As we know how to adjust the size accuracy of the 3D printer is one of the key activities. Although we are normally inclined to think only of resolution in 3D printing, size accuracy is the most important variable if we want to get to have prints faithful to the project. And maybe even able to combine with others to form compound objects.
Normally printers leave the house with acceptable accuracy, in the order of 1 or 2 tenths of a millimeter. But if we have to print mechanical parts, or with joints for real objects this accuracy may not be enough! So how do we increase it?
The system is very simple and very similar to the one already used for the flow regulation.
In fact it will be enough to print an object with known measures and increase or decrease the necessary steps of the engines to get to the print.
Adjust size accuracy, we’ll need:
- a measuring instrument (ruler/linear/calibre)
- A printer-computer dialogue program (we use Repetier Host, free of charge)
Print any figure, better if easily measurable, technical and even large. The greater the error of accuracy, the more it will be revealed. To adjust the accuracy I recommend a drawing of mine, which you can find on Thingiverse (at this address). This object was born as an analyzer for the first layer, but it can be measured and used to adjust the accuracy, since it occupies almost the entire plate. Of course you can also use the calibration cube, of 2 cm cubes. Here the tests were done with the cube.
Then you print and start with the first measurement, if this is greater than expected you will decrease the micro steps, otherwise, they will increase.
The operation to determine how much to decrease or increase the steps is a simple equation:
Size from project : Steps set = Size found : X then -> X = Size found x Steps set / Size project
X obviously in our equation is the new value of the steps. We can, for ease of representation, also summarize as follows:
—————————- x Gived steps = Right number of steps
Size accuracy: Let’s print a practical example:
In this case we have a found measure of 20.11, although our cube should have been 20.00. The printer in question is set at the factory with 80 step/mm. (This is a variable value and depends on the microstep of the drivers)
Using our formula we will have:
—————- x 80 steps/mm = 79,56/mm
So the new value that our printer should have for the Y axis will be 79.56 steps/mm. As you have already understood this operation must be done for all 3 axes (X, Y and Z) of the printer.
If you accept my advice, however, do not pursue perfection, which is not achievable. FDM printers have an error that depends not only on the limits of the machine itself, but also on the type of material used, the adjustment of the extruded material … The error is always at least a few hundredths of a millimeter. And moreover, the Z axis, besides being affected by the amount of flow (like X and Y) is also very affected by the adjustment of the plate, so a plate with more or less offset can vary the height of a few tenths.
Communication of new values in the machine – Size Accuracy
Once the new values have been found, they must be communicated to the machine. The lucky ones can edit directly on the keypad and save in EEPROM. If the printer does not have this possibility you can use Repetiter Host (free program). Notify the printer of the new values:
Keeping the values good in the example above you have to go to the Repetier screen where you can enter the G-code and type:
M92 Y79,56 and press Enter
Next, the command
to save in EEPROM!
It can be done one axis at a time or all at once. (M92 X80,xx Y79,56 Z160,xx).
Small errors, of the order of a few cents can be further reduced by performing a series of times this test for each individual filament and if you have a stable printer. And it will be the case to do it if you need to print functional prototypes with pieces that go to fit. It’s not worth it for typical prints, having the benchy a tenth of a millimeter longer or shorter does not change anything!