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Why is it so hard to tell the software the sled is centered?

I buid a maslow (makermade cnc kit) in our local fablab.
I can only work on it 2 nights a week.

The ideal situation is: When the sled is centered on the machine, the red dot in groundcontrol is in center.
This is now the third time the machine loses center. and when pushed home, the sled is to high on the board.

One thing that frustrates me so hard is that there is no button to tell the software the sled is back in center position… So software and hardware are aligned.

I need to calibrate again and again and again… This is verry frustrating and take so much of the time window we have at the lab.

Why o why is their no option to physical position the sled with the arrows in ground control and then tell the software the sled is centered? (like define home for Z, a define center for XY.) This takes literaly 2 minutes, as my center of the board is drilled and i printed a part so the sled is dead center in a few clicks.
But then the red dot in groundcontrol is off center.

As far is i can read here i’m not the only one with this problem an for sure not alone who thinks this is frustrating.

So this might be the best update for Groundcontrol 1.27 i guess. :wink:
I’m no programmer at all, but if someone can create a programm like ground control, adding a center xy button, can’t be that hard i think. :slight_smile:

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First, don’t fret too much over center being precisely centered.

Second, it’s very likely that if center is not close to center, then the controller has lost its positional setting (i.e., how much chain has been extended from the left and right motor) and all you need to do is to reset the chain lengths, not recalibrate. There’s a wiki post here on the forum on how to reset the chain lengths.

So, what causes the controller to lose its positional setting? The positional setting is stored in eeprom. Because you can wear out an eeprom by continually writing to it, it’s only written to after the motors have moved and then stopped moving for two seconds. If you are in the process of making a cut and the controller loses USB connection, the controller will automatically restart and load the position from eeprom… but if you in a cut, the position from eeprom is not likely to be the position of the sled. This can be why the sled isn’t in the center when you tell it to go there. Another thing I discovered is that if you shut down ground control too quickly after doing a move (like within the two second window), then the controller will reset before the position is saved to eeprom.

With that said, if people are losing position on a regular basis and neither of the above is happening, maybe there’s a bug in the firmware we need to find.

As for the button you suggest, read the wiki forum article on resetting chain lengths. What’s important and the only thing that can be used to reset the position of the sled is to know as precisely as possible how much chain has been extended.

What would need to be done to support what you say is to do a calibration, move to center and get it aligned as precisely as possible, tell the controller to store those chain lengths to the firmware, and then next time you need to reset the position, you move the sled precisely back to center and then tell the controller to load the chain lengths previously stored. That’s possible to do, but I don’t know it will result in a result as good as the current method. I think the current method of setting the sprockets tooths vertical and then replacing the chain on the sprockets is very precise. I would worry that it might be too hard to get to center as precisely as getting a sprocket tooth vertical.