No More Calibration Cubes! Here's how you do it right!

Summary

The video discusses the common practice of using calibration cubes to tune 3D printer accuracy, arguing this method has flaws. The presenter explains measurement errors, extrusion inconsistency, and axis skew undermine using cubes. Instead, a purpose-designed diagnostic part, the CaliFlower, is demonstrated to properly calibrate. Its thoughtful design and guided process account for real-world factors while enabling firmware tweaks for precision. Though dismissing cubes for accuracy, other test uses validate print quality. The presenter measures several printers, finding axis skew varies widely, advocating calibration even for esthetic prints.

Takeaways

• 😕 Calibration cubes are commonly used but can actually make accuracy worse instead of better
• 😢 Key issues with calibration cubes are measurement errors, over/under-extrusion, elephant footing, and not accounting for skew
• 😊 The CaliFlower design from Vector3D is a better alternative for properly calibrating
• 🚀 Take multiple measurements at different spots to reduce errors
• 💡 Combine outer and inner measurements to remove extrusion's impact
• ✅ Compensate for material shrinkage with scaling factors instead of steps/mm
• 🔎 Most printers have some amount of skew between X and Y axes
• 🌄 Acceptable skew is below 0.1 degrees - compensate if higher
• 😃 Calibration cubes still useful for assessing print quality issues
• 🍰 CaliFlower makes a nice coaster when done!

Q & A

Why does Stefan think that calibration cubes are bad?

Stefan thinks calibration cubes are bad because measuring their outer dimensions is useless and even wrong for properly scaling a 3D printer. Factors like elephant foot, over/under-extrusion, and measuring error impact the accuracy of calibration cubes.

What are some flaws with using a calibration cube for size calibration?

Some flaws are that the measurements can be impacted by elephant foot, over/under-extrusion, measuring error due to the small size, and calibration cubes don't account for axis skew.

What is axis skew and why does it matter?

Axis skew is when the X and Y axes of a 3D printer are not perfectly perpendicular to each other. This matters because it can prevent parts, like a box and lid, from properly fitting together.

How can you check for and compensate for axis skew?

You can check for skew by measuring the diagonals of a printed square. If they are unequal, skew exists. Skew can be compensated for in firmware like Klipper or in slicers with skew add-ons and post-processing scripts.

What is the CaliFlower used for?

The CaliFlower is used to accurately calibrate a 3D printer's X/Y dimensions and skew. It is designed to minimize measurement errors and its spreadsheet calculates necessary compensation values.

Why does Stefan suggest using scaling factors instead of changing steps/mm values?

Because adjusting steps/mm assumes incorrect printer motion, when dimensional inaccuracies are actually caused by material shrinkage. Scaling factors compensate for shrinkage differences between materials.

How much skew did Stefan measure on his printers?

The skew ranged from 0.0-0.05 degrees on well calibrated machines up to 0.55 degrees on a pre-production unit. Stefan says below 0.1 degrees is generally acceptable.

What use does Stefan think there still is for calibration cubes?

Stefan thinks calibration cubes can still judge print quality in terms of consistency, pressure advance tuning, cooling, etc when using a compact test part.

Why does Stefan say that whereas calibration cubes are booby traps, the CaliFlower makes a nice coaster?

Because calibration cubes look innocuous but can negatively impact tuning, while the more effective CaliFlower has a nicer aesthetic design that could be reused as a decorative coaster.

What materials did Stefan test for shrinkage differences when printing the CaliFlower?

Stefan printed the CaliFlower in PLA, PETG, ABS, and ASA filaments. He had to compensate 0.35% for PLA up to 0.7% for ABS and ASA.

Outlines

00:00

😡 Why Calibration Cubes are Bad for Tuning Print Dimensions

Calibration cubes are commonly used to tune print dimensions, but have major flaws. Key issues are measurement errors due to small size, impact of extrusion width and elephant foot, and inability to detect skew. A better alternative is the CaliFlower design, which allows more precise measurements over larger dimensions. Calibrating skew and compensating for material shrinkage is also important.

05:03

👍 Using the CaliFlower Design for Precise Printer Calibration

The CaliFlower design helps calibrate dimensions and skew properly. It has larger reference dimensions to minimize measurement errors, averages inner and outer measurements to eliminate over/under-extrusion effects, and includes consistent measuring stops. After printing and measuring, the provided spreadsheet calculates error percentages and skew angle. Adjustments can then be made in firmware or slicer.

