Z-axis unreliable zeroing

[zhangxueyou]

The process of uploading firmware is similar to this page:
http://www.geeetech.com/forum/viewtopic ... 20&t=16433
But you have to ignore step 2-4. And the board type you need to choose is "Arduino Mega2560 or MegaADK".

[TheDreamMaster]

Perfect, I will take a look. Thank you.

In the mean time I have been doing more investigation on the issue.

The Z-axis when zeroed, comes back the same spot every time +-0.03mm. BUT the extruder head varies height with respect to the hot bed.

For example:

-Last night I leveled the extruder with the hot bed, while they were still hot, to a paper thickness, and turned off the printer.
-This morning I turned on the printer, as I left it from last night and zeroed the axes. The extruder head, instead of being one paper thickness from the hot bed was actually below the hot bed glass surface (it s off the bed to the left side).

But then... I heated up the extruder and hot bed and once they were hot, the extruder seemed to be at the level I left them last night.

So it seems the problem is caused by the heating of the bed or the extruder. I will test which one it is, I assume it is the hot bed that is warping when hot.

This is problematic because calibrating the printer while hot is not only uncomfortable but also dangerous.

Any ideas?

[zhangxueyou]

There is also another potential reason: Wrong g- code may cause this problem. You can try to print with the attachment. Before printing ,please raise the temperature properly.

Test_40x30x10_No_preheating.zip

(17.84 KiB) Downloaded 424 times

[TheDreamMaster]

Wrong g-code?

I am sorry but I do not understand how g-code could affect the extruder+hot bed leveling. The problem I have been describing has nothing to do with printing, since I am not even printing.

No g-code is involved in the problem.

If you read my posts the problem is clearly described: The extruder head changes distance from the hot bed when I zero the axes. And in my last post I mentioned that it has to do with temperature. There is no printing, no object and therefore no g-code involved.

[zhangxueyou]

Oh, sorry, my bad.
How about swapping the z endstop with x or y endstop? Let's check if it is endstop issue.

[TheDreamMaster]

The end stop seems to be working fine. I did try to exchange it with the y-axis one, and it is the same.

As I said in my posts, the z-axis seems fine, it zeroes correctly. It is the extruder head and the hot bed that are changing separation.

So that you can see the problem, I adjusted the heat bed so that it is touching the extruder nozzle. Then, without moving anything, I set the temperature of the heat bed to 95 degrees. Here is how it looks:

23 degrees

Temp1-23deg.jpg (32.43 KiB) Viewed 11315 times

Extruder Nozzle making contact with glass at 23 degrees

ContactAt23deg.jpg (98.94 KiB) Viewed 11315 times

After rising the temperature of the heat bed to 95 degrees

Temp2-95deg.jpg (28.49 KiB) Viewed 11315 times

The nozzle is not making contact with the heat bed at 95 degrees. The separation is around 1mm.

NocontactAt95deg.jpg (101.56 KiB) Viewed 11315 times

What do I do?

[zhangxueyou]

When the distance changed after your heating the extruder, are the z motors move, or only the nozzle raised itself?

[TheDreamMaster]

The motors did not move. Either the nozzle rised itself or the heat bed lowered itself.

Please note (read my previous post carefully): I did not change the temperature of the extruder. I just changed the temperature of the heat bed!

[zhangxueyou]

Sorry, I typed so fast that I typed "extruder" instead of "hot bed".
I notice that there is no clamp at the front-left corner of the bed, is that the reason?

[TheDreamMaster]

There is a clamp. It is just outside the picture, but it is there.

I have the 4 clamps firmly attached.