Guides

[GUIDE] Steps calibration – Set step/mm to optimize size accuracy of 3D printers

Today we are talking about steps calibration of the X Y and Z axes, a simple and practical guide on how to obtain exact dimensions of our 3D prints.

Steps calibration: Practical Guide

First specific that this is a practical guide.  Therefore it involves the direct comparison of practical results. The process consists of redoing the same process several times. Each time you do it again, you will add precision. So get ready to print your favorite known figure at least 2 or 3 times. However, you will not be repeating this procedure more than 5 times. 3D FDM printing has a myriad of unknowns and variables, not always easy to consider. For this test I suggest you to take a sample of a simple figure, easy to measure and fast to print.
Steps calibrationMe too, normally are a big fan of Benchy, chose the calibration cube for this test. And I did it for these reasons.

  • It’s fast to print
  • Can suffer few malformations
  • It’s easy to measure, just a few tricks I’ll tell you later
  • No need for full printing, but only a quarter (if you’re in a hurry and need to set just x and y)

Steps calibration: Theoretical value and actual value

First we will have to get the first data on which to work, which are 2, the theoretical value and the real value.

The real value corresponds to the value that our printer executes in reality. What does it correspond to? It simply corresponds to the size of our printed cube, with the preset values. So as an example we can use the cube in the picture here. Measure the cube with a digital caliper like this in the photo to get a correct and precise measurement to the hundredth of a millimeter.

The theoretical value must instead be obtained from our printer. This will be different depending on the mechanics (belts, pulleys, etc. ..) in use but also depending on the drivers. (Normally basic with 4988 drivers they have 16 microsteps and are set to 80 step/mm.

In this case in this example I will use my 32 microstep printer with 8825 driver and this leads to a higher level of precision. So 160 steps each mm. (as you can see in the image). 

This value can be obtained from the keypad (if you use the Marlin firmware), or in other ways. One of the simplest is to connect the printer to the PC via Repetier Host. (If you don’t know how to do it, you can follow the link). As soon as you connect your printer you have to check at the top, between the text, the command M92 what it shows. Those will be the values of your steps/mm on the X Y and Z axes.

Calculations: a simple proportion

Now that we’ve found the values, we can do the calculations. As already mentioned it is an elementary calculation, in fact it is a proportion in which we have 3 data, and we only have to find the fourth.

Indeed:

(real value VR) stands a (theoretical value VT) as (real value corrected VRC) stands a (theoretical value corrected VTC)

some math:      VR:VT=VRC:VTC 

our data VR=20.21 VT=160 VRC=20 (the measurement that has the correct cube) VTC=X (the value to be found)

now a bit of mate: 20.21:160=20:X —> ( 160*20) / 20.21 = X —> X= 158,33

So to have the new values to be inserted in each axis you have to repeat this calculation that we did above for the X axis also for the Y and Z axes. Mark the results on a sheet of paper and do not lose, for the moment, these new values!

Enter new values

Steps calibration

Steps calibration

If you have the option, you can change the values directly from the keypad. However, remember to save the new data before switching off and Save to EEPROM. Otherwise connect again to the printer via Repetier Host and give the command M92 X158.33 Yxxx.xx Zxxx.xx. To save in EEPROM, remember to insert the M500 command immediately afterwards. This command will store the new values inside the card.

A third way allows us to directly enter the new values in the start Gcode on your favorite slicer. We have seen how to do it in the first guide of Cura 3.0. This is the most challenging method but also the most precise.
I think it is the most precise because as we have seen in the reviews of the filaments each wire has a different response to the same parameters of the same printer.  

A good solution, if you are looking for maximum precision is to keep the values of each filament and enter them in the start gcode when you start to print just that material. It is dangerous, however, because if you forget this you risk amplifying the minimum difference that could have existed initially.

This is a good solution only for those who print professionally or maybe if you need to match the print with a product from another printer. In fact, 2 printed pieces  with the same printer will match because they will have the same error!

A few recommendations

FDM printing is not as precise as other methods, so I recommend that you do not fossilize to the nearest hundredth of a millimetre. Correct steps calibration in the order of tenths of a millimeter has more than enough precision to print Pikachu Low Poly or other figurines. Only go for maximum precision if necessary! Or you’ll go crazy and find your house full of cubes. Consider that a filament with a diameter that is not perfectly constant can, on its own, increase or decrease your creation by a tenth of a millimetre or more. For this reason, it would also be useful to follow the guide on the amount of extruded filament before you try this one.

The last recommendation expressly concerns the measurement methods. Some printers may be adjusted very close to the plate to increase adhesion. All right if it were not for the fact that this causes 2 problems.

  • The elephant foot effect, so the base of the object widens. Try not to touch the base of the object when measuring the x and y sides. It can be measured by keeping the gauge horizontal to the measurement. Exactly as you see in the image where I measure the blue cube.
  • Adjusting the very squashed nozzle can also lower the total print by a few tenths, “eating” the first layers. Be careful to calibrate the plate well and adjust the offset correctly. If this operation is not easy because you lose grip try to apply our advice for adhesion.

 


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