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Delta Printer Calibration Guide

Posted by Jochemczyk_&_Ward 
Delta Printer Calibration Guide
May 18, 2015 07:18PM
I've noticed that theres a fair few threads about Delta bed calibration so we thought that maybe some of you may benefit from the procedure I use.
Theres a spreadsheet attached, the first page is the values we measured calibrating our Kossel mini and the second is blank for you to fill in.

All you need is a set of metric feeler gauges. If you've not used them before you gently slide a gauge or stack of gauges between 2 surfaces. When they move quite freely but you can feel the grip of the 2 surfaces the gap is the thickness of the feeler gauge or sum of all the gauges stacked.

The position Column in the table refers to the calibration positions that usually are set as x,y,z and center buttons for the paper test. The printers documentation should cover setting these up so I'll just say c is at x=0, y=0. x is by the X tower, y by the Y tower and z by the Z tower. If that doesn't make sense I'm happy to elaborate, just ask.

The z Height column in the table is where you put your feeler gauge measurements at each of the positions, taken between the bed and the tip of the nozzle.

On your sheet if you make sure that the screw pitch is correct (in blue) when you measure the x,y and z positions you can put the imbalance in the blue box at the top right and the green box will tell you how much to turn the screw. If the carriage needs to go down screw out and screw in for up. The screw I'm referring to is the adjuster screw on each carriage for the endstop.

Sorry that was a bit long winded, heres how to use the sheet.

1. Firstly make sure that the x,y and z endstops are at the same height and the bed is levelled as much as possible by hand.

2. Home all motors and then manually bring the effector downwards in the z direction until it is just above the bed. Be careful not to let the tip touch the bed, if it does home all motors and lower the effector again. Keep lowering the effector onto a 0.40mm feeler gauge until there is resistance when the feeler gauge is moved. If it gets to z=0 before you reach the feeler gauge then you need to increase the z height travel by approximately the amount that it falls short. If you reach the feeler gauge but z is above 0 then you need to reduce the z height travel by the remaining amount (ie if z=4.1 when the feeler gauge is gripping and the z height is set to 220 then set the z height to 220 - 4.1= 215.9)

3. Repeat 2. until the feeler gauge just pulls at z=0.

4. Home all motors and bring the nozzle to the x position, take a measurement and record in the first table.
Repeat for y and z positions, remember to home motors between each reading.

Look at the 3 values and decide which is the most high or low compared to the others. This is the one that will be adjusted.

To decide how much it needs adjusting work out the difference between it and the other values and divide this number by the thread pitch. The answer is how many turns of the adjustment screw for that tower are necessary. Turn the screw in if the value was lower than the others and out if it was higher. Alternatively put the difference in the top right blue box and the number of turns will be displayed in the green box, this will only work if the thread pitch is correct in the left blue box.

5. Repeat step 4. until all 3 readings are the same.

6. Home motors and take repeat readings, if they stay the same move onto 7. if not repeat from 4. after inspecting printer for loose components.

7. Repeat 4. again, but this time we also take a reading from the center position c. Remember to home motors between each reading.
You should have virtually equal readings on x,y and z with 0.40 at c.

8. if x,y and z readings were greater than c the delta smooth rod offset needs to be lowered, if they were less than c it needs to be raised.
I would suggest an initial change of 0.4 and further changes of no greater than 0.4 at a time.

9. Repeat 7. and 8. until the x,y,z and c are the same. Note that changing the delta rod offset should move x,y and z by the same amount but have no effect on c.

10. All the readings are the same now and your effector is levelled to your bed. An autoprobe will now be effective in measuring the imperfections and contour on your bed. I was unhappy with the z probe supplied with the Kossel Mini and have designed this [forums.reprap.org] which works very well for me.

Any questions I'll be happy to answer, I'm sure I've missed something anyway.

Edited 1 time(s). Last edit at 05/18/2015 07:21PM by Jochemczyk_&_Ward.
Attachments:
open | download - DeltaCalibration.xlsx (38.9 KB)
Re: Delta Printer Calibration Guide
May 21, 2015 02:31PM
What screw are you using for the adjustment? The offset screw at the top of the kossel towers (see below)? Wouldn't that screw up the belt tension?


Re: Delta Printer Calibration Guide
May 21, 2015 03:57PM
Quote
Jochemczyk_&_Ward
I've noticed that theres a fair few threads about Delta bed calibration so we thought that maybe some of you may benefit from the procedure I use.
Theres a spreadsheet attached, the first page is the values we measured calibrating our Kossel mini and the second is blank for you to fill in.

...

Nice set of instructions for anyone using Marlin; but I prefer the following:

1. Use Duet electronics and RepRapFirmware (see my blog).

2. Home the printer, lower the nozzle so that it touches the bed, and read off the height. If necessary, adjust the H (homed height) parameter in the M665 command in the config.g file to bring this to within about +/-1mm of zero.

3. Get the Z probe working.

4. Press the Auto Calibration button in the web interface, and wait 35 seconds for the machine to do all the work. This adjusts not only the endstop corrections and delta radius, but also the tower positions, and the diagonal rod length if you want.

5. Review the results to find out what (if anything) you could do to improve the accuracy of your build.

I don't like the Heath Robinson feel of the mechanical probe on the standard Mini Kossel either, yet I found it generally gave reproducible readings to within about 0.015mm (i.e. about 1 microstep) if I ignored the first reading after deploying it.

Edited 2 time(s). Last edit at 05/21/2015 04:06PM by dc42.



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: Delta Printer Calibration Guide
May 21, 2015 06:51PM
Yes the screw you are looking at will adjust belt tension.
I meant the one on the top of the carriage contacting the microswitch in the lower middle of this picture.


DC42 thank you for showing me that. I was unaware of any worthwhile automatic calibration routines and will be having a good look. Thats kind of the direction I was hoping to go with this eventually as well.
Re: Delta Printer Calibration Guide
May 21, 2015 06:57PM
Interesting. Which kit is that from? I don't see a screw like that in the "standard" Kossel carriage model (https://github.com/jcrocholl/kossel/blob/master/carriage.stl)
Re: Delta Printer Calibration Guide
May 22, 2015 03:33AM
My Mini Kossel kit from T3P3 had those screws as well. I never needed to adjust them, so I left them out in my 2020 rebuild.



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

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