Extruder motor torque calculation

Hello everyone,

This is my first post and i am sorry my poor English. I'm mechatronic student and i have been searching information about filament extruder for 1 month and i started to create my own extruder. But i didn't calculate motor torque. I know 4-10 rpm and 45-60 Nm are ok but i would like to learn how to calculate.
What are the parameters or what are the formulas?

According to your experiences: What should the properties of dc motor be ? I mean how do i choose right motor ?

Also i am thinking to use industrial screw like a barrel-screw. What do you suggest ? Does it make a sense to use a industrial screw according to price/performance ratio?
what size commonly used screw do i need for extruder ?

Thank you for answers..

Edited 1 time(s). Last edit at 07/25/2014 06:35PM by machine3.

No one knows about it ?

1. It's not exactly trivial, if equitations exist at all.

2. Most RepRappers simply don't care, many of them think "NEMA17" describes a motors' torque. Accordingly they simply use what vendor XYZ sells.

3. Investigations, starting with a known-to-work setup are more than welcome, of course. Wiki has lots of space, waiting for your investigation descriptions and results.

---

Generation 7 Electronics	Teacup Firmware	RepRap DIY

Thank you for answers.

According to your message Nema 17 is useable for extruder. Do you think it is possible to use stepper motor for filament extruder ? I usually see dc motor.

Edited 1 time(s). Last edit at 07/29/2014 10:50AM by machine3.

Possible? Yes, of course. Ideal? I think not. DC motors, e.g. windshield wiper motors, are much cheaper and often available at scrapyards. Also, DC motors need no stepper drivers and precise motor position control doesn't matter in this application.

From Hugh Lymans description of his filament extruder I estimated he requires about 5 RPM and about 5 Nm. Note how he runs the 12V wiper motor at just 3V. A smaller motor with higher gearing should do also fine.

---

Generation 7 Electronics	Teacup Firmware	RepRap DIY

I am also building a filament extruder, and torque is one of the parameters that were harder to estimate.

What I did was scale the results I saw in the other's project documentation. Since most DIY extruders use 16mm screws, if your project also uses the same diameter, you can scale the torque with the melting zone length ratio. I mean, if we both use same screw diameter, and my melting zone (where polymer is molten) is twice as long, I need twice the torque you need. More complex scale factors can be calculated for different diameter screws.

That said, I am finally using this motor, since my extruder is longer than Lyman's: [www.phidgets.com].

---

Developing my owm filament extruder: [github.com]