I wanted to do a better job with the newest version of my Longworth chuck. My old one wasn’t perfectly centered and the bolts would often jam in their slots.
This time I did all the layout on the lathe rather than by hand. This eliminates the inaccuracies of marking lines and drilling holes by hand. This isn’t a full guide for how to build a Longworth chuck, just some additional ideas on the topic.
The “pivot holes” I’m referring to are where you pivot your router while creating the arc lines. Most guides have you drawing 4 lines on your chuck creating intersections every 45 degrees. I’m using my lathe’s indexing feature to stop every 45 degrees and then a dowel to guide a drill bit. So instead of making holes with an awl at pencil line intersections I’m making those (shallow) holes in the same way every time.
In use this chuck does work much better than my previous! Mounted bowls run pretty close to true and it opens and closes with just a bit of help to keep the bolts from jamming. It’s not perfect but was a good step forward in usability.