autocalibration target



  • Hi,

    I have been through, and I am still working through the calibration on my delta. what is a good deviation result on the autocalibration. I am typically getting 0.067-0.052.

    I am still struggling to get prints suitable to use for calibrating my initiall steps/mm at this level.

    what should I be aiming for?



  • @Dugee said in autocalibration target:

    I am still struggling to get prints suitable to use for calibrating my initiall steps/mm at this level.

    are you talking about steps/mm of your extruder?
    what do you mean by prints suitable for use for calibration?
    something like this? https://www.thingiverse.com/thing:3397997



  • @Veti

    a print of differing heights to allow me to calibrate my steps/mm on my motors.

    my extruder is fairly close (I have been checking the actual feed vs requested feed)

    the delta calibration guide suggests printing 2 objects of different height to calibrated the steps/mm.

    edited to add

    I am using S8 in my bed.g file as there is some reported tilt and I am returning a deviation of 0.063 at the
    moment



  • @Dugee said in autocalibration target:

    the delta calibration guide suggests printing 2 objects of different height to calibrated the steps/mm.

    which guide are you referring to?

    i find no mention of that in https://duet3d.dozuki.com/Wiki/Calibrating_a_delta_printer



  • @Veti you're right, it isn't in the guide, it was in a forum reply from @dc42 where he recommends printing 2 towers of different heights to allow for accurate measurements for the printed z height so that the motor steps /mm can be adjusted to give the correct z height. Then try and print straight lines to verify x/y dimensions, or to concentrate on arm lengths /delta radius if the lines aren't straight.



  • how big is the error that you are trying to compensate for?

    what you are talking about should not be required normally



  • I'm not sure yet! I'm trying to print a few towers to compare the height, to see if there is a variation in my z height, But I'm not sure if it is worth it.

    I am following from this:

    @dc42 said in dimensional accuracy:

    @Dugee said in dimensional accuracy:

    Finally got my 1st calibration cube from my upgraded Monoprice Mini Delta. Small machine, but there is definitely a lot of potential lurking in there. Some parts very much built down to a price, but these are easily replacable, like bed clips and drive gears. Delta calibration and bed mesh has come in to 2 decimal places pretty easily and after working through the config files to get it operational I am very pleased so far, so firstly thanks for the help I have had from this site, directly and by searching old posts.

    On to my question - the MPMD FB groups aim for dimensional accuracy via adjustment of the steps/mm of the steppers, but the guide for calibrating Delta printers on the dozuki recommends using M579 to do this. Admittedly MPMD uses a customised version of Marlin, not RepRap, which doesnt support M579 so they may use this for that reason.

    What are the pros/cons of the two methods of adjusting the scaling this way, and which should I use?

    Thanks in advance.

    Adjust the tower steps/mm (keep all 3 the same) to get the correct Z height. To avoid first and last layer effects, print 2 otherwise similar test cuboids of different heights, and measure the difference to calibrate the steps/mm. It should be very close to the theoretical value.

    After doing that and setting the correct steps/mm, re-run calibration, then print a noughts-and-crosses/tic-tac-toe pattern. Check that the lines are straight. If they are, use M570 to adjust the X and Y scaling if necessary. If they are not, you will need to adjust the configured rod length, recalibrate, and repeat.

    But my initial question was to determine whether an autocalibration deviation of 0.067 is close enough?

    I haven't seen anywhere what a suitable deviation is for this. Is my figure good/bad/average? Is there any point printing height towers if I need to tweak some physical aspects of the machine to improve my calibration?

    edited to add:

    I probably did 20-25 autocalibrations this morning, but (following from some comments on the forum) didn't save via M500, entering my values in my config.g file instead. the 0.067 figure above is what I reached after this and it became consistent as before/after deviation when running the autocalibration.



  • I get around 0.015 with my little delta and 0.025 with my bigger delta.
    I used to get values around 0.1 on my bigger one until I changed my rods for magball ones.
    Generally its down to slop in either your rods or pulleys/linear rails.

    The values you're getting aren't that bad so I would print and see what your models come out like.



  • @jay_s_uk so theoretically there are physical aspects that can be improved that would bring this down, but what I have should be enough to start getting decent prints that I can then fine-tune my dimensions from?

    Perhaps it would be worth putting in the guides somewhere what the autocalibration deviation figure means in real life @dc42? I have done loads of reading and havent found anything that gives an indication of what this actually means. I can understand the mesh bed as the picture tells a huge part of the story and you can see what needs to be resolved!

    0.067 sounds small to me, but is three time what you bigger delta is returning @jay_s_uk



  • @Dugee It'll certainly be fine to get you printing.

    What type of effector and rods do you have?
    And are you rollers or linear rails for your XYZ towers?



  • @jay_s_uk it's a monoprice mini delta that I'm slowly going to enlarge and improve. 8mm linear rods, igus bearings, under bed switches for z probe.

    As I get accuracy I'm going to add an e3d hot end, I'm waiting for carbon fibre to arrive to make better, more accurate arms,

    It's as much a learning experience for me as it is an actual printer.!



  • @Dugee Changing the arms on my big delta made the biggest improvement in the deviation value for me.



  • @jay_s_uk magball arms would be a pain on this machine at the moment, but I don't have a lot of confidence in the existing ones all being the same. I'm going to gt2 from s2m belts soon, but I don't want to do this until I can get the dimensional accuracy dialled in enough to print some upgraded parts printed.

    Hell, I need to get some printing done so I can get my psu and duet board mounted properly., before I do anything else!!!!! And for this I need to get the set up right!



  • @Dugee I would just go ahead and get printing. For getting everything mounted you'll have no problems with what you can print.
    I would also print all the parts you need to change the belts etc. Then change your arms and see how everything comes out.
    Then, if needed, you can reprint parts with your more accurate printer.



  • i agree with @jay_s_uk. dont try to fix a problem before you know that you actually have a problem.

    any change can also have a negative effect. that is why you also only change on thing at a time.

    start with the basic setup for the delta. look at the results and then decide on the next step.

    dont jump into the advanced parts before you have done the basics.



  • @Veti yup. I know I have a way to go before getting that advanced. Getting there slowly though. 6 months ago I'd never even considered trying 3d printing.



  • @Veti by necessity I've changed drive gear and idler, upgraded to capricorn tubing, installed different endstops, upgraded bed clips, rewired under bed switches and installed a glass bed. Not to mention getting a Duet board.

    Although it's a much better board, it only cost me about £10 more than getting a replacement standard board from USA and was actually in stock.

    The biggest thing I've learned from what I've done so far is to triple check nozzle/heater block/throat position. The problems I had because the nozzle didn't seat against the throat were mental. Couldn't understand why pla was oozing when the nozzle was tight against the block. Noob.



  • Can't be too bad generally. I'm about half way through a 100mm cylindrical multi height tower to check z height. Looks OK, printing on glass with a brim.

    Allowing me to measure 5, 20, 50, 80, 95 and 100mm on my z. I may have gone too far with the design, but gives the machine a good work out and looks pretty. Spreadsheet sitting waiting for measurements to be inputted. At least I'll get my motor steps /mm sorted out today.

    If I can I'll stick a pic up when it's done.



  • FYI, I adjusted my belt tensions and immediately the autocalibration deviation fell to 0.35-0.40. Simple improvement.



  • @Dugee You're getting there!


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