How do you tune (einfahren) a D3/600 (or a 420 or 840)? My experiences.

In this message I describe the dificulties I had on tuning a D3/600.
I came up with a procedure (with the help of Stepcraft) to sovle the issues.
If following the procedure looks is 'boring' to you, good! you have not so many problems but at least your ears got used to what to expect on 'normal operations'.
And if it is not so boring then I hope this procedure helped you to locate the problem area (not necicarily in solving it).

Building a D3/600 kit I ran into problems at step 9.0 (Maschinen einfahren, Machine tuning).

These were my problems:
z-axis: when bolds tightend to 3 Nm I could run is but it got stuck in the upper and lower parts. Could not reliably home the z-axis.
x-axis: not running at all, stepper-motor making a rattling noise.
y-axes: running but only in the -Y direction, nothing at all in the +Y direction.

I asked Stepcraft for advise.
The advise was: "grease the spindle well and if this does not help center the spindle nut."
And a remark on the Y asis: "it moves only in one direction when it is not homed".

The 'spindle nut' mentioned is part 20, 'Lead screw nut' or 'Spindelmutter'.

Having a closer look at the construction the cause of problems is clear. With a lead screw nut just a little bit off (in angle, not alligned with the axis) is will cause a lot of friction.
Since inserting the lead spindle nuts in A1, B2, C10 and C11 is just guessing the correct position it does not make any sense tightening them at 3 Nm yet.
Thightening it at 3 Nm has the disadvantage that untightening runs the rist on damaging the nut head. Compared to your tools hardness the bolt is quite 'soft' and you might end up with a round hole in stead of a hexagon.

To center the Z-axis lead screw nut you have to remove the Z-axis assemly from the X-axis track.
For this there are two approches. One is to remove it at the end where the stepper-motor is.
This is easy (I think) but you have to be carefull for all the threads passing from x-axis to the z-azis assembly. This is what I have done.
The other one is to do it at the other end. You might be a bit short on movement space there due to wires all extended. I have not tried this.
After removement I placed the x-axis assembly in a vice so that I could run it at any speed without the risk of it jumping around.

I came up with the following procedure for aligning the lead screw nut and tuning the axis movements.
Steps.
1. loosen all three end bolds for the axis and the two bolds for the lead spindle nut up to about 1 Nm (fasten it by hand, just until you find some resistance).
2. Do a homing procedure then jog the total length up and down on a setting of 10.
3. Repeat for 20..100 in steps of 10.

There are multiple purposes for these three steps.
First, find any problem area depending on jogging speed starting with the lowest speed of 10%.
Second, get your ears tuned to the 'normal' jogging sound at any speed. If you hear some clicking, ratling, whatever disturbance, investigate its source!
Third, let the lead screw nut find its most natural position.

4. Jog to the side with the end switch, then tighten the three bolds for the axis to 3 Nm (or the advised torque from the manual).
5. Jog at 10 to the other end, if any strange sound occures investigates its source, if ariving at the other end without problems tighten the bolds for the axis to 3 Nm (or the advised torque from the manual).
6. Repeat steps 2 and 3, skip any speeds for convinience but never skip homing, 10, 50 and 100.

7. Jog to the side with the end switch, then tighten the two bolds for the lead screw nut at 3 Nm (or the advised torque from the manual).
8. Jog at 10 to the other end, if any strange soud occures investigates is source.
9. Repeat steps 2 and 3, skip any speeds for convinience but never skip homing, 10, 50 and 100.

This way I was able to tune my D3/600 (and my ears) and it now runs on full speed without a problem (and I recognise any 'strange' sounds).

More about me:
I have more than 30 years of experience with electornics and software using stepper-motors, servomotors and brushless motors but have no experience with the mechanical side.

If you see some (mechanical) points that I miss (or pay too much attention to) please adevise me on how I can improbe this procedure.

I also have a D2/420. Compared to the D3 series I think the tuning of a D3 is more dificult (in accessing some bolds, in clear documentation, in You-Tube examples) than the D2 series.
But tuning a D2 involves many more variables and needs to be repeated after some time. To me tuning a D3 is an improvement over tuning a D2. But that is just my two cents.