I need to create a "thumb screw" or "hand wheel" out of a 1/2-20 UNF threaded rod to serve as fine linear adjustment screw for a heavy load. (I can't find ready-made knobs with this thread, nor thumb screws in any reasonable length.)
I have hex nuts matching the threads, so I can use two nuts to "thread-lock" the cut end of the rod. But how can I attach an extended knob or handle to the nuts so that I can easily turn the rod when it's under a load?
There are many variations on this answer, allowing you to fine tune the results to your liking.
If you have a disk cut from thin plywood or similarly flat material and tighten your locking nuts on each side, you have a knob of sorts. The larger the diameter of the disk, the greater control you will have, as the resulting lever become longer.
You didn't note that the nuts are at the end of the threaded rod, but the above method will work regardless of the location.
If you need a knobby knob, just about any dome or spherical shape will suffice.
Instead of a disk, you could use a hexagon or octagon shape, or a pointed star shape. At the simplest form, a single flat rod with a hole at one end, locked into the nuts provides a lever for adjustment, somewhat like the lever on a ball valve assembly. If a balanced control is required, a longer flat bar with a hole in the center would also work.
In all of the above designs, the force with which you secure the locking nuts will determine how much load the system will handle when you want to make an adjustment. If the load is high, your lever or disk may slip if the nuts cannot apply sufficient force.
If you want a nice clean solution then you want to check out a selection of hand wheels. Some types even have a crank built into them. Many even have a provision for a set screw to lock it to the shaft to which they mount. There are styles made of various types of materials. Those shown here are made of aluminum.
If you cannot find s suitable knob, take some nuts and short pieces of solid rod to a weld shop and have them weld the rod to the sides of the nuts.
This makes an improvised wing nut.
Good luck!
