We have to replace a 6" diameter x 1.5" wide cast iron gear that has two broken teeth. It's in the middle of a 4' long 1.25" dia. shaft. The original gear was pinned to the shaft with a .5" taper pin through a boss on the gear, but the pin bore was drilled and reamed by hand at the factory and it's not centered. A mechanic wants to try to hit the tapered hole in the shaft and I don't think that will ever work. If anything, the new pin should go 90 degrees from the original.
My idea is to turn down the boss from 2.75" to 2.25" and saw-cut across the boss in two places (+) and clamp the gear on the shaft with a split collar on the bisected boss. I think it'll hold almost as good as the pin.
put the shaft in a Bridgeport or other vertical and hold the thing with a steady rest on each end. Line up the hole with the drill and then slide the shaft to where you want to drill the hole... then drill it and then ream it for the pin... Make sure you index mark the gear to the shaft because it will only go on one way, Also make sure you ream the hole the same way the old taper goes in the shaft
It may hold, but you're taking a chance putting a highly-loaded chunk of cast iron under stress while it's simultaneously under another load -- the shear load that will appear between the inner diameter of the gear and the split collar.
The tapered pin was there for a reason.
Why not get a steel gear to replace it? That would solve your problem; the clamp should work fine.
The shaft has 10 things on it, mostly on the left side. To remove the gear from the right only involves 3 things. To remove the shaft and get everything timed again is a major undertaking. But, you're idea is valid and would work.
another way would be to line up on the hole on the old gear mounted on a spare shaft like in my first post, drill the shaft, remove the gear and put the new gear on the shaft and drill. Ream for the pin after the gear is in the new shaft.
This is not so difficult, but you must never drill another hole in the shaft....it will certainly fail. You can either remove the shaft and place it in a Bridgeport or use a Mag drill as has been suggested, but centering the hole is essential. You cannot center the hole with a drill, as it is tapered. You must center the hole with a tapered reamer chucked in the Bridgeport. Once centered remove the reamer, chuck the minimum diameter drill, then slide the new gear in place over the shaft hole and drill. Then ream the shaft and gear together to size. Replacement pins come in extended lengths, you may need one, as the new reaming operation will cause the pin to seat deeper in the assembly.
Now, I have done this with a hand drill as well, but you have to be very careful. To do this, drill the large diameter hole on the new gear to the minimum size on only one side of the bore. Place the gear over the hole in the shaft. Place the minimum size drill through the hole in the gear and shaft together. Balance the center as good as you can and drill the other side of the gear in place. Clean well and ream everything together and hope you have a taper pin the fits at right depth.. Steve
broken teeth. It's in the middle of a 4' long 1.25"
length of 1.25" bar clamped to V block high enough for gear to slide on, sticking out far enough for pin holes in boss to be clear of bar. Sat loose. on mill table. Taper pin reamer in collet in mill. Put gear on bar. Align gear with reamer in collar. Clamp V block to table. Remove old gear. slide new gear on. Dab of Loctite or nut + washer to retain on bar. Step drill hole, ream. Finish ream in place. Done :-)
How about put the taper pin reamer in the collet or chuck, and use it to position the original hole properly under the spindle (and clamp firmly). Then slide the gear in place and drill the pilot hole and ream it to fit with the original hole -- probably ream just a little deeper and use a longer taper pin. (hmm ... you may need an extension on the drill bit and on the reamer to reach with a 16" diameter gear, depending on how long the boss is.