Know-How Notes: How to Cut Metal Tubing
Work with cars long enough and you will have to cut some tubing. Whether you just need to replace a fitting with stripped threads, replace an entire hard line, or need to build an exhaust system you will need to cut metal tubing cleanly with precision. This may require special tools, depending on what you are working with.
Under no circumstances should you cut metal tubing (hard line) with anything other than a tubing cutter. A hacksaw will leave the end of the tubing jagged and sharp, which will not flare well. In most instances, a hard line must be flared before put into service. The only way for the flare to function correctly is with a clean cut without any jagged edges.
There are multiples types of hard line tubing: Steel, Stainless Steel, Aluminum, and Copper. A standard tubing cutter can handle all of them, so you don’t need special cutters for different types. A tubing cutter consists of a base, a threaded clamp with typically two or more support bearings, and a sharp cutting disc.
Operating the cutter is simple. First, you place the tubing inside the jaws of the tool and thread the vise until the cutting wheel makes contact with the tubing.
Spin the tool or the tubing (it doesn’t matter which) and make sure the jaws are snug to the tubing. Continue to the rotate the tool around the tubing a couple of full turns, then tighten the knob a little, and repeat rotations. Every couple of rotations, tighten the knob a little more.
Once you reach the inside of the tubing, the line with come apart, and the tubing is cut. The basic mini cutters are just a cutter, but the larger tubing cutters typically have a built-in file and deburring tool on the handle. If so equipped, swing it out and use the pointed end to deburr the tubing. This is done by inserting the tip into the tubing and twisting the tool. Pretty simple stuff.
That is all there is to cutting hard line tubing. Don’t forget to the blow out the line after filing, as you don’t want any shavings to get into whatever system you are working with.
Large tubes, such that used for exhaust, don’t have to be quite so perfect. You still don’t want to go hacking at it with hacksaw. You want a clean, straight cut so that your tubing will butt up to the next piece. This is done two ways- bandsaw or a chop saw.
A chop saw, which is what most shops use, looks like a radial arm saw for wood, but instead of a metal blade, it has a large abrasive disc. The tubing is clamped into the jaws of the built-in vise (very important to use this feature), and the disc cuts through the pipe. This is very loud, throws a lot of sparks and typically leaves a little tail on edge of the pipe. This can be removed with a sander or file.
A bandsaw gives you more flexibility when cutting large tubing, as you can make compound cuts to create crossover pipes, V-cuts, etc. The trick of this is that you have to be very careful not to get off your cut, as you can easily end up with a cut that doesn’t work. Cutting tubing on a bandsaw can be done with a vertical saw or a horizontal (stationary or portable)saw. The typical horizontal saw is designed for cutting metal, so the blade runs quite slowly, which is what you want. A vertical bandsaw is most commonly used for wood, so the blade will run much faster, which means you will burn up blades.
There are of course vertical bandsaws that have adjustable speeds, either through an electrical control or through changing the belt to different pulleys. These units will allow you to slow the speed down to the 300-700 RPM range that you want for cutting metal. Your blade is just as important as the speed. For metal, you need a high tooth count, 14 tpi or more in order to minimize the grabbing-action of the blade, and give you a smoother cut. Horizontal bandsaws run much slower than verticals, and they can run fewer teeth.
Most hobbyists and DIYers might have a small vertical bandsaw, but very few have a horizontal saw. The solution is a portable band saw. These are great little tools that are affordable and very useful. Instead of a big table, you take the saw to the part and cut it. You do need a good vise setup, but you probably already have one. Just grab the bandsaw and get after it.
When you need to cut metal tubing, make sure you have the right tools for the job. The end results will be far more professional and you will spend less time doing it.
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