Please review this router gantry idea

[mekanik]

OK how about this, if you have a lathe that will swing a couple of inches greater than the pipe you intend to use you could manufacture a faceplate mounted fixture that will hold suitable size blocks of steel, preferably machined square on all faces, set up in the fixture and produce the radius to conform to your pipe OD.
Then you want substantial section gauge plate to use as the mounting surface for your profile rails, drill&tap the support blocks rail ect attach the two end blocks to both rail supports & align them on pipe, tack them up and add the remainder of the blocks & tack also,REMOVE mounting rails to prevent twisting ect, finish weld the blocks to pipe, using your support rails and blue marker, file & scrape the blocks so you have a flat datum,fix one rail, measuring from that set to on the opposite side and finish the faces on the other blocks to bring them parallel, rail support beams can now be fine tuned with brass shim.
Does that make any sense ?
That's close enough, Stainton with Adgarley