Z axis gaps between layers (bridging)

Hello, since building a new 3D printer with RAMPS 1.6 and TMC2130 I cannot wrap my head around an issue that I have whilst printing calibration cubes.

When I try to print a hollow 20 mm cube, watching the cube as it begins to shape circa 5mm from bottom layer, it stops "pushing" or "bonding" the outher shell layers on top of each other but it rather bridges from one corner to the other.

I can visibly see that it does not stick because I think the Z axis steps are maybe incorrectly set? I think it moves too high from previous layer and that is why it starts to bridge.

This is my Marlin steps configuration. The printer is based of off Anet A8. It is a conversion to Anet AM8, with metal frame, better motors, drivers, display. I however kept the original steps.

Any help is appreciated.

#define DEFAULT_AXIS_STEPS_PER_UNIT   { 100, 100, 400, 105 }

#define DEFAULT_MAX_FEEDRATE          { 400, 400, 8, 50 }

#define DEFAULT_MAX_ACCELERATION      { 2000, 2000, 100, 10000 }

#define DEFAULT_ACCELERATION          1000    // X, Y, Z and E acceleration for printing moves
#define DEFAULT_RETRACT_ACCELERATION  2000    // E acceleration for retracts
#define DEFAULT_TRAVEL_ACCELERATION   2000    // X, Y, Z acceleration for travel (non printing) moves

#define DEFAULT_XJERK                  20.0
#define DEFAULT_YJERK                  20.0
#define DEFAULT_ZJERK                  0.3
#define DEFAULT_EJERK                  5.0

Do you use TMC2130 for the extruder too? IMHO they don't have enough grunt to extrude fast enough.
Your e-steps of '105' tell me, there is no gear either...

Edited 1 time(s). Last edit at 08/27/2018 12:17AM by o_lampe.

I do not think underextrusion is the problem, first layer on glass is flawless. Sticks great and has a smooth finish. The problem is as the print gets higher ... the problems start rougly 5mm from bed.

I use mk8 extruder in bowden setup. TMC2130 is used on all axis even extruder with stealthchop ON and hybrid/spreadcycle off.

Like I said before the gaps are not that it does not extrude properly, it does, but the Z height is layer from layer too high. I watched it lay the back and front layer.

Ok I found some information regarding the TMC2130 stepping.

TMC2130 stepping settings

Seems like you do not actually use the 256 (interpolating) stepping when calculating the steps needed. Since it uses 1/16 stepping interpolated to 256. The correct math should look like this. Can anybody confirm this ?

P.S. It does make sense when I calculate my X and Y stepping being circa 100. Cube does have 20mm in X and Y direction.

Here are the calculator results that I should set for Z axis with TMC2130 set to 1/16 steps.


Here is the calculator results that I should get on X and Y, and which are correct.


Can anybody confirm this information ?

The culprit is most likely the microstep settings on the TMC2130. Confirm that you have the jumpers set correctly for 1/16 microstepping and that the jumpers are properly seated. I'm assuming you are using jumpers and not SPI to set the microstep settings.

What leadscrew are you using? Most 8mm diameter leadscrews from China have an 8mm pitch (2mm lead and 4 starts). 400 steps per unit is correct for an 8mm pitch leadscrew and 1/16 microsteps (assuming you are using a 1.8 degree stepper). Setting the steps per unit to 1600 will most certainly not move the bed less if it's already moving too far with 400 steps per unit.

You should measure the distance the bed actually moves. Home the printer and then run a "G1 Z20" command from a PC, or use Marlins Move Axis menu to move the bed 20 mm. Measure the actual distance. If it moved 20mm then you have a different problem.

You could also measure the distance the leadscrew moves the bed with one turn. Measure the bed height (from the bottom of the frame). Make a full turn and measure it again. That will give you the actual leadscrew pitch.

Hey thanks for the reply. I have a video because one video says more than thousand words.
[photos.app.goo.gl]
As you can see from the video above, it moves UP a "layer" but it moves too much and starts to have too large of a gap on each "slice" or layer.

I have a 8mm lead screw with pitch of 2, just like you said in your post. And 1.8 motors rated for 2A.

I left the jumpers on the board in all positions since I read that it does not matter when using SPI mode correct? So I assume it uses 16 microsteps interpolated to 256 from configuration.
I have TMC2130 drivers on all axis and I use SPI mode with these settings:

#define R_SENSE           0.11  // R_sense resistor for SilentStepStick2130
  #define HOLD_MULTIPLIER    0.5  // Scales down the holding current from run current
  #define INTERPOLATE       true  // Interpolate X/Y/Z_MICROSTEPS to 256

  #define X_CURRENT          800  // rms current in mA. Multiply by 1.41 for peak current.
  #define X_MICROSTEPS        16  // 0..256

  #define Y_CURRENT          800
  #define Y_MICROSTEPS        16

  #define Z_CURRENT          800
  #define Z_MICROSTEPS        16

  #define X2_CURRENT         800
  #define X2_MICROSTEPS       16

  #define Y2_CURRENT         800
  #define Y2_MICROSTEPS       16

  #define Z2_CURRENT         800
  #define Z2_MICROSTEPS       16

  #define E0_CURRENT         800
  #define E0_MICROSTEPS       16

I tested these settings for Z stepping 200, 400, 1600 ... a 200 stepping produced a great print but a freaking cylinder not a cube in Z direction. All other settings produced gaps. I tried yesterday with 350 stepping but one of the motors overheated. It did show great results for about 20-30 layers.

Are you sure that your 8mm lead screw has a LEAD of 2? Pitch and lead are not the same thing.

I have many 8mm lead screws with a pitch of 2mm and a lead of 8mm. At 16X microstepping, and a 1.8 degree/step motor, that comes to 400 steps/mm.

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Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

Quote
welo78
Hey thanks for the reply. I have a video because one video says more than thousand words.
[photos.app.goo.gl]

What layer height are you using for your slicer.

Lets try something! Home 3D Printer, Drop the nozzle to the bed then raise the nozzle 10mm above the bed and measure the distance above the bed and maybe even 50mm and measure these distances.

How far did the Z-Axis actually move on the 10 and 50mm distances, Please the results.

Edited 2 time(s). Last edit at 08/28/2018 07:06PM by Roberts_Clif.

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Computer Programmer / Electronics Technician

This may sound odd, but check to make sure that your extruder doesn't have a loose set screw in its gears. This is exactly what happened to me once, and I had the same symptoms as you.

DLC

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My apologies. I caused some confusion. In my original post I used "pitch" where i should have used "lead" and vica versa.

You really should first determine the amount of distance your bed is actually moving when you issue a move command.

Which version of Marlin are you using? According to this article RAMPS-14-With-TMC2130-Stepper-Drivers you need Marlin bugfix-1.1.x for SPI configuration to work properly.