im assemblying my longtail and just got all the parts in today i had my shaft which is 4140 steel machined to 3/4 #10 threads. i was just messing around seeing if my prop would fit on the shaft i get it almost all the way to the bottom of the threads on the prop and it stops turning. i go to try to take it back off and it wont move at all ive clamped my shaft in the vise and put a pry bar between the two prop cups and tried heating the prop and cooling the shaft nothing will work.

I feel like an idiot ive restored old tractors and overhauled engines and a threaded prop is stopping me...

I'm sure you checked to make sure the thread count is matching?

Galling

U screwed.....no pun intended

From a machinist/engineer standpoint, the only thing I can think of is the threads don't match is that when the shaft was machined it had runout in it.

I had stuff gall up already and it was always pretty much done. Talk to the machinist that did the shaft and see what he thinks.

Exact same thing happened to me. You should have have cleaned off the threads. Good Luck, I had to take a grinder to my propeller and grind it close to shaft, without hitting shaft threads, Then i wedge the cut ope and got it to open up to unscrew it.

I'm thinking youve picked up a thread, ie the grain of the metals has lifted and grabbed each other s/s is bad for it. Don't panic you still have options.
Option 1 weld up a tool to turn the prop off with than fits right up against the hub. Like a lenght of bar with 2 bolts coming out at 90 degrees, lock your shaft down solid then heat the prop hub till red hot and unwind it. Once hot you can't stop it will pull up harder if you do. This option will need threads cleaned up after and shouldn't wreak it worse than out is now.

Option 2. Cut the shaft off behind the hub. Drill a hole square and centre down thought the shaft using a sharp drill. Keep using bigger drill until the inside of the shaft is all but gone and can be wound out. This is best done on a lathe our good radial drill press. Your shaft looks long enough to get away with this but 4140 is going to be hard as a whores dreams.

Opinion 3 cut the prop hub.

Best of luck. Use lubricant on your thread next time.
Let me know how you get on.

Have you tried putting the prop in the vice and using a pipe wrench on the shaft ? Less flex that way dont put the pipe wrench where the bearings will contact the shaft. If it does come apart clean up the gouges left from the pipe wrench.

im going to try to heat the prop up until its red hot and try to turn it off if that doesnt work ill cut off the prop with a grinder and save the shaft and get a new prop.

ya ill use an oxy/act torch to do it its at the big shop so ill have to take it up with me next week.

Looks like a lesson learned. Stainless galls so never try it without some never seize.

How did you get on?

will mess with it tomorrow when i can take it up to the shop i just put it on by hand to see if the threads would line up.

well the shaft broke off inside the prop but just melted it out and got a new shaft made and retapped the prop.