Door knobs keep falling off spindles

[Surfing Bird]

Several door knobs in my 1908 home keep falling off their spindles. The set screws are in all the way in each case, but the knobs slip off when opening the doors. Are the spindles stripped? Are the set screws ground down too short? Most often I'm not able to get the opposing door knob off to change out the spindle and see if that is the problem. So, how do I get the knobs to stay on the spindles I have and yet still have the latch mechanism work? PLEASE HELP!!!

[Nestor]

Almost certainly if you take a picture of the kind of locks you have and take that picture down to any locksmith, he'd be able to tell you what you can do to keep the handles on. My guess would be that you just need to use longer set screws.

But, if these lock sets are original to the house, my guess is that they're simply worn out. They are, after all, over 100 years old.

[HayZee518]

old locksets used a square spindle with a round hole. the thread was a 1/4-20 or a 1/4-24 thread. next thread size up would be a 5/16-18 but it might not clear the sides of it.
Take the spindles with the worn inside thread to someone that does tig welding and have him fill in the hole. then drill and tap new holes. use a #7 drill for a 1/4-20 screw tap.
Now that I think of it, the thread might even be a 10-24 coarse thread. rarely in the old days did they ever use a fine thread for a door handle