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Printing onto an uneven printbed (e.g. inside a wells plate)

Posted by Tsu 
Printing onto an uneven printbed (e.g. inside a wells plate)
March 20, 2019 11:37AM
Hi dear RepRap ers,

I am currently modifying a printer to print soft material. Ideally, the printer would print inside a Petri dish or a wells plate placed on the build platform.
Is there any way to make sure the printhead does not crash into the given geometry (for example walls of the Petri dish)?

My first thought was to somehow load a model of my actual modified build platform with the geometry on top, into the slicer, so that the slicer calculates a machine path that avoids all obstacles. I couldn't find any such features in any slicer yet. I think it should be possible in theory though, as for example cura contains a feature to print multiple objects onto the same build plate, one after the other. In that case, and if the dimensions of the print head are put in correctly, the machine should not crash into geometries that were already built, right?

Any ideas on how to make it work? or on workarounds?

I have also considered reducing the print volume in software to the size of the plate, and add some custome start and end g code to make sure the head enters the volume from the top. I am not sure yet if that works and even if it wouldn t be my preferred solution.

Any help or ideas are welcome!!

Please let me know if you have troubles understanding my problem. I had some trouble describing it properly in english.

Thank you very much for taking the time for reading or even answering!

Re: Printing onto an uneven printbed (e.g. inside a wells plate)
March 20, 2019 11:51AM
I would guess that the second option is the most likely to work without a full custom slicer. Define the petri dish as a custom machine and use the start/end custom gcode to move the nozzle/pipette around and prevent crashing into the edges of the dish. I'd put the origin at the center of the petri dish and then make sure you center the petri dish on the printer's bed, preferrably with it's origin at the center, too.

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Printing onto an uneven printbed (e.g. inside a wells plate)
March 20, 2019 12:23PM
yes like you suggested i would tape you petri dish onto the bed and define a round print bed in you slicer that is 1-2cm smaller than the dish to avoid hotend crashes. you probably need to manually define you homing procedure on a cartesian machine or move you x/y endstops so that the head doesnt crash in to the dish walls when you home. although with a delta that would be easier.

the wells plate is probably a bit more complicated but you can model the plate and place your printable objects in a way that they fit the pattern of the plate. also an high z-hop could be used to jump over the walls of your plate. but id start with the petri dish smiling smiley
Re: Printing onto an uneven printbed (e.g. inside a wells plate)
March 20, 2019 01:08PM
1. If the printer is a delta, you could temporarily change the print radius setting to keep the nozzle within a defined radius - assuming that the firmware of your printer supports a movement radius limit.

2. If it's a Cartesian, then you can tell your slicer that it is a delta so that the slicer applies a circular bed limit. Then reconfigure your printer firmware if necessary so that X0 Y0 is the centre of the bed - assuming that you place the petri dish in the centre. [I set up all my printers this way, so that they can use the same GCode.]

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

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Printing onto an uneven printbed (e.g. inside a wells plate)
March 21, 2019 12:48PM
My first thought was the same as dc42, that is that a Delta has a circular limit anyway.

I would probably opt for "none of the above."

What is the actual result that you want? Putting something into a dish in a precision manner is all well and good, but you'll need to have that precisely aligned with your build platform. For a petri dish, these typically have flat bottoms anyway, why not put hte build culture on something that can be easily transplanted without contamination? A thin sheet of plastic, or your culture material on a plastic disc that will fit well into the petri dish? This presents far fewer technical challenges different from what we all deal with on a regular basis. While it's more extreme than we'd normally want to see it, mesh compensation with a fine enough grid could handle a curved or irregular surface. If you design your model well, and program things like homing routines well, there's no reason that you can't just print in a dish.

For example, set up your printer to always raise 20mm in Z before homing X and Y, then go back to the center to home Z, then your print head is at the center of the print bed/petri dish/wells plate. Engineer your model in CAD to conform to the bottom of the Wells plate, and slice it without supports. For the petri dish, those are (As I recall) flat on the bottom anyway, so nothing special needed there. You will need to accurately mark/place your stuff at print centre, but you'll need to do that no matter what solution you use.

It might be different if you want to take someone else's models and just print them without modifying them.

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