Nozzle Scraping during Travel Moves

So, I was having banding issues with my AnyCubic Kossel Delta and found threads here that suggested replacing the smooth idler pullies with toothed ones. Never thought to even look at that before. And that fixed all the banding issues! So Many THANKS for that suggestion!

However, another issue persists:
On travel moves, the nozzle often scrapes the infill on travel moves.

I was hoping replacing the idler pullies with toothed ones would fix this as well, but the problem persists.
I've calibrated the extruder multiple times and adjusted the extrusion multiplier so I'm sure I'm not over-extruding, and the infill is not raised above the shell.
Currently printing only PLA: 210c and 60c bed. And the prints look great, but the scraping is concerning me.

I'm leaning toward z-hops on travel moves, if there is no fix for this.

Anyone have any suggestions for a fix?

BTW: This is Marlin 2.0.3 on an SKR 1.3 32bit ARM mainboard with TMC2208 UART mode drivers running at 32microsteps.

Thanks!

How violent is the scraping? Does the scraping go away when you reduce the printing and travel speed by a significant amount (50% or more)?

I vaguely remember having this problem with Marlin but not RepRapFirmware but that may have been a coincidence. Dual extrusion systems like Chimera suffer from a light scraping from the inactive nozzle, different situation but similar cause - the nozzle is moving over plastic that's already been extruded for the current layer.

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thehankinator
How violent is the scraping? Does the scraping go away when you reduce the printing and travel speed by a significant amount (50% or more)?

I don't hear any scraping on my non-delta printers, and its loud enough that I hear it over the fans (which are fairly quiet). It's rough enough that I'm afraid a thin tower or support would get knocked over.
For now, I've added a 0.5mm Z-hope on retractions, which eliminates almost all of the scraping (the remainder happens when the travel move is short enough to not require a retraction).

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DaHai8
However, another issue persists:
On travel moves, the nozzle often scrapes the infill on travel moves.

I assume that you get a good first layer, so it isn't that the delta radius is wrong.

Does the problem get worse the higher the print goes? If so, one possible cause is that the towers are not exactly parallel, so that the printing plane is flat close to the bed but less flat as you go higher.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

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dc42
I assume that you get a good first layer, so it isn't that the delta radius is wrong.

Does the problem get worse the higher the print goes? If so, one possible cause is that the towers are not exactly parallel, so that the printing plane is flat close to the bed but less flat as you go higher.

First layer is perfect.
I've printed up to 250mm tall and the scaping doesn't get any better or worse. The print itself looks very nice, I don't see any artifacts from the scraping: no squished layers or bulging.

Maybe it's just slight over-extrusion then?

On a delta printer Z motion is fast, so there's no real disadvantage to using Z hop.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].