Dimension issues - calibration rectangle



  • My printer is a delta running RRF 2.02(RTOS) (2018-12-24b1) with DWC 1.22.6 and WiFi Server 1.22 running on Duet2 WiFi. My auto-calibration uses six factors and 12 probe points; config.g and bed.g attached. I have ball-cup CF arms with AL ball joints on the effector; the carriages have magball ends instead of single-piece ball joints.

    I've been trying to sort out dimensionality/accuracy issues on my delta. 20x20x20 cubes are printing at about 21x20x20mm. A 50x50x5 print was 51.47 x 49.86 mm (measured each side 3x and averaged). Also, one corner is visibly non-square. The short side of the shape is always oriented towards the Z column. Prints are sliced with KISSslicer and the Gcode looks fine in Gcode.ws. There's some odd gapping in the top layer that may be related.

    I'm trying to figure out what to look at next; I found this issue after I did a number of printer upgrades (Delrin to polycarbonate wheels, new belts, new bed; carriages unchanged). Belts are tensioned to about 30hz (measured as well as possible with EasyTension).

    2_1564079541205_20mm cube.jpg 1_1564079541205_20mm cube-1.jpg 0_1564079541204_50 mm.jpg

    1_1564079515448_config.g 0_1564079515448_bed.g



  • on a delta, dimensional errors can arise from wrong rod length.
    try a 7 factor calibration.



  • Coming back to this - I don't believe it's my arm length since I got my arms from Ultibots before they closed and I used the arm length written on the arms.

    Since this post I've checked on my carriage tensions and belt tensions - one carriage was tensioned a bit wrong and I've got all my belts at about 30hz.

    My cubes are a lot moreā€¦cubical now when you just check the raw side lengths. Unfortunately, they still have non-square sides. I've attached pics of the latest cube.

    1_1564525482789_One.jpg 0_1564525482788_Two.jpg



  • here is a good read about the effects of mechanical inaccuracies.
    http://boim.com/DeltaUtil/CalDoc/Calibration.html



  • Given how the sides of your 'cubes' are dished, and the other dimension problems, it would seem most likely that there's an incorrect dimension somewhere. Just a guess - though the rods come with the length on them, you have a mix of mag balls and ball joints; does the rod length include the radius of the mag ball, or the additional length of the ball joint? It really would be worth checking length of an arm to the centres. Also check the delta radius has not changed with the change of the carriages (you say it hasn't, but still worth checking).

    Ian


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