I have been thinking about this idea to fix ski and snowboard ptex with 3D printing.
Last year I made a little manual repair tool out of a hot end with a base and spring setup where I could push the hot end down into scratches, then feed PE repair filament by hand as I moved the repair tool by hand.
This was a pretty cool proof of concept and I think my results were probably at least as good as traditional methods but still not perfect.

I could make a simple working prototype for flatter areas by making something pretty close to a traditional 3D printer that mounts to the surface and prints a small flat area but this doesn't address the curved areas so I would love to make a working prototype that at least started to show something could work on non flat geometry.
One idea was wheels that roll along the surface and a pressure wheel that rolls along the back (or really top) side. Even this has challenges with the width changing and some skis and snowboards having non flat top sides. Along with wanting to be able to print right up to the edge of the board.

The other big challenge if this is recognizing the gouges, assigning them a coordinate system, and then slicing and printing.
I could do this by doing something like mounting a printer, 3D scanning the surface with some reference points on the printer I can use to assign coordinates, then do some mesh work to fill the void and create a solid object to put into a slicer. This again works easier for flat areas.

More ideal would be to be able to scan the surface from the 3D print head. If you had an axis that rolled along the curved surface and say a laser scanner or something that scanned perpendicular to that axis it could then basically interpolate the scan as a flat surface.
I have been wondering if there is anything that could be done easily that could take advantage of existing bed leveling firmware.
Would it be possible to do this with a capacitive sensor or is there anything similar that could easily work mostly off existing tech and firmware?

Then the next question would be whether you would need to send the scan to other software. I expect the answer is yes but I have been wondering how hard it would be to take that "bed mapping" determine a best fit surface, detect any imperfections say more than .1mm deep by a couple mm squared, create a watertight geometry of the scratch/gouge, generate a simple slicing profile for that geometry and fill it in.
I recognize this would be a good ways beyond your average bed leveling gcode but I am curious if it would be possible to achieve with a reasonable amount of work.
Otherwise we could do something like send scan to a mesh editor, create 3D geometry, send to slicer, generate Gcode, then back to the printer.

Another thought i had the other day was using a robot arm to do this. This eliminates the issue of trying to get a 3 axis machine to track a non flat surface. I imagine it would add a good bit of complexity in other ways though. A quick search makes it look like at least some development is going into getting Duet to run a robotic arm.
This could allow the arm to be mounted separately. If the arm scanned the surface the scan would be tied to it's coordinate system. Then it is just that matter of creating geometry for the voids, slicing, and sending back to the machine.

I know this would be a pretty big undertaking.
If a finished product could be delivered for the right price I think there could be some interest in the ski industry. If it was dialed in I suspect there are even some hobbyists would would be interested in building their own.

@droftarts

Haha I made the suggestion ages ago to adjust heat based on volumetric flow rate here and in Prusa Slicer forums and more people than not basically told me I was being stupid lol. I will check it out as that would be huge especially with filaments like TPU which I print with a lot.
I think nonlinear extrusion is still valuable especially with TPU.
I am currently running 3.5 RC2 but I have had frustrations with nonlinear extrusion for ages and several different versions.

I have been using nonlinear extrusion for years with mixed results. I have gotten setups dialed in better than running without it but it always felt like it wasn't consistent.
I have been using this calculator.

I tried setting it up doing static extrusion tests marking 100mm on the filament then extruding 100mm.
I found a better method has been to see where a print is under/over extruding then tweak those tables.

I started to feel like sometimes trying to increase extrusion by using a lower number at higher flow rates actually decreased the flow.
Tonight I think I finally confirmed this with the volumetric flow readout on the Duet web display. I was printing something that should have been 5mm3/s.
I started with a moderately aggressive NE number. Like say 100 at 0mm3/s and 78 at 6mm3/s (this is for TPU BTW).
The display showed something like 5.1mm3/s
So I went to an aggressive number. Something like 68 at 6mm3/s and the number Duet was reporting went down to 5mm3/s.
So then I clicked through the history and started selecting various ones I had tried before and finally found one that bumped it up to 5.3mm3/s. This was a less extreme ratio than at least one but I think several of the others I tried. Reverse engineering the numbers I think around 72 at 6mm3/s.

I can test this more soon but it makes me think maybe this isn't working like it should and maybe that is why it has been such a struggle for me to dial in these settings.
All of the threads I have found on this are either very old and include these two calculators often discussed, or are newer and really don't have much information.
I will admit that the math goes a little beyond me so I need a calculator or an easy way for me to get from seeing under extrusion at a flow rate and understanding how to change values to address it.
One thing that would be amazing is if there was actually an interface in the web interface where you could just enter values to create a curve then it just does the math in the background. Even better if there was a way to link it to slicer profiles or something but that's probably getting complicated unless the slicers worked to integrate something there too IDK.

