Z axis launches up when starting a print after homing properly

So I just built my first printer (prusa i3, big surprise) and there is one problem that I just can't figure out. I had some issues with the x and y axis not wanting to home in the right direction and my heater blew open on the first heat up, but I got all that worked out. The problem that I'm having is the z axis launching up when ever I feed it gcode, the printer will home just fine to one of the lower corners, but when you would expect it to move to the center of the build platform it just goes up and I have to unplug it before it falls off the lead screws. I've looked up and down the configure.h file but nothing seems to work. Any help or advice would be very helpful.

sounds like you have your Z inverted and probably changed it to home to max to fix it. (incorrectly)

So the first thing it does is home, then it thinks im at z200, you then tell it to go to layer 1, the printer goes I better get to z0 (ish) and off it goes...

make sure you set #define Z_HOME_DIR -1
and if it goes up when you try and home then find your #define INVERT_Z_DIR if its set to true change it to false, and if its false change it to true

Edited 2 time(s). Last edit at 01/12/2016 03:02AM by Dust.

Just checked and #define Z_HOME_DIR was set to -1 and when I invert the z motor I have the same problem, just reversed. So it tries to home at the top of the printer and if I press the endswitch it tries to jam into the bed.

The first file is an image of pronterface when I send the M119 command. It shows all mins as triggered and this is the position that it gets to when I click home in pronterface or try to start a print before it launches up. The second file shows the two lines that Dust mentioned before.

ok.. other ideas.


what are your steps/mm settings set to and what is you Z drive system, m5 threaded rod or something else?
and what is your hardware micro-stepping set to?

For eg if you have no microsepping jumpers on say a ramps and your firmware expects micro stepping you going to move a lot more than expected

Still rather novice at 3d printing. Where would I have to check to find and set the steps/mm? The Z drive is two m5 rods connected by belt to a stepper. Also I'm sure you're correct about it being the steps, I used the M92 command in pronterface to change the steps to 350.00 and that has seemed to fix my problem for the most part. Now the Z motor seems to miss steps, when homing it will stop at least once and when the z should move up to home more slowly, it just fails all together.

In configuration.h

#define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,4000,500}

These are the steps per mm for X,Y,Z,E

These numbers are fine for a normal I3 (for X Y and Z, E is always different for everyone)

I suspect you have a ramps and you haven’t put any jumpers on the micro stepping jumpers under the pololu modules

Ie all the coloured Jumpers blocks in the following image.



RE skipping on Z.

find
#define DEFAULT_MAX_FEEDRATE {300, 300, 5, 25} // (mm/sec)
change it to
#define DEFAULT_MAX_FEEDRATE {300, 300, 3, 25} // (mm/sec)

This slows down the Z speed to a level you can actuly do on a M5 rod.

Edited 2 time(s). Last edit at 01/12/2016 04:28PM by Dust.

The board that I have is a mks base 1.4. Also I have the printer printing right now, poorly but printing, so I won't be able to try any of your recent advice until I get off of work in 10 hours.

Interesting conflicting information on the internet

its its MKS-SBASE or MKS-BASE?

The former being a smoothiware compatible board that has a configuration file on the SD card?

if not, I cant see how from what I can google it changes it microstepping...

The board is MKS-BASE. With the help you've given me, I have been able to change the steps to what work with my printer. I had to change the steps a bit more than I thought I would have to and I think that's why I was having such a hard time. The major thing that fixed my printer was just figuring out the right steps. I had to change the defaults from {80,80,4000,500} to {80,80,370,100}. I still need to change the X and Y axis so that it is dimensionally accurate, but I can print models very well. Thank you, Dust, for your help diagnosing the problems that I was having. Now I'm off to see how far I can push my printer.