Aligning and evaluating big things to small tolerances
In the world of metrology, each measuring technology has its place. The place for Optical Tooling is in alignment, which is the geometric orientation of various components of a system, such that all components can work harmoniously as they were designed to. This is different from three-dimensional measurement technologies. These technologies, for example, can take measurements over the curve of a satellite dish to determine if the dish has the proper curvature. Optical Tooling is not the answer for such problems. Instead, “OT” allows you to evaluate geometric relationships such as linearity, parallelism, squareness, flatness, etc., between various components, especially if those components are large – and do this in a manner that is easy to see and understand.
To evaluate these geometric relationships, some or all of four basic questions often must be answered. These four fundamental questions are:
Is it straight?… Is it level?… Is it plumb?… Is it square?
In answering these questions, Optical Tooling combines very high accuracy with a great degree of flexibility. That is, not only can optical tooling provide excellent answers to these four questions, but the very same tools can be used over and over to measure a wide variety of things – everything from paper mills to particle accelerators.
Optical instruments are used instead of mechanical tools in order to gain increased accuracy. Using optical instruments, you are creating absolute references for your measurements, which do not change over distances the way mechanical or relative references do.
Using optical lines of sight for reference, along with scales and optical micrometers used as verniers, it is possible to perform measurements that are almost impossible to do any other way. For example, how do you know if a roll on one side of a piece of machinery is parallel to a roll on the opposite side? How do you know whether a line of bearing journals are all really in a straight line, when they stretch out over 40 feet and the shaft that they support is suspected to be bent? And by the way, how straight is “straight”?
Remember that the four questions above appear simple to answer, but like everything else, the real question is the amount of error that is tolerable. Also, with answers to the four basic questions, you can figure out a number of other important things about your machinery, engines, turbines, presses, rolling mills, airframes, ships, etc. You can answer questions like, “is it straight or is it bent?”, or “is it out of line?”, or “…flat?”, or “…out of round?”, or “…concentric?”, and many others.
Addressing the Four Fundamental Questions
Is it straight? …What is the straightest reference line created by an optical tooling instrument? The line of sight! Each optical tooling instrument is specially crafted to maintain a straight line of sight within extremely close tolerances. To measure the alignment of several points that are supposed to be on a straight line over a distance, the line of sight itself is used as a reference line. This invisible line is straight as an arrow, has no weight, cannot sag, become fouled, or be disturbed. It constitutes a precise, unvarying reference, determining straightness to within thousandths of an inch.
Is it level? …If you need to level equipment that is only a few feet long to tolerances of 0.001″ to 0.003″, it may not be a big deal – but what if that equipment is 25′ or 50′ long and equally wide, or has components at different elevations which all need to be level? Then what? Optical alignment methods overcome the disadvantages of other methods and assure an object is level to within a few thousandths of an inch, even when the area in question is large. This is accomplished by sweeping a level line of sight back and forth which creates a precise horizontal reference plane. This plane can also be used to determine if something is flat – and although we sometimes use the terms interchangeably, “flat” is definitely different than “level”.
Is it plumb? …This is similar to the question “Is it level?”, but this time we are concerned with relationship to a vertical line or plane. Again, the biggest problems are presented when you’re talking about something big. What are the choices – a plumb bob? A machinist’s level? These and similar tools may be used to establish a single vertical reference line, but most have significant drawbacks when dealing with large or awkward objects. Even when they can be used to establish a vertical plane, they cannot determine a particular azimuth orientation of that plane. In the optical alignment method, sweeping a transit’s telescope is used to efficiently define a vertical reference plane. The degree of parallelism between this vertical plane of sight and any other surface can then be determined by measuring the offset between the two planes. As a result, measurements can be made to within 0.001″, and even very large vertical areas can be made perfectly plumb.
Is it square? …Squareness implies that one plane forms a 90° angle with another intersecting plane. Again, using tools such as steel squares have significant limitations unless the scope of work is small. Also, if the two surfaces in question do not even meet to form something close to a corner, then there are real problems. However, Optical Tooling has several methods of solving this type of problem. OT transits are built specifically to give you the ability to evaluate squareness of the line of sight of two transits.
Optical Tooling is Flexible
“Flexibility” means a couple of things. First, it means using pretty much the same set of equipment to evaluate all sorts of different mechanical relationships. But it also means that you can apply Optical Tooling products and principles to all sorts of different problems. We have used optical tooling on everything from particle accelerators to drawbridge gearboxes, and from giant cranes to hydroelectric turbines, and everything in between. That’s because most of the equipment is not specifically tied to one single application. We also have a number of measuring tricks up our sleeve to increase that flexibility (we’ve been doing this a long time). You can use various mirrors, targets, fixtures, instrument bases, and techniques to measure all sorts of different things. Here are just a few examples of jobs you can do: