# Steps per mm of extruder are incorrect after rebuilding

I have got a problem that after upgrading my printer to an aluminum frame my extruder went from around 400 steps per mm at 16 micro steps (which did match the manufacturer's recommendation perfectly) to a bit over 1000 steps per mm at 16 micro steps.

This is a problem for me, since the limited amount of steps per second lower my maximum retraction speed.

What I tried since the rebuild:

1. Replace and adjust the current of the stepper driver - no change, even with another type of driver on different micro steps, of course with other values, but also about 2.5 times too high;

2. Connecting another motor with another cable - the other motor with nothing attached to it drove the same angle as my extruder stepper.

Could it be that the ATmega2560 on my MKS gen 1.4 board got damaged? Or did I change something in the firmware, which does have this effect?

I am using Marlin 1.8.5 and a E3D Titan 1:3 geared extruder and I am using the same setup as before! E3D claims to have 437 steps per mm on a 200 steps/revolution Nema 17 stepper and 16 micro steps. This value was working perfectly fine before.

### Update:

With an Arduino Nano I measured the amount of steps my board sends at 418.5 steps/mm (programmed in EEPROM and in firmware) on a specific amount of extrusion length

G92 E0 -> G1 F100 E30


and I got

5220 steps for 30mm extrusion (reproducible).


It should be

418.5 steps/mm*30mm = 12555 steps.


Where,

(12555/5220) * 418.5 steps/mm = 1007 steps/mm


to have the effect of 418.5 steps/mm

...which is, oddly, the exact number that I got by marking filament, extruding, measuring and calculating.

• If you have changed the extruder drive, the one that press and feed the filament your steps per mm could change. – Fernando Baltazar Jun 15 '18 at 4:30
• That's totally right, but i forgot to mention, i got a geared extruder and there are no spare parts that i could have mixed up – Bastian__ Jun 15 '18 at 6:46
• There you are, when you change the extruder, you should re-calibrate the extrusion length. Let me guess, the gear uses a 1:2.5 gear ratio :) – 0scar Jun 15 '18 at 8:34
• You should put that information (geared extruder) into your question, rather than in a comment. – Carl Witthoft Jun 15 '18 at 11:46
• I did edit my question. The ratio of the e3d titan extruder is 1:3 and it hat the ~400 steps per mm before – Bastian__ Jun 15 '18 at 12:05

The Problem is an absolute mess and there are two possible reasons:

-> the octoprint eeprom editor is broken

-> the ATMega2560's eeprom is broken. as far as i know companies buy used atmegas to cheapen the price and the >100k writes on my chip has been reached

I will try to figure out the exact problem, if i find time in the next days. My current setup is just deactivate eeprom and i'm good to go. Even wiping eeprom with a small arduino sketch will get the error to return.

Now i will be able to sleep again :D

• Good that you post the possible culprits so that others may learn from it that even the electronics that you don't expect to fail may fail. This reminds me of the old days of a failing co-processor due to a print board crack failing to produce consistent log() function results (once in every thousand it failed to produce the correct value) try to trouble shoot that! It took days to find out. – 0scar Jun 16 '18 at 16:08