Geeetech

I have a i3 pro B which has a problem with z axis ringing on the prints due to bent threaded rods.
The original rods that came with the Pinter were hugely out of tolerance and caused massive binding problems so I have purchased a set of 8mm trapezoidal lead screws to replace them.
The travel per rotation is appears to be 7mm and they have a point start on the threads
Can anyone advise me on how to correct calculate the new pitch and where to add this in the marlin code.

Hi


If you use RepetierHost it has a calculator to calculate this ratio.

You will find it in : Menu -> Tools.

Neil wrote: ↑

Sat Aug 11, 2018 2:58 am

The travel per rotation is appears to be 7mm and they have a point start on the threads

Are you sure of your words
A screw with such a pitch is not suitable for this application.

I am already explaining why.
The motor has a pitch of 1/16.
Your screw (TR8 x7.0) provides a linear displacement of 7mm for full rotation.
So 7mm/16 gives a minimum linear displacement of 0.4375mm. This is far too little for the printer to work properly. The printer shall provide a resolution of 0.1 and 0.2 mm.

All screws are then standardised. And I'm not sure if such a trapezoidal screw exists at all - TR8 x7,0. But I'm not an expert in this field.

As for the source code, however.
The forum explained how to improve this parameter in the code.
If my memory does not disappoint, Gingko explained it with examples. You only need to find this post.

1,
The motor step angle: 1.8 degrees (200 steps per revolution)
Driver micro stepping: 1/16

So that from my poor understanding, the motor needs 3200 pulses per revolution = 200 steps per revolution * 16 pulses per step.

You can look for the specification of your new rods, especially the LEAD (how far it goes per revolution).
I guess it's 8mm, in most of the situation.

Then it should have 400 pulses per mm = 3200 pulses per revolution / 8 mm per revolution.

2,
How to change it in Marlin?

Method A:
Change the code in configuration.h :
#define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,2560,93}

To (for example):
#define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,400,93}

Method B(more simple one):
Send G-Code through control box in slicer software.

M92 Z400 (400 for example)
M500 (for saving)

After doing this, you can go to LCD->CONTROL->MOTION->STEPS/MM, to check if you change it successfully or not.

Hi


In the calculation of linear motion Gingko is right, I forgot about the fact that there is something like micro stepping.

Hi


I was inclined to reflect on the subject.
The trapezoidal screw of the dimensions you specified, as opposed to TR8x1.5 or TR8x2.0, provides faster linear motion at the same rotation angle.

Is this a good solution for this model, I do not know.
But it will certainly be a perfect experiment.

Thank you both for the advice I will tinker later on and hopefully I will be successful

Hi
I have just upgraded my lead screws on this printer for the same reasons. The ones I bought were 8mm with a 2mm pitch with 4 starts.
Using the calculator it works out to be 1600 so sending M92 Z400 (1600/4 for 4 starts) gcode to the printer followed by M500 to save worked perfectly for me.
The print is now looking perfect.

Applause martinyazz.