If you are building a custom exhaust system, you can bend your own exhaust tubing, buy mandrel bends, or hire a muffler shop to fabricate the pieces for you. Bending the exhaust tube yourself is a delicate process but entirely feasible with the right equipment. Fill the pipe with sand to prevent crimping when you bend it. Attach a thick walled squash pipe to provide a gripping point for the vise or clamp.
Step 1 - Design Pipe
Measure and sketch out the curves of the exhaust pipe you wish to fabricate. If you construct a model or pattern of the pipe, it will make it easier to bend the pipe later. Buy materials slightly longer than the intended final length. Attaching and removing the squash pipe results in a small amount of waste.
Step 2 - Create Squash Pipe
Square off the ends of the pipe length. Place the nut face down on a flat surface and center the pipe over it. Spot weld the nut onto the pipe and screw in the bolt. Check the thread and finish the weld if it’s good.
Step 3 - Flatten End of Bending Pipe
Take the thin metal exhaust pipe and flatten one end by striking it with a hammer or squashing it in a vice grip.
Step 4 - Weld Squash Pipe to Exhaust Pipe
Weld the squash pipe to the open end of the flattened pipe. Fill the exhaust pipe with sand by pouring it through the nut on the squash pipe. The sand must be completely dry or it will produce steam and pressure when the pipe is heated later. This could cause the piece to rupture. Use coarse builder’s sand that has been dried in an oven on low heat overnight. Compact the sand by tapping it and poking it. After the pipe is full, clear any sand away from the threads of the nut and close it by screwing in the bolt. Grip the squash pipe in the vise and tap along the length of the tube with a wooden mallet while tightening the bolt.
Step 5 - Heat Pipe and Bend
For best results, preheat the tube in the oven. Grip the squash pipe in the vise and use a torch to heat it until it glows red. Work slowly while bending the pipe. Pull it as you bend it to prevent kinks from forming. Check against your patterns as you work. If you are bending a pipe in more than one location, allow it to cool completely between bends.
Step 6 - Cut and Clean Pipes
Now that the pipe is bent, you can cut off the squash pipe and drain out the sand. Clean the pipe thoroughly inside and out. Tidy up the welds with a file or grinder. Clean off any scale that formed on the elbow when the pipe was heated.