How to print the purge block first?

With Chroma and Cura or S3D the purge block printed before the object, this helped to purged the previous color from the printer. It seems that Canvas starts printing the object first and then prints the first layer of the purge block. Is there anyway to get canvas to print the purge block first? This would improve the quality of our prints and save a little filament.

if not can this please be added to Canvas?

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Or, could we at least get a purge line before the model prints? My models always start under extruded until the filament catches up with the nozzle, so I get spots for the first 5 or so mm. I thought about adding a purge line to the gcode in Canvas, but would that throw off the splices?

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canvas should account for a purge line in the gcode header. if it does not, then that would be considered a bug. I've recently added P3 support to Kiri:Moto, and have had to deal with all of these issues.

having the purge tower pre-purge the first color creates a unique starting problem that would ripple through the tower for the rest of the print. it isn't really possible if there is a color change in the first layer. if not, it is possible. but this creates a situation where some prints could benefit from this where others could not.

it's best to either hand-purge it or add a purge line. in Kiri:Moto, I added an "offset" parameter for this reason that allows you to add *n* millimeters to the first splice segment where you can purge by hand while loading.

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I can confirm Canvas does properly account for pre-print purge lines in GCode headers (YAY! definitely very useful!). I use an off-the-edge purge setup with a box under the desk and the first section of my print is a purge of about 50mm of filament. Serves to both clear out any of the old color (between that 50 and the 20-30 that gets used in a skirt / brim) and to make sure that the filament at the end of the nozzle hasn't gotten over-cooked from sitting in an idle nozzle too long (If I preheat the printer early and then get distracted before starting the print)

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Canvas does properly account for the purge block and the purge line. I wasn't asking for it to change it to always print the purge block base first just how to get it to do this.

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Thanks Stewart, Zeno, and Randy! That's great news about Canvas handling the extra bit of a purge line in its computations, and I will go and add one in the starting gcode section. I appreciate the help.

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