Prusa Mini : difference between CAD sizes and Printed sizes (both X, Y and Z) : any correction through M92 command on Prusa Slicer?  

RE: Prusa Mini : difference between CAD sizes and Printed sizes (both X, Y and Z) : any correction through M92 command on Prusa Slicer?

Big thanks for this excellent write-up and PDF report!

I printed the calibration model with default values (99,44 / 99,50) and then changed the values to the following from the calculator:

M92 X100.563 Y100.502

Measured in on 100,00 and 100,00 (not joking...) at the first attempt, amazing. The values seems to be very close to yours, so might be a standard defect/flaw with the Mini.

RE: Prusa Mini : difference between CAD sizes and Printed sizes (both X, Y and Z) : any correction through M92 command on Prusa Slicer?

I don´t think there is a standard value for all the Minis.

In my case the correction values where:

M92 X100.282 Y100 Z401.86

RE: Prusa Mini : difference between CAD sizes and Printed sizes (both X, Y and Z) : any correction through M92 command on Prusa Slicer?

Hello guys,

Happy to read that the "M92 community" is growing! 🤗 

Dimensions accuracy into printed part can be improved. Lot of people ignore this, few tried...and succeed.

Hope more and more will move forward...should they need to.

Best regards

S.T.

RE: Prusa Mini : difference between CAD sizes and Printed sizes (both X, Y and Z) : any correction through M92 command on Prusa Slicer?

According to several printer builders changing the steps/mm ratio is generally speaking  a wrong approach.

Is is a fixed ratio defined by belt pitch and number of teeths on the wheels, nothing else.

The dimensional errors are mostly due to

1. belt not enough tight (or even too much),
2. missed steps by motors,
3. spring effect on belts during accel/decelerations,
4. frame skew,
5. not precise alignment of the belts, motors shafts, etc...

In the end don't forget  the impact of the thermal expansion of the plastic. Sadly this affects parts in various ways depending on how they are made and how much heat is released or kept during the print process and final cooling. 

as a reference example: https://github.com/prusa3d/Original-Prusa-MINI/blob/master/DOCUMENTATION/PRINT%20SETTINGS/recommended%20print%20settings%20for%20Original%20Prusa%20MINI.md

That said, if You live happy (and precise) by adjusting steps/mm it is ok, anyway remember that a tolerance of +-0.1mm is standard on fdm  and You are masking an error by introducing another error.

Fortunately many people don't need this level of accuracy when printing owls.

Regards

RE: Prusa Mini : difference between CAD sizes and Printed sizes (both X, Y and Z) : any correction through M92 command on Prusa Slicer?

@ Turro75:

I agree with this: if most users are happy with ± 0,1 mm (and more often ±0,2 mm...) , then...fine for me. And by the way , not every user is fine with G-code, starting script and so on...

For my own purpose: I was often embarrassed , starting 3D printing couple years ago, when trying to assemble multiples parts without willingness to introduce ± 0,5 mm clearance everywhere.

(By the way: this was not for "multiple parts owl" assembly, neither vases...)  😊 

So looking for solution, on the Web,  I found several guys using this "easy to do" ...let's say "adjustment M92".

What are all reasons and causes leading the 3D printing process to make a dimension equal to 99.80 mm instead of 100 mm? I don't know... I suspected some, I observed some....and you listed most... but I observed this somehow "proportional versus wanted" dimensions drift. And being not an owl maker, that was not suitable for me . And since I am not a millionaire (unfortunately), I looked for any affordable solution...on printers I have.

 I tried to expose the approach on page 1 of this post:  Prusa-Mini-dimensions-accuracy-test-extruder-or-M92.pdf  (did you read it?)

What you described to be "masking an error by introducing another error."  is not my point of view. For me this (M92) can be updated/modified to balance (compensate?) negative effect of all (and probably others) causes you listed. Maybe it's just a question of semantics, because English is not my language, so sorry for any mistakes ...

If some other ways leads to same improvements, on parts results, I will be more interested to read and to try,...but  so far no one (as far as I know) submitted alternative ways leading to same results.

