Ian, how can I calculate how fast my extruder can melt plastic at certain layer height and speed, to do experiments like that guy?

There was a post floating around (cant remember where in here or date) about looking into a group buy of aluminum carriages, something like $50 if I remember. If it makes that big a difference thats $50 well spent.

Right here http://www.soliforum.com/topic/8848/wou … -worth-it/

The Solidoodle is super sloppy mechanically. Printed parts on machines end up being out of tolerance too (inside holes too small, etc) and end up being mechanically sloppy as well. CNC machined aluminum means nice and true parts for smooth motion.

I understand, but the parts doing the motion: bearings, belts, rods, pulleys are the same, not 3d printed.
The only difference I can see at faster speeds is bending or breaking of the ABS parts holding the bearings and belt screws/clamps in place, but solid printed ABS parts don't seem likely to from that.
What am I missing?

You can count me in.
Right now I don't understand the need for aluminum carriages though for the reason mentioned.

EDIT: Not talking about stock 3d printed carriage of course. It is very poorly printed and at 50% infill...

You would be amazed what using proper mechanical parts effects linear motion.

Well thats, wow.

And doesn't seem to use anything new other than aluminum carriage with LM8UU bearings, heatsink and a fan blowing on the extrusion.

Is machined aluminum carriage pieces necessary here though? Can anyone explain?
It doesn't seem like something a solid ABS pieces like lawsy's wouldn't handle. The motors, belts, rods, bushings on the back drive rod and extruder all seem stock.