Current limiting factors for plastruder performance

While I've been working on electronics and delta bots, I haven't paid much attention to extruders. I have heard that the extruder is currently a limitation in how fast printing can go.

Is this a fluid dynamics problem (increased resistance in the filament at higher speeds) or is it a thermodynamics problem (the plastic is not being heated fast enough)? Or, is it something else entirely?

Heat conduction rates ultimately limit the extrusion speed, but there are lots of variable to consider. I'll try an dump what I know to be factors. Dig in.

1. Peek, used as an insulator in the cold (extruder) to hot (melt pot) interface melts ~240°C. This sets an upper limit of around 230°C for the melt pot.

2. It has been found by many that a short melt pot is better at avoiding jams, and less mass means more speed, but the heat is pulled out of the smaller mass of brass very quickly, so the heat transfer from the resistor needs to be very efficient. Having a very thin wall between the resistor, and the melt pot helps improve this efficiency.

3. Using bowden extruders reduces overall mass, but has other problems with reversing. Don't know how well these issues are currently being addressed.

4. Filament chemistry varies greatly by supplier/batch/color/day of the week, etc., so you might get great results one day, and nothing the next. This is true for all types of printers, not just deltas.

Thanks for taking the time to lay it out for me.


1. Not really my specialty. Unfortunately, I'm not a materials person. But I'll keep my eyes open for a material that has a. A high melt point, b. low friction, c. is easy to work. Do you know if anyone has tried enamelled ceramics?
2. I have a few ideas for dumping heat into the hot end much faster, but I still need to do some experimentation.
3. There seem to be a few light-weight extruder models. I wonder if using a smaller motor with gearing is practical.
4. Is it the melt point of the filament that varies? Its viscosity? Its crossectional area? Or something else?

[Edited for broken list formatting]

Edited 1 time(s). Last edit at 10/14/2013 09:57AM by Annirak.