In this old blueprint from 1944, it calls for a lead of helix, 1 turn in .2" on red arrow: enter image description here

No other info is provided.
This is a top view of the part.

Here's the link to the full blueprint: http://library.centerofthewest.org/digital/collection/WRAC/id/2777/rec/8932

It also has other calls for lead of helix cuts. Also the same call is used in another place of the blueprint. Maybe the 7/16" cutter should be used for it, not sure.

In CAD, would one use a helix to cut from top to bottom?
Or to cut from back to front (direction of face normal)?

  • $\begingroup$ You may have to provide more of the print. It's hard to tell what here is getting a feature similar to 5 threads per inch. Probably a whole face is supposed to be helically swept. $\endgroup$
    – Abel
    Nov 30, 2023 at 12:27
  • $\begingroup$ @Abel I added a link to the blueprint. $\endgroup$ Nov 30, 2023 at 12:33
  • $\begingroup$ I'd probably rough it out with just a square cut, then (since that face is supposed to be ground) use a toolpost grinder on the lathe, with it set for a thread pitch equal to the helix they call out. $\endgroup$ Nov 30, 2023 at 16:52

1 Answer 1


That note refers to making two surfaces helically swept. These surfaces are also the ones that have the grind to notes tied to them regarding where the swept surfaces should reside, and the intent that the ground surfaces should not be ground again after heat treat.

I would make sweeps originate at the "GRIND TO" dimensioned edge and go in the opposite direction, just to have those edges be what were dimensioned in my CAD file.

Cutter choices should mind the nearby fillet radii or specific cutter callouts, but the key surface in question here is to be ground not cut though- basically .001" tolerance before heat treats and ~.002 after. Focus on getting a grasp of the geometry right before worrying on how to make it.


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