Beaufort Ink of England is an excellent source of materials for anyone considering making a custom pen. They carry nibs, refills, clips, and lots of other components for creating an excellent writing instrument.
They also work hard to publish documents that may be helpful to those starting out - and one of them is an excellent paper written by Phil Dart on creating a custom pen from scratch. Copyright laws prevent me from putting the document here, but it is a great reference document that any up and coming pen turner should read. The link to the PDF - released in 2020 and revised in 2022 is here Phil Dart's Custom Penmaking PDF
Phil covers basic tools, techniques, measurements, refinements, materials in some depth.
The Beaufort Inks site is here Beaufort Ink Site
Enjoy!
Kevin Seiler