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Originally Posted by Jay H 237
If you don't have a broach set it is possible to mill a keyway into the shaft. Not sure of the resources available to your team but I wanted to bring up that option.
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Actually, a keyway is usually milled/cut in a shaft and broached in a bore.
Now, for making a keyway in a bore without an arbor press. There is the possibility you can use something different for your press, like a mill or a drill press. Although I wouldn't recommend it. It could damage the machine. Another possibility would be to use a vise (such as a mill vise) that can open it's jaws wide enough to fit the gear and broach. Close the vise, and it presses the broach through. A precision vise can make an excellent press in a pinch.
For making a keyway in a bore without a broach, there is a way you can sort of "fudge" it. We've done this before and haven't had any real problems. What you can do, is set up the sprocket/gear on a mill so that it's face plane is parallel to the plane of the mill table. Using an edgefinder (and DRO) or a drill blank, locate the center of the gear and lock one of your mill axes in place. If you are using an 1/8" key, put a 1/8" endmill in a collet in the machine. Move the other mill axis such that the center of the endmill is directly above the point on the circumference of the bore. Take a plunge cut nice and easy straight down. (when I say easy I mean it. Touch the downfeed handle with something like the weight of a couple feathers. Those 1/8" tools are quite fragile) Now, move the axis of the mill table that is unlocked another 1/16" into the gear and take another plunge cut. You now have a 1/16" by 1/8" rectangle of material gone (just like a regular keyway) with the added "bonus" of a half circle on top. The key will fit just fine and be able to transmit torque reliably. However, over time it will want to move into that half circle area. So, fill the half cirle with something, anything, a toothpick, piece of paperclip, epoxy, whatever.
Alternatively, you could reduce the "rectangle" portion of this keyway and grind the key rounded somewhat. Or maybe get a 1/8" by 3/16" key, and grind it round one one side so it fits perfectly into your rectangle with half round on top keyway.
EDIT: If you use this method to make a keyway, make sure you are using a center cutting endmill.