I have one, but at a casual glance, wow, that would be a lot of work to copy it! I think the weak point of the design is that it relies on its own compound slide system. The 'cross slide' as it were, which controls the offset of the tool from the centerline is simply a graduated scale, and you loosen the bolts off and nudge it sideways. Hardly accurate enough to produce a known radius. You could eventually get the tool radius to gauge right, but then you were never sure if the tool was slightly 'bullnose' or not, because determining the true axis of the cutter relative to the pivot of the attachment was a crapshoot.
It might be better to try to set up and grind them on a cnc mill. I have not done it, but with a wheel in the spindle, and a vertical 5C chuck on the table, and some help from a cadcam, it should be possible to create the toolpath to grind the tools accurately.
You'd spend a couple of hundred hours duplicating the Darex thing and you'd still not have much for your effort.
Darn it, maybe I talked myself out of owning the attachment! I've even got an old cnc mill sitting around doing nothing. I could dedicate it to ball end mill resharpening!
