Print Head Height

I’ve been printing ABS for a little while now, and think I mostly have that down. However, I just tried my first PLA print and think I have some initial layer height issues on the printhead. It would be so much easier for me if I just had a definitive spacing for that height at temp. I’ve already done the paper spacer method, which seemed to work well for ABS, but I’m guessing that the head ends up higher at the lower PLA temps.

Could anyone provide a height recommendation for at temperature that I could just verify with a freshly cleaned tip and some feeler guages?


Well, this won’t answer your question directly, but maybe it can help.

If you’re using Slic3r and the lulzbot profiles, I’ve noticed that the ABS profile has a higher initial layer height than the PLA profile. You can adjust that setting. Maybe this could be the difference, or part of the difference?

If the issue is that the first layer isn’t adhering well, here’s what I do:
I still use the paper method for zeroing the Z axis, but for PLA I make it much much tighter than for ABS. Because of the spring bed suspension on the Taz, I believe this puts the nozzle tip right against the bed, so I don’t think the feeler gauge would work for me. That gets me good adhesion for the first layer of PLA.

Thanks for the reply.

If I’m reading between the lines correctly, you are attempting to start with the tip directly in contact with the build plate, yes? So, the paper test may just be a spacer to approximate where the head will be at temp?

If so, maybe I just need to measure the height difference on the extruder heads between the two temps, and calculate an expansion offset?

I was trying to print the rear portion of the Lulzbot dual extruder mount, so I’m reasonably sure the slicer settings yielding that gecode aren’t the problem.

Oddly enough, I had very good adhesion from the 1st layer to the bed. My problem was the adhesion between the first and second layer. There were already some imperfections elsewhere, but I had a chunk of the part start to delaminate under the force needed to pry it off (after bringing the print bed to room temperature). The bed still had some ABS glue on it from about 6 largish ABS prints prior, so perhaps that’s a factor? In any case, I’ll get back to that soon enough.

Well, for PLA I’m leveling the bed so that in the zero z-axis position, the nozzle is touching the build plate. The first layer height would be somewhat above that, depending on the slice settings. It will be interesting to see if you can reliably measure the difference in nozzle height between PLA temperature and ABS temperature. I think that number will be quite small, but let me know if you can quantify it.

Yes, I also think that is odd to have adhesion problems between the 1st and 2nd layers. I don’t know what to make of that. Does your slicing profile have any drastic changes in temperature, extrusion speed, or fan speed between those layers? It sounds like you might be pulling the part up to detach it – do you have anything you can get between the part and the build plate to start working a corner or edge loose, to lift from beneath the part? I’ve been using a curved-blade exacto knife to get corners started. This is much easier now that I’m printing directly on the glass and I don’t have to worry about gouging the PET.

Are you building the extruder mount pieces with PLA? My personal feeling is that I would want to do those parts in ABS, because I’d be afraid that the PLA might soften and deform, being that close to a hot build plate and extruder. ABS will provide another 40 C or so of margin there. But when you can make your own parts, it’s easy to try different things. Maybe it will work just fine.

But let me know how the dual extruder goes. That’s on my to-do list, along with too many other things.

For PLA I calibrate my Z=0 height so that the paper test is very very loose. You get friction on the paper between the nozzle and the bed but very little so it moves around really easy. For ABS I usually calibrate the paper test to where it moves but there is a pretty good amount of friction on the paper.

I’m not sure why this works better for PLA versus ABS, but I get flawless PLA prints with that method every time.