broken main shaft key

Are things slipping? or loose? Beside the piece of the key, of course.

Taking it all apart is a bit of work. The small head is press fit onto the shaft and not easy to remove. Especially with part of the key remaining. You’ll need a good size gear puller, likely. If necessary the remaining key section will need to be drilled out. I’d probably pull the flywheel and take off the one sidearm to get better access to the area.

Once you manage to get things apart, then the keyways may need to be recut and a new key purchased to fit the new keyways. Putting the small head back on it’s shaft may require heat (and cold) to expand the hole (and shrink the shaft).

Thanks Arie!

Yes, things are slipping. The key keeps popping out, which makes the press extremely unhappy. I got a piece of 7/16” key stock that might work as a replacement key if I cut it down (it’s 12” long).

The small head came off with no trouble. I did it with my own bare hands… Does that mean it’s too loose? I can get it back on most of the way… It doesn’t want to go the last quarter inch or so. I will try heat/cold as you suggested. Thanks. It doesn’t seem like the rest of the key is in there, so I’m wondering if the original was actually broken, or if it’s just a short one? Which makes me wonder how long I’ll need to cut the new piece. I have no idea…

Thank you!

I suggest you get a bright flashlight and peer into the keyway to see what shape it is. You could also probe the keyway with a piece of coathanger wire to see if there is any remaining key in there. If you can push a piece of wire the depth of the width of the crank disc, there should be room for a piece of key that long. In the photos the keyway doesn’t look damaged so a key of the correct square dimensions should be fine. You could leave a short bit sticking out as long as it has sufficient clearance for the arm.

Bob

I’ve never managed to get a small head off a press, even with the mid sized gear puller I own. If the entire small head is rotating freely and you can pull it off it’s shaft, there is something quite wrong. There should also be a lot more to the key than the tiny bit you are showing.

Look for serious wear on the shaft and in the hole of the small head. Either/both may need some attention at a machine shop. The key can likely be cut from the stock you have if it is a straight keyway. If not then a new key can probably be purchased or made fairly easily.

Following up on Arie’s comments. These small gears are really hard to get off.

We have a press where this gear tends to work loose and move towards coming off. Usually it can be put back all the way with a few taps. It only moves off maybe an eight of an inch. The key is all the way in so it can’t be tightened any more. We just live with it and are happy the 125 year old press still prints well.

If you can pull the gear even partially off, you should be able to check for any remainder of the pin. With the small piece you recovered I wonder if it broke off long ago and someone tried to hold it on with the small piece. A normal size key would probably keep it tight.

If the key seems inclined to slip out with use you could also think about bending it slightly so it is sprung against the gear, wedging it in place.

Bob