Z axis problem on a Bottom up 3D Printer

Hello gentlemen,

I built a 3D printer, bottom up style, and I am having a lot of trouble to set the Z-Axis corretly. Perhaps you have seen this before.

When I home the Z-Axis it goes all the way down to Z-MAX but when I try to move up it keeps trying to move down. I´ve changed a lot of parameters but none seem to work.

As far as I know, in this kind of build zero should be at the nozzle but correct me if I am wrong.

I´ve attached part of the code here, just in case.

// @section homing

// Specify here all the endstop connectors that are connected to any endstop or probe.
// Almost all printers will be using one per axis. Probes will use one or more of the
// extra connectors. Leave undefined any used for non-endstop and non-probe purposes.
#define USE_XMIN_PLUG
#define USE_YMIN_PLUG
//#define USE_ZMIN_PLUG
//#define USE_XMAX_PLUG
//#define USE_YMAX_PLUG
#define USE_ZMAX_PLUG

// Invert the stepper direction. Change (or reverse the motor connector) if an axis goes the wrong way.
#define INVERT_X_DIR true
#define INVERT_Y_DIR true
#define INVERT_Z_DIR false

// Direction of endstops when homing; 1=MAX, -1=MIN
// :[-1,1]
#define X_HOME_DIR -1
#define Y_HOME_DIR -1
#define Z_HOME_DIR  1

// @section machine

// The size of the print bed
#define X_BED_SIZE 310
#define Y_BED_SIZE 215

// Travel limits (mm) after homing, corresponding to endstop positions.
#define X_MIN_POS 0
#define Y_MIN_POS 0
#define Z_MIN_POS 0
#define X_MAX_POS X_BED_SIZE
#define Y_MAX_POS Y_BED_SIZE
#define Z_MAX_POS 200

Let me know if you need further info.

Thanks,

Marcus

"but when I try to move up it keeps trying to move down"

correct

the controls are not as you expect

Try no to think in up and down but rather increased and decreased space between the nozzle and the bed.


so Z+ increases the distance from the nozzle to the bed (by moving the bed down)
and Z- decreases the distance from the nozzle to the bed (by moving the bed up)

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Hi guys,

The missing parts of my printer just arrived and I decided to explore this thread a little bit further.

As mentioned before, I buit a bottom up 3d printer (similar to Ultimaker) and my Z axis is simply crazy.

I have a Z-Max endstop configured (Z_MAX 200) and when I press home it goes all the way to the bottom, hits the endstop, stops and shows 200mm. So far so good.

Decided to move from 200mm to 100mm and instead of going up it went down and broke my coupling (therefore the parts I´ve been waiting for).

To avoid the same mistake, manually placed the bed at the mid point and hit Home. It began to move down and then I manually pressed the endstop and again 200mm in Repetier Host.

Tried to move up in small increments (1mm) and the bed went all the way down until I hit Emergency Stop. Repeated the procedure with the bed at mid point. Pressed home, went down a little bit, manually pressed Z-Max endtop. The bed stopped and now I tried to move down in small increments (1mm). Once again the bed was moving all the way down untill I hit the Emergency Stop.

Changed the configuration and hardware to have Z-Min = 0mm instead of Z-Max. Pressed home, bed went down, hit the Endstop, stopped and gave me 0mm.

Sent G1 Z100 and the axis went all the way up to 100. Sent G1 Z50 and the axis went down to 50mm. Moved the bed up and down in small increments without any issues. Pressed home and the bed went down to 0mm again.

Have any of you seen this before? Any suggestions you can give me to try to find out where the problem is?

Your help is really appreciated.

Regards,

Marcus

Quote

Changed the configuration and hardware to have Z-Min = 0mm instead of Z-Max.

How did you do that? It's hard to give advice without knowing the changes...

Hi,

In the code

// @section homing

// Specify here all the endstop connectors that are connected to any endstop or probe.
// Almost all printers will be using one per axis. Probes will use one or more of the
// extra connectors. Leave undefined any used for non-endstop and non-probe purposes.
#define USE_XMIN_PLUG
#define USE_YMIN_PLUG
#define USE_ZMIN_PLUG
//#define USE_XMAX_PLUG
//#define USE_YMAX_PLUG
//#define USE_ZMAX_PLUG

In RAMPS1.4 board, changed the endstop connector from Z-Max to Z-min. Tested with M119 to make sure Z-Min was triggering. The endstop is still at the bottom, far away from the printer head.

Hope this clarifies.

Regards,

Marcus

Sounds like you have the motor direction incorrect in firmware/wiring and are just trying to compensate by changing the homing settings.

change to

//#define USE_ZMIN_PLUG
#define USE_ZMAX_PLUG
#define Z_HOME_DIR 1
#define INVERT_Z_DIR true

move the Z endstop back to ZMAX

check the following distance is correct for your machine or it will crash into the head trying to get to Z0
#define Z_MAX_POS 200

NB clicking Z+ will move bed down and Z- will move bed up

If this doesnt work... please describe what you mean by a "Bottom up 3D Printer"
normally this would be a printer with X/Y gantry fixed at the top of the machine with a bed that goes up and down in the Z

Hi Dust,

Thank you for your reply. You are correct, my printer has a fixed gantry with a bed that moves up and down.

I am not at home at this moment to try what you mentioned but it does not seem different from what was before.

The problem is that if I command the bed to go up, it goes down regardless of the distance commanded. If I command the bed to go up it still goes down, again regardless of the distance commanded.

When I home, it homes correctly.

Thanks for your suggestion.

Marcus

That a slightly different description from what you gave before

That more sounds like a hardware fault in that the direction line going to the stepper driver is not working

The direction line is connected to D48 of the mega check for continuity

Check the soldering on the corners of the Z pololo module
Check the soldering on the corners of the Z pololu sockets on the ramps
Check the soldering along the right edge or the ramps where the two rows of the socket pins are on the ramps (next to where you plug in a LCD)

If all these are good, try swapping the pololu modules from Z to X and see if the fault moves or stays the same.
If it moves, faulty pololu module, if it stays, bad mega or ramps.

Hi Dust,

I am sorry if I did not make myself clear. English is not my mother language.

I've suspected that. That's the reason why I've changed the Z endstop from Z-Max to Z-min in the firmware and in RAMPS and retested.

If the Z Endstop is configured as Z-Min, the bed homes correctly and goes up and down correctly.

If the Z Endstop is configured as Z-Max, the bed homes corrrectly but commanding the bed up or down makes the bed goes down all the way even if the command was, i.e. go up 1 mm or go down 1mm.

Thanks for your support.

Marcus