than the product being printed as the wires need to be kept well away from vertical and horizontal, but the frame is only three columns and a base so could be easily assembled when required.