Print goes wrong halfway through first layer

Hi,

Just built a Prusa i3 P3Steel XL and having issues with my first print.

I'm currently just trying to print some test objects (a 4x4x4cm cube and the Ultimaker robot). I've tried using Cura as well as Slic3r + PrintRun but getting the same issue with both.

The print starts out perfectly fine until about halfway through the first layer were it then stops extruding at the correct times - the head moves as if it should be printing but the extruder isn't turning half of the time (there's no indication that it's stuck, just that it's not turning at the correct time). It then extrudes back and forth in a line about 2cm long making a big blob that it just smears back and forth for a bit before moving onto the second layer which it seems to want to try and print offset by 50% in the positive Y axis. While printing the second layer it exhibits the same behaviour as the second half of the first layer (were the extruder is not turning half of the time that it's meant to be printing). I've not let it continue beyond this point to see if it does the same offset for the 3rd layer.

I've attached an image of the first two layers of an attempt to print the ultimaker robot.

Hardware setup:
- Arduino Mega + RAMPS
- DRV8825 Steppers
- Numa 17's
- e3d V6 hotend
- A big rubber heated bed with a glass top

Using slightly modified firmware from here: [github.com] (modified for my larger print area)

All my initial calibration/tests have gone well - motors seem to move as expected in printrun/ponterface, endstops trigger ok and homing works well. Hotend and bed heat up OK too. And as I mentioned, the first half of the first layer seems to print really well - it just goes a bit bonkers after that point.

At a bit of a loss as to where I should be looking to resolve this issue.

Any help is much appreciated.

Thanks
Hobsie



Edited 1 time(s). Last edit at 05/09/2016 10:49AM by Hobsie.

Three questions:

Are you printing via USB or SD card?
What kind of extruder you have?
Did you check the STL file and G-code for errors?

If your printer is truly calibrated and your stepper drivers current set properly, then most likely the g-code is corrupted.
The extrusion problem could be due to the G-code errors or the idle bearing is not tight enough.

Looks like your Y axis is jamming... the offset between layers is because the printer thinks the nozzle is at a different point from where it actually is, because some of the Y motion commands haven't been executed properly.

With the power off, move the X axis by hand to the middle of where the printer "extrudes back and forth in a line about 2cm long", then move the Y axis back and forth by hand across that line and feel for any increased resistance. If you feel something, the problem could be anywhere in the mechanicals between the Y axis motor and the nozzle... check the motor drive gear (including its grub screws), belt, pulleys, rails, etc. Check for interference between physical parts. Check for wires getting tight or catching.

Try using nozzle movement commands in Cura (or whatever) to move the nozzle in the Y axis across the place where that 2cm line is.

Are there any clunks or buzzes from the Y stepper? It could also be that the amount of current going to that stepper is a bit marginal, so that where the movement is just slightly stickier, the Y axis doesn't physically move. You could try increasing the current to that stepper.

Thanks for the feedback guys.

I'm not feeling any extra resistance around that point in the Y axis so i've slightly upped the current for that motor as frankvdh suggested (also slightly upped it on the extruder incase that's why it keeps stopping). That seemed to help a little but what's helped much more is that I've gone and installed repetier firmware instead of the Marlin set up by the vendor who sold me the kit.

Now i'm getting well beyond the first layer printing well but hitting some offset issues later on (at least the extruder seems to be working consistently now).

So I think this issue has been resolved and I'm just hitting some subsequent calibration issues.

Thanks again guys for the feedback, it gave me some good ideas to look out for.

Cheers,
Hobsie

(p.s. to answer some of ggherbaz's questions - currently printing over USB and my extruder is like this one: [www.thingiverse.com])