I just finished up making my owm wipers, so will post what I know here and try to find other discusions where it is pertinent, and post there as well.
I did end up using 60a durometer polyurethane sheet from McMaster... this after reading the merits of poly vs. felt.. the idea of felt becoming abrassive struck a cord, so poly it was. Initially I got a sheet 5/16 thick (I think).. too thick, really difficult to get a good clean cut (even tossed it in the freezer, no dice). It also seems that to get a really good fit, pressing down on the wiper as you tighten the 'cap' is necessary... the ticker polyurethane was just too much.
So I just got 1/16 all else the same, and bingo. I was able to take the corner of a protractor, line a fresh blade along it, whack it with a hammer, and got perfect 90 degree contour... at the tip, I didn't overlap the cuts, and went back and sliced a small flat, as the top of the ways are flat. Great fit... they absolutely wipe the ways totally clean... hardly any oil residue even! My 'caps' are just Al stock contoured to match, and drilled for the mounting bolt. Next step is to install some oilers on the carriage.
bb