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New to deltas and z height

Posted by Ben.folkes 
New to deltas and z height
May 29, 2015 04:09AM
I'm currently tinkering with a cherry pi delta 111 for the first time and I've noticed after the printer homes and then starts printing, the nozzle is too high. Even after putting g29 in my start gcode after homing so that the z probe is deployed, it doesn't change anything. I've also increased the z probe offset in marlin and nothing either. I feel like I'm missing something simple as I don't fully know how deltas work.
Cheers
Ben
Re: New to deltas and z height
May 29, 2015 06:54AM
I think you need to increase your Z height by the distance of the gap between the nozzle and the print bed when its at 0. I don't use marlin so I'm not sure exactly what the setting would be called but it should be fairly easy to find.
I've had a look now and I think its
#define Z_MAX_POS
in the configuration.h file.

Edited 1 time(s). Last edit at 05/29/2015 07:00AM by asbo.
Re: New to deltas and z height
May 29, 2015 07:45AM
That makes sense, thanks for that. I'll give it a try when I'm home. Could you explain to me the purpose of the z probe then as I thought it was used to find z=0.
Cheers
Ben
Re: New to deltas and z height
May 29, 2015 08:20AM
Well the nozzle has to try and go lower than the bed, then if you've got your Z probe offset just right, it will detect the surface and stop the nozzle at the exact distance it needs to be from the bed to print. It can also then probe other locations on the bed to check it's level in relation to the nozzle and, if it's not, compensate(assuming the firmware supports it).
So be very careful when you increase the Z height and try the probe again as it may try to crash into the bed if the offset isn't spot on.
Re: New to deltas and z height
May 29, 2015 08:20AM
Quote
Ben.folkes
That makes sense, thanks for that. I'll give it a try when I'm home. Could you explain to me the purpose of the z probe then as I thought it was used to find z=0.
Cheers
Ben

Yes, the Z probe on a delta printer is normally used to find Z=0, and for autocalibration. But I don't use Marlin, so I can't tell you how to use it to find Z=0 with that firmware.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: New to deltas and z height
May 29, 2015 08:45AM
So should I put auto calibration into the start gcode after every print?
Cheers
Re: New to deltas and z height
June 01, 2015 05:24PM
First thing I would do is home your printer, this should raise all of the carriages to the top of the printer, just slightly below the endstops. Measure from the tip of the nozzle to your build plate. This is the approximate Z height of your printer. Round up to the nearest whole number and set this number both in your printer software and your firmware (you will need to reload the firmware after making the change).

At this point, the printer should believe that z=0 is at some point under your actual build plate. So whatever code you were using to find z=0 should work, and your printer will now realize that it is some fraction of mm shorter than you originally told it. Unless you save this information to your EEPROM, you will need to recalibrate everytime you restart your printer.

However, if you have not done so yet, it is strongly recommended that you manually calibrate (http://minow.blogspot.com/)your printer as accurately as possible first. This helps you to understand what the auto-calibration process entails as well as allowing you to only rely on the auto-calibration process periodically to keep things reliable.
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