I'm currently working on a project that needs a lot of Technic Wedge Belt Wheels (4185) that can freely spin.  I realize that modifying Lego parts is a sin.  But other people such as TJ Avery have done this modification.  So i thought that it would be ok as long as i did the modification the correct way.  The following pictures show the end result, the intended use, and the process used to do the modification.

pictures IMG_4283 - IMG_4298 show the process used to mill out the centers.  a milling machine was used so that the centers would be as accurate as possible.  How lucky am i to have access to a milling machine at work!  since i had a lot of pieces to mill i needed to make a jig that would allow me to swap the pieces rather quickly without re-centering every piece.  i used some sacrificial technic bricks and 2 technic pin long with friction.  the 4185 does not set complete flat because the center is slightly taller than the outer edge.  so the area between the 2 pins on the technic brick was shaved down a little to allow for the center of the 4185 to set slightly recessed. (i know another sin)  A 3/16ths 4 fluted hardened steel milling machine bit was used.  the centers are just right for an axle to rotate snuggly.  i'm hopping that after the holes are debured that they will spin more freely.  the centers are milled using 4 shallow plunges rather that a single get it all in one shot plunge.  this was done to allow the refuse to clear form the bit and so that the plastic would not over heat and possibly warp.  (i wanted round holes not oval)  
pictures IMG_4271 - IMG_4274 show the final product.  You will notice that they have not been debured yet.  i will probably use an exacto knife to do this.

pictures IMG_4275 - IMG_4275 show my intended use.  the hook design is shamelessly copied form TJ.  I just don't think that i could come up with a better and stronger design.  Hope you don't mind TJ?


i'm very please with the results.  was it over kill?  probably.  why did i not use a drill press or a hand drill?  hey, i just wanted to learn how to use a milling machine, ok.


Bob Kojima
bob@fial.com

http://www.bong69.com   
http://www.partscatalog.da.ru