Know-How Notes: How to cut metal tubing

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.

Hardline Tubing

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.

Tubing cutters have a rolling cutting wheel with two support rollers on the bottom to support the tube. Note the large groove, that is for close-cutting flared tips.

Tubing cutters have a rolling cutting wheel with two support rollers on the bottom to support the tube. Note the large groove, that is for close-cutting flared tips.

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.

On the outside of the tool, there is a file and internal chamfering tool.

On the outside of the tool, there is a file and internal chamfering tool.

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.

The cutter is placed on the tubing and the tool was tightened onto the tubing. Then the tool is spun on the tube.

The cutter is placed on the tubing and the tool was tightened onto the tubing. Then the tool is spun on the tube.

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.

About every other turn, tighten the knob a bit.

About every other turn, tighten the knob a bit.

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.

We used the file to clean up the outside edges.

We used the file to clean up the outside edges.

 

Don't forget to deburr the interior of the tubing.

Don’t forget to deburr the interior of the tubing.

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 Tubing

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.

Most DIYers will have a chop saw for this kind of work, they are functional and fast. They are limited for complex cuts though.

Most DIYers will have a chop saw for this kind of work, they are functional and fast. They are limited for complex cuts though.

 

Chop saws almost always leave a little tail like this on the outside and inside of the tubing, you will have to remove it. Be careful, this stuff is usually razor sharp.

Chop saws almost always leave a little tail like this on the outside and inside of the tubing, you will have to remove it. Be careful, this stuff is usually razor sharp.

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.

A full-size bandsaw with adjustable speeds is the best way to make complicated cuts, because you are in control of the tube. Don't forget to lube the blade though.

A full-size bandsaw with adjustable speeds is the best way to make complicated cuts, because you are in control of the tube. Don’t forget to lube the blade though.

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.

Tooth count for the blade is critical for band saws. You want as many teeth as possible for cutting metal.

Tooth count for the blade is critical for band saws. You want as many teeth as possible for cutting metal.

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.

A portable band saw like this one is really handy, you would be surprised just how often you find a new use for one.

A portable band saw like this one is really handy, you would be surprised just how often you find a new use for one.

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.

Check out all the tools & equipment available on NAPA Online or trust one of our 16,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to cut metal tubing, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

about author

Jefferson Bryant

A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.

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