Our big German screw box had handles that made the whole thing about 18" long. That is a guesstimate since I haven't seen it for over 2 years. It did get tiresome turning it,though!! Saturating the wood with mineral oil did help,and did no harm to the wood.
I was thinking I could make a large tap. What I can't figure is how to make it available to everyone on a loaner basis. It would be a good amount of work to make a 2" tap,3 TPI.. The tool steel would cost money,and it would be fairly valuable. Even if a person paid a $200.00 security fee to borrow it,the tap would still be worth more than that. It is a service I would like to provide somehow,though.
I don't know if I want to get into threading everyone's screws,either. That could become a big job,and I am too creaky to want a lot of physical labor like twisting big taps.