I had to show off my newest acquisition. Picked up an old Rockwell 22-650 planer from a guy on Craigslist. I replaced the knives, greased it, and dialed it in. It works great! If I ever have to move it again, I'll get someone with a tractor to help. Still not sure how I managed to muscle all 400+ lbs of it into the basement by myself. I was dumb enough to try that once but not enough to do it twice.
What is a flap knife clamp?
Basically when in old planners the actual knives and the part of the spindle above it is only secured by screws pushing the spindle and knife together. These are VERY prone to material fatigue of the screws, even if you replace the screws and which then send the knives and the fold towards you due to the centrifugal forces.
They have been banned from commercial use since the 90ies in a lot of countries,but are still very present,sadly.
In modern spindles the knives are held tighter by centrifugal forces due to a different construction method and it should not happen normally.