Cherry Pi III

Author: AndyCart, published on 2014-05-27

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Summary

Update 19/08/2014
Added improved filament spool holder and disc and also a wiring grommet for where the cable bundle from the hot end and extruder stepper pass through the Z tower extrusion. The hole in the extrusion should be drilled 180mm from the base of the Z tower stepper mount. This allows full travel on the Z carriage with the 225mm rods (tube length) that I use with the 8mm drilled ball bearing and spring/string retention system. I normally drill two 5mm holes adjacent to each other and file the bridge between them out to form an oval. I’ve also added some detailed assembly images and a drawing that shows where the T nuts in the lower base are required.
Update 08/08/2014
I’ve changed the design of the delta rods. Instead of using magnets I am now using 8mm stainless ball bearings drilled with a 4mm diameter, 4mm deep hole. They are sold for some sort of use in photography. Readily available on ebay. The effector and rod carrier designs have been changed so that they have 8mm sockets to accept the 8mm balls. The whole thing is locked together with Spectra line (100lb) and springs. I used 85mm, fairly strong ones. A little silicone grease before assembly should stop any wear. I’ve uploaded the amended .stl files and some images of how I assembled it all. There is also a write up in my thread on the Reprap forum. It really does make a rock solid, backlash free connection between the effectors and the towers. There is absolutely no play at the nozzle and I’ve been able to up ‘quality’ print speeds considerably.
Anyone that has followed my previous designs has probably been expecting this 🙂 I’ve now got to a point where my Cherry Pi printer is at iteration three and I’m really happy with it. Version III incorporates mini V wheels for the carriages and a hot end Z probe for auto levelling and calibration. I use Rich Cattell’s Marlin fork which enables all that. I have managed to substantially reduce the number of parts required and, due to the v wheels leaving the rear face of the extrusion free, been able to mount te extruder to the Z tower which results in a relatively short Bowden tube to the extruder. I have renamed the plastic parts to incorporate details of the quantity required and the settings and materials I used to print mine (P=perimeter, B=bottom layers, T=top layers). I’ve also switched to using a centrifugal fan as I feel it gives greater airflow. It’s also easier to incorporate into the Z probe hot end design. The print areTa is around 190mm x 190mm x 250mm. I print at 100mm/s infill, 60mm/s outer perimeter, 70mm/s inner perimeter and 200mm/s travel. Acceleration is 3000 throughout and XY Jerk is 20. It would probably go higher but I’m happy at that and it doesn’t seem to stress the machine too much.
BOM
Plastic parts as required
3 x 2020 Bosch/Rexroth Extrusion @ 600mm
9 x 2020 Bosch/Rexroth Extrusion @ 250mm
6 x 16mm x 5mm x 4mm flanged bearings
9 x Open Builds Mini V Wheel Kits
12 x 10mm spherical neodymium magnets
6 x 6mm aluminium tube (with 5mm ID, I drilled mine to this) @ 225mm
12 x M5 8mm SHCS machined with a 10mm ball end mill to form cup for magnet (rod ends)
4M GT2 belt
3 x GT2 pulleys
4 x 13mm x 6mm x 7mm micro switches
4 x NEMA 17 stepper motors
1 x Arduino Mega 2560
1 x RAMPS 1.4
1 x RRD Smart LCD Display
4 x 4988 stepper drivers
12V 5A PSU
Mains lead
1 x 50mm brushless centrifugal fan
250mm diameter glass/mirror build plate
J Head (Bowden type)
0.5M 4mm OD 2mm ID PTFE tube
2 x 1/8 NPT 4mm pneumatic fittings
5 x 608 bearings (extruder and spool holder)
100mm M8 threaded rod (spool holder)
M8 60mm hobbed bolt (hobbed at 25mm)
3 x M8 nut
8 x M8 washers
2 x M3 50mm SHCS (extruder clamp)
2 x compression springs to suit above
2 x tension springs to suit effector/hot end hinge
8 x M3 nut
3 x M5 45mm SHCS (top idlers)
3 x M5 nut
6 x M5 washer
18 x M3 8mm SHCS (stepper fixing, effector)
2 x M3 30mm SHCS (effector/hot end hinge & fan mount)
3 x M3 25mm SHCS (carriage adjuster)
2 x M3 15mm SHCS (effector springs)
61 M5 T-Nuts (i use these http://www.thingiverse.com/thing:28788)
61 M5 8mm SHCS
Apologies if I missed anything but I think it’s mainly all there. Let me know.
Enjoy

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