Help! PRINTED Z thickness?

[Turbojoe]

OK. So I'm tired of seeing posts all over the internet by myself and others asking this simple and very basic question: Let's say my "asked for PRINTED Z height is 3.0mm but my printed height is 2.76mm. WHAT do I need to change to make it 3.0mm? Please no like so many post "try this or "try that". What ACTUALLY changes final Z print thickness? All I want is a true 3.0mm total thickness. Why do this have to be so mind bendingly hard to accomplish?

 

[Merv]

..All I want is a true 3.0mm total thickness...

No idea what is the cause of your problem but if you want 3mm, just change the height of your model to 3.26mm.

3 / 2.76 = 1.0869
1.0869 x 3 = 3.26

 

[LitterBug]

Are you talking first layer height, or the average height for say 10 layers? There are several factors at play here which I will try to spell out some of the key factors.

1) is your print bed flat? If not, there may be some variances in height because of that.
2) Is your print bed level in comparison to the X and Y motions of the hot-end? If not, there will be variences in a wedge based on how far out of level it is.
3) is the printer's Z axis step count calibrated correctly? If not, your prints will be taller or shorter based on how far off the calibration is.
4) Are you using a Z height that is evenly divisible by the layer height you are using? If not, you could be seeing rounding errors +- the remainder.

Just a few thoughts off the top of my head, I can dig in deeper if you have some specific questions and/or examples.

Cheers!
LitterBug

 

[LitterBug]

Just a few more misc mumblings going on in my head on this....

Make sure you have no slop in your Z-axis. If anything in the frame, motion path, hotend, etc has slop, your height can be imprecise.

Errors in the software used to create the print file can cause problems. The original CAD program, slicer, and anything else in between can add imprecision.

Are your parts lifting off the bed during printing? That can cause parts to be short in the area where they lifted from the bed.

What material are you printing with? Some materials do shrink a bit more than others when they cool down.

If your first layer height has too much "squish" because the hot end is too close to the bed, that layer will be short. Everything is built on top of that layer. Try printing a single layer test print and look at the true height your printer gives you at varying points around the print bed. You want the first layer to be consistent and have good adhesion.

Have you printed any known valid calibration cubes and measured your X, Y, and Z?

What printer are you using?

There may or may not be a single simple answer. You could have multiple compounding issues affecting the Z-height


Cheers!
LitterBug

 

[bwarz]

you may want to do several test prints with thickness. keep your layer
thickness regular .... 0.2mm. do prints at 5mm 10mm etc. you may have a calibration issue where you will need to correct your z axis settings in your firmware build

 

[Turbojoe]

Z stop set. Bed leveled nine ways to Sunday. Silicone bed springs, Creality 4mm glass bed (Z-stop adjusted to compensate) Bed leveled even with a digital dial indicator mounted to the hot end fan. Belts tight. All parts, rollers etc. checked and tight with no binding. All Z parts removed, cleaned and lightly lubed. No binding!

Models, whether my own design or someone else's that should be 3mm height come out at 2.76mm +-. I've never in almost 3 years that I've had this printer gotten a properly printed Z build height. Z-step adjustments in even the new BTT SK3 3.0 silent driver motherboard effect no change in build height. Steps/mm can change everything for X and Y axis. Why not Z axis? This is absolutely the single most annoying thing for me right now.

 

[Turbojoe]

you may want to do several test prints with thickness. keep your layer
thickness regular .... 0.2mm. do prints at 5mm 10mm etc. you may have a calibration issue where you will need to correct your z axis settings in your firmware build

Correct what firmware build setting? How and how much? Prints at all heights are off consistently by right at .22-.25mm regardless of height. Firmware is not of my design and I wouldn't know how or what to change within it. Gonna need more in depth help with that.

