To pass this spring break I finally got around to building a 3D printer, a project which I’ve wanted to do for a long time. I bought an Anycubic Linear Plus Kossel and everything went fairly smooth in the assembly until I reached calibrations. I’ve gotten the towers level with each other, and at the center of the bed the nozzle puts pressure on a sheet of paper when z is at 0 mm. The issue is that at tower positions (-69.28,-40), (69.28,-40) and (0,80) each of which are directly in front of a tower, the nozzle hits the bed above where the printer thinks z is. I’ve been playing around with my configuration, tweaking “delta_smooth_rod_offset” to try and change delta radius but the closest I’ve gotten to flat was at a value of 158 (151 was the stock value) where I got the nozzles to hit the bed at 0.4 mm. I’ll post the Delta Settings below to see if anyone whose willing to look can spot any red flags. I also think that maybe the lead screws that hit the limit switches on each rail provided in the kit are just too long so I might buy extras and try cutting them down to make shorter lead screws since one of mine is currently bottomed out and can’t be tightened any further . Any suggestions would be greatly appreciated. Thanks!

//============================== Delta Settings =============================
// Enable DELTA kinematics and most of the default configuration for Deltas
#define DELTA


// Make delta curves from many straight lines (linear interpolation).
// This is a trade-off between visible corners (not enough segments)
// and processor overload (too many expensive sqrt calls).

// NOTE NB all values for DELTA_* values MUST be floating point, so always have a decimal point in them

// Center-to-center distance of the holes in the diagonal push rods.
#define DELTA_DIAGONAL_ROD 267.5 // mm

// Horizontal offset from middle of printer to smooth rod center.
#define DELTA_SMOOTH_ROD_OFFSET 140 // mm

// Horizontal offset of the universal joints on the end effector.
#define DELTA_EFFECTOR_OFFSET 40 // mm

// Horizontal offset of the universal joints on the carriages.
#define DELTA_CARRIAGE_OFFSET 26 // mm

// Horizontal distance bridged by diagonal push rods when effector is centered.

// Print surface diameter/2 minus unreachable space (avoid collisions with vertical towers).

// Delta calibration menu
// uncomment to add three points calibration menu option.
// See [minow.blogspot.com]
// If needed, adjust the X, Y, Z calibration coordinates
// in ultralcd.cpp@lcd_delta_calibrate_menu()

Welcome to the wacky world of Delta printers, a pig to set up but once done the results are superb.

I have attached the instructions that came with my Kossel Mini Delta. It’s the ‘older’ model with pulleys rather than linear slides but the operating logic regarding calibration is identical. You are absolutely correct that the issue lies with the DELTA SMOOTH ROD OFFSET value. This number controls the ‘curvature’ of the effector in relation to the build plate. if the value is too small the nozzle will be higher at X-Y 0 than when near to the towers, too big and the nozzle will be lower at X-Y 0.

The section in the attached instructions that deals with curvature starts on page 23 (section 7) but I’d advise reading from Section 5 on page 19.

It involves a lot of messing about but I promise it is worth taking the time as it completely removes the need for auto levelling. I’ve printed circular objects at the limits of my machine with no issues.

Please be aware that the attached instructions are not for your model of printer so any other information may not be valid and should be used at your own risk
user_manual_0.pdf (3.77 MB)