Layer height variation on small objects - effector tilt? Hotend tilt?

saffi

Something is slightly tilted on my printer and I'm not quite sure how to fix it yet.

I'm printing 16mm diameter calibration circles at each of my probe points (6 outer 120mm points and 6 mid) and the circles vary in layer height if you measure around the edges of them. They vary from 0.28 to 0.33 on the mid probe points (which is pretty good) but once you get farther outer, they seem to vary 0.25 to 0.45 at the highest variance (which might be right below the towers).

What are some things I can check on to reduce this?

Is it likely effector tilt, hotend tilt, or could it be some sort of belt tension? I was also wondering if longer arms might help something like this?

I may get a level and check the effector tomorrow.

dc42

See https://duet3d.com/wiki/Calibrating_a_delta_printer#Make_sure_your_build_is_accurate for some likely causes.

DjDemonD

What calibration deviation are you achieving? How large is your bed? I would be unsurprised if you are getting variation of 0.1mm across the bed unless your calibration deviation is 0.006 or some other very tiny number. A huge amount of compensation and correction has to take place for a delta to track exactly parallel to a flat surface especially a large one, this is not that case for cartesian machines. How flat is your bed? Is it tooling plate? Anything else is quite likely to be at least that non-flat if not more.

Have you enabled grid compensation?

Longer arms wil help at the peripheries but might slightly reduce the precision in the centre, albeit its very marginal.

saffi

I'll try to add a different spring set to tighten any play in the carriage joint. I'm using a mostly Max Metal build with the ball cup arms, so it should be fairly well built. I've swapped between rubber bands tightening the ball cup arms and then to the regular springs

It might be something I end up ignoring, I'm going to print a large cylinder instead of tiny cylinders and see how that comes out today.

My variation across the bed right now is about 0.15mm if I print a 230mm+ object.

I am considering a rails setup when the new PCB effector comes out simply to see if there is a difference in tilt.

Also, tiny cylinders around a 120mm radius is probably a torture test for a Delta and not reflective of actual use, so maybe I'm trying to overdo it here.

I will also post my bed.g file later when I get it a little closer to what I want. It definitely works fine now, so "Perfection being the enemy of good enough" is relevant as well.

saffi

Also if anyone wants my OpenSCAD print object it's the following (just paste it into OpenSCAD and render)

[c]// Calibration "Cylinder" for Delta printer

$fn = 360;

cylinder_radius = 130;
cylinder_height = 0.3;

difference() {
cylinder(r=cylinder_radius, h=cylinder_height, center=true);
cylinder(r=cylinder_radius-15, h=cylinder_height, center=true);
}

cylinder(r=7.5, h=cylinder_height, center=true);[/c]