What can cause Z height loss in the first few layers?

Question

All my prints come out about 1 mm too short in the Z dimension. So for example a 20 mm cube comes out 19 mm high. A 10 mm cube comes out 9 mm high. The X and Y dimensions are fine. There's a little bit of visible elephant's foot at the bottom, so I assume whatever is happening is in the first couple of layers. The problem is fairly consistently around 1 mm even for larger prints.

The printer is an Ender 3 Pro with a glass bed and BLTouch for automatic leveling, but otherwise stock.

I had a similar issue with another Ender 3 Pro that was resolved thanks to a link to this question about problems in the first 3 mm. The solution was turning the eccentric nuts on the left and right to loosen the rollers that connect the X-axis gantry to the vertical posts. There the Z issue was not as pronounced, and I was getting really messy prints in the first few Z layers. Here that is not an issue; the first few layers look fine while they're printing. Loosening the rollers did not resolve it.

Things I've tried:

• Tightening and loosening the gantry rollers using the eccentric nuts. They're currently just tight enough that turning them moves the gantry, but loose enough that I can turn them without moving the gantry if I hold it still.
• Tightening and loosening the two little screws that attach the extruder mount to the Z-axis lead screw. Currently I made them just tight, then backed off 1/4 turn.
• Adding a shim between the vertical post and the Z-axis lead screw. The lead screw is now pretty much parallel to the post.
• Slowly turning the lead screw by hand to raise and lower the gantry. There's no noticeable catching or increased resistance anywhere.
• Varying the brand and type of PLA filament.
• Varying the temperature from 190 °C to 210 °C.
• Obsessively leveling and re-leveling the bed. Manually leveling, auto leveling with the BLTouch, and adjusting the z-offset.

I'm using the stock Ender 3 Pro profile in Cura, and printing at 0.2 mm layer height. I've kind of run out of things to check. What else can cause Z height loss in the first few layers like this?

Answer 1

Do you have any “slop” on the right side (non motor) of the gantry?

I’ve noticed that my gantry will settle on the right side and lag behind the motor driven - ever so slightly - when it starts to drive up. It will, after that first lag, move fine for the rest of the time. Z axis travel seems barely affected but all my prints are consistently about 0.5 mm short.

Answer 2

I have the exact same issue on my Ender 3 V2, perfect bed level using a dial gauge, perfect first layer test prints (printing 9 squares all 1 layer high).

I can only get rid of it two ways:

1. Using a Raft as you have said (annoying).
2. Adjusting the Z-height Just exactly as the 1st layer finishes. I raise the height by 0.15-0.20 mm (in my case), and the resulting elephant foot is about 80-90 % better.

I recommend you follow Luke Hatfields guide on Ender 3 rework for The X-Gantry, as well as his other sections. Youtube channel "Edge Of Tech" does a decent job covering the rework in video form. Following most of these reworks I have made everything else in the print absolutely perfect, unfortunately EF remains.