Stepper torque requirement for extruder and some questions (3 replies)

Hello,

I'm new here and this is my first post.
I'm planing to build my first printer from the scratch, found extruder is most tricky part for me.
I'm trying to find myself all the information needed, but still vague and not clear.

Here are my questions.

1. What is the minimum torque requirement for extruder stepper?
- I mean final torque including gears (if any)

2. Is there any specific meaning to gear raio of Wade' geared extruder or others?
- Wade's extruder has gear raio of 39:11, I'm wondering I could change that ratio to meet the torque requirement.

3. Step angle of 7.5 is OK for extruder motor?
- I found similar motor as PG35L-048, with METAL gear box, but it's step angle is 7.5 degree,
Can I use it?

Thank you in advance.
dwonh