Help! Printed Z thickness issues

[Turbojoe]

So after a ton of mechanical work and a solid day of tweaking my Cura 4.9 settings I've got X and Y as well as hole printing right to expected dimensions. Z however is kicking my butt and always has. As an example on a 3mm thick piece it always prints at 2.47mm. I'm just not Cura savvy enough to know what changes I need to make to compensate. I wish there was a vertical expansion adjustment like there is for horizontal. I've done Google searches but most everything I found assumed you would be well versed in Cura and I'm not. Even though I'm not a Cura newbie I need some suggestions in beginners terms. Any help?

Joe

 

[JasonK]

that much off seems odd, have you checked your z movement on your printer to verify that the movement is 3mm when you do 3mm of jog?

if it was less then that that, I could see it being to close to the bed on the first layer or minor under extrusion. but for the zeroing/bed leveling, you would be destroying your surface if you were off enough to account for 0.5mm (that is >2 layers at 0.2mm layer..) same thing with under extrusion, you wouldn't get that there..

 

[Boberticus]

I think you need to tune your stepper motors for realsies, instead of using horzontal expansion as a "crutch"

I had a huge amount of trouble getting my delta printer tuned to correct dimensions for printing single wall airplane wings, and I used horizontal expansion to initially get to usable, somewhat correct dimensions, but as soon as I tried printing things that were bigger than a calibration cube, all my tunes simply wouldn't work and I started getting bad dimensions again.

turns out if your printer is told to move 100mm, and only moves 99.9mm, then making it extrude out that extra bit to make up for the difference might make your part dimensionally accurate, but your printer is only still moving 99.9mm. In your case, there is no way to squeeze out extra plastic upwards, so your left short of your dimensions, and its worse now because your X&Y are always going to print in a slightly bigger dimension than Z, so scaleing parts in your slicer wont work, and printing multi component stuff is harder too now parts wont square up to each other unless printed in specific orientation to match the poor tune.

 

[TheWW1FlyingAce]

The first thing to do to debug this is to print something taller, like a 20x20x20 calibration cube. Measure that and see what you get.
There are two likely scenarios:

• The cube ends up being around 16.5mm tall
• The cube ends up at 19.47mm tall

(there are other possible values, but those are the most likely).
If you see the first then there's something wrong with your Z steps/mm (assuming this is a cartesian printer) and there's a linear relationship between desired height and achieved height. If the latter there's an offset of some sort being applied.

 

[Turbojoe]

Thanks for the helpful posts guys. Using Pronterface I have now made certain all M92 settings are set to original specs:
X=80.0 Y=80.0 Z=400.00 E=100.00. All expansions settings in Cura 4.9 are now set to zero. I printed out a 20mm CHEP cube and got X= 20.07mm Y= 20.07mm Z= 20.09. EXACT printed measurements should be possible as I see so may videos where people make this happen. That is my quest. To find and implement the needed adjustments to get the magical printed size that I ask the printer to actually print.

Any suggestions based on my AS STOCK settings what I should adjust? Belts are tight. I use a 4mm glass bed. I just got the BigTreeTech SKR Mini E3 V2.0 32 bit Control Board from Amazon. Bought it mainly for the silent drivers but will it have any bearing on print quality? I plan to install it this weekend.

Joe

 

[dap35]

Thanks for the helpful posts guys. Using Pronterface I have now made certain all M92 settings are set to original specs:
X=80.0 Y=80.0 Z=400.00 E=100.00. All expansions settings in Cura 4.9 are now set to zero. I printed out a 20mm CHEP cube and got X= 20.07mm Y= 20.07mm Z= 20.09. EXACT printed measurements should be possible as I see so may videos where people make this happen. That is my quest. To find and implement the needed adjustments to get the magical printed size that I ask the printer to actually print.

Any suggestions based on my AS STOCK settings what I should adjust? Belts are tight. I use a 4mm glass bed. I just got the BigTreeTech SKR Mini E3 V2.0 32 bit Control Board from Amazon. Bought it mainly for the silent drivers but will it have any bearing on print quality? I plan to install it this weekend.

Joe

Any fabrication technique has some tolerance to it and less than 3/1000 of an inch is pretty darned good, especially for a what I assume is a home 3d printer. Now, if that problem grows as you scale to significantly larger parts, you might have a challenge.

 

[JasonK]

I would try a 40mm cube first and see if those slight errors are scale errors or just extrusion errors or what not. the lines put down by the printer are not 'square' so you can get some slight thickening on the sides and if your bead is off ever so slightly that could account for the z error.

for context on the z error -> a 3x5 card on my desk is 0.19mm thick, a piece of paper is 0.11mm thick, so your error is less then a thickness of paper in all directions. Probably the extent of what you can expect from a home 3D printer.

