auto homing?

[ahgu]

I noticed that this type CNC is not very accurate, after it does HOME ALL, or turn on the next day, the HOME can be off by 0.# mm . As you know, that 0.##mm is very critical for the first layer.

Is there a AUTO HOME feature so I don't have to do this manually everytime I print? Put a home device on the edge, everytime it prints, it can go there and sense the home position. Only the Z homing is important for now.

[Eaglezsoar]

I noticed that this type CNC is not very accurate, after it does HOME ALL, or turn on the next day, the HOME can be off by 0.# mm . As you know, that 0.##mm is very critical for the first layer.

Is there a AUTO HOME feature so I don't have to do this manually everytime I print? Put a home device on the edge, everytime it prints, it can go there and sense the home position. Only the Z homing is important for now.

You can add a custom start G-Code in your Slicer to tell it to go Home before printing.
Just add a G28 to that custom start G-Code. If you are using Slic3r it is under Printer Settings, Custom G-Codes.
Don't forget to press the save button after entering the G28 in the Start Code.

[ahgu]

I believe everytime you do home as the head moves to the top, it loses some accuracy at the bottom. I need to calibrate the Z everytime I print.
In regular CNC, people have Homing device that measures the conductivity to check if things are touch. On this type of machine, first the accuracy is not that high. That limit switch is not enough to give me accurate zero everytime.
second, there is heating and that thermal expansion changes things a little. And I am not sure about the stepper motor. I think you must need linear encoder for good accuracy like a regular CNC.

The best thing to do is to calibrate if everytime when the glass is heated to the working temperature, which is what I am doing right now and I found that necessary.

[int2str]

I believe everytime you do home as the head moves to the top, it loses some accuracy at the bottom.
...
The best thing to do is to calibrate if everytime when the glass is heated to the working temperature, which is what I am doing right now and I found that necessary.

That does not seem normal and certainly in no way matches my experience.
Other than loose end-stops or too high homing speed (if you modified the firmware), I can't imagine that your printer is off every time you home.
Make sure you're not trapping any dirt under the glass plate and secure it firmly every time and you should be fine. If that's not the case, I'd check your mechanics for loose elements.

And if you're talking 0.0# mm, then I'm not sure it really matter all that much - doesn't seem to for me at least.

[Captain Starfish]

If it's /that/ critical then build a throwaway first layer into it. It will squeeze or string out any minor errors and the rest of the build will sit pretty on top of that.