Dropouts
If you have a cheap derailleur that attaches to the axle, then all you need to do is machine two Item 33 dropouts. If however you have a screw in derailleur then you will need to construct Items 32 and 33.
The blanks must be perfectly square on the edge that is going to be welded to the drive train forks. Sharpening my chalk on the bench grinder, I marked the most important guide lines on the larger of the two blanks. Then I clamped them together at the square edge using my vice grip adjustable spanner.
After center punching the holes, start by drilling a 5mm pilot hole, then follow with the 10 mm axle hole and 8.5mm hole for the derailleur mount thread.
Now keeping the pieces clamped together use the cut off saw on the angle grinder to cut the quick release slots. To do this you need to place the work in a big vice. Hold the grinder firmly with both hands, keep your feet apart so you have good balance and apply gentle pressure. Make sure you keep the cut off saw square to the work and the center of the saw above the work so the blade doesn't bite. If its too low, it will bite and really kick, quite dangerously, so be careful and ware all the appropriate safty gear.
Once you have finished the quick release slot, you can machine the remaining bits individually.
Here are the finished dropouts. They are actually easier to make than they look. By clamping them together along the square edge and machining them as a group you end up with perfectly symmetric axle holes and quick release slots, which makes attaching them to the forks a whole lot easier.
I didn't get the M10 x 1mm tap until after I had already mounted the dropouts onto the front forks. Nevertheless, there was plenty of room to cut the thread.
Here is the finished dropout with the screw in derailleur mounted on it.
Copyright © 2007 Henry Thomas