So as long as your error stays roughtly at that amount, your as accurate as your going to get with the printer. if it changes significantly when you print something larger, then you might have a very small scale error. But right now, it sounds like it is doing rather good.

 

[Turbojoe]

Damn, I was really hoping to be able to print pieces that fit together (based on my dimensions) and have them actually fit together or fit into the space available.

Joe

 

[JasonK]

Damn, I was really hoping to be able to print pieces that fit together (based on my dimensions) and have them actually fit together or fit into the space available.

Joe

your worried about paper thicknesses level of precision in your prints? that little bit of error will push together just fine.

 

[dap35]

Damn, I was really hoping to be able to print pieces that fit together (based on my dimensions) and have them actually fit together or fit into the space available.

Joe

Any part has tolerances that have to be accounted for in the design. There must be payoff for things to fit together, whether it is from a 3D printer, or the finest aerospace fabrication.

 

[Turbojoe]

your worried about paper thicknesses level of precision in your prints? that little bit of error will push together just fine.

If it's this close why not spend a bit of time to get it spot on? I'm retired so time spent isn't a problem. I'm just not certain what adjustments to work with for this minute fitment issue.

Joe

 

[JasonK]

If it's this close why not spend a bit of time to get it spot on? I'm retired so time spent isn't a problem. I'm just not certain what adjustments to work with for this minute fitment issue.

Joe

when you level your build plate, you use a piece of paper and are adjusting manual dials and using the friction amount from pulling the paper (at least that is how I zero my bed). your tools for calibrating are at best a paper thickness worth of accuracy...

Not only that, your printer is probably using a mechanical switch for the z-zero switch. I again doubt that switch is going to give you repeatability better then a thickness of paper.

This is why I said to print a larger calibration cube, which will help ID if this is a scale issue - something you can adjust for, or an equipment precision issue - something that you likely can't adjust for.

Another thing you could do, would be to print 5 calibration cubes and see if they are all the same size. I would absolutely expect a small amount of variation between them.

Honestly, right now it sounds like your expecting more out of a home 3D printer then is reasonable to expect. if your that close in tolerance already, your talking about very fine levels of adjustments needs to get it just right. Not only that, your stepper motors have a limited number of steps that they can make, so there is a minimum resolution to the printer no matter how well you tune everything (assuming there is anything that can still be tuned out).

So your asking "what can I adjust to get more accuracy then seems reasonable for the equipment?" and we are answering "it looks like it is probably as accurate as it gets"

If you really think it can get better, print a 40x40x40 cube and see what it measures, this will help us ID if you might have a scale issue or precision issue. then 2 more 20x20x20 cubes and see what the variation between them is. if your variation is close to the amount of error, you have hit the max accuracy of the equipment.

 

[JasonK]

I realize my last comment might sound a bit harsh on reflection. I had a headache and tend to get frustrated sometimes trying to explain technical things.

To help understand what I am talking about, I printed a 20mm calibration cube on my ender3 (which I haven't done any calibration on before). I am also able to build parts that fit together and have them work out just fine. I occasionally have to make minor modifications to something that have a _very_ exacting tolerance to get it to fit, this typically has to do with holes (which has to do with over flow of filament and how the slicer approximates curves to create g-code).

For my calibration cube, I found the following:
my Z measurement varies between 19.99 and 20.05 with most measurements very close to 20.00. So I have ~0.06mm of variance, which is unlikely to be a scale issue. Could be a minor bead leveling issue or over/under extrusion or other issue.
my Y measurement varies between 20.04 to 20.15 with most measurements very close to 20.05. Here I have ~0.10mm of variance, and that variance is mostly related to some ringing at a corner (I can visually see the raised bit) - if I was to slow down the print speed this variance would likely get smaller
my X measurement varies between 20.00 and 20.13 with most measurements very close to 20.01. Again, I think that corner with some ringing accounts for most of the variation.

I also see some ringing/overshoot on both the X and Y cutouts, this is caused by the inertia of the print head (and in my case the print plate, as the print plate moves for X or Y.)

If I wanted to get my printer to be even more accurate/consistent then this, I would need to slow down the print head speed and change from belts to screw drives for the 2 axis that have belts (and change my bead setup as it can rock under not a whole lot of pressure).

This is why I said that a paper thickness of error is not likely something to even worry about as it is likely less then the accuracy/precision of the equipment.

