First, we must, and I emphasize must, commit to memory the correct terms for measuring and how they apply to our business.
To begin understanding measuring and the terms associated with it, let's look at how a unitized vehicle is constructed. Vehicle manufacturers begin with placing the floor section on some sort of fixture at four control points. These four control points are mounted at a height above the holding fixture. The distance from the fixture to control points is known as datum height. The flat surface of the fixture is known as a datum plane. You need to understand that datum plane and datum height are arbitrary.
Think of all the different frame machines on the market and the different types of pinch weld clamps. Now place a '98 Ford Mustang on each of these different frame machines and you get 20 or 30 different datum heights (in this scenario the datum height is measured from the bed on the frame machine to control points).
Don't despair, each of the measuring systems will show you how to establish a datum plane and height and the datum plane will be constant with your particular frame machine and measuring systems. We can now find a height measurement for every point on a vehicle.
The second part of any measurement on a unitized vehicle is the width. Think of a car as an Oreo® Cookie but without the filling. Yea, I know it's not fun thinking of an Oreo without the filling, but what I want you to do is to rotate the cookie on its side and so each half is facing you. Now place a piece of paper between the 2 halves. You can measure the distance from the outside of one half cookie to the piece of paper as well as the other half and that distance will be equal. As with the datum plane, vehicle manufacturers establish center plane and that splits the vehicle in half. From this center plane, we will give this dimension a zero rating on the measuring scale. We can now measure from zero all points to the right and left of the center plane.
Here are two more words to commit to memory: symmetrical and asymmetrical. Symmetrical means that any point on the left side of the plane will have the same length, width and height as the same point on the right side of the center plane. Asymmetrical means that the point on the left of the plane will be different than the same point on the right side of the plane. Most of the asymmetrical points are usually found in the width dimensions.
To understand which points are symmetrical and which are asymmetrical, a good frame measuring dimensional book is essential. The latest electronic measuring systems incorporate this information in a computer database and conveniently display it on the system's video screen, but for non-electronic systems, a subscription to a dimensional book service is essential. Just imagine the problems which would arise if you did not have a dimensional guide and you assumed that all of the measurements to either side of the center line were symmetrical. You could pull that car all day and never get it right.
The next important term in unitized vehicle repair is mash. It is defined as a shortening of the length of the vehicle. When analyzing a mash condition, pay particular attention to crush zones and kinks that might occur in the collision. These items should be noted on the estimate and most often replaced as per I-CAR recommendations.
Sway condition is the movement of the structure to the right or left of the center line/center plane. When looking at a sway condition, play particular attention to sealant, which has a tendency to open up. I find this very helpful when trying to determine how far back the damage has traveled through the inner structure.
Sag, a term which refers to my stomach as I get older, also refers to the movement of structure up or down.
Diamond refers to a condition of one rail being farther back than the other. This particular condition is very common on ladder or full frame vehicles such as trucks. The final type of damage is twist, which is usually associated with the height of the center section of the vehicle.
Now that you understand these tems, lets start using them in the description of the damage when writing our estimates. For example, you should write "pull and correct sag condition" or "pull and correct sway condition" (2 separate line entries) instead of "pull and square body." These terms are more descriptive of the type of damage and of the scope of work to be done to correct it. With the damage correctly described, we are ready to measure.
First, we establish reference points or location points to set up the measuring system. Because most accidents involve front or rear damage, I will give you an overview of this type of repair. We know that a vehicle is divided into 3 sections -- front, center and rear. The center or passenger section is the strongest of the three for obvious reasons. A front or rear section could have as much as a 45% reduction in length yet the passenger section would suffer only a 3% reduction. Being the strongest and the least likely to suffer much damage, this is where we usually set up our measuring system. On unitized vehicles, the location of the reference points is usually at the 4 corners of the floor/passenger compartment. Most measuring systems will use three of these points to set up the system and establish a base or zero measurement. Once the zero points are established, we now have the ability to measure every point for width, length and height. With measurements taken, we can begin the pulling process.
It is beyond the scope of this article to describe in detail how to pull a vehicle. For that you need to enroll in a hands on technical program offered by the frame rack manufacturers. For now, I would like to offer some pointers which apply to all types of equipment.
When we begin to pull and correct damage, we need to first repair the last damage done in the collision. For example, we have a front-end collision and the damage has traveled back to where the rail attaches at the firewall. The firewall, then, is the area that you fix first. Once that part is corrected, you proceed to the front of the vehicle correcting each point to length, width and height. When you write an estimate, you need to note specifically how far the damage has traveled to justify the amount of hours that are needed to correct it.
Another term we need to become familiar with is blocking. We use blocks, chains and cables to secure to secure the components from moving as we are pulling. Visualize a rail that has sag condition and has been driven upwards (the bend is approximately 18" back from the front). If we were to begin a down pull, the entire rail would move down and this is would create more damage. We need to isolate the bend and we accomplish this with blocks placed at bend or slightly in back of it, creating a fulcrum effect. When we pull, the rail will only move from the edge of the block forward.
Let's say we have a vehicle that has been in a front-end collision which resulted in a sway condition with the left rail moved 15 mm farther than the right. We would pull the structure and correct the right rail first. Since they are tied together by way of the core support, we would want to isolate the right rail with either another tower or with a cable/strap. With the right rail isolated so that it cannot move, we can now pull the left rail.
Correctly repairing a unitized vehicle takes the right equipment, training and proper planning for each pull. Be certain that your frame techs always analyze the damage, measure the vehicle with a 3 dimensional measuring system, and then construct a complete a pulling plan for the entire vehicle before making that first pull. As an estimator or manager, you should take the time to observe the pulling process to better understand it. Remember, if you haven't got the time to do it right, when will you find the time to do it over?