Dynotech Driveshaft Standards
There are several key factors that Dynotech produces all driveshafts to: Tube runout, U-joint yoke phasing, U-joint clearance, Balance repeatability and Balance speed. By controlling each of these factors they produce a smooth running, reliable driveshaft.
All of Dynotech's driveshafts are built with the following targets:
- U-joint clearances are held to less than 0.002"
- Shaft runout is held to less than 0.015"
- All driveshafts are balanced to less than 0.12 oz-in
- All driveshafts are built to within 1/16" (0.0625")
- All driveshafts are high speed balanced between 5,000 and 8,000 RPM
Learn more about these targets and how they're met below.
Tube Runout is a measurement of how straight your driveshaft is as it rotates about its diametric centerline (axis of rotation).Dynotech suggests that at least three locations be controlled during the build of the driveshaft (both ends and center). Tube runout is a direct contributor to driveshaft balance. If you have high enough runout your driveshaft will not balance without welding excessive weight on one side. Dynotech keeps all of their tube runouts at 0.020” or less over the entire length of the tube. During both the weld and balance phase of the driveshaft development runouts are checked and minimized.
U-Joint Phasing and Clearance
U-Joint Phasing and Clearance can play another significant roll in the build and balance of your driveshaft. During the assembly of your driveshaft you must make sure that the U-joint is centered in the weld and slip yoke. If the U-joint is off center the entire weight of the driveshaft is rotating off the driveshaft centerline. In addition, if you do not have your U-joint phasing correct you will create a fourth order vibration as a result of the non-constant velocity of the standard U-Joint. (A detailed subject for another time.) U-joint phasing is the alignment of the weld yokes during the build process. The centerline of the U-joint hole on the weld yoke at one end will be in line with the centerline of the U-joint hole on the other end. Dynotech uses specialty fixturing to ensure that the driveshaft is built with less than 0.0025” joint clearance after the U-joint installation and weld yokes are phased to within 0.1 degrees from one end to the other.
Balance Repeatability and Speed
Balance Repeatability and Speed is the final ingredient to what makes a good driveshaft. Dynotech balances all driveshafