Calibration of a delta printer on the example of Prism Mini

Delta printers are extremely demanding on the accuracy of manufacturing components (frame geometry, diagonal lengths, gap diagonals, effector and carriages) and the entire geometry of the printer. Also, if the limit switches (EndStop) are located at different heights (or different triggering moment in the case of contact limiters), then the height along each axis is different and we get an inclined plane that does not coincide with the plane of the working table (glass). These inaccuracies can be corrected either mechanically (by adjusting the limit switches in height) or programmatically. We use the software calibration method.
Next will be discussed the basic settings delta printer.
To control and configure the printer, we use the program Pronterface .
Calibration of the printer is divided into three stages:

Stage 1. Adjust the plane by three points

Placing in one plane of three points - A, B, C (located next to the three guides). In fact, it is necessary to clarify the height from the plane to the limit switches for each of the axes.
Most (if not all) boards for controlling a three-dimensional printer (in our case RAMPS 1.4) work in a Cartesian coordinate system, in other words there is a drive on the axis: X, Y, Z.
In a delta printer, you must go from Cartesian to Polar coordinates. Therefore, we will agree that connected to the engines X, Y, Z corresponds to the axes A, B, C. (Counterclockwise starting with any engine, in our case looking at the logo on the left - XA, on the right YB, far ZC) Next, when slicing, print and managing the printer in manual mode, we will operate on the classical Cartesian coordinate system, the printer electronics will themselves recalculate the data in the desired system. This convention is necessary for us to understand the principle of operation and direct calibration of the printer.

The points at which we will perform the calibration will be called like (A, B, C) and the position of these points is A = X-52 Y-30 ; B = X + 52 Y-30 ; C = X0 Y60 .

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Algorithm settings:

1. Connect to the printer. (In the case of “hacking” in the command line, you must change the speed of the COM port. In our case, from 115200 to 250000 and reconnect)
   
   Then we will see all the printer settings.
   
   
2. Zero the heights of the axes X, Y, Z with the command M666 x0 y0 z0 .
   And save the changes with the M500 team. After each change of settings, you must press home (or the g28 command) in order for the printer to know where to take the countdown.
   
3. The printer is calibrated “hot”, that is, the table must be heated (if available) and the print head (HotEnd) is heated (Table 60 hail., Nozzle is 185 hail.) We also need a probe, preferably metal, of known size. For these tasks, the allen key is quite suitable (the largest, in our case 8mm, it is provided complete with Prizm Pro and Prizm Mini printers)
   
4. We lower the print head to a height (conditionally) 9mm (from the table, so that the nozzle would barely touch our probe, because the height has not yet been precisely set.) Command: G1 Z9 .
   
5. Now we proceed directly to setting up our three points.
   For convenience, instead of g-commands you can create four buttons in Pronterface , to move the print head to points A, B, C, 0-zero.
   
   Creating buttons in Pronterface

   To do this, in the central part of the window there is a “+” button, clicking on which opens a window with three fields: Button Title, Command (Command), Color (The color of the future button)
   Fill in:
   Buttom Title: Min A; Command: G1 X-52 Y-30; Color: Orange
   Buttom Title: Min B; Command: G1 X + 52 Y-30; Color: Blue
   Buttom Title: Min C; Command: G1 X0 Y60; Color: Green
   Buttom Title: Zero; Command: G1 X0 Y0; Color: White
   
   
   
6. By successively moving between three points (created by buttons or commands), we find out which of them is below everything (visually) and takes this axis as zero, with respect to it we will change the height of the other two points.
   
7. Suppose that point A is lower than the rest. Move the head to point B (Y) and lower the nozzle with the height-control buttons in Pronterface until it touches our probe, counting the amount by which we lowered the nozzle (we count the number of clicks on the +1 and +0.1 buttons on the forehead)
   Next, the command changes the parameters of the height of the Y axis: M666 Y {calculated value}
   M666 Y0.75
   M500
   G28
   
8. We perform the same operation with the remaining axes. After that, the height of all points should be checked again, it may turn out that the spread of heights after the first calibration will decrease, but the height will still be different, and the lowest point may change. In this case, repeat steps 6-7.
   

Stage 2. Fix lens

After we set three points in one plane, it is necessary to correct the height of the center point. Due to the special features of the mechanics of the delta, when the print head moves between the extreme points in the center, it can pass either below or above our plane, thus we get not a plane, but a lens, either concave or convex.

This parameter is corrected so-called. delta radius, which is chosen experimentally.

Calibration:

1. Send the head to the height of the probe in any of the three points of the table. For example G1 Z9 X-52 Y-30
2. Compare the height of the center point and the height of points A, B, C. (If the height of points A, B, C is different, you must return to the previous calibration.)
3. If the height of the center point is greater than the others, then the lens is convex and it is necessary to increase the delta radius value. It is desirable to increase or decrease with a step of + -0.2 mm, if necessary, reduce or increase the step depending on the nature and magnitude of the curvature (selected experimentally)
4. Commands:
   G666 R67,7
   M500
   G28
   
5. Adjust the delta radius until our plane is aligned

Stage 3. Find the true height from the nozzle to the table

By the third stage, we adjust the print height (from the nozzle to the lower plane - the table). Since we believed that the overall height was obviously not correct, it was necessary to correct it, after all the adjustments of the axle heights. You can go two ways to solve this problem:
1 Way:
By hand-fitting our nozzle under the probe, so that it would freely pass under it, but there was no tangible play,

• With the command M114 we display the value of the actual height of our HotEnd
• With the command M666 L we get the full height value (Parameter H)
• Then we subtract the actual height from the full height.
• The resulting value is subtracted from the height of the probe.

Thus, we get the non-revenue value of the nozzle to the lower plane, which must be added to the full height value and written to the printer’s memory with the commands:
G666 H 235.2
M500
G28

2 Way:
The second method is simple as boots. From the “ceiling”, “by eye” we add the height value (after each change, we don’t forget to “go” to the home), achieving the required height value, but there is a chance to overdo the values ​​and your nozzle with a crunch will crash against the glass.



How to do auto-calibration for your printer and that while auto-calibrates the printer, you will learn from the following articles.