Summary

The challenge was to be able to print the spokes of a bike wheel on Mendel (0.5 nozzle) using ABS. I used SCAD to generate the components of the wheel. Combined each component manually, and this was my result.

A video of the printing process is here: http://www.youtube.com/watch?v=j69QjNhJAVU

Instructions

To print the bike wheel spokes I have manually edited the g-code so this is not for the faint hearted.

The scad script used to generate the wheel has been uploaded if anyone else would like to give it a try. I have also uploaded the g-code generated for my machine, but do not expect this will work on another machine, but it can be used as a reference.

The script generates a number of objects that need to be edited together. The process I used (there are probably better ways) is as follows.

Use the script to generate stl files for; the first side hub and half the rim, 4 sets of spokes, the centre hub, the outer hub, lastly the second half of the rim. When generating each of the 4 spoke stlâ€™s set the parameter c=0 so the spokes are printed flat, so they will slice in one layer. They should be small enough so the only slice to one extrusion width and height.
Use your g-code generator to create the g-code for each stl file. I am using ReplicatorG and skeinforge40. Make sure all the stlâ€™s are sliced with the same settings. With all but the first hub and rim, the objects were NOT put on the platform, in effect sliced in mid-air, this meant the layer heights did not have to be changed when the files are merged.
Copy to a new file the g-code file for the first (hub and rim) and open in a text editor. Locate the point where the print object finished and add some comments to locate it easily.
In each of the other stl files locate the code that prints the object, (that is get rid of the initialize, raft and any support, and the ending) and copy each in turn to the new file, adding comments so you can identify the joins. The order should be;
Hub and rim
Spoke1
Spoke2
Centre hub
Spoke3
Spoke4
Outer hub
Half rim
At each of the joins, correct the E values. In my case the retraction values had to be corrected into the next bit of added code.
Now for the spokes. I used skeinlayer to view the g-code to locate the hub end of each spoke and make the Z value equal to the last hub layer plus one layer thickness. Modify the rim end Z values to be the last rim layer plus one layer. For spoke3 and spoke4 centres the Z values will be the last layer of the centre hub plus 1.
For each spoke the feed rate has to be reduced to something your printer can handle. Trial and error showed for me the F250 value worked most of the time.
Lastly I had to add some gcode to the second rim print as it tried to move the head across the middle taking out the spokes and the centre hub. The rim is lower than the centre. The added g-code moved the head around the outside of the print.

I think that is all, but let me know if I appear to have missed anything.

Spoked Bike Wheel