Wrench Tips – Tip #18: Cut a Slit to Tweak a Tube
Sometimes the tubes just don’t end up where you want them to. I’ve scratch-built a single-digit number of exhaust systems in my day, for example, and that isn’t enough experience to make me any good at it. Inevitably, when the last couple of mandrel bends come together, they don’t match up. Historically, I’ve solved the problem by pie cutting that last mandrel bend, making a “mandrel pie” to cover my tracks. It’s half-assed, but it works…
I recently figured out a whole new way to half-ass my way through tubing fab. If you think about it, bending a tube means making one side of the tube longer and the other side shorter. If you need the bend radius to be a little different, or a straight piece to bend just a little, you can easily shorten one side with a saw.
Just cut a slit about 3/4 of the way through the tube and then bend the tube until the slit closes up. Cutting 3/4 of the way through makes it easy to bend that little fraction of an inch. For each slit you cut, you’re shortening that side of the tube by the thickness of your saw blade. Stack up several slits nearby and you’ll start to get a gently radiused bend.
To get the most from this technique, its best to use it as far as possible from where you want to see results. If the rear of your exhaust system missed its target by an inch, just one or two slits at the front of the system might be enough to line it up. if two of the runners on your stock Hayabusa header don’t get along with your Miata’s frame rails, three slits right up by the port might be enough to solve the problem.
Needless to say, you should weld the slits while you’re holding the slits shut….
These three little slits tightened up the bend radius on the Miatabusa’s center two primaries just enough to make them match the outer two.
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