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Posted · Custom nozzle prime

Hey, I'm in the process of making a custom definition file for my delta printer, I also have variant files for different nozzle sizes.


For priming my nozzle I used to use skirts because that was easy. I experimented a bit and was able to determine that my printer needed about 60mm^3 of filament to fully prime my nozzles. This allowed me to calculate my minimal skirt length, for different layer heights and nozzle/line_widths, in the "overides":{...} section of my definition file:

"skirt_brim_minimal_length": {
	"default_value": 750,
	"value": "60/(layer_height_0*line_width)",


The problem with using skirts is that my maximum build area is reduced. So I'm looking at other ways of priming my nozzle which have a minimal influence on my printing area and which I don't have to worry about removing during the print because the might interfere with the print it self. I thought of using a G2 arc command in the start code of my machine. This way I can print at the very outside of my bed and the gcode itself is very small.

The problem I'm encountering during the implementation ist that I would ne to insert calculated values into the start code. And I'm not sure on how to achieve this. Here is an example of what I would like to do but what sadly doesn't work:

"platform_adhesion": {
	"children": {
		"_prime_arc_start_x": {
			"label": "Prime arc start point in x",
			"description": "The starting point in x-axis direction of the priming arc",
			"unit": "mm",
			"type": "float",
			"default_value": "0"

"overrides": {
"default_value": "G1 X + '_prime_arc_start_x'"


I've played around quite a bit with this but haven't been successful. I've tried:

- changing the type from "float" to string"

- using python syntax to put variable into the string (link)

Even if I get this to work I'm not sure on how this would behave if I change my nozzle/variant once cura has been started.


Does anyone have any ideas on how I could either put values into my start code or have any other suggestions on how to prime my nozzle in a good way using the priming volume of 60mm^3?



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    Posted · Custom nozzle prime

    Default_value can never be anything that is interpreted by python. I think you could try the following:


    "value": "'G1 X' + str(_prime_arc_start_x)"

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    Posted (edited) · Custom nozzle prime
    On 4/7/2020 at 3:38 PM, nallath said:

    Default_value can never be anything that is interpreted by python. I think you could try the following:


    "value": "'G1 X' + str(_prime_arc_start_x)"


    Thanks for the answer, that worked perfectly. 

    But I must admit I found a simpler solution to my problem. I was frustrated by using skirts because it took away too much from my build area. But this was only due to the fact that I had set the skirt distance to 10 mm. should work out perfectly:


    "adhesion_type": { "default_value": "skirt"},
    	"default_value": 750,
    	"value": "60/(layer_height_0*line_width)",
    	"minimum_value": "0",
    	"minimum_value_warning": "25",
    	"maximum_value_warning": "4000"
    "skirt_gap": { 
    	"default_value": "1`",
    	"value": "3*wall_line_width_0"


    Edited by schpongo
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