Filament
TODO - add a proper introduction and description of filament
Die swell and Stretching
The extruder produces filament by pushing molten plastic thru a very tiny hole. As the plastic deforms and exits the hole, it may 'rebound' somewhat and produce, when not constrained by any other factors, a final diameter slightly larger than the hole. "Die Swell" shall describe this process.
However, as a machine will rarely extrude filament without additional constraint, such as pressing it against previously extruded material and stretching it to new positions, this die swell diameter does not entirely determine the final metrics that determine your printer quality. "Stretch" shall describe this process.
As a result of these two principles, if you extrude at a somewhat slower rate, and move the extruder head at a somewhat higher rate, the filament will stretch and produce a thinner thread; at the extreme, the filament will stretch and break, an undesirable result. If you extrude at a somewhat greater rate, and move the extruder head at a somewhat slower rate, the filament will bulge out slightly, and at extremes, will produce nodules and blobs, an undesirable result. To tune for either high quality prints, or faster printing time, a minimum and maximum range of final thread rates can prove useful. The following table list some values that user:Nophead listed in the forums for possible viable ranges of extruder, based on the properties of the material an the extrusion hole diameter:
| Material | Nozzle Diameter | Minimum Range | Maximum Range |
|---|---|---|---|
| ABS | 0.5mm | 0.3mm | 0.5mm |
| ABS | 0.3mm | 0.25mm | 0.4mm |
| PLA | 0.4mm | 0.3mm | 0.4mm (*) |
(*) NOTE - Nophead indicated that trying to extrude 0.5mm PLA thru 0.4mm nozzle resulted in poor quality because PLA does not have much die swell.
TODO - adding to this table for actual measured rates might be good, if people are willing to volunteer their data.
G Code control of filament
The RepRap Darwin 3D G-Code uses M codes to define a power rate to the extruder motor. This technique does not always produce exact extrusion rates, and the 5D gcode, using a direct stepper or position sensitive extruder will produce higher quality printing.
The Mendel 5D G-Code (Mendel_User_Manual:_RepRapGCodes) uses the 'E' axis as a fully independant axis for G1 motion. The number, in imperial or in metric, represents the length of extruded filament. Different machines can and usually do have different filament diameters, and thus, each machine should be tuned to the desired target final filament diameter desired.
- Example: with a 0.5mm extruder, using metric units, the gcode "G1 E50.93" should extrude about 10mm^3 of material.
