Titanium pie cuts before deburring and surface conditioning and 3D-printed tube clamp
I’m going to run an x-pipe under the transaxle. Since I’m primarily interested in smoothing and reducing the magnitude of the exhaust, as opposed to maximizing HP, I went for what would fit best. The x-pipe is composed of pie cuts sourced from 3.5” OD 0.047” wall Grade 1 titanium tube. They were cut at a 9.5-degree angle on a horizontal bandsaw using the tube clamp that I designed and 3D printed in a previous post. The edges were touched up on a belt sander, the inside edges were where deburred and the exterior face was brushed with a tube sander running a conditioning belt.
Pie cuts tack welded to form the left and right sides of the x-pipe. The sharpie lines on the table indicate the target spacing of the exhaust tips. Note that the pipes have a 3.5” OD and the tips have a 4.0” OD.
The pie cuts were tacked into curved symmetrical left and right pipes. A scrap straight section (not pictured above) was tacked to both ends of each pipe to prevent the end pie cuts from deforming during welding. After welding, the two pipes were scalloped on the bandsaw and tack welded to form an “X.” They won’t be permanently welded together until the rest of the exhaust is in place. That’s a total of 22 pie cuts and 20 welds spanning 78” just for the two pipes!
Pie cuts welded, but the left and right pipes are just tacked
Abe's a pro so he was able to achieve the relatively low alpha case without any special equipment. When welding titanium he takes extra care to ensure that the bead is completely shielded by the cup until it cools. While he's used a parts-per-million (PPM) oxygen analyzer at other job to insure a proper shield, he doesn't have one in his shop. Instead he just runs more argon than he normally would. To ensure that the hot bead is always under the cup he closes the doors to prevent an errant breeze, he's careful with torch angle and he only does 10-12 dabs before stopping. At which point he flips his helmet up while keeping the cup over the bead with the gas running for another 15-20 seconds after which he rotates the tube and repeats the process. Given his experience level and that this isn't an aerospace part, he doesn't use a thermometer to determine when the bead is cooled. An excess of argon wastes a little gas and takes a few more seconds per cycle. Too little and you get alpha case.
I decided to try heat coloring the scraps from the scallop cuts with a MAP torch. Titanium goes from yellow, to purple, to dark blue to light blue as it’s heated. I cleaned the one on the left with acetone. For the right one, I removed all of the weld oxidation with a surface conditioning before cleaning it with acetone. It looks significantly more blue in person. I’m going to experiment some more. That said, I’m not sure that the cool colors that can be achieved will remain after the car has been run hard a couple of times.