10:04

😕 Dealing with Material Shrinkage Differences

After calibration, different filament materials showed varying shrinkage, from 0.35% for PLA to 0.7% for ABS/ASA. Rather than adjusting steps/mm globally, it is better to define per-material shrinkage compensation. This can be done with slicer settings for scale or flow.

15:06

🤔 Evaluating Printer Skew Across Different Machines

Measurement of various printers showed significant skew differences, from negligible on Prusa MK3 to over 0.5 degrees on a BambuLab machine. Acceptable skew depends on use case, but below 0.1 degrees is generally good. Proper skew calibration can minimize dimensional errors across the print area.

Keywords

💡calibration cube

A calibration cube is a small 20mm or 30mm cube that is commonly 3D printed to help calibrate and tune the accuracy of a 3D printer. They are often used to adjust the steps/mm on a printer to achieve the proper dimensions. However, the video explains that calibration cubes are flawed for this purpose due to issues like measurement error on small parts, not accounting for skew, and being affected by over/under extrusion.

💡skew

Skew refers to when the X and Y axes of a 3D printer are not perfectly perpendicular to each other. This can cause issues with printed parts fitting together properly. The video demonstrates measuring skew using the diagonals of a printed square. It also shows how to compensate for skew in firmware like Klipper or by using software tools.

💡shrinking

Shrinking refers to the contraction of 3D printed parts as they cool after being printed due to thermal stresses. Different materials can shrink by different amounts. The video shows accounting for shrinking by applying scaling factors in the slicer settings rather than adjusting the steps/mm.

💡squishing

Squishing refers to the compression of each layer as it is extruded by the nozzle. This affects the final dimensions of the printed part. The CaliFlower design accounts for squishing by having both external and internal measurements that are averaged.

💡measurement error

Measurement error refers to the tolerance and variability inherent in taking physical measurements with tools like calipers. The video explains how this error is proportionally greater when measuring small calibration cubes vs larger objects like the 100mm CaliFlower.

💡firmware

Firmware refers to the software and programming that controls the electronics and motors of a 3D printer. The video discusses adjusting firmware settings like steps/mm to calibrate a printer's dimensions as an alternative to physical modifications.

💡slicer

A slicer is software that converts 3D model files into gcode instructions for the printer. The video suggests using slicing tools like Cura to scale parts to account for material shrinking rather than adjusting firmware steps/mm.

💡steps/mm

Steps/mm is a firmware setting that determines how many motor steps are required to move the print head by 1mm in the X, Y, and Z axes. Adjusting this can help calibrate part dimensions, but the video suggests drawbacks to this approach.

💡tolerance

Tolerance refers to the permissible amount of error or variability in a measurement or specification. The video discusses how mechanical tolerances and assembly can contribute to skew. Tight tolerances help achieve high accuracy.

💡CaliFlower

The CaliFlower is an alternative calibration part designed to overcome the shortcomings of cubes for tuning printer dimensions and skew. Its larger size and averaging of inner/outer measurements improve precision.

Highlights

Calibration cubes are one of the most 3D-printed parts but are considered harmful for tuning printer's dimensions.

The video explains why calibration cubes are bad and introduces proper methods for tuning printer dimensions.

Introduction of the RatRig V-Core 3 and the issues encountered with electronics housing due to skipped calibration.

Critique of calibration cubes for size calibration due to their simplicity and potential for worsening accuracy.

Explanation of factors affecting 3D print accuracy, including printhead movement, extrusion width, and thermal contraction.

Discussion on the flaws of calibration cubes, including measurement errors and their impact on perceived accuracy.

Introduction of skew as a common but often overlooked flaw in 3D printers, and how to measure it.

Presentation of the CaliFlower tool for comprehensive printer calibration, including skew correction.

Explanation of preparing for and executing the CaliFlower calibration process.

The importance of using high-quality calipers for accurate measurements during calibration.

The impact of material choice on part dimensions and the suggestion to use scaling factors for different materials.

Overview of the benefits of having a professional website with Squarespace sponsorship mention.

