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New CoreXY 3D Printer

Posted by Cyclonit 
New CoreXY 3D Printer
October 09, 2015 09:16AM

I'm working on my own core xy printer. My goal is to have a fairly large printing area of 40x40x40 cm without wasting lots of space. The current outer dimensions are 62x54x60 cm, which I am fairly happy about. I'll use a bowden extruder (not yet implemented), which will add some more stuff to the back of the printer (plus spool holder) and I'll have the bowden tube sticking out on the top. Unless I've made some grave mistakes, the final machine will end up filling an area of ~62x60x80 cm, the height not being a problem. Let me point out, that the size isn't as much of an actual restraint, but something which I like to keep in mind. I prefer neat and tidy things and don't what the printer to end up being a huge hunk of wasted space.

I have more or less finished designing most printed parts. Some screw dimensions may change to reduce the number of differently sized screws and I'm missing mounts for the driver, computer, LCD and hotend. The remaining parts should be done until this upcoming Sunday, if nothing major gets in the way.

What I'd like to see, is to have some guys take a look at my designs and point out mistakes I may have made. This is my very first attempt at properly designing something consisting of more than a few parts. There are some spots in particular, which I'd like you to examine.

1. belt clearance
There are several areas where the belts have clearance of ~3mm. On the stretches close to the XY motors, where they run parallel to themselves, beneath the left Z-axis motor assembly and whenever they run across the SH12 shaft holders holding the Z-axis steel rods. I am assuming that, since the belts are supposed to be under tension, they're not going to move in any way that could possibly have them make contact with any other part. Is this assumption correct or should I try to increase the available space?

2. motor mounts
The motors are sitting on top of very simple mounting plates. They are fixed to the frame using 2 14mm M4 screws. Does this suffice or should I add additional strengthening? Adding additional mounting screws wouldn't involve any rescaling, but it'd mess up the current simplicity. Especially the Z-axis mounts, carrying part of the Z-axis' weight are of interest.

3. bearing assemblies
All bearing assemblies are designed to use a center 30mm M3 screw. This screw will be shrouded with a 1mm thick cylinder, giving it the required OD of 5mm to hold the bearings. Switching to use M5 screws would result in resizing lots of mounting plates, which would in turn end up having to move lots of parts around to make room for the larger screws.

4. T-Matic connectors
I would like to use T-Matic connectors in the frame. Typical corner braces require additional space, whilst T-Matic connectors reside within the aluminum extrusions' grooves, therefor provoding a cleaner frame. The forces acting on a 3D printer's frame aren't particularly great, but I do not have the expertise to figure out whether the added strength of using corner braces is required.

5. captured nuts
As you may notice I'm using loads of captured nuts and many of them do not yet have anything attached to them. Some of them will be used to add end-stops, lighting etc. Does using this many of them have any significant impact on the parts' structural integrity? All of them will be attached using glue/epoxy.

I am using Blender for my design. Therefor I do not have any "proper cad" files, but I hope that you'll take a look regardless. There are numerous groups defined to select individual components (i.e. the individual motor assemblies).

Lastly, some pictures:

Blend file: [forums.reprap.org]

Thank you very much for your time smiling smiley

Edited 1 time(s). Last edit at 10/09/2015 10:41AM by Cyclonit.
Re: New CoreXY 3D Printer
October 09, 2015 10:03AM

Overall i like you design, is simple and very clean.
I have some suggestions and questions to make.

1) one of the Z motor is very close of the belts, this will not be a problem?

2) The printer will have an generous dimension, If you will use 2020 extrution i thing you must add more bars to increase the overall rigidity of the structure or replace the 2020 for 20x40 bars.

3) You really need 2 Z motores on the top? You will have lots of cables on top of the printer. I already see good solutions using only 1 motor at the bottom and an closed belt to move the 2 z screws.

4) where you will put the power supply, board, lcd?

5) the x and y motor are in mounting plate. Can you use an mounting plate in the L format and this way remove the need of using the bearing to redirect the belt.
Re: New CoreXY 3D Printer
October 09, 2015 10:41AM
1) I don't think so, but I am not 100% certain. The clearance is ~3mm. If I were to replace the aluminum SH12 rod holders and use printed holders for the Z-rods instead, I'd be able to increase the clearance to ~1cm, but this would require additional printing and I've got the SH12s already.

3) Having the motors up top saves space on the bottom. However, this arrangement prohibits me from using a belt to drive both Z-screws, because it would collide with the hotend assembly. I don't think the additional cables will be a problem and this adds some more regidity to the Z-axis by having greater torque in general.

4) Those will be located at the back.

5) I placed the motors on individual plates to allow for easy belt tensioning by moving them in-/outwards.

I also added the .blend file to the initial post.
Re: New CoreXY 3D Printer
October 09, 2015 10:56AM
"I placed the motors on individual plates to allow for easy belt tensioning by moving them in-/outwards. "
This way you can only tension the belt by hand force, it will work in general but it will be difficult to obtain an good and equal tension in both belts.
In my printer the tension of each belt is made using 4 M3 screw that secure the belt in the carriage. Why not use the L mounting plate i have suggest and make the tension in the carriage using an similar screws mechanism?

example of an L mounting plate:
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