Tube Notching 101 - Fit To Be Welded

Within the confines of chassis fabrication and general upkeep and development of your race car, you are sometimes required to join round tubes to round tubes, round tubes to flat stock, and round tubes to square tubes. The majority of these tubes are steel, although occasionally other metals are the basis of construction, including aluminum. For the most part, though, steel tubes are the material of choice.

There are many different ways to prepare a tube or a section of steel to be joined to another tube before the welding process. From a strength or durability perspective, the level of preparation is often more or equally important as the method utilized to join the tubes. Essentially, the quality of the weld will be greatly dependent on the quality of the tube joint and the preparation of the metal prior to any welding process.

You could just cut the tube, place it in the approximate position required, and weld away with little or no regard for precision of fitment between the tube or tubes. There is, of course, a right way and a wrong way to accomplish any given task. Just welding with abandon and lack of forethought is the wrong way. While this is an extreme example, no one should construct a race car with that much abandon and disregard to precision. We all know there are plenty of people with welders who have little if any business using them to construct a race car or any part of a race car. Your ability to buy a welder doesn't qualify you to be a welder.

The fit of the tubes is a critical component of the construction process and a major contributor to a strong weld joint. A poor-fitting tube joint leads to poor, weak weld joints. In the process of preparing the tubes for welding, cutting of the fitment (also referred to as notching or fishmouthing) is required.

Notching can be done in a number of different ways, and some methods are easier than others. The amount of time spent and the quality yielded are not as dependent on each other now as they were in days gone by. The quality of the notching is greatly affected by the tooling used to make the notch. You don't have to use power tools to notch tubes. You can perform the task with simple hand tools such as a file or grinder, but the results are not always as good as the ones received from a more automated method. For the most part, tool makers have made this task way too simple, and the costs for the specific tooling required are far too economical to ever consider using simple hand tools for notching. For that matter, we have no good reason to have tube joints that are not well executed.

For less than it costs to take your crew out to lunch at the local burger joint, you can purchase many of the tools required to notch tubes in a first-class fashion. The local home improvement centers usually have the majority of the tools you need to notch tubing. The sizes of the tubes you notch for your race car will range from 3/4 inch to 2 inches in diameter. The tool section of the local Home Depot or Lowe's has hole saws that can be used in the notching process. Short of having a milling machine and an assortment of end mills of the correct size to notch tubes, a hole saw mounted in your drill press is a great way to get a first-class notch of the correct radius.

Be forewarned that not all hole saws are compatible with metal, so check to see that the ones you may be purchasing will suit your needs. There are many brands of hole saws that work on metal and, given even minimal care, they last longer than the normal race car. Best of all, hole saws come in the same sizes as the tubes normally used in the construction of race cars. Using a 1 1/2-inch hole saw on a 1 1/2-inch tube yields a notch with the perfect radius to mate up to the 1 1/2-inch tube you are welding. This hole saw also works on smaller tubing to give you the correct radius to mate up to the 1 1/2-inch tube you may be working with.

If you are fortunate enough to have a mill, you own the ultimate in tube notchers, as using an end mill of the correct size makes a perfect notch. The larger end mills can be quite expensive, though, so this makes the hole saw option look even better. Even a lathe can be used to notch tubing by placing an end mill in the head stock and fabricating a special holding fixture to mount the tube in the tool holder. While this is an extreme setup, it works.