spreading clamp.jpg

This allows you to glue kerfings on both sides and wind in later for removal - first test works really well.
Threaded rod, 2 nyloc nuts, 2 T-nuts, 2 washers, scrap timber and about 10 mins. ($1.20ish each)
Nyloc nuts just capture end blocks. Counterbored hole in end block to allows nut to slide in and travel - short section at rod size for neat travel.
Two ended winding allows for greater travel.
The one in pieces is for illustration and not rounded yet.
Pictured in tenor ukulele form - one piece eliminates tail join.
Version 2 was going to have 3D printed winding wheels - that's just me going over the top.