chassis
TECH Photos & Text by Vahok Hill
JOINING TUBES WITHIN THE REALM of chassis fabrication, maintenance and or making new parts for your race car, you will be required to join a plethora of tubes together. It may be round tubes to round tubes, round tubes to flat stock and round tubes to square tubes. For the purpose of this discussion, the majority of these tubes will be steel in a number of different alloys - 1010, or at the other end of the scale, 4130 tube stock. There are many different ways to prepare a tube or a section of steel to be joined to another tube in preparation for the welding process. The level of preparation to the weld joint is often more or equally important as the method utilized to join the tubes from a strength or durability perspective. 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. Even the best welder cannot make up for poorly fitting tubes joints. You could just cut the tube, place it in the approximate position required and weld away with little or no regard for any precision of any fit between the tubes. As with most things, there is a right way and a wrong way to accomplish any given task. Notching a tube will give you the most area to weld and spread the loads over the greatest area of the tubes
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or possibly more than two tubes to be joined. This will give you the strongest joint possible and that is what we are trying to obtain. The fit of the tubes is a critical component of the construction process. A poor fitting tube joint leads to poor weld joints and joints that are much lower in strength than joints that were properly welded with well-fitting tubes. There is more to welding a race car together than just having the manual dexterity to work the welder. The whole package includes developing the capability and capacity to make all of the correct fits. The fitting of the tubes is a major contributor to a strong weld joint. The process of preparing the tubes for welding the cutting of the fit is called notching or fish-mouthing or coping. The matter is not the nomenclature but the process for developing a quality fit is paramount to building a strong joint. Notching tubes can be done in a number of different ways. Some methods are easier than others. The amount of time spent and the quality yielded are not dependent on each other as it was in days gone by. The quality of the notching has a good deal to do with the tooling used to make the notch. You do not have to have any power tools to notch tubes. You could perform the task with simple hand tools like a file or a handheld grinder or a nibbler, but the results are not always as good as they might be as with a more automated method. For the most part, the tool makers and marketers have made this task way too simple and the costs for the specific tooling required far too economical to
ever use simple hand tools to accomplish this task. There is no good reason to not have tube joints on our race cars that are well executed. For a very reasonable cost, you can purchase the tooling / tools required that will enable you to notch tubes in a first-class fashion. You may have many of the required tools in your shop right now. The local home improvement centers usually have the majority of the tools you need to notch tubing. The majority of tubes you will be notching for your race car will range in size from ¾ of an inch to 2 inches in diameter. If you spend a little time at the local Home Depot or Lowe’s in the tool section, you will find hole saws that can be used in the notching process; short of having a milling machine and an assortment of the correct sized end mills 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 in a tube. Be forewarned that all hole saws are not compatible with metal, check to see that the hole saws you may be purchasing will work on metal. There are many fine brands of hole saws on the market that work on metal and given even minimal care they will 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 ½ inch hole saw on a 1 ½ inch tube will yield a notch with the perfect radius to mate up to the 1 ½ tube you are joining. This same hole saw will also work on a smaller tubing to give you the correct radius to mate up a variety of tubes together, that is a ¾ tube that may be joined to a 2-inch tube will
A selection of tubes that will be welded together to form a structural part of a race car, in this case a set of nerf bars. You can see that the tubes do not fit together in a way that would yield a strong weldment. The coping or fish mouthing of the tubes will allow a strong elegant weldment.
DIRT EMPIRE MAGAZINE • ISSUE 03 - 2021
