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Kossel Mini spring-string effector and carriage
A backlash-free effector and carriage design for a (Kossel Mini) Delta printer3D printer parts and enhancements
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I liked AndyCart's spring-string design for his Cherry Pi design a lot so I adapted it for my enlarged Kossel Mini.
I tried magnet based designs before but didn't like the failure mode where large accelerations or blocking of the hotend causes the magnet bond to break, leaving the hotend limping around in a puddle of molten plastic for as long as the print remains.
There are provisions for using the hotend as Z-probe, a 50mm radial fan and a 70mm LED ring.
An E3Dv6 fits just about perfect.
I modified the switch actuator's height such that ~0.4mm lift of the switch end of the hotend mount trips the switch. This way the hotend doesn't have to rotate and lift too much, dragging its tip across the build plate.
The carriages use a MGN-12H interface and the GT2 belts are self locking.
For the springs I used the ones from my desk-lamp together with 100lbs Spectra line. Now my desk lamp falls down :-/
The springs apply about 14N of pull which although an arbitrary number seems to work OK. The springs for the Z=probe I had laying around, I don't think they are very critical.
For the arms I glued the 10mm hardened steel ball bearings to the ball bearing adapters first using slow curing epoxy. After that I glued the assemblies on the 8mm carbon rods. So far this has worked fine: the load on the ball bearings is mostly compression anyway so the glue isn't stressed too much.
I use a jig for this that consists of two parallel beams set at the distance you want for the arms + one ball bearing diameter. This way I get them within ~30 micron.
For the supplied configuration;
DELTA_EFFECTOR_OFFSET = 35.15mm
DELTA_CARRIAGE_OFFSET = 38.7mm
- at least 1.2mm perimiter, <=0.1mm layer height and >=60% infill for effector and carriages
- at least 0.7mm perimeter, <=0.2mm layer height and >=20% infill for the rest
Parametric design files are included so you can adjust for your components
Materials and methods
- 12 pcs 10mm hardened steel ball bearings
- 8mm carbon rod, as needed
- 9pcs M3x10
- 3pcs M3x16
- 1pcs M3x36
- 1pcs M3 nut
- 1pcs M3 washer
- 4pcs M2.5x12
- 2pcs self tapping plastic screws
- 3 springs 14N
- 100lbs Spectra braided fishing line, as needed
- 2 springs for Z probe
- Z probe switch
- 50mm radial fan (optional)
- 70mm LED ring (optional)
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