Z AXIS CRASHES INTO HEATBED WHEN PRINT START

Hello everyone,


I have an issue with my reprap crashing into the heatbed when I start printing.

I first home all locations and check the pre-print settings. I have the z axis set to about paper thin width between the nozzel and the heatbed for best print quality. As soon as I send the print command from pronter face my z axis re-adjusts and crashes into the heat bed. I have tried various reprap prints and they all do the same thing.

You either didn't set the z bed clearance at the home position correctly or your bed is not level or flat.

Did you check the bed clearance at the four bed corners and center?
Did you adjust the bed clearance after the bed and the nozzle have been at operating temperature for a few minutes?

I would check the start/end gcode section in whatever you are slicing with. It sounds like you are taking care of manually homing and setting the z height. If that is the case, then you want to make sure that the slicer doesn't add any home commands. G28 is the home command. I think there may be another one that does a similar thing. Look in there and see what's there.

Just to ask all of the right questions - do you have endstops installed and defined properly? If you hit the home button, does every axis move toward the end switch and then stop once it hits it? Has your machine always acted like this, or did it just start? What happens if you start your machine with the z axis a few cm above the bed?

Yes all home locations stop when they hit the endstops, X,Y,Z.

When I start a print the bed and nozzle heat up and then right before it begins to extrude the z axis nozzle crashes into my heat bed. Well I was only able to successfully print one item, but I somehow managed to get the z axis to stop from moving so the nozzle and heatbed didn't crash together.

Edited 2 time(s). Last edit at 11/08/2012 12:02AM by khaiz21.

Quote

It sounds like you are taking care of manually homing and setting the z height. If that is the case, then you want to make sure that the slicer doesn't add any home commands. G28 is the home command.

With all endstops disabled, G28 should be a no-op. So it doesn't matter wether it's sent or not.

However, that's apparently not the case here. khaiz21, please open your G-code file with a text editor and copy the file line by line into Pronterface's command input (the single line to the lower right). Wait a moment each time to see what happens. This should tell you which line causes the crash. Please copy this line and a few of the previous ones here.

---

Generation 7 Electronics	Teacup Firmware	RepRap DIY

khaiz21 Wrote:
-------------------------------------------------------
> Yes all home locations stop when they hit the
> endstops, X,Y,Z.
>
> When I start a print the bed and nozzle heat up
> and then right before it begins to extrude the z
> axis nozzle crashes into my heat bed. Well I was
> only able to successfully print one item, but I
> somehow managed to get the z axis to stop from
> moving so the nozzle and heatbed didn't crash
> together.

When the nozzle heats up, parts will expand towards the bed. So, if you adjust your bed clearance while the nozzle is cold, it will crash on the bed once you heat it to operating temperature. You need to adjust the clearance while the nozzle and the bed are at operating temperature to prevent that.

Hey


G1 Z0.400 F7800.000


This line crashes my z extruder into the bed after I had all ready set the perfect distance for extrusion. How can I fix this? Thanks

G1 Z0.400 F7800.000 This line crahes my z axis into the heat bed after I had it perfectly aligned to print. How do I fix this? Thank you.


generated by Slic3r 0.7.1 on 2012-11-12 at 11:57:49

; layer_height = 0.4
; perimeters = 3
; solid_layers = 3
; fill_density = 0.4
; nozzle_diameter = 0.5
; filament_diameter = 3
; extrusion_multiplier = 1
; perimeter_speed = 30
; infill_speed = 60
; travel_speed = 130
; extrusion_width_ratio = 0
; scale = 1
; single wall width = 0.53mm

M104 S200 ; set temperature
G28 ; home all axes
M109 S200 ; wait for temperature to be reached
G90 ; use absolute coordinates
G21 ; set units to millimeters
G92 E0 ; reset extrusion distance
M83 ; use relative distances for extrusion
G1 Z0.400 F7800.000
G1 X145.460 Y117.561

khaiz21 Wrote:
-------------------------------------------------------
> G1 Z0.400 F7800.000 This line crahes my z axis
> into the heat bed after I had it perfectly aligned
> to print. How do I fix this? Thank you.
>

Have you read my previous responses? How did you adjust the bed clearance after homing z?

I paused and used pronter face to moze the z axis closer to the bed.

Have you leveled your bed already? How did you check to make sure that it's level?

If you have it already leveled the bed, then you adjust the z endstop by heating up the nozzle and the bed to operating temperature. Then adjust the z endstop to a rough position. Put a piece of paper on the bed below the nozzle. I like to do this with the nozzle at the center (100,100). Click on the home Z button. Pull on the paper slightly. If it moves freely, then the nozzle is too high. If it's tight, then the nozzle is too low. It will be correct when you have a slight resistance.

If you are manually adjusting the position of the head after homing, you need to explicitly tell the firmware that the current position is 0.
G92 Z0 will do that.
If you're using Marlin M114 will report the position the firmware thinks you are at. Both Repetier Host and Pronterface incorrectly report positions after certain G-Code sequences.

If you home to the bottom then Ideally you want to adjust the endstop so that the G28 positions the head correctly.