Polar 3D printer design



  • Hey all!

    For purely entertainment and learning purposes, I'm having a go at designing and making a Polar style 3D printer.

    Here's the design so far - https://a360.co/2KovobS.

    Are there any gotchas/pitfalls to watch out for when running a polar with a Duet 2?

    Also, I'd like some general opinions on the design, and advice if available.

    The horizontal axis uses an Openbuilds mini V Gantry plate, and both horizontal and vertical use V-slot wheels. My aim it to try to use stuff I already have, and while I have a few spare MGN12 rails, they're all 400mm, and I've not got the tools to cut them (my lowly hacksaw just slides around on the hardened steel 😛 ). So as I've got a few spare Vslot wheels, I'm going with them.

    I'm not 100% sure on the Horizontal/Vertical coupler part - not sure if I should split it up into 3 parts: another mini V gantry plate for coupling/movement, a printed part for horiz movement, and another printed part for vertical to hold the Acme Nut.

    The main base part seems "fine", but there's an itch that's bugging me, telling me it could be better, but not sure how.

    No design for the extruder yet, but I'll likely keep it as a very simple bowden E3D V6 + either BLTouch, or a DC42 IR sensor that screws straight into the gantry plate.



  • What is your strategy for getting the nozzle at least 0.2mm from the dead center of your bed (or else all your prints will have a hole in the middle of it)? Using shims/springs/screws/slots on your extruder mount is an OK solution, definitely don't simply reprint the entire bottom of your printer simply for calibrating that position.

    There's noooo way those two angle braces are enough to keep your Z axis perfectly vertical. Add some sort of horizontal stabilizers. Mount the Z stepper up on top if you have to (I know this is counter intuitive) I would personally want the bottom of the printer to look like a "H" or at least a "T" and not a "I". Mounting the stepper on top would ruin your center of gravity but it gives you less headaches when arranging parts.

    (you probably want to bolt this whole thing down onto a slab of wood anyways, right?)

    Doing a T shape or a H shape on the bottom would probably make calibrating the centerline much easier, you can just slide along the new beam a bit.

    I am also not familiar at all with autoleveling for polar printers...

    I'm not sure how you are making that bottom lazy susan bearing, or where you are buying it from, but it looks like it's meant for radial loads and not thrust loads. I would use something that has a tapered race at least, which is a easier geometry to machine anyways (as opposed to an internal groove). I get that the load is probably not very high but it just looks weird to me to see balls like that.

    Or forget about a lazy susan bearing and put three ordinary cheap skateboard bearings near the outer rim of the build plate, if your plate is stiff enough. I see you have bars on the bottom that make this not practical though.



  • frank26080115 9 Apr 2019, 18:32

    What is your strategy for getting the nozzle at least 0.2mm from the dead center of your bed (or else all your prints will have a hole in the middle of it)? Using shims/springs/screws/slots on your extruder mount is an OK solution, definitely don't simply reprint the entire bottom of your printer simply for calibrating that position.

    Probably Shims for getting dead centre.

    There's noooo way those two angle braces are enough to keep your Z axis perfectly vertical. Add some sort of horizontal stabilizers. Mount the Z stepper up on top if you have to (I know this is counter intuitive) I would personally want the bottom of the printer to look like a "H" or at least a "T" and not a "I". Mounting the stepper on top would ruin your center of gravity but it gives you less headaches when arranging parts.

    I guess if I go for a T shape, with an extra bit of 2020 laying flat and perpendicular to the main bottom extrusion, I can use a t joining plate at the back, with some angled brackets on top, and I'd only have to move the Z motor up 10 or so mm. May need to tweak the motor mount slightly too.

    I'm not sure how you are making that bottom lazy susan bearing, or where you are buying it from, but it looks like it's meant for radial loads and not thrust loads. I would use something that has a tapered race at least, which is a easier geometry to machine anyways (as opposed to an internal groove). I get that the load is probably not very high but it just looks weird to me to see balls like that.

    I have it left over from building a Ciclop 3D scanner, it's a 16014ZZ. So yeah, for radial loads, but I'm probably not even going to put a metal bed on it (definitely not heated), so there'll be minimal axial load, aside from any heavy handedness on my part. If you can recommend anything specific, I can take a look.

    I didn't however mention that I'm attempting to only use parts I already have, so I'll likely stick with that bearing, at least until I've got a physical, working proof of concept (which, knowing my track record, I may never reach).

    Or forget about a lazy susan bearing and put three ordinary cheap skateboard bearings near the outer rim of the build plate, if your plate is stiff enough. I see you have bars on the bottom that make this not practical though

    This is just a few hours work on a first draft design - so open to changes, even major to it. The bars are a 3 point bed attachment, to allow screws and springs at the end for some manual levelling - so that the bed itself would be attached at these points. So that would be trivial enough to redesign, and just have the bed run on rollers, with a centrally attached shaft. Would have to make the mounts for the bearings vertically adjustable somehow to allow for some levelling.

    With a 3 point system though, it'd only require 2 of those bearing to be adjustable, so less complex.


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