Pandora RepStrap
Release status: experimental
Description |
Large format 3D printer
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License |
public domain
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Pandora: ancient Gk. Bringer of "all gifts", creation of Maker god Hephaestus.
What it is, and what it is for
Pandora is a large format RepStrap with a build volume of approximately 450 x 850 x 900mm. It is built of aluminium V-slot extrusion, with CoreXY gantry geometry at the top face, and a bed that lowers away from the extruder on leadscrews.
Its purpose is to print body parts for velomobiles (streamlined bicycles) and perhaps other light but bulky structures.
Progressive build pictures
Top frame with gantry in place.
Top corner plate showing two idler wheels for the CoreXY belts.
Idler rollers on corner bracket, mounted on top frame.
Plate at end of gantry. Two rollers have eccentric spacers allowing fine adjustment.
Gantry plate with angle connector.
Nema23 motor plate for low belt.
Nema23 motor plate for high belt, mounted up on spacers.
Overall view of frame, with tension cables on three sides. The front is left open.
This corner plate is sold to help build square-section steel shelving. It just happens to be a perfect fit for 20mm square V-slot. There is even a little hole for the tension cable end!
Corner plate in place at top of frame. Note swaged stainless-steel cable end.
The bottle screw used to tension up the cables and hold the frame square. These parts are stainless-steel cables etc. used in balustrades.
Overall view of bed frame.
Bed sitting in frame. The leadscrews are not in place yet.
Wheel at corner of bed, engaged with the V-slot leg.
Another view of the corner of the bed frame. The notch will allow the bed to be easily lifted clear of the leadscrew.
Carriage plate, and brackets with D-shaped holes to terminate the belts.
Carriage with CoreXY belts strung up.
Carriage at corner showing belts and stepper motor.
Parts for the top bearing for the idle (non-driven) leadscrew.
Parts for the top bearing for the driven leadscrew.
Zaxis home.jpg
The bed is homed (LED on endstop)
Problems encountered
Homing such a large bed is problematic. Any missed steps on one motor will cause it to go out of level. Unfortunately the Rambo doesn't support independent leveling (where each side has its own endstop). I'm building a counterweight for both sides, which will ease some of the friction in the nut blocks. From here, the next step is to connect the Z motors in series rather than Rambo's default parallel (to get more current into them) and/or to replace them with Nema23's.
Pulley block for conterweight.