Best way to do extra tricks on tool change & retraction?
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I work with a lot of flexibles on IDEX printers, with two color models. Stringing keeps me up at night, but I had a vision of a way to solve my problems. I need to add a microstepper to actuate a lil steel wiper onto the nozzles at tool change and maybe during retractions as well.
I'm not sure where to start with this idea tho, can I add an axis for the aforementioned microstepper and some gcode to move that axis during firmware retraction? Or is there a simpler gcode command I could include to accomplish this without having to set up whole new axes about it?
Any ideas or pointers or suggested readings would be much appreciated!
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@curtisb1986 I think this is one for @Phaedrux - unless I'm mistaken, he posted a link to something that made any oozed plastic form a blob which was then knocked out of the way with some sort of mechanism.
Failing that, do you need a mechanical wiper? I've had great success using a passive arrangement consisting of a silicone strip against which the nozzle is wiped back and forth whilst travelling slowly from left to right.
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@curtisb1986 Perhaps some sort of micro servo (as used in model aircraft etc.), easy to control from RRF.
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@curtisb1986 Hi, research the "pebble wiper" as an active solution with an additional servo arm, and/or how Stratasys and Bambulab do it as passive solutions. Stratasys use a purge bucket with a silicone lip and brass brush, Bambu use a purge bucket and a short piece of PTFE tube that is flexibly mounted and that the nozzle brushes against after purging. With both solutions the "smart" is in the way the purging and brushing is being done. Both sell the brushes as consumables which points to the fact that there is wear on the brush and the nozzle.
For the parked nozzle it might make sense to have a little piece of spring steel sheet pushing against the nozzle orifice and keeping it shut which should all but eliminate material oozing out. It should still be purged when the tool is picked up since the material will degrade and change viscosity when it stays in the nozzle for even only a short time (some materials are more resistant to this than others, and moisture [see below] is a big factor in any case).
Aside from that, my recommendation from years of experience with multi material printing is to take great care of drying the material properly for printing, as this already helps a lot with unwanted ooze from the nozzle (however it will not eliminate it when the nozzle is parked, just for retractions etc.)
hope this helps,
Niklas -
As far as passive solutions, I have these steel wipers that sit at either end of the X axis:
https://www.tronxyonline.com/h-product-detail.html?goods_id=1977303
They are better than the original brass brush solution, and the inspiration for my active solution, but their stationary position can only help so much.
Ideally that steel sheet would quickly rotate into place simultaneously with a retraction and Z hop, effectively eliminating any stringing or oozing (in my idealized version anyway)
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The pebble wiper is very similar to what I'm thinking, but I don't have a tool changer per se, just two hot ends that home at either end of the X axis on an otherwise pretty traditional cartesian printer. The pebble wiper seems to be a solution to a different problem, but full of useful tricks to accomplish my end goal. You can all count on me being back with lots of questions haha
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@gloomyandy said in Best way to do extra tricks on tool change & retraction?:
@curtisb1986 Perhaps some sort of micro servo (as used in model aircraft etc.), easy to control from RRF.
Can you point me to the documentation for this? Is it handled as another axis as I suspected? It would be lovely if I could simply add it to the firmware retraction gcode instead of going through the additional hassle of creating axes, which I can only assume would require endstops and a stepper.
This feels like a bit of a n00b question, but does a microservo not require a driver in the same way a stepper does?
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@curtisb1986 JUst to be clear the servo I'm talking about is something like this: https://www.3dxr.co.uk//fixed-wing-c27/fixed-wing-accesories-c172/servos-c117/kst-ds215mg-v3-0-mini-servo-p5044/s5817
These are commonly used for model aircraft, but can easily be controlled using the M280 gcode command (you will need to also create a control pin using M950). See here: https://docs.duet3d.com/User_manual/Connecting_hardware/Motors_servos for details on how to control them.
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@deckingman Yes that was the Pebble Wiper.
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I wonder if using M571 to control a solenoid or servo to move a plate across the nozzle would be suitable?
Not sure if it would close during retraction or whether you could get a solenoid or servo that would work fast enough if it did. -
@OwenD said in Best way to do extra tricks on tool change & retraction?:
I wonder if using M571 to control a solenoid or servo to move a plate across the nozzle would be suitable?
Not sure if it would close during retraction or whether you could get a solenoid or servo that would work fast enough if it did.I think I could solve the speed problem with some creative thinking. The trick will probably be keeping whatever solution I come up with light enough, since it's traveling with the extruder.
I'm sure some combination of slicer settings and firmware retraction will give me a way to add the gcode I ultimately decide on. If nothing else I can probably make a post-processor of some kind, maybe a plugin in DWC.
My debate is how to implement the idea in my gcode. M280 seems the more flexible option and would be simple to tune in, with adjustments to the servo angle just requiring a change in gcode. M571 seems more straightforward, just by assuming the wiper/servo position covering the nozzle as home. When the extruder is running, make M571 actively move and hold the wiper away from the nozzle. It's more of a binary choice in the gcode and would probably have to be physically tuned, but bending a lil thin steel and iterating a few parts is easy enough.
