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What's Your Angle?

Fabricating parts that aren't square

In another article on fabrication, we studied the benefits of manufacturing parts for vehicles that could not be obtained, did not fit our purpose or were easier to make than to track down and buy. Next we will go into some of the finer details of manufacturing these parts.

Even if you have decided to produce the part yourself, it is unlikely you have the luxury of access to a full array of computer-controlled machines and computer-aided design software. Here is some of the machinery more common to a home machine shop.

Home Shopping

The main piece of equipment is a vertical milling machine, and the accessories often found with it. This machine looks like a really stout drill press with a table that can be moved very accurately with hand cranks. It allows you to drill and cut and shape a variety of metal components (including those rare car parts mentioned at the outset). Angles and radii present their own special problems in manufacturing, and yes, even their own special math; therefore, there are several special tools to assist you in creating certain shapes.

Chances are that if you are making a custom part for your vehicle, it will not be shaped like a simple rectangle. A quick look at just about any car part will tell you that they have complex angles and curves due to the complicated jobs that the parts accomplish. When one of these components must be made, however, they will often start out as square or rectangular stock. And the more accurately you can make the square, the easier it is to maintain the accuracy of the part throughout the manufacturing process.

First of all, let's begin by saying that no piece of machine equipment comes perfectly aligned and square from the factory. Before any machine work is attempted, it is important to make sure that your milling machine head is perfectly square to the table by taking a variety of measurements (.005 of an inch in tolerance is typical).

Machine Prep

Even if the head was squared earlier, it has a tendency to move out of alignment with continued use, so this aspect is a critical thing to check. If the machine is not square, then your part will not be square or accurate in any way.

Once the machine is determined to be in good order, you'll need to be concerned about how the part is being held in place. A lot more force is involved in cutting metal than wood, so you will need some tools that can hold the material very tightly.

The first choice is a vise. These specially constructed vises are bolted to the milling machine table, and are the most common way for you to hold a part to be machined. As with the milling machine head, these vises must be made as square to the machine table as possible. Any inaccuracies will be transferred directly to the part.

Parallel Grip

The most common size of a milling machine vise is about six inches wide, and will open up about six inches. The jaws on the vise are about 1.5 inches tall. Obviously if the part does not readily fit into these dimensions, then a different size vise or another way to hold the part must be found.

A common accessory to the vise is called a parallel. These are thin, precision-ground metal plates that come in pairs. These can be inserted into the open vise jaws to space the part off of the bottom of the vise. This way, parts that are too small to stick up past the top of the vise jaws can be held up and gripped by only a small portion of the jaw. Since they are precision ground in pairs, they will still keep the part parallel to the vise and machine table (hence the name).

But now what if you need to cut an angle into the part? Suddenly things can become more complex. We will start out with two simple choices:

Pointers

The first and very easy manner to angle a part is to angle the vise. Some vises can be mounted on a swivel. The vise can simply be loosened and turned until the proper angle is obtained. Somewhere on this tool is a pointer that will correspond to degree markings on its base. As you can imagine, this is not accurate enough for all machining operations, and the swivel portion makes the vise taller and less precise for other machining operations.

If you do not have a swivel vise, then your regular vise can be angled on the milling machine table and clamped down at the proper angle. This method works very well, and can be very accurate, but you had better have some experience in trigonometry before you try to guess the angle at which the vise is positioned (more on this aspect in another article).

Another tool that is available is called an angle block. This tool is similar to a parallel but, as you might imagine, it is not parallel. It has a precision angle ground into it. It is also designed to be placed in a vise with the part on top of it. Thus, as the part sits on top of the angle, it can be clamped down in the vise at the particular angle needed.

Options

Methods and tools mentioned in this article are the most common ways of holding a part and making a part with an angle. Obviously these are not the only methods for accomplishing the job. One of the really great things about manufacturing and machining is that there is very rarely only one way to do a job. As long as it's done safely, relatively fast and accurately, then you will probably get it right, even if you did it differently than what you read here.

In another article, some other methods and tools will be investigated, which will allow for far more complex shapes to be very accurately machined. Included will be some of the mathematics used to make it all possible. Don't let the idea of doing the math intimidate you, because we'll show you how to cheat even if you don't have a calculator. Remember, if all this work isn't fun, then machinists and restoration folks wouldn't be doing it.