This is a compilation of the making of posts I made while carving and crafting by hand the two katana for my Youmu cosplay. If you're looking to make something similar I hope this of help to you. I will warn that I worked diligently on these for about a year before they were completed.
Youmu Konpaku, Myon & Touhou Project © ZUN
Youmu's two katana were made with lots of swearing. Lots and lots of swearing. Also patience and glue.
The sword blades are 5-ply model airplane wood (sourced from Hobby Hobby in Mississauga, Ontario), a solid piece each, cut and then sanded into the shape. I could have made them much truer but I left them somewhat rounded for convention-safety. I roughly scaled their length and curve from how Youmu's are so they're kind of ridiculous in length - the long one is just on the edge of me being able to comfortably draw. The whole project of swords and sheaths cost less than $30 in material but took ages to do.
The tsuba (guard), seppa (spacers) and tsuka (grip) are all removable from the tang so I can exchange them for alternate cosplays without having to remake the whole blade but the habaki (er... neck-fitting) is permanently fixed (layers of cardboard shaped and wrapped and coated in glue). I've got screws as the mekugi (hilt-pins) of the tsuka to keep them all stable.
The tsuka are two levels of craft foam, hollowed to the shape of the plywood hilt, paper mache'd for rigidity, and painted all pretty. The sheaths are constructed of foamboard, glue/paper mache, and strips cut from bamboo blinds.
Photo courtesy of W1N9Zr0 from the Anime North 2011 Masquerade.
Any search for "prop cosplay katana making" should result in some helpful tutorials but here are a few of the most helpful links that I used as research and general guidance before and throughout this project:
These two tutorials provide a pretty good basis to get started on making the different elements of the swords themselves. I only followed them loosely for my designs but I don't think I would have gotten anywhere with out them as references.
I got the tsukamaki (handle wrapping) technique from this tutorial: