I got the idea to build a Longworth chuck when I watched a video of Jason Beam make one on his home made CNC machine when I saw it I knew I could make one with my router and, a home made trammel jig.
I laid everything out on some particle board than made some test cuts to see how it would work out for the final cuts on the 1/2” baltic birch ply.
I mounted the face plate on a blank of the baltic birch ply with 1/4-20 T-nuts than mounted the blank to my lathe slid the tail stock over until the live center made contact tightened it down turned the hand wheel until I made a dimple on the ply now I had my center and took the face plate off. Than I laid the every thing out with my compass onto the blank screwed that to the other baltic birch blank and a sacrificial blank took this over to my drill press and drilled the 1/4” holes for the pivot points of the arcs and, the outer perimeter of the chuck.
I bought some #6 1/2 solid rubber bottle stoppers I needed a 1/4” inch hole centered perfectly in the middle of each of the eight stoppers so I needed a jig for that the tapper on the stoppers was around 7 deg. so I planned some 2×6 down to the height of the stoppers ripped some strips down to the 7 deg. bevel and cross cut the middle strip to the same bevel mounted the strips to some scrap ply using one of the stoppers to align the the drilling jig with my brad gun.
Here is the finished Longworth cuck
-- A friend will help you move, a good friend will help you move a body