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autohome ends up off bed so z axis doesn't home out

Posted by bradinvancouver 
autohome ends up off bed so z axis doesn't home out
September 07, 2018 05:00PM
repost from reddit (do most users look at both?)

Hi all - just built my first 3d printer from super cheapo ebay vendor. Had ordered a Tronxy 802MA with autolevel but received a dmyco 001 3dp. Appears to be basically the same prusa i3 knockoff. Went together pretty smoothly but the z axis supports are a bit long and stick out the top (not sure if that will affect printing as it makes it tough to get that plane tight). Probably a lousy choice for a first printer but will force me to learn.

After all set up, first step in manual (such that is supplied anyway) is to push autohome and printhead should go to center of plate. Hit the autohome and it scans x an y but ends up midway x at the far left (facing the printer) off the print plate and then gradually lowers til the printhead mashes on the plate as the sensor is nowhere near the plate. Appears the stop switch on the left (x stop?) is not hitting the printhead assembly at all but, even if it did, sensor would still be off the plate. Based on googling, I'm thinking I just need to change the x and y offsets so that it centers properly. Sound right? I confirmed the proximity center lights up when close to metal. Question is how to set those offsets via the touchpad as it refused to be seen by my computer on usb (bad usb cable? gotta find another to check). If it's off to the front left, do I set the offsets negative or positive to move back?

Thanks for any help/thoughts on this, looking forward to figuring all this out (or salvaging parts and trying again with a new control board??).

I did find on this forum that for the i3 knockoffs, X is left/right. Min is left, Max is right, X- moves head left, X+ moves head right.
Y is front/back, Since the bed moves vs the head. Min is at back, Max is at front. Y- moves the bed back, Y+ moves the bed forward
Z is up/down. Min at the bed, Max is up top. Z- moves head down, Z+ moves head up. If I change the x and y offsets (positive for x and negative for y according to this), the z axis should be centered over the plate?
Re: autohome ends up off bed so z axis doesn't home out
September 08, 2018 01:35AM
Find a firmware for it you can edit on Arduino IDE, and find "Z safe homing". Set xy coordinates on it, and it should home x and y, then move the head to the selected coordinates to lower and home z with the probe over the plate. I set mine to home z in the middle of the plate (half of x build area, half of y build area) after that, make sure to have the correct settings to upload it to the board via USB b cable. (You can look up IDE settings for that board) I hope this helps, as it has helped me install abl on my tronxy x5s
Re: autohome ends up off bed so z axis doesn't home out
September 08, 2018 04:27AM
If you have not already, install the arduino ide,this comes with the needed usb drivers to communicate with your printer controller.
You are correct in your analysis of axis movement, therefor HOME should be either front left of bed (x y min home) or rear right of bed (x y max home).
If the X endstop is not triggered when you try to home X, you need to either move the endstop. When the X and Y endstop is triggered, this is the X Y min position and can somtimes be off the bed(in this case,X min and Y min is set to a negative in the firmware eeprom(if enabled in firmware))
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