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What limits extruder feed rate?

Posted by Media Conversions 
What limits extruder feed rate?
April 10, 2017 06:22PM
I'm working with a pair of Trinity Labs A1's – one driven by it's original Marlin/Ardunio hardware and one using Smoothieware/Smoothie Board. I'm running into a problem with the extruder on both of them. My question comes down to: What limits extruder feed rate?

The easy answer is (taken from the moving from Marlin to Smoothie documentation)
[smoothieware.org][]=marlin
In Marlin, you set the maximum feed rates ( speeds ) by changing :
/**
* Default Max Feed Rate (mm/s)
* Override with M203
* X, Y, Z, E0 [, E1[, E2[, E3]]]
*/
in the latest version of the Marlin software this was
#define DEFAULT_MAX_FEEDRATE {500, 500, 5, 45} // (mm/sec)
In Smoothie you set the maximum feedrate for each extruder by modifying each extruder's module configuration :
extruder.hotend.max_speed 45 # Maximum speed in mm/s (default was 50)
Note the unit is millimeters per second

I say 'easy' because that's not all there is to it. The extruder is taking filament (potentially small variations in size), melting it (at different temperatures), and pushing it out thru a nozzle (fixed size, but potentially worn) against a surface that may be a varying distance away (eg z-height at z=0). But most of those parameters are relatively stable.

Here's the problem I'm observing: It's an artificial 'test' case. I'm doing this on the Smoothie A1 with an E3Dv5 extruder. I'm using the “extrude” (5mm/click) button in Pronterface to make sure my extruder is 'working' (more later). If I click, pause, click, pause, repeat... I'm OK as long as the pause is “long enough” to guarantee that the filament has time to melt. If I try to go '”too fast” the stepper motor driving the extruder complains and the hobbed bolt drive either strips the filament or bucks backward. You can hear when it happens!

Using M203 Exx commands I've been cranking down the feed rate. It does not seem to help. It's down to 10mm/s from the default of 45mm/s. I've also got the temperature cranked up 5-10 degrees above the normal 240 deg C that I use for ABS. [I've verified the temp with a digital thermcouple thermometer.] The E3D is driven by a 30W cartridge heater so there's plenty of power available. The temperature stays steady.

On the Marlin/J-head A1 the effect is that I can print 20x20x10 calibration cubes without any problem. When I go to print a batch of 12 rectangles 10x80x8 I run into problems. The extruder seems to have problems on the long edges once I've got the first layer down and print speed goes up. I'll try next on the Smoothie e3d machine but based on the 'test' case described above I'm not optimistic.

What am I missing?

Anyone have an A1 tuned Marlin or Smoothie config they would care to share?.
I've attached a version of the “marlin to smoothie” document with Marlin default values from “Marlin.3.0.0.chris”edited in.

Frank Pirz
Media Conversions
Attachments:
open | download - marlin.to.smoothie.doc (23.5 KB)
Re: What limits extruder feed rate?
April 16, 2017 09:58AM
I think you're pushing your extruder too hard. My e3d v6 clone can happily extrude into open air at 200mm/m but if you go much faster you start to get issues. A print speed of 60mm/s with layer height 0.2mm and width 0.4mm is in the ballpark of 2mm/s of filament, so expecting you'd be able to extrude 50mm/s is I think unrealistic. This has been discussed a lot before and I think a google will find you a lot of useful info.
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