Prusa Mendel I2 Z-Axis Binding

I can't seem to find the solution to my problem. I'm using ramps 1.4 with 5/16 threaded rods. Everytime I start a print it will home the z-axis (I use slicer). It goes down, then up, then down again but when it is suppose to jump up really quick again the motors just grind. I have full move ment normally. It only grinds during that part.

It sounds like the maximum feed rate for the Z axis in your firmware is set too high. Trying to force the stepper motors to move too fast can cause missed steps and the grinding noise you're hearing. Which firmware do you use?

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[3DKarma.com] - suppliers of quality, affordable 3D printer kits and filament for the UK market.

I'm using marlin. Could you help me configure it?

I'm assuming you already have Marlin and have configured it and flashed it yourself already. If not, let me know.

There are two values you need to set to get the speed right:

#define HOMING_FEEDRATE {50*60, 50*60, 3*60, 0} // set the homing speeds (mm/min)

The third value in the above sets the Z axis homing feed rate in mm per minute. 3*60 (=3mm/s) is a good, safe speed; 2*60 is even safer.

#define DEFAULT_MAX_FEEDRATE {200, 200, 3, 25} // (mm/sec)

The third value in the above sets the absolute maximum speed for the Z axis, in mm/s (don't ask me why two different scales are used). 3 is a good, safe speed; 2 is even safer.

Once you've got a speed that works, you can try upping it slightly to find the maximum your printer can tolerate.

You might also want to take a look at your acceleration settings, but only if the above doesn't work.

Hope this helps.

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[3DKarma.com] - suppliers of quality, affordable 3D printer kits and filament for the UK market.

I'm using marlin. Im not sure if I've flashed it or not.

OK, you can do this without flashing the firmware, but you'll need to do it every time you power on your printer. At this point, it's good for a test to make sure you've got a solution to the problem.

Send M503 to the printer to get its current settings. You should get back something like this:

Steps per unit:
M92 X80.00 Y80.00 Z4000.00 E665.11
Maximum feedrates (mm/s):
M203 X200.00 Y200.00 Z3.00 E25.00
Maximum Acceleration (mm/s2):
M201 X500 Y500 Z50 E2000
Acceleration: S=acceleration, T=retract acceleration
M204 S500.00 T2000.00
Advanced variables: S=Min feedrate (mm/s), T=Min travel feedrate (mm/s), B=minimum segment time (ms), X=maximum XY jerk (mm/s), Z=maximum Z jerk (mm/s), E=maximum E jerk (mm/s)
M205 S0.00 T0.00 B20000 X5.00 Z0.40 E5.00
Home offset (mm):
M206 X0.00 Y0.00 Z0.00
PID settings:
M301 P22.20 I1.08 D114.00

Underneath the line "Maximum feedrates (mm/s):" you should see the current settings for your printer, prefixed with "M203." Copy that line, including the M203 command, drop the Z value down to 3 or 2 and send it back to the printer, e.g.:

M203 X200.00 Y200.00 Z2.00 E25.00

Now run a print and see what you get.

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[3DKarma.com] - suppliers of quality, affordable 3D printer kits and filament for the UK market.

Hi,

I had the same problem, solved it by lowering the Z-axis speed.

Hanging 10mm above the heatbed the extruder is waiting to receive the printcommand. When the printingcycle starts, the printhead should go down and move to the spot were it should start printing the skirt. Instead of doing that it makes that same grinding sound and moves it's printinghead to that spot and start printing the skirt, but without lowering it's printhead first. So it starts printing in the air.
Why is that...?