Question about adjusting second layer height due to end play in z axis

Hello All!

To the point, here's my problem.

So I was having trouble printing in petg because after the first couple of layers, the nozzle would begin to drag across the print. Suspecting a z movement calibration problem, I rigged up a dial indicator to check. What I found was that any time my z axis changed direction, there would be about .4mm of movement required before the z axis would actually begin moving the right distance. So obviously I have some end play issues in the z axis somewhere. Either in the threaded rod and nut or motor coupler, I'm not sure. But I found that since the printer moves down to print the first layer, then up to print the second, it was getting behind on the second layer and since petg firms up fast and doesn't really re-melt, the error would never self correct. So now i have to baby-sit the printer to step the z up .4mm as it transitions to layer 2.

My question.
Is there any way I can do this with software/firmware? The play is very consistent so manual tweaking shouldn't really be required.

The z-axis movement probably depends on gravity to reduce/remove backlash, which you've noted is in effect. The movement "lag" you've measured indicates that the z motor is dropping the nozzle lower than it should and creating the backlash.

What aspect of the printer or slicer allows your nozzle to drop below the required level for a correct layer print, such that the screw turns for downward movement but the nozzle doesn't move downward? It's that extra downward movement that should be removed so the remaining upward movements are on the "correct side" of the backlash.

Thank you so much for this comment. I started looking closer and realized that the stopper on the end of my linear rail was making contact with the bearing block! It wasn't strong enough to stop the z axis from moving down, but it did cause the block to drag and make the motor push against it. That's where the backlash was being introduced!

MAN! Sometimes all you need is someone to point you in the right direction!!

THanks again!!