Mini Kossel bed leveling

I'm needing to see if I can get some assistance on the last bit of calibrating my kossel. So far I have X, Y, Z and C parallel within +- .001". Right now I am having trouble with LFR between the towers. L is -.007" off parallel, R is -.006" and F is -.005".
I have obtained these with a dial indicator mounted to my end effector.

So far I have remeasured and corrected the distance between all towers top and bottom, all measurements match within .01 mm. Through my searches I have came across this forum post http://forums.reprap.org/read.php?178,201301,214977#msg-214977. I was able to adjust the position of tower X to achieve the current state of L, F and R. The test points for my bed where calculated with a radius of 75 with COS 60 and SIN 60 to get {X,Y} for each tower (formulas in marlin firmware) for DELTA_TOWER1_X, etc... The test points between the towers where found with the same math but with COS 120 and SIN 120 to give account for the necessary rotation.

Should I keep trudging on and tweaking the positions of the towers in my firmware until I get these last points dialed in or is there a better/easier way to go about this. I haven't setup an auto level probe yet since I would rather have this as tuned as accurately as I can and using the probe if at all just to keep the machine working properly.

Sorry for the multiple units of measure, I haven't been able to find digital dial indicator locally but will be ordering one online soon enough.

The old forum thread does not have the picture any more so I cannot interpret what is wrong. But it does not matter. I can give you few ideas.
There are 2 kinds of auto-leveling:
* the original grid based (this one does not fix calibration errors, it only fixes Z-height error while leaving X and Y errors there)
* Rich's auto-leveling [github.com] (this one actually fixes the calibration parameters and if you do not have too many errors there then there is a good chance it will converge; Rich provides some level of support on google deltabot group)

There are at least two ways how to calibrate the firmware manually:
* the old manual way (even in this case it may be useful to read the beginning of the calibration document mentioned in the next point)
* for math geeks only: there is a semi-manual way using this: [github.com]
* and of course there are tens of delta calibration how-to pages on the internet (some of them may be even correct )

I've looked at that wxm file at least a dozen times, didn't start making sense until I got this far into calibration. Thanks for the reminder it was there . I still have a question on it though

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* moving tower radially has the biggest z-height impact on the oposite side of the tower
(if it is symetricaly high/low on the oposite side then you need to move it nearer/further in firmware)
* moving tower diagonally has the biggest z-height impact just to the left/right of the tower - one side
is going up and the other side is going down
(if e.g. left side is up and right is down then you need to move tower in firmware to the right)

The way I'm reading it they switched the terms radially and diagonally. To me to move a tower radially means moving it left or right on it's radius from the center which would move it closer or further to the points to it's left and right. Likewise moving it diagnoally would move it further/closer to the center which would affect it's distance from the point opposite. For example moving tower X diagonally would move it further or closer to point R while moving it radially clockwise would make it closer to point L and further from R.

My understanding of how to move it radially is to calculate it's position with a different angel for SIN and COS, so if I want to move tower X radially clockwise I would use COS 61 and SIN 61 instead of the default 60 (all multiplied by DELTA_RADIUS). To move it diagonally I would use the default COS/SIN calculations and increase/decrease the DELTA_RADIUS that's been used for that tower.

Am I just misreading this text? It has been a while since I've dealt with geometry at this level. For reference I'm using this as my diagram Delta Chart

You are right meaning for your radial/diagonal movement is just the opposite of the radial/diagonal in the maxima notebook.

Thanks for the help hercek. I've just about got it dialed in, probably a few more hours of tweaking the tower positions. Would you consider this forum post as good a spot as any to post my final steps that I had to take (so we have yet another calibration technique )?

Yes.

What was the final outcome of this calibration? I recently comleted a 3DR simple delta printer and I found I am having similar issues. I level X, Y, Z, C and then R is low while L and F are high. Does this indicate that tower X needs to be moved diagonally? or that tower Z needs to be moved radially?

The picture with L/F meaning is gone from this forum -> no exact comment on which tower to move.

If L/F are high the same amount and R is low then you probably need to:
* adjust the tower against R so that it R is hight the same as L/F
* adjust diagonal rod and delta radius so that RLF are the same as XYZC
Each partial tower position (or also diagonal rod or delta radius) adjustment to will need endstop adjustment first.

It is hard to fix it using manual calibration only. Rather try Rich's firmware or calibration.wxm notebook (if you are good at math).

can you provide a primer on using your calibration notebook?

L/F are both slightly high but the same and point R is low (below the build plate) on my 3DR Simple. The current position for my Z-tower is X:0, Yelta_Radius. If my understanding is correct, you are suggesting that tower Z needs to virtually move closer to R radially? Or, should I move tower X closer to R via changing it's Delta_Radius?

Edited 1 time(s). Last edit at 06/03/2014 12:18PM by umdpru.

Quote
umdpru
can you provide a primer on using your calibration notebook?

I plan to improve the comments in the notebook a bit. Especially because what I considered radial movement is diagonal for some other people (and vice versa). I'll avoid these terms. There are also some conditions when required adjustment directions change. This is about how far points LFR are measured. Maybe I'll get free time to do it this weekend. Check for new commits in the github repository.

Anyway I do not plan to do some kind of manual calibration tutorial mostly because:

• there already is a lot of them (though they sometimes contain misleading information and they are almost always incomplete)
• it would be too long since a lot of terms would need to be defined (e.g. what is a virtual tower) and a lot of preconditions would need to be enumerated and explained
• it is a pain to do it manually anyway (believe me I had tried, and then I rather wrote down the equations in the maxima notebook)
• I just do not have time to do it now or in the near future

If you want to use the math supported option in the notebook then there is not much more to write anyway. Many maxima tutorials are out there. And once you know maxima all the rest is straight in the calibration.wxm. I doubt there is anything more to write.

People should try Rich's firmware. If they have only one calibration error then there is a good chance it will converge well.

Quote
umdpru
L/F are both slightly high but the same and point R is low (below the build plate) on my 3DR Simple. The current position for my Z-tower is X:0, Yelta_Radius. If my understanding is correct, you are suggesting that tower Z needs to virtually move closer to R radially? Or, should I move tower X closer to R via changing it's Delta_Radius?

You need to move the tower which is against point R (I do not know which one it is since the picture is gone). The tower needs to be moved nearer or further from build bed centre. The direction of the move depends on how far you measure the point R. In most cases, people measure it far enough. In such a case, it needs to be moved in firmware a bit further away from centre. Positions of the other towers should not change. Endstops may need adjustment after the each tower position change. This should give you points LFR at the same height (in your case all a bit higher). Then you will need to adjust diagonal rod or delta radius or both of them to get all the 7 points to the same height.

Edited 1 time(s). Last edit at 06/04/2014 04:27AM by hercek.