Rigidbot CoreXY v1

Update Dec 2019: If considering this conversion, wait for the v2 which uses premium Gates idlers, pulleys and belt resulting in better dimensional accuracy.

Update Mar 2020: The v2 has been published and can also be used with stock steel rods.

A stock Rigidbot is a sturdy machine overall and can produce quite nice prints. My goal of this conversion was to have a stationary bed, and be able to enclose the printer while relocating motors and electronics outside. End goal is to heat up enclosure up to 70C for best ABS part strength.

This conversion is inspired by Hypercube and HEVO 3d printers. Rigidbot has most necessary components for XY conversion. The bed needs some improvising.

There will be two versions of this conversion:

• v1 - use as many stock components as possible (steel X rods and linear bearings)
• v2 - upgrade to lighter X carriage (carbon rods and bushings)

Be sure to watch the videos by Tech2C. It will help understand the functionality and limitations of corexy system, and also aid in tuning the printer for best performance. CoreXY is a bit fiddly in comparison, but capable of high acceleration and jerk and hence high print speed.

Design

The parts were designed in Rhino 3d. The CAD file is provided.

Bed

I used 1/4" MDF for bed base. Other options are 2020 extrusion like Hypercube, or even a slotted angle. Eventually, I will migrate to using a 3mm aluminum plate. It is difficult to drill accurate holes in MDF using hand tools. The stl files for MDF base are included.

Additional Material needed

• Two identical stepper motors (buy another Y stepper)
• 4 - LM8UU linear bearings for Z rods
• 6 - GT2 20T toothed idlers with 3mm ID
• 4 - GT2 20T smooth idlers with 3mm ID
• 1 - 5m GT2 belt
• E3D hotend
• Bowden tube with couplers
• 40mm blower fan
• M3 assorted screw set, in size 6mm to 35mm
• M4 screws 15mm and 10mm

Assembly instructions

Print Rigidbot nut retainers and Allen Key screwdriver for 2 or 2.5mm key depending on your screws.

Flip the frame upside down. Swap the Z rod holders, so that Z motors mount to the bottom rail. Use nut retainers where the frame threads are stripped.

I removed front middle rod so as to have unobstructed view of print area.

My parts were printed in ABS, which holds screws quite well. If using PETG, all screw holes will have to be tapped for M3.

To install linear bearings into plastic parts

• Slide the bearings on rod
• Heat up the plastic part with heat gun for 5-10 seconds (do not melt)
• Slide in bearings from both sides
• If binding, remove and try again.

Similarly for X carriage, install lower bearing after installing top bearing with both X rods clamped in the XY joiners. The carriages should slide freely on the rods.

For Y axis, slide bearings on rods and clamp rods. Install whole X assembly on the bearings and tighten while ensuring the assembly is perfectly perpendicular to Y rods. (slide assembly all the way back so that linear bearings touch the stepper assembly).

In the corexy, belts should be same length and tension. After equal tension on top and bottom belt, slide X assembly all the way back to ensure it is still perpendicular to Y rods.

Install Z stepper after screwing lead screw nut to MDF. Hand turn to ensure that Z lead screws turn freely throughout the whole range.

The X limit switch was wired in the now empty extruder JST-XH4 connector on the PCB. Two additional pins are available for Z bed-leveling probe.

The stepper assembly and Z limit switch can be installed with a cable tie or drilled/tapped and mounted with screws.