What are your best resources for winding custom transformers?
As from my experience:


You have to make a form (probably a wooden form) which is exactly the form of the transformer core, but longer.
For convenience make a winding rig - a place to attach the form connected with a handle and a shaft for wire spool. Wire spool has to have some kind of breaking mechanism attached to you get some tension on the wire.
Make a sheet of plywood with a hole exactly the shape of the form - you will use it slide the finished coil from the form.
Wrap a form with a thin cardboard, leave edges of the cardboard so that you can fold them and glue them together after you finish the winding.


The idea is that you attach a form to a handle, put a plywood sheet on it, then put cardboard, then wind the wire, fold cardboard around and use a plywood sheet to pull the coil off the form. Cover the form with soap or paraffin so the coil will slide off more easily.

This is all I have in terms of photos, please excuse the quality and incomprehension.