Hello keith , this is what I do . I use a tapered drill bit . drill the hole in handle . then meticulesly cut your mekugi to fit . the mekugi is also tapered but, make it a little long . (So when you tap it in with mekugi hammer it will really tighten up ).Then put blade in tsuka and mark blade tang for hole . Just make sure everything is tight before you mark hole then drill nakago ( tang ) and tap into place .I hope this helps. I use smoked bamboo for mekugi .
" If it ain't 6 " long it ain't no tanto"
25 Year Member Japanese sword society........ lifetime member Tenshin Dojo