Random sinks into model, Hot end squashes model

Hi all;

Im having random collisions with mi prints.
Its printing fine, suddenly the hot end sinks into the model, sometimes it goes through it, and then it keeps printing it fine.
I have seen this al different heights and with different models.

I`ve checked the Gcode but it seems fine, no Z decrements. I´ve also used a Gcode from a friend, he printed fine, i had the same issues.

Im using a Sav mki Rev D and its Lcd 3d on a Prusa i3. And Cura to generate the Gcode, with no plugins.

What can it be? What should I check, and how?

Thanks.

Check the Z motor wiring and current. Check the screws on the coupler that connects the Z motor(s) to the drive screw(s).

Im pretty sure the installation is correct. It works fine 99.9% of the time, but once or twice in each model the hot end penetrates around 1cm into it...

I think it maybe a firmware problem. Is there a way to import the firmware from the Sav, to backup that firmware and then install the last marlin?

Firmware doesn't run differently 'sometimes'. Mechanic problems can give inconsistent behaviour though. I would suggest to observe your machine closely while printing.

It can be overextrusion, wrong z-height for your mm/revolution of the Z-axis (z-mm/rev should be dividable by your layer-height), or indeed something like threaded rods that slip on the stepper motor.

Could also be overheating stepper drivers, however, it's very uncommon on Z-axis as it doesn't move so much. Furthermore, it could also be that the Z-axis moves are too quickly, or the bearings are binding on the smooth rod sometimes. These things are however less common compared to what I mentioned in the previous sentence.

Edited 1 time(s). Last edit at 02/09/2015 08:15AM by Ohmarinus.

---

http://www.marinusdebeer.nl/

I´ve been observing the printing and this is what happens:

Manual control works perfect, accurate moves and no issues while pulling the wires a bit or shaking the Sav.

When printing:

It´s printing fine, X,Y and Z moves are accurate. Then at a random point, (maybe at a layer change, or X, Y changing direction) both Z engines start to spin fast, lowering the hot end and sinking it into the print. This Z decrement is not a slip, I´ve seen it last for more than 3 seconds. And then it rises up fast and continues printing fine, (if the model has not move).

It seems as if the higher it is, longer is this decrement...

VID-20150210-WA0003.mp4

Edited 1 time(s). Last edit at 02/10/2015 04:59AM by Dark_Fenix.

Just a thought,

I have seen this behavior if the g-code data becomes truncated so that if the line of code originally was:

G1 Z0.5 F200

changes to:

G1 Z0.

Do you see any strange movements in the X and Y axis?

Data loss can happen if too much EMI is present near the wires transmitting data. Common switching power supplies and high voltage (110V or 220V) wires put out EMF. They should be kept away from low voltage data lines.