Live Z Adjust - PLA vs ABS  

Re: Live Z Adjust - PLA vs ABS

Yes, that's normal. First, ABS needs different force to make first layer stick to bed (needs more squeezed layer), second when you preheat for ABS (higher bed temperature), there is a bit of height offset on Z probe caused by temperature dependency of the probe.
It shouldn't be a problem at all since you always need to watch printing of first layer (and be ready to make some adjustments) after filament change or recalibration. You can minimize the effect by preheating with extruder at higher positions and near sides of the bed.

Re: Live Z Adjust - PLA vs ABS

➡ from my point of view, the correct live z-adjustment value is the same for all kind of filaments. the effect that the pinda probe will heat up and therefore be closer to the printbed is marginal.
i did several tests with my test-sheet and pla, abs, bdp & petg and i always got the optimum at the same height.

💡 but the point is that abs doesn't stick as well as pla to the pei surface.... so if the z-live adjustment level is to high (nozzle a little bit to far away from the bed during print), you'll notice it with abs much earlier than with pla.

🙄 just my experience...

@david.t2: as far as i understood the i3 mk2, the force that squishes down the filament comes from the extruder stepper, so in my eyes there is no need to alter the nozzle height. furthermore: at the correct printing temperature the filament should flow quite easy through the hotend... even abs.

Re: Live Z Adjust - PLA vs ABS

I am printing first time with ABS right now too, and I find things very strage on the ABS side of the fence.

First, I just upped the temperature and tried a print. Did not go well, didn't stick at all, and lots of room between extruded "lines".

Next I lowered z-adjust a lot. from -235 to -420, and Now it sticks but still had visible space between extruded strands.

I'm not sure why, because when printing with PLA I get perfect layers very smooth, etc.

Just switching to ABS and it looks like it should never have been able to print anything.

I did put a plastic box over the printer (not touching the printer) and use Filament from a "new" (for me) supplier.

I don't really understand what can make such a massive difference just by printing hotter.
I need to print some things in ABS, but its certainly going in the cupboard-of-never-again, once this project is finished, not just because I hate those finetuning troubles, but also because of the terrible smell.

Re: Live Z Adjust - PLA vs ABS

Reactivating this post, because today I had my first experience with ABS... after 6 hours I start to frustrate...

I needed to use the "Z live" function to adjust the height to -400. With this, I managed to get the first layer sticking to the bed, but after a few layers (more or less 1.5mm) the first layer began to detach from the bed, and about 1.8mm just took off ... a lot Before finishing the model.

I tried with several configurations, from the 225/60 (according to the specifications of the filament manufacturer) to 245/105 (according to a post from this same forum) ...

Will I have to use ABS juice? Is there any trick in this regard?

My Prusa MK2 is perfectly calibrated (I had a hard time getting the "Congratulations" message when running the XYZ setting), so I guess there should be no alignment problem.

Any suggestions?

Re: Live Z Adjust - PLA vs ABS

I just went through the same ABS ordeal.

Things I learned:

use this: http://www.thingiverse.com/thing:1831902

Print it with 0.2 and see how it looks. It needs to have smooth top surfaces (touch it, measuring is only half the story)
should be as close to 0.2mm as you can get everywhere (except maybe on corners)
mine ended up at between 0.19mm and 2.3mm with a few minor imperfections when I called it good enough.

I printed about 5 or 6, wrote the settings on them and just tweaked the settings until it was as uniform as I could get it.

ABS seems to stick very well, only if you have the first layer perfect everywhere.
My bed was low on 2 spots and I had to shim it and correct the rest with the "bed level correct" in the callibration menu.
I never noticed it with PLA, because it does not warp (as much) and thus the bed "interface layer" is not as critical.

Next, manually move the probe to 60mm up from the bed before preheat, and always move it to the same height!
The probe gets hot when too close to the bed, and delivers slightly different measurements. Eliminate that vaiable during testing, by having it always in the same spot, off the bed.

You will very probably need an enclosure fo printing ABS. I used the biggest plastic storage box the local hardware store had on offfer, and it just barely fit. See here : http://shop.prusa3d.com/forum/improvements-f14/prusa-box-t998-s40.html#p26156

Also make sure to clean the bed after each print to start each test from the exact same conditions.
I switched to using Acetone (dont use when bed is hot...) and have very good "sticking" with that (if the leveling is done as decribed)

Now after I did all that, the print I did, which was almost full bed sized, worked perfectly, and I even had a very hard time detaching it from the bed.

Good luck!

Re: Live Z Adjust - PLA vs ABS

thank you mavu for this report !
just a short question about printing your abs objects inside the box: do you print completely without print fan ? or do you enable it moderately at structures with overhang and/or bridges ?

Re: Live Z Adjust - PLA vs ABS

thank you mavu for this report !
just a short question about printing your abs objects inside the box: do you print completely without print fan ? or do you enable it moderately at structures with overhang and/or bridges ?

I use the complete stock settings in the lates Prusa edition slic3r, which has the fan completely disabled.

But This specific print does not have any overhangs. after I have finished those parts, I might do a bridge teset.

Fan 10%

I have to use 10% fan and using enclusure - otherwise the printed items have some deformations. The surface gets perfect with this 10% fan.
By the way- using 105/255

Re: Live Z Adjust - PLA vs ABS

I don't know but to me, its been the opposite the ABS stick so strongly on the pei that I raise the z and lower the bed temperature to 95 to be able to get the prints to release

It could be something with the formulation

Re: Live Z Adjust - PLA vs ABS

Been practising printing with ABS and have noticed that I need to lower the Live Z Adjust when using ABS vs PLA, just wondering if this is normal?
So far I have gone done 0.15mm lower and still need it lower to get a good first layer.

Thanks

Same here, I had to adjust 0.08mm down for ABS.

Cheers

Re: Live Z Adjust - PLA vs ABS

Just watch the first layer as it prints, keep lowering the Z until you have no voids between your parallel strips of ABS as it lays it out. Disregard what you think it needs or what others say theirs is. There are several factors that make the displayed number different on each build of the Prusa printers. Everyone's probe will be slightly different and that alone is big enough that the numbers we trade are useless. Use your eyes, when the layers squish together and create no voids between lines its at the correct height. Keep your PLA number recorded and your ABS number recorded and start there each time you change material and or manufacturers. I do find it stays pretty consistent from print to print so I usually play with a few factors to get everything perfect and then record those numbers on the box. Z offset height (liveZ adjustment), bed temp and extruder temp.

Works great once you get used to it. By the way it took literally days playing with these things to get it right on my machine and the numbers I have to use are crazy but when I ignored the numbers and set the Z height by eye it works every time and for every material I have tried.

Mike