So to try to clarify my words: I am neither the inventor nor the guru of the M92 code. But since I was very annoyed with this dimension problem before using it, I just posted my findings and trials results here, this post I created. If this can help some other guy, nice. I'm not begging anyone to try.

Thank you for your inputs and opinion on this.

Best Regards

S.T.

RE: Prusa Mini : difference between CAD sizes and Printed sizes (both X, Y and Z) : any correction through M92 command on Prusa Slicer?

So a better approach would be X, Y, and Z compensation values that would adjust the model before its sent to gcode. I also read that steps/mm is set for a stepper motor, and I am curious if using M92 introduces any other unwanted effects. It sounds like those effects are not measurable so we have to make due with M92. 

RE: Prusa Mini : difference between CAD sizes and Printed sizes (both X, Y and Z) : any correction through M92 command on Prusa Slicer?

If the error is relative to the size of tje model, say 10% so a 10mm cube comes out 11mm and a 20mm comes out 22mm then I would say adjusting the steps per mm is a good idea.

I the error is static we're probably talking extrusion errors or something else than steps. And if the error varies between different prints of the same model you might have reached the linits of the printer precision.

Just my ideas

RE: Prusa Mini : difference between CAD sizes and Printed sizes (both X, Y and Z) : any correction through M92 command on Prusa Slicer?

Amazing work!!You did a great job sharing your personal guide.

RE: Prusa Mini : difference between CAD sizes and Printed sizes (both X, Y and Z) : any correction through M92 command on Prusa Slicer?

I just thought i share my insomnia thoughts;

Printed dimensions would also depend on local enviroment to each printer (placement, temp around it, snaggning force of filament path, bearings, lube etc).

If you printer repeatedly produce the same model, in the same dimensions then the printer is accurate and could be corrected with M92, if those dimensions vary between prints, then machine is inaccurate (ever so slightly) machinemaintenence should go first.

Then add in the variable of different filaments, or even different brands of the same type. All expand/skrink differently and behaive in their local enviroment as well.

I cant say much of the internal accuracy of parts as this seems to be with external dimensioning.

On youtube Clough42 had a good video on dimensional accuracy for mounting pcb inside enclosure.

RE: Prusa Mini : difference between CAD sizes and Printed sizes (both X, Y and Z) : any correction through M92 command on Prusa Slicer?

@daniel-16

I wrote what I wrote as I realized on my damn skin exactly this, during one of the numerous assembly/reassembly cycle I performed on my mini clone I had the great idea to replace the belts by using an unused gt2 belt lost at the end of the last drawer... result? calib cube became 20.2 and a 100mm squared shape became 101mm. Even the print quality was definitely lower with a lot of ghosting. Of course I tested many level of tensioning, no changes.

After several test I back to the stock belt on X only and magically the X size came back to the design size (within tolerances) as expected while Y were still wrong, so I realized the even the spring effect on belts has an impact (at least 1%) on real dimension. As a Result I'm back to stock belts and dimensions are now fine and no more ghosting. In case I'll need to replace belt I'll do it only with high quality belts. I wouldn't imagine the effect of a low quality belt on a corexy....

RE: Prusa Mini : difference between CAD sizes and Printed sizes (both X, Y and Z) : any correction through M92 command on Prusa Slicer?

@rick-3 - @sylvain-t2

3d modeling for fdm 3d printing can't be the same as 3d modeling for mechanical tools, different tolerances, one is additive while the other is subtractive, etc..

The slicer generates nozzle paths according to the defined filament width, in case of a square object the lenght of the external perimeter generated path is "design size" - "filament width" and so on.

This is why the first calibration MUST be the extruder efficiency check and the thin wall test adjusting the flow %.

Please note I said extruder efficiency CHECK, not extruder steps calibration.

