Are you asking how you get a rounded profile on the scales, so that when you lay one flat you have kind of a semi circle, or are you asking how do you get the scales to bow out from the spacer so that there is clearance for the tang and the blade fits right? If the former, I've kind of wondered that myself (I'd guess a belt sander with the scales cemented together). If the latter, the wedge is "V" shaped.