The results of calibrating the RatRig V-Core 3, including adjustments for skew and dimensions.

Discussion on the variability of shrinkage across different materials and its impact on calibration.

A comparative analysis of printer skew across different models, highlighting the effectiveness of calibration.

The potential use of calibration cubes for evaluating printer or material quality, despite their limitations for size calibration.

Transcripts

These are calibration cubes, probably one of the most 3D-printed parts ever.

Yet I think they are one of the worst and even harmful parts for your machine that you

can print!

In this video, I’ll show why calibration cubes are bad, how you properly tune your

printer's dimensions, and how accurate the machines I have in my studio are!

Let’s find out more!

Guten Tag everybody, I’m Stefan and welcome to CNC Kitchen.

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After I recently finished building my new RatRig V-Core 3, I thought it would be a great

test for the machine to print the electronics housing for my new precision oven for temperature

tests.

Unfortunately, after the first print, I noticed that the holes I had properly measured didn’t

fit the electronics, and the lid didn’t fit the base.

At that moment, I realized I forgot a crucial step of setting up a new, especially self-built

machine and that was doing the size calibration.

Many, and in my opinion, way too many, use one of these calibration cubes for that step.

Over the years, there have been dozens of different variants of calibration cubes popping

up and most of them have one distinct feature.

They are cubes, usually marked with letters for the axes, and are 20 or 30 mm wide.

You’re supposed to measure them in order to figure out if your machine prints dimensionally

accurately or not.

And this is exactly the problem.

If you ever used a calibration cube to tune your steps/mm, there is a big chance that

you made its accuracy worse instead of better.

Hate me for this take, dislike, unsubscribe or leave a shitty comment.

I don’t care!

I’m convinced THIS is one of the worst things in 3D printing that you can do!

There are some legitimate uses for calibration cubes, yet not size calibration and I’ll

touch on that later.

The accuracy of a 3D print is affected by a ton of different factors.

The most obvious is how accurately the printhead can move to a certain position, and this is

what people often think they need to tune.

What many don’t realize is that the dimensions of a part are only partly impacted by the

accuracy of the print move and also a result of how wide an extrusion gets squished and

how much the part shrinks due to thermal contraction!

In order to understand why I think people make a mistake when using calibration cubes,

let me quickly explain the process.

So the common calibration cube has a nominal edge length of 20 mm.

When people print it, they take calipers and measure how wide it is in reality and then

adjust the steps/mm, so basically how much the stepper motors need to rotate for a mm

of movement of the printhead.

Once they adjusted this value in their firmware, they print the cube again and are happy if

it really measures the exact dimensions.

Yet what many don’t realize is that calibration cubes have some major flaws, which makes measuring

their outer dimensions useless and even wrong for scaling.

Let’s start with the most obvious, and this is that regardless of which orientation you’re

measuring the calibration cube, your measurement is flawed by either the elephant foot the

cube might have or overextended corners.

The next problem is that if you’re just measuring outer dimensions, these are highly

affected by the amount of over-or under extrusion that you’re having.

And finally comes the measuring error.

Measuring something always comes with a tolerance, which can be a result of imprecise measuring

equipment or even just the amount of pressure that you’re applying on the tool or your

part.

A measuring error of 0.1 mm on a 20 mm block is a .5% error.

The same measuring error on a 100 mm part is only .1%.

So the smaller the dimension that you’re measuring, the higher the impact if you measure

something wrong.

The 20 mm calibration cube is rather on the small side, and a 0.1 mm measuring error is

completely normal on cheap calipers or if you measure incorrectly.

The last big letdown of calibration cubes is that even if you were able to use them

to get your x and y dimensions right, they don’t tell you anything about an often overlooked

flaw of 3D printers, and this is skew.

If you have a skewed printer, this means that the x and y axis are not particular to each

other.

This can be a result of tolerances, bad assembly or even just unequal belt tension.

This is mostly irrelevant and even unnoticeable if you mainly print esthetic parts, but as

soon as you print a box with a lid, you will notice that the top and bottom don’t fit

nicely onto each other if your axes are skewed.

Measuring skewness is pretty simple by measuring the diagonals of a square.

If they are not the same, your printer is skewed.

