Frame Reference Point Description
Reference points are locations on a vehicle which correspond to specific measuring points. Use the reference points when checking the vehicle structure.
Dimension charts may use the center of a hole, bolt head, or nut, etc. as a reference point. A description and location chart will tell you how and where the measurements should be taken. The most accurate reference point is a gauge hole or a control hole used by the assembly plant in order to control tolerances when the vehicle was built. Refer to Frame Control Hole Description for more information about control holes.
Frame Control Hole Description
Control holes are round or oval holes located in the underbody structure sections, the upper body, and the body sides. Some control holes can be identified from other holes by a turned up lip on the inside of the hole. This reinforced lip reduces the possibility of hole distortion and increases accuracy during assembly. Utilize control points whenever possible when measuring underbody dimensions, in order to obtain the most accurate readings.
Scheme 2
Frame Reference Point Description - Symmetrical
Symmetrical reference points are 2 corresponding points on opposite sides of the centerline that have equal specifications in length, width, and height. Use symmetrical reference points in order to make quick inspections for underbody structural damage.
Scheme 3
Frame Reference Point Description - Asymmetrical
When 2 corresponding reference points have different measurements, they are called asymmetrical. If you perform a quick cross check and the measurements are unequal, you should check the dimension charts in order to find out if the measuring points are symmetrical or asymmetrical.
Minimizing Frame Service Description
Frame service can be minimized by lessening the concentration of stress in small areas of the frame.
- Use vehicles only for the purposes for which they were designed. Do not overload the vehicle. Load the vehicle evenly. Avoid localized loads. Do not operate the vehicle on extremely rough terrain at excessive speeds. Determine the forces placed on a frame from the operation of equipment when picking a frame for a new vehicle or reinforcing a frame.
- Follow the recommended practices when repairing a frame. Follow the recommended practices when mounting a body or equipment on a frame. Avoid sudden changes in the section modulus. Do not drill holes in the frame rail flanges. Space holes in the web section of a rail at least 13 mm (1/2 inch) apart. Use existing holes whenever possible. Do not cut holes with a torch. Do not overheat the frame rails. Avoid welding on the flanges. Do not allow 4 or more holes to exist on the same vertical line of the web.