3D printer design - fixed extruder?

Old timers will remember Makerbot Cupcake and Thing-O-Matic which moved their platforms in X & Y, while only lifting the extruder per layer.

You're dead on target for one issue, the desk space needed is a bit over double the build area, per axis.

Another issue is that the larger your total volume, the more mass you need to shift without it pulling loose, and the more your poor little steppers have to torque to get it moving at all, while moving the extruder is a predictable load on them.

Yup. Also think about how the over-all weight of the bed changes as the print goes form 1% to 100%. The print itself dynamically changes the weight of the bed, but the stepper acceleration and speed are constant factors in the firmware. In order to have enough torque for the weight at the end of the print, you could be over-shooting your movement at the beginning of the print.

Plus, the idea of pushing the print and the bed weight around at fast speeds is less accurate than just the extruder.

Thanks guys. My assumptions were the opposite regarding weight. That's why I asked the question here.

To me, the wires and filament pull are not consistent hence my thought that a gradually increasing part weight would be more accurate than the varying pull toward the back of the doodle in the forward direction and the near weightless return to the back of the machine. I had assumed that the weight of the part was rather insignificant but I am apparently wrong.

I'm doing the top mount as well, with ball bearings too:

http://www.soliforum.com/topic/4170/gar … ol-holder/

I definitely got better print quality when I eliminated all the excess drag from the filament.