I mean I’m probably not the first one telling you that many printers have a way to compensate

for that, but did you ever check your machine or even compensate it?

I was curious myself and tested all the printers I have in my studio and we’ll take a look

at the results later.

So how can we get around the letdowns of calibration cubes and even do our skew correction at the

same time?

You can find several different solutions for that on the typical model repositories, yet

the one that I’ve been using for a while is the so-called CaliFlower from YouTube colleague

Adam of Vector3D.

Yes, this is a paid download, but what you’re getting is not only the STL for printing but

also this super convenient spreadsheet that gathers your measurements and then does all

the calculations for you and even creates the inputs to compensate for the deviations

in your firmware or slicer.

So let's use my new RatRig V-Core 3 as an example, which I just built but didn’t check

for proper dimensions and skew yet.

Before I printed the CaliFlower, I made sure I properly tuned my filament profile.

So I figured out the optimal extrusion temperature, adjusted the flow percentage, tuned retractions,

and figured out the optimal pressure advance value.

With everything set up, I then printed the Calibration Flower, which takes around an

hour to finish.

Adam, who designed the CaliFlower put a ton of thought into the design so that the measurements

you’re taking are as precise and repeatable as possible.

Obviously, the part is bigger, with nominal dimensions of 100 and 50 mm, so measuring

errors are less severe.

Then the locations where you’re measuring are on flat faces, so no text or over-extrusion

on corners will impact your measurements.

There are chamfers at the top and the bottom to avoid an elephant foot or the impact of

overly squished upper layers.

And finally, every dimension is measured as an outer and an inner measurement.

By taking the average of these two measurements, you get rid of any effect from over or under-extrusion.

For example - over-extrusion would make the outer dimensions bigger and the inner dimensions

smaller, but the average, so basically, the middle will stay the same.

Make sure to use proper calipers.

I love my Mitutoyos with the thumb wheel that helps to apply consistent pressure during

the measurements.

Link in the description by the way.

Make sure that the calipers are always parallel to the part, and maybe even wiggle a little

to find the sweet spot.

There are ten reference dimensions on the part, and in order to reduce the effect of

measuring error, you should measure each dimension three times.

This takes maybe 5 minutes which leaves you with the calculation of your x and y error

as well as skew of your axes.

If you have used Adams CaliFlower before, you might notice that mine looks a bit different.

This is because I initially had the idea to make something myself because I wasn’t satisfied

with the way the old CaliFlower had to be measured.

Yet instead of re-inventing the wheel and ripping off a YouTube colleague, I rather

decided to chat with Adam, so that he could improve his design.

Adam had a pretty rough last year with a cancer diagnosis, so every purchase helps him to

get back on track!

Whereas on the old one, it was a hit-or-miss placing the caliper correctly, there are now

stops on the new design that will make sure that you always measure at the right location.

The new design is now available in his shop and if you already bought the old design,

you can download the new one with the same link you initially got.

If you have a cool idea for an innovative product, just like Adam had with his CaliFlower,

if you want to share detailed written guides or just show off your portfolio, you should

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So my measurements told me that my x and y dimensions are around 0.3% to 0.4% off and

the skew of my axes is 0.4° which is quite significant which also explains why my top

ond bottom housing didn’t properly fit.

My RatRig runs Klipper, where compensating the skew is really simple by just adding a

line to the configuration file, sending two commands via the console, and adding a command

to the start and the end g-code.

If you run RepRap firmware or can compile your own Marlin, there are also the commands

generated in the spreadsheet.

If you can’t change your firmware like on a BambuLab machine, or even the new Prusas

if you don’t want to void your warranty, it’s tougher, but there are skew compensation

add-ons for Octoprint or G-Code post-processing scripts that you can use.

If you want to fix this problem properly you might even want to try to square your machine

manually!

Next might come a little controversial topic.

My measurements told me that my part was around 0.35% undersized and even the spreadsheet

suggests the steps/mm adjustment.

And here comes my controversial opinion.

If you only print one material type, go ahead and change your steps/mm if your machine allows

it.

But for anyone else, who regularly works with different materials, I’d rather define a

scaling factor for each of the materials that you use.

To demonstrate what I mean, I printed the califlower on my RatRig in PLA, PETG, ABS

and ASA and even though the skew was always relatively small in terms of measuring tolerance,

because skew is a property of the printer and not the material, the part shrinkage was

different.

