An answer ...

    And now I know that the leadscrew is indeed Acme . I mentioned in the other thread about making a mold of the threads using a lead ball and a c-clamp. Well there ain't enough room under there for a clamp , but there is room for a pair of vise grips . And now I have a perfect impression of an unworn section of the threads . You can't tell from looking at the screw what the profile is . But after forming the lead then cutting it with a utility knife blade to see the cross section it's definitely acme . I shall be setting up a fixture* to hold a cutter at precisely 14.5° on the mill and grinding the profile with my grinding disc I bought for the end mill sharpening fixture . I'll need to hold the small screwless vise in the mill vise to get a relief angle on the cutters . I'll be recutting  another piece of stock - with the proper angle and dimensions - as a fit check .
   Clare Snyder and Joe Gwinn were both instrumental in my decision to make the lead impression ... Thanks Guys !
   * I'll need to grind both a 3/16" cutter for the boring bar and a 1/4" for the OD thread . This project needs more precision than I can manage freehand . And I'll probably end up making one for the Y axis too .
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Snag
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