It ensures consistency through three separate datum surfaces, ultimately leading to tighter pieces and extremely precise parts. Six degrees of freedom are considered along a 3D coordinate system through datum surfaces A, B and C. With A controlling three degrees, B controlling two degrees and C controlling one degree along the different axis’. This triangulation method is instrumental in pinpointing exact locations on both the parts and the fixtures. Using the six degrees of freedom established by the datum surfaces, GD&T is a means of continually attaining and measuring consistency.
Through the implementation of this technique, our machinists and engineers are able to refer back to a controlled feature on each part at any point during the manufacturing process. First, GD&T is essential to maintaining and controlling the part’s weight, balance and dimensional accuracy. Next, the inspection process remains consistent from part-to-part and batch-to-batch, allowing for materials to flow smoothly on the production line. Lastly, by constantly referencing back to the datum surfaces we are able to make finite adjustments and improvements without abandoning even the smallest detail. Not only do our strategies determine a strict standard for all individual products, but they serve as a built-in auditing system active in maintaining that standard day-to-day and for years to come.
A typical V8 racing engine running at 10,000 rpm equates to the rotating assembly spinning at over 166 times per second with virtually all of the force then being transferred through the connecting rod. For every revolution, the piston and connecting rod must go through one full compression cycle and one full tension cycle. Under these extreme conditions, connecting rods manufactured with a wider tolerance margin are at risk of causing oscillations and stress concentrations in the rotating assembly. In turn, the friction of the reciprocating assembly is compromised. GD&T works to eliminate these risks by enabling Oliver to reach the highest possible degrees of concentricity, circularity, parallelism, perpendicularity and a number of other factors that govern the relationship between the crank and pin bores of our connecting rods.
Concentricity of the bores is critical to ensure friction free runout relative to the piston pin and crank journal. Twist and bend in the automotive world is often associated with the quality of connecting rods. Oliver goes well beyond these simple concepts and fully defines the relationship between the pin and crank bores.
As one of the most challenging measurements in GD&T, concentricity is obtained through in-process air gauging, verifying that Oliver rods adhere to the highest accuracy standards. Air gauging, described in detail below, is an extremely precise measurement device for this particular feature. Even better than the most accurate coordinate measuring machine (CMM), air-gauging effectively monitors concentricity of every Oliver rod. Since World War I machinists have used jig borers to ensure accuracy of bores. Through Oliver’s multi-step GD&T governed process, we have developed a modern day systemic version of the jig borer specific to connecting rods. This confirms that every Oliver rod has met our strict tolerances.
It seems like this would be a common practice for all connecting rod manufacturers. However, modern machining practices allow some manufacturers to cut corners and create concentricity of the bores through the honing operation, a function and tolerance never intended for any hone machine.
At Oliver concentricity is built into the part throughout our multi-step process, ensuring that the hone operation is correctly utilized to impart the final surface finish optimized for lubrication. Because extremely small tolerances, reaching beyond visibility, are often taken for granted, it is what we cannot see through conventional measurement techniques, that makes Oliver rods stand above the rest.
Ultimately, our commitment to achieving exact measurements between the pin bores and intangible axis surfaces of our connecting rods is only possible through GD&T. We are confident in our rods’ ability to reduce frictional loss to the absolute minimum amount, directly improving engine durability, performance and longevity. Most importantly, it allows the entire reciprocating assembly to be more efficient and ultimately generate more power.