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Frame design suggestions: Large CoreXY printer

Posted by CrazyBlackStone 
Frame design suggestions: Large CoreXY printer
July 13, 2020 03:18AM
I am a newbie when it comes to designing 3D printers, so I'd like to hear some suggestions from the experienced.

I started a project on designing and building a big 500x500 build area CoreXY 3D printer with the intent of mostly building it for myself. But I will work on improvements and fixes along the way and in the end publish it on Thingiverse. So having a design that everyone can build is definitely a part of what I'm aiming for.

The printer has a 720x740mm footprint, and it uses 2040 extrusions for the most part. Most the corners and joints will be mounted using blind joints and then braced with both corner brackets and plates for the maximum rigidity in those joints, though it's not shown in the pictures.
The goal is to have a printer that is capable of both printing big parts using big nozzles and small parts using small nozzles (with quick-change x-carriage) at a decent speed (100mm/s). Ringing is definitely something I want to minimize with a printer this big, so having a rigid frame and wide belts is important.

I would like to hear some thoughts on the design of the frame. Do I need to upgrade to 4040 extrusions or is this current design going to be rigid enough? What improvements can be made to make the frame more rigid?
I have already designed most of the basic parts required for the printer to function, so I'd prefer to keep the current frame profile if possible, and adding reinforcements may be better than redesigning all the parts touching the extrusions.

(the pictures attached have the frame isolated, but the X and Z gantry extrusions are also included)


PS: the four 2020 extrusions I put at the bottom are partly for mounting electronics, but It'd be interesting to hear if they would stop any shearing in the frame.

Edited 2 time(s). Last edit at 07/13/2020 03:24AM by CrazyBlackStone.
open | download - corner.PNG (199.7 KB)
open | download - front.PNG (79.4 KB)
open | download - view.PNG (117.4 KB)
Re: Frame design suggestions: Large CoreXY printer
July 13, 2020 07:40AM
Take out the third linear guide in the Z axis. It is not necessary and will make it extremely difficult to align with the other two- linear guides are very intolerant of misalignment. Use three screws to lift the bed, with two of them close to the linear guides, and drive them all with a single motor. If the machine is built solidly, the bed will stay level and won't require leveling adjustment after initial setup. Put the bed on a kinematic mount to allow for expansion when heated. I know, no one wants to watch a youtube video of a printer with a bed that stays level- they want to see motors spinning and the bed magically righting itself. Are you building a printer to print with or is this going to be the start of your professional youtube channel? Why does the bed get out of level and require releveling so often that it needs motors and sensors to make it usable?

Adding side panels will increase the rigidity of the frame. While you're at it, just enclose the whole thing. 3D printers produce a lot of little bits of plastic that tend to land on everything around the machine. A full enclosure will tend to keep them confined, allow you to do things like add air filters to suck up particles and VOCs, etc., and will make the whole thing much more rigid.

A lot of commercial and amateur corexy printers have electronics in the bottom of the printer. Have you considered that a large printer is heavy and that if the electronics isn't working right and the bed is at the bottom, it will be difficult to access the electronics? You'll have to get the bed up, out of the way in order to get to the electronics- how will you do that?. The weight and size of the machine mean that it will probably sit on the floor. That means you'll be on your hands and knees to service it. Most of the wiring has to connect to the XY stage at the top of the printer. You can keep most of the cables much shorter and allow easier access by putting electronics at the top of the machine.

Thingiverse is full of corexy printer designs, some that work and many that are poorly designed/built. What will be different about your printer that makes it worth creating yet another Thingiverse design? What will your printer do that the others don't? I suggest that you focus on making the machine perform the way you want instead of focusing in the Thingiverse release idea. If you're thinking about Thingiverse from the start you're going to compromise component choices to cheap, readily available junk that is usually poor performance because the Thingiverse crowd (and 3D printing crowd, in general) cares mostly about cheapness. Don't worry about accounting for every last nut and bolt to make a BOM that any dope with a web browser can order. Anyone trying to build a printer themselves should be able to make component substitutions and design changes as needed and recognize when a nut and bolt is needed even when it isn't in the CAD model or on the BOM. If they can't, they should buy a kit, or maybe get into fishing instead of 3D printing.

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
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