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Improving the CoreXY mechanism on my G&C printer

Posted by David J 
Improving the CoreXY mechanism on my G&C printer
July 25, 2020 10:52AM
I have a G&C CoreXY printer (Thingiverse) that is working acceptably well, apart from a small number of niggles. If I pay attention to slicing details I can produce a decent print in PLA, PLA+ and ABS. The frame is quite solid, and I am content with the bed and the Z mechanism for the time being. The biggest hurdle is that its CoreXY mechanism is a complete PITA to maintain. I have just had to do some maintenance to the belts and bearings that took me the best part of a day to complete, including the partial disassembly of the frame (the guide rods and belts are within the frame). A lot has to be removed to do any sort of maintenance, which means that all calibration is right out the window when the job is completed. It's also a PITA to get the belt tension correct (something I've posted about recently!).

The printer is now working again, but I am planning a near-future upgrade to a CoreXY mechanism that sits on a plate mounted on top of the frame. Mark Rehort's web page (Link) shows what I'm considering, preferably using linear guides. Here is the sort of thing I'm looking at:

The designer of the G&C CoreXY printer has designed an all-metal version (Thingiverse) but I have some reservations about it - getting guides that match the DXF design being one of them.

I have various questions, including:
  • What length of rail should I use to cover a bed of 200mm x 200mm? (300mm?)
  • What width of rail should I use? The easiest to source come in 9mm, 12mm or 15mm - I guess 15mm is best, but it's also the most expensive!
  • If I draw up a DXF file, is water jet cutting the best option for something like 5mm aluminium plate? Is it accurate enough, or should I plan for small-diameter holes and drill out to the target size?

My aim will be to create a CoreXY mechanism off the printer that can be mounted when I'm sure that it's working correctly, with minimum disruption.

All helpful comments and advice gratefully received...

Re: Improving the CoreXY mechanism on my G&C printer
July 25, 2020 12:47PM
I suggest that you start the design with the extruder carriage. Its size and the size of the bed will determine how long the linear guides need to be. If the extruder carriage is 100 mm square, and you want the X and Y addressable space to be 200x200, you'll need rails that are at least 300 mm long. If you buy rails that are "too long" you can always cut them down to size with a cut-off wheel on a grinder.

The size of the rails doesn't really matter because loads that a 3D printer applies to them is minimal. What does matter is the length of the rails and length and number of bearing blocks that come with the rails.

Don't buy crappy HiWin knockoffs. Get quality rails. If you shop carefully, you can often find new-old-stock rails made by Japanese and German makers for little more than the cost of HiWin knockoffs. Search ebay for brands like IKO, THK, NSK and Nippon Bearing. Use advanced search to block the HiWin knockoffs by entering " -MGN -MGH". Real HiWin rails are good, but there are so many knockoffs you'll never know if you're getting the real thing unless you pay full price and buy directly from HiWin.

Here's one: [www.ebay.com]

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Improving the CoreXY mechanism on my G&C printer
July 25, 2020 12:53PM
Thanks for that good info - gives me a few clues. Your links are good, except buying stuff from the USA means that I pay almost as much for shipping as for the items themselves! (I'm in the UK). That's supposing that the supplier will even ship to the UK.

I can try those searches within Europe though, to see what's around.

I've found the UK's HiWin distributor, but no prices showing on their website... eye rolling smiley

Edited 1 time(s). Last edit at 07/25/2020 12:56PM by David J.
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