I had to compensate 0.35% for PLA, 0.4% for PETG and around 0.7% for ABS and ASA.

This shows that not the machine is printing incorrectly but the materials are just shrinking

and resulting in wrong dimensions.

CURA and OrcaSlicer have a material shrinking factor for that, in most other slicers, you

have to scale your parts manually if it’s something where you need to get your dimensions

right.

After adjusting your skew and compensating for shrinking, it’s a good idea to print

another CaliFlower to check, how good your part dimensions now are.

Due to tolerances and simply the complexity of the printer, material and environment system,

you can’t expect to have perfect dimensions, but from my experience, running the calibration

cycle once reduces your machine error by an order of magnitude which is usually good enough.

I think, for most applications, a dimensional accuracy below 1/10 of a mm or 4 thou precise

enough!

But I was curious.

I have a bunch of printers here in the studio and at home and wanted to find out, how good

in terms of dimensions they all were.

One of them is also really special in that regard.

The good old Prusa Mk3 is the only printer besides the MK2 I’m aware of that does automatic

skew calibration by measuring special points on the bed.

But is this just a gimmick, or does this make this machine more dimensionally accurate?

Let’s start with size.

First things first.

All parts came out undersized, which also indicates that the deviation in size is primarily

thermal contraction.

Yet there were still significant differences with some parts coming out of the machine

almost spot on and others already .4% smaller.

I first thought this might be due to the different brands and colors of PLA that I used and reprinted

them all in the same, green VOXELPLA, yet a size difference still was there.

I can only suspect that some might already compensate for shrinking in their steps/mm.

The other interesting part to see was that the x and y error was not always the same,

so a global material scaling factor might not perfectly work on all printers and in

these cases, adjusting the steps/mm or unevenly scaling the stls in the slicer might be the

better way.

I can only assume that the reason for this is uneven belt tension, but maybe you have

thoughts as well?

Size can be easily compensated for, so the more interesting metric was the skew of my

machines.

Whereas I still had 0.4° of skew on my uncalibrated RatRig, I was able to completely get rid of

it by using the CaliFlower.

My A1 Mini, the P1S, Prusas Mk3, the A1, the Artillery Hornet, the Prusa XL, my old X1

and the QIDI X-Max 3 only had a very insignificant amount of skew.

Starting with the MK4, the skew got worse, from 0.05° to almost 0.1° on my other X1

to over 0.3° on the Snapmaker J1S to finally a staggering 0.55° on my transparent Bambu

Lab A1 Mini.

If you used the whole printbed of the A1 Mini, this would be a 1.7 mm shift on a part.

Yet I have to say that my transparent A1 Mini is a special pre-production unit that might

not have seen the QC of the retail printers, especially looking at my other A1 Mini that

was basically not skewed at all.

But have you ever measured yours?

Looking at these results begs the question, which skew is still acceptable?

I mean, if you primarily print esthetic parts, and nothing functional that needs to be assembled,

you don’t really need to care about that property.

For everyone else, it of course depends on the application, but everything below 0.1°

seems to be normal, but skew calibration can get you even closer to perfect!

I was kind or cruel to the classic calibration cube in the last 15 minutes, but in the end,

I think there is still a use for it and this is judging the quality of a printer or a material

with a very compact part.

Flat surfaces tell you something about extrusion consistency or vertical line artifacts.

Corners show you if pressure advance is tuned properly.

The upper surface will show under or over-extrusion and the letters will tell you something about

cooling and overhang performance.

Many other designs will even include more tests.

But I hope I was able to convince you that you should never use them to tune the dimensional

accuracy of your printer.

There are better ways!

And something you might not even have considered is that whereas calibration cubes are rather

boobie traps (UGH!), if don’t properly dispose of them, the CaliFlower at least makes a unique

coaster for your next party!

But what are your thoughts on this?

Was this totally new to you, do you still think this is BS or did I speak from your

heart?

Leave a comment below!

Thanks for watching, everyone!

I hope you found this video interesting!

If you want to support my work, consider becoming a Patron or YouTube member.

Also check out the other videos in my library!

I hope to see you in the next one!

Auf wiedersehen and goodbye!