Machining post heat treat.
Spidertrax | Thom Kingston | CC BY 3.0
Heat treating has become commonplace in our shop these days. The continued push for stronger and faster Ultra4 vehicles demands it, and in terms of “engineering porn” heat treating is about as good as it gets. Only problem is maintaining high tolerances in parts, like the Spidertrax 2-piece axle shaft yoke shown here, which after heat treating will often be sized incorrectly.
So, post heat treat machining gets added to the mix on nearly all heat treated parts. For our 2-piece axle shaft, this means boring both top and bottom ears in one single pass AFTER heat treatment, holding a hole tolerance of 0.0005″ (a single hair measures roughly 3 times that amount, 0.0015″ thick, to put things into perspective) while maintaining concentricity between both top and bottom holes. It’s a time killer, but ensures every part is tolerances exactly as we intend.
