I’ve decided to remove the alpha case with Scotch-Brite pads and then let the heat cycles do what they will.
In a previous post I designed brackets that mounted the heatshield to threaded bosses on the transaxle via vibration/heat isolators. The next step was to hang the X-pipe from those same brackets via a different set of isolators. I considered fabricating the hanger from titanium and welding it to the X-pipe, but given the size I figured that it would be difficult to get it perfect and I could damage it when not on the car. Instead, I decided to weld threaded bosses to the X-pipe and laser cut a piece of 6061 to connect the bosses to the bracket.
Blue isolator mounted to transaxle boss (top-left of bracket), heatshield (bottom of bracket), blue isolator supporting the hanger (middle right of bracket), hangar (long vertical piece) and threaded boss tack welded to the X-pipe.
The bosses are visible in this view. Note that the hangers are too long and they extended further past the bosses on the X-pipe than they need to. While the hangers have slots to accommodate this, I’m going to laser cut shorter ones which locates the bolts in the middle of the slot… that the way that I roll LOL. If this piece were titanium welded to X-pipe it would be messy to fix.
I fabricated threaded 1/4”-20 bosses from 1/2” Grade 5 titanium rod. With aluminum, stainless steel or 4130, I’d have the material laying around and the machining would be straight forward. However, titanium is a different beast. A piece of 6” long by 1/2” OD Grade 5 titanium rod cost me $33.85 and part way through drilling my first hole I wrecked a high-quality, made-in-the-USA drill bit. After replacing it with one specifically designed for titanium, I quickly determined that my tap was a no go. NFW was I going to finish the hole without breaking the tap.
Apparently, titanium’s low modulus of elasticity makes it “springy,” so the workpiece tends to close in on the tap causing galling and tearing of the threads which also increases the torque on the tap. Taps designed for titanium have a different coating and spiral flutes, so I ordered a $47.17 tap from McMaster. With tools, my general philosophy is “buy once, cry once” and while McMaster charges a premium, I get it one day and I don’t need to worry about quality.
My takeaway for titanium is that in addition to material the tooling and machining costs are noticeably higher.
From left to right; 3-jaw chuck, titanium rod, tap, tap handle, spring-loaded tap guide, and Jacob’s chuck mounted in the tailstock. This horizontal can approach can be used vertically in a mill or drill press.
Note the indent in the top center of the tap handle that receives the tip of the spring-loaded tap guide.
The tap is made with cobalt steel, a high helix angle and an open spiral flute design to provide the cutting strength needed to tap threads in titanium.