I also must have my z-calibration rather good today, as I don't have any visible elephant footing (something I often get), nor do I have any signs that the first layer was 'floating' off the bead (were it gets lots of space between the lines instead of being solid).

What 3D printer do you have? I could glance at the mechanic design of it and give my opinion if I think it could give more accurate prints then my printer (Ender 3). However, I doubt your going to get much better as you mentioned belts for drive mechanics (belts can streach/flex/move slightly, which makes ringing more likely.

 

[Turbojoe]

I realize my last comment might sound a bit harsh on reflection. .

Not harsh at all and hard headed guys like me sometimes need a kick to that hard head for things to sink in. All of what you have been saying has made perfect sense and I just need to accept what I have is probably better than to be expected.

I have an early Ender 3. because it's around two years old I replaced the belts a few months back. I installed adjustable belt tensioners and the belts are tight. I replaced all of the axis rollers. Nozzle is new. Aluminum extruder. The Enotepad filament I'm currently using has a .002mm dimensional accuracy and prints beautifully. 4mm glass bed. I use Cura 4.9 for slicing and Pronterface for printer control from my desktop computer. The printer has been restored to factory axis settings. I couldn't ask for my prints to look any better.

I'll admit that .5mm Z axis discrepancy will continue to haunt me but I'll try to let it go. One thing I haven't done yet is to go over everything mechanical for the Z axis so hopefully today I can pull everything apart, clean and lube all moving parts again and ensure everything is straight and no binding anywhere. After that I'll just leave things alone save for the new 32 bit SKR Mini E3 V 2.0 control board with silent drivers. I got it mainly for the silent drivers. I hope it doesn't end up creating a whole new set of problems for me after I get it installed. LOL.

Mega thanks for everyone's help!!

Joe

 

[quorneng]

Turbojoe
What is your print layer thickness?
In your case unless it is an exact multiple of 3 mm the printer will always round up or down to the nearest layer so the end product will be very slightly thick or thin.
Of course unless the bed is exactly parallel to the X & Y running beams then there will be differences in the product final thickness across the bed.
If you can afford the print time use a 0.1 mm layer height to give the greatest dimensional Z accuracy of which the machine is capable.

 

[Turbojoe]

Turbojoe
What is your print layer thickness?
In your case unless it is an exact multiple of 3 mm the printer will always round up or down to the nearest layer so the end product will be very slightly thick or thin.
Of course unless the bed is exactly parallel to the X & Y running beams then there will be differences in the product final thickness across the bed.
If you can afford the print time use a 0.1 mm layer height to give the greatest dimensional Z accuracy of which the machine is capable.

Argh! This is the kind of stuff that I haven't learned yet. I was going to tear Z axis apart but by hand it operates super smooth with no binding anywhere so I'm going to leave it alone rather than add to my problems.

I'm retired so have nothing but time. I've been printing at .02mm with beautiful results but didn't think that might be the source of my Z axis concerns. I'll print a 20mm cube at 0.1 and see how it comes out. I'll report back in an hour or so.

Joe

 

[JasonK]

I print at 0.2mm layer height for most stuff 3mm/0.2mm => 15 (no sub layer rounding needed) definatly would cover the situation of 3mm part printing at ~2.5mm thick (that is 2.5 layers off).

 

[Turbojoe]

Holy CRAP!!!! The 20mm cube just finished and after cool down at 0.1mm thickness my readings are as follows.
X= 20.01
Y=20.01
z=20.02

Even a moron like me knows it doesn't get any better than that and if I NEED total accuracy I'll need to change settings. That's OK. I don't need exact fit on everything. When I did it was always a huge problem for me having to compensate in the .stl files.

Thanks again everybody. I got a schooling today.

Joe

 

[Boberticus]

The first thing to do to debug this is to print something taller, like a 20x20x20 calibration cube. Measure that and see what you get.
There are two likely scenarios:

• The cube ends up being around 16.5mm tall
• The cube ends up at 19.47mm tall

(there are other possible values, but those are the most likely).
If you see the first then there's something wrong with your Z steps/mm (assuming this is a cartesian printer) and there's a linear relationship between desired height and achieved height. If the latter there's an offset of some sort being applied.

Where does the multiple of 3mm come from? on a .4mm nozzle, my printer is way more accurate at .3 and 1.5 than at .2 in z heights, and I never really had a decent explanation as to why, was just figuring the flow rates were just working out right with the dimensions and speeds.

 

[dutchmonkey]

Here is how you should tune your movment. After this you tune your filament for flow