1 Topic by accusedmonk

  • accusedmonk
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Topic: Limits for gearing on an extruder?

I'm going to be ordering a geared stepper motor soon for my bowden.  I don't think a higher ratio will affect actual printed extruding in a negative way since its so slow anyway.  I'm mainly concerned about the retraction aspect.

At the moment I'm looking at either 27:1 or 14:1 stepper.  I can go to 32 microsteps,  which if my math is right would give me about 5208 steps per mm for the extruder.  Is there a good way to figure out limitations running some numbers they have detailed for the steppers?

Here's the link for one I'm considering :
http://m.omc-stepperonline.com/item_description/41

Bowden SD3, Rumba, E3D hotend, Mk5 with RtRyder changes, Direct drive Y axis and bearings, GT2 pulleys and braided fishing line, Lawsy linear bearing conversion, M3 Z screw.

2 Reply by elmoret

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Re: Limits for gearing on an extruder?

Two limitations:

1.) Available torque. Stepper torque falls off as a function of speed.
2.) Marlin's step rate. Can't exceed 15k steps/sec.

You're fine in both cases. Go with the lighter/cheaper option.

Filastruder - the robust, inexpensive filament extruder
E3Dv6 All Metal Hotend - the premier 3D printing hotend

3 Reply by accusedmonk

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Re: Limits for gearing on an extruder?

Ahh, i forgot about the software side of things, thanks for pointing that out. 

I'm going to make up a test bench for this.  It's probably already been done somewhere but i could use the hands on.

Is the 15k limit due to a limit in frequency or memory buffer?

Bowden SD3, Rumba, E3D hotend, Mk5 with RtRyder changes, Direct drive Y axis and bearings, GT2 pulleys and braided fishing line, Lawsy linear bearing conversion, M3 Z screw.

4 Reply by accusedmonk

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Re: Limits for gearing on an extruder?

Did a little digging, it is limited in Marlin by the frequency capabilities of the chip and electronics.  Apparently some at megas have a quad step function, anyone know anything about that?

Just so i have the limitations correct in my head, i can't go over what would end up totaling more than the 16k in one second correct? 

So say 2500 steps per mm, would limit at 16khz around 6mm/s.

Am i understanding this correctly?  Thanks for the help too, i appreciate it greatly!

Bowden SD3, Rumba, E3D hotend, Mk5 with RtRyder changes, Direct drive Y axis and bearings, GT2 pulleys and braided fishing line, Lawsy linear bearing conversion, M3 Z screw.

5 Reply by elmoret

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Re: Limits for gearing on an extruder?

Yes, that is correct - but with reductions like that (27:1), you shouldn't be micro stepping at all. With a 14:1 reduction I'd do a 2x microstep.

Filastruder - the robust, inexpensive filament extruder
E3Dv6 All Metal Hotend - the premier 3D printing hotend

6 Reply by accusedmonk

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Re: Limits for gearing on an extruder?

I was considering the same conclusion, it would be pointless to gain that torque only to lose it in micro steps.  I'm going to order a motor tonight then.

Bowden SD3, Rumba, E3D hotend, Mk5 with RtRyder changes, Direct drive Y axis and bearings, GT2 pulleys and braided fishing line, Lawsy linear bearing conversion, M3 Z screw.