A personal thought about extruder steps calibration which is so popular on many youtubers, this is definitely an error as if You have to adjust the steps to get more (or less) filament You are actually trying to compensate an extruder that is not able to properly push the filament and this would be variable during the print, can have different behavior on different filaments and different extrusion temperatures as the nozzle offer a different resistance on filament flow. On some materials even part cooling fan can have an impact on filament thickness.

let me tell a (imagined) story: a guy doesn't know his 3d printer has a poor extruder and he followed the instructions of a youtuber that show him how to adjust the E steps getting inconsistent flow totally unjoined from what the slicer expects, in fact that fix generates many other issues as random under/over-extrusion (filament cannot consistently slide) which leads in random wider/thicker walls , stringing, etc... So he starts adjusting the other axes step because out of dimensions as another youtuber said that the cube must be 20.0000000 measured by a 8$ caliper (not You sylvain-t2, I see You know how to seriously measure stuff) and then after a while he discovers that on some shapes the sizes are good while other shapes are not precise and he get mad continuously changing parameters. Then one day after weeks of frustrating tests while disassembling the hotend trying to fix a massive stringing he brakes the thermistor creating a short that burns the pcb, so everything goes to the basket shouting that 3d printers are shit.  

That said if people live happy (and precise) with fully managed steps values there is nothing wrong on my side, what is important is being aware that is not the best way.

RE: Prusa Mini : difference between CAD sizes and Printed sizes (both X, Y and Z) : any correction through M92 command on Prusa Slicer?

Hello,

Lot of hypothesis, interesting ones, 🤔 ... I would like also to read some test/measurements results as well, even on any alternative ways to improve. 🙄 

...however looks like many did not read (understood?) the pdf test report I wrote and attached in this post. 😵 

A forest of "It could..., it should..., I would..., it "zould", we "fould", they "pould" ...are nice philosophically speaking, even technically, but alternative solutions, supported by validation tests, measures, hours of real works, that will be also nice to see. 🧐 

Of course, basic controls such as machine axis geometry, extruder settings, belt tensioning and so on to be checked upfront... Then for years I observed this: whatever is the Brand: Creality, Tiertime, Artillery, and even Prusa ....dimensions accuracy issue (for the ones impacted by, including me) is 99% caused by multiples factors, inducing a proportional error. And even with high quality belts from GATES, I also deploy this to reduce part variances....successfully. 😎  

This is why the testing part I designed has specific dimensions like 10 mm , 20 mm , 50 mm, 100mm, 150 mm 🤗 : (before/after M92 measurements somehow interesting, at least for me)

For those not keen , or terrified, by this approach, don't use it, but please: don't blame nor discourage others willing to progress, to test, to improve 😒 . Some guys around me here are very satisfied I improved their 3D printed parts without heavy/costly mods but just 1 line G-code of few letters and numbers... 🤭 

I don't sell anything nor win anything here, just trying to help some, and sorry to disturb the others: they can open another post such as  "We don't believe into M92 black magic" or "the French disciple of M92 command will lead you to your doom!"

And overall this, don't worry, just kidding (but not for using M92!)

Rgds!

RE: Prusa Mini: diferença entre tamanhos CAD e tamanhos impressos (ambos X, Y e Z): alguma correção através do comando M92 no Prusa Slicer?

@sylvain-t2

Adorei o teu trabalho so é  pena a empresa que faz a impressora não por isso nas configurações da impressora é que nos compramos a impressora não foi dada nem roubado foi um bom trabalho muitos parabéns obrigado pela ajuda. PT Portugal 

RE: Prusa Mini : difference between CAD sizes and Printed sizes (both X, Y and Z) : any correction through M92 command on Prusa Slicer?

@joker-borges

Obrigado pela sua mensagem. Felizmente, existe o google tradutor! 😊 

Os fabricantes de impressoras 3D fornecem uma máquina produzida em massa. 
E o preço de venda é muito baixo. Eles produzem em grandes volumes. 
Estrutura e componentes nem sempre são ideais 🤔 

Eles, portanto, fornecem um amplo intervalo de tolerância na precisão das impressões. Então ninguém pode reclamar.
O que não quer dizer que um usuário não possa melhorar os resultados ...
A prova com meu post aqui! 😀 

Atenciosamente da França