Anyway I love the concept and when it works it is amazing but it feels about like 50% science and 50% pulling the lever on a slot machine. Or maybe I'm just doing it totally wrong.

@o_lampe

Thanks for the input.

There wouldn't be any easy way to use a Duet board controlled by LinuxCNC or something like that would there?

@T3P3Tony
Yes you are talking about constant surface speed and that would be critical to a properly functioning turning setup. But it's not what I was talking about.
I guess what I was reading about must be what @dc42 is talking about.

@oliof
@dc42

It's my understanding that RRF doesn't do constant state or infinite rotation type operations, or something related to the spindle . As I remember from what I have read that seems to be the big hangup but I feel like I read of other things that sounded less than ideal as well.

Also to clarify, this would be using a stepper or servo motor on the spindle with a toothed belt or similar so spindle angle is fixed to the motor to be able to do threading and operations like that, and hopefully eventually fifth axis machining. So it wouldn't just be "set spindle voltage or PWM to approximate RPM" but would be operations that precisely tie the spindle moves to other axis moves.
Of course now I am trying to find the threads or places I found this being discussed and can't find it.

Ah here is one. So I guess the issue is less regarding defined rotation operations but theoretically infinite or continuous rotation operations.

I have been toying with the idea of making a lathe with a 3D printed toolchanger and ultimately I would love to make it 4 or 5 axis but that would be a long ways down the road.
Reading the posts here it sound like Duet might just not be acceptable but I am running Duet boards on my printers and I would love to stay as much as possible in this ecosystem. I would also love to build it around a board like the 6HC and avoid buying controllers, drives, etc, If I'm going to use a single board I would love for it to be Duet.

Is there any way to get away from RRF if it won't be acceptable for this?
I am most familiar with using linuxcnc for non 3D printer stuff so that would definitely be my prefered route if going outside the Duet web interface.
So for example would there be any way to set up a 6HC board to be run by linuxcnc?
Or other similar alternatives that would work better and overcome the mentioned shortcomings of RRF?

@deckingman
I have different 592 and 572 settings for various materials. Particularly different TPU materials and profiles. So I have those profiles saved in my slicer custom Gcode.

Also the way these call out D instead of E makes it a little confusing as well. With commands like 567 that call out E it seems to accept the value:value format for multiple extruders but I haven't seen anything that shows how to address ones that call out D0, D1, etc.

It would make a lot more sense if it all used E value:value

I have an IDEX machine and I want to know the right way to set pressure advance and nonlinear extrusion for all configurations.

I have it set up so that tool 1 is the left print head, tool 2 the right print head, and tool 3 set up as duplicate where both heads print identically with a fixed offset from each other.

I am a little confused how the gcode should look for this.
Tool 1 prints as drive 0 and tool 2 as drive 1. Then tool 3 prints with drive 0 and 1.

So if I am making adjustments in the console how should that look.
Like let's say I am printing with tool 1 using drive 0 I assume it's just something like this?
M592 D0 A-0.125378 B0.197786
M572 D0 S.2
Then for tool 2 it would just change to D1 correct?

Then for tool 3 where it is using drive/extruder/heater 0 and 1 is where I'm really confused.
Like would I do
M592 D0 A-0.125378 B0.197786
M592 D1 A-0.125378 B0.197786
Or
M592 D0 A-0.125378 B0.197786:M592 D0 A-0.125378 B0.197786
Or something else?

Then in Prusa Slicer in my filament custom gcode section how would I do the gcode to apply the proper nonlinear extrusion and pressure advance for all configurations?
To clarify, if I am using a given filament profile and select "extruder 1" in filament settings and all extruders to 1 in print settings it applies the correct nonlinear extrusion to drive 1, and same with extruder 2, but then if I select "extruder 3" in Prusa Slicer having it apply nonlinear extrusion and pressure advance to drive 0 and 1.
At least at the moment I don't think I would ever need to run a different parameter for drive 1 for tool 1 or tool 3. If I can specify in one place that D0 gets the same nonlinear extrusion and pressure advance whether tool 1 or tool 3 is selected that should be fine.

Thanks

@zapta

It's kind of mind boggling to me that people keep talking about trying to prove the concept.
Like am I really the only one who changes temp manually during printing to maximize performance? I mean not on a regular basis but in special situations.
Like if you have a big model that you want to print fast you can set it to print nice and hot and fast.
Then if there are a couple detail areas that are getting too hot you just turn the temp and if needed feed down in those areas.

It works really well. It would just be nice to be able to automate it and if it was then it would add a lot of capability to printing. It's weird to me this concept seems so foreign or unheard of.