Sunday, 20 November 2011
A better dropout fixture
Up until now my jig has made use of a piece of threaded 10mm rod as the "axle" supporting the dropouts. This has been okay, but has been the most annoying thing about the jig.
So I figured I'd improve it. I noticed Alex Meade was selling dummy axles at quite reasonable prices, so figured I'd buy a couple and adapt them to my jig.
First thing I did was to turn up a sleeve to slide over the dummy axle. This is simply a piece of brass tube 50mm long, turned 19.05mm on the inside and 25mm on the outside. I made sure it was a nice accurate slip fit over Alex's axle. I used brass because it doesn't rust, is easy to work with, and is easy to soft solder.
Then I drilled and tapped a hole for an M6 grubscrew in the middle. Now the dummy axle can be held accurately in my brass tube.
I made a pair of flange pieces with 25mm holes in the middle, and 9mm holes to suit my 8020 extrusion. I used 3mm copper sheet because there was some in the scrap bin. Brass would have been fine here as well.
Then I jigged one flange piece on the axle, so it was accurately perpendicular, and soft soldered the two together. This is much like brazing, except that you use lead/tin filler and soft-solder flux. The solder melts at 180 degrees, so the pieces don't distort. Be careful to orient the tube on the flange to ensure the grub screw hole is accessible once it's all assembled.
Finally I bored a 26mm hole through the 8020 extrusion where the original 10mm hole was, and slipped the tube through. I then put the other flange on the other side of the extrusion to provide a bit more support.
If you have a thumping big bit of brass to hand, you could turn flange and tube out of one piece. I didn't, so made it out of what was kicking around.