 

[bwarz]

my apologies, I was thinking of the steps/mm on the X and Y axis. It has been quite some time since I set up my other printer. Since you are off the exact same amount no matter the thickness it wouldn't be steps/mm anyways (if that's even a thing on the Z... again don't remember)

A quick question and thought though (and apologies if you've thought of this) . zeroing your hotend to the bed.... how far is it? I only ask as I just calibrated a delta printer for a friend and the docs told me to set the end at 0.009" away from the bed. 0.2286mm. ( I've always zeroed my other printer at the thickness of a sheet of paper, however thick that is)

I'm not sure when it comes to slicing if and how that distance is compensated for - meaning does the printer do the first layer at that 0.2286 distance or if it's at 0.4288 with a 0.2mm layer height for example, but my first layers are darned near perfect with no gapping or elephant foot issues based on that calibration distance.

 

[WillL84]

my apologies, I was thinking of the steps/mm on the X and Y axis. It has been quite some time since I set up my other printer. Since you are off the exact same amount no matter the thickness it wouldn't be steps/mm anyways (if that's even a thing on the Z... again don't remember)

A quick question and thought though (and apologies if you've thought of this) . zeroing your hotend to the bed.... how far is it? I only ask as I just calibrated a delta printer for a friend and the docs told me to set the end at 0.009" away from the bed. 0.2286mm. ( I've always zeroed my other printer at the thickness of a sheet of paper, however thick that is)

I'm not sure when it comes to slicing if and how that distance is compensated for - meaning does the printer do the first layer at that 0.2286 distance or if it's at 0.4288 with a 0.2mm layer height for example, but my first layers are darned near perfect with no gapping or elephant foot issues based on that calibration distance.

I always do the piece of paper method as well. A standard sheet of printer paper is usually around 0.003"-0.004" (0.076-.102mm)

 

[Turbojoe]

Thanks guys. LOTS of good info. You have me pretty much convinced something is wonky with something Z mechanically. I'll tear apart the entire Z axis for inspection. All of the belts and roller wheels were replaced about a year ago. Maybe a wheel is binding now? I recently cleaned and lubed the lead screw but I'll do it again.

 

[Merv]

...Prints at all heights are off consistently by right at .22-.25mm regardless of height...

Im a noob when it comes to 3D printing.
If the problem were something mechanical, I would except the error to be proportional. The higher the print the larger the error. The error would consistently be 8.7%.

Instead the error appears to be consistently .22-.25 mm regardless of the print height.

 

[FlamingRCAirplanes]

Are you printing with a raft? I have found that using a thin raft absorbs all of the board leveling/z height and that helped me a ton when Iw as first learning.

 

[JasonK]

some questions:
- what is your layer height that your printing at?
- is the offset the same if you print a calibration cube that isn't 3mm tall?
- are your x & y dimensions correct on a calibration cube?
- are you zeroing your z axis with the bed hot or cold?

either you have some sort of offset error (like printing the first layer at the wrong 'height' or slight under extrusion issue) or a step size error (which would make the error bigger and bigger each layer).

if this is true "Prints at all heights are off consistently by right at .22-.25mm regardless of height." then my first though is your bead is _not_ zeroed correctly some how and your first layer is printing to close to the bead, causing you to loose 1 layer of height (given 1 layer is .2mm at 'standard' print height).

 

[LitterBug]

What firmware are you running on the BTT board? Depending on the firmware, the Z-step adjustment may be different. I picked up a BTT board to upgrade my oldest printer that had proprietary firmware because I was tired of not having control over all the adjustments.

 

[Turbojoe]

OK so I tore the bloody thing apart to kit level and went over everything with a fine tooth comb. I found two bad rollers on the Z left side and two bad rollers on the top of the X axis. Replaced them and readjusted so movement is as smooth as a baby's bottom. One of the hot end fans was getting noisy and the hot end was looking pretty cooked so I took the opportunity to upgrade to the Creality direct drive extruder kit. Using the "BIGTREETECH Upgraded SKR Mini E3 V3.0 32 bit mainboard" I'm having some config issues that I'll start yet ANOTHER thread on so as to not add any confusion.