Calibrating Flat Print Surface

Hello all,
I'm having trouble getting my delta to have a flat print surface. I'm using Marlin. As of now, I have each of the towers square, my end stops are all at the same height, and the nozzle passes the paper test at each of the towers. But, I'm experiencing a convex print surface so the nozzle sits about 4mm above the bed in the center. I have tried making changes to Delta_Radius by changing smooth_rod_offset but this doesn't have any effect on the convex situation. In fact, messing with smooth_rod_offset too much causes the print head to move beyond the area of the print surface at my tower locations. I've been following Minow's configuration steps but I'm stuck at this point. My config.h is attached. Any help is greatly appreciated!

Use the calibration in dc42's firmware if you have a Duet board.
Otherwise use one of these:

• [escher3d.com]
• [github.com]

Changing delta radius won't alter the nozzle position at 0,0,zmax. It changes the nozzle height out at the towers. You need to get your ZMax set up in firmware so that the nozzle is at the print surface when at 0,0,zmax(in the middle of the bed). Only then can you adjust your delta radius, to bring the tower points into the same plane as the center point.

Quote
faithblinded
Changing delta radius won't alter the nozzle position at 0,0,zmax. It changes the nozzle height out at the towers. You need to get your ZMax set up in firmware so that the nozzle is at the print surface when at 0,0,zmax(in the middle of the bed). Only then can you adjust your delta radius, to bring the tower points into the same plane as the center point.

Hmm I've also done that and have had troubles getting things working that way as well. I'll switch things around this evening after work and get the nozzle position correct at 0,0 and play with delta_radius for my corner positions. Stay tuned!

Man, make a Z-probe. Something simple like this is enough: [forums.reprap.org]
Get a firmware which supports z-probing. If you do not have a duet board and your Marlin does not support z-probing then take mine: [github.com]
Use one of the two approaches I posted. If you are not good at math then the web page is probably a better option. The calibration itself takes about an hour and you will have it calibrated perfectly provided your system does not have some unwanted play in joints or the towers are not skewed. If your towers are skewed only a bit then it will calibrate quite well anyway.

Or you may decide to fight it the hard way ...

I may look into a z probe but I was hoping to get the machine calibrated the manual way first. Based on what the minow guide says...better to rely on manual calibration first then use the probe. Although I may consider it at this point. Working on my calibration tonight and appear to be making some progress. I've got the machine passing the paper test at the center of the build plate and am getting fairly close at my towers. I think I just need to keep tweaking and I'll get there. Fingers crossed!

Well my 2 cents worth, get a good reliable/repeatable z probe and auto calibrate. If your desire if to learn how this is done and the ins and outs of it interest you, then fear not, you will see and appreciate the process by using autocalibration, depending on the firmware the values chosen will be displayed in your host so you can see the effect of the changes, or you may need to add them to firmware/eeprom manually based on the probing results.

However you will get going with printing much sooner and your objects will be the correct dimensions.

If the auto calibration protocol is struggling i.e. the probing points drift away from the optimum then you may have a mechanical problem like loose belts, backlash in rods/ends, moderately tilted or out of position towers, poor probe repeatability etc...

Edited 2 time(s). Last edit at 01/26/2016 05:42AM by DjDemonD.

Make sure you are editing the correct variable in the Config.h file. Then, after making changes to the delta radius, you will need to re-calibrate your tower heights again. It can be a very repetitive process.

EDIT: Also make sure your EEPROM is disabled while calibrating. Not sure if it is updated when you re-upload new firmware.

Edited 1 time(s). Last edit at 01/26/2016 04:05PM by Kurzaa.

Quote
Kurzaa
Make sure you are editing the correct variable in the Config.h file. Then, after making changes to the delta radius, you will need to re-calibrate your tower heights again. It can be a very repetitive process.

It's a much less repetitive process if you use my calculator at [escher3d.com].

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].