|
This is a scan of the broaching fixture I made to quarter my locomotive drive wheels. It's made of 1" thick aluminum with a steel broach bushing or guide. The crankpin hole is bored on location at exactly 45 degrees from the axle hole at the proper, straight line distance (1 1/2" for 3" stroke) from the axle hole. The trigonometry formula to use is: The full piston stroke divided by 2, multiplied by .70711". This give you the distance to move up and over to achieve the proper hole location for a given stroke. A pin that fits snuggly into the crankpin hole is then pressed in. The broach bushing is machined to size so it slipped into the axle hole in the wheel with no play. A slot to match the broach was then milled in the bushing and it was then pressed into the fixture at 90 degrees. (see photo above)To locate the broach bushing properly, a small slot was milled into the fixture body on the axle hole centerline and at 90 degrees, and a piece of rectangular steel stock was inserted (This slot is the same width as the broach bushing slot) The stock was wide enough to engage both the fixture and the bushing. This guided the bushing as it was pressed into the fixture, The fixture is placed on the wheel and the axle hole is broached in the arbor press.
This method is simpler than quartering the axles themselves, as the fixture automatically produces right and left hand wheels. Only the broaching fixture is needed as the axles are machine using a standard milling vise. The key slots on the axles are milled in line with each other in one machining operation which reduces the chance of error by eliminating a secondary machining operation on the axle. Both slots are machined without removing the axle from the vise. It also reduces quartering error by exactly matching the wheels on one side to each other. Even if the fixture holes aren't exactly at 45 degrees (they should be as close as possible), the wheelsets will not bind when the connecting rods are assembled. Here is a picture of the finished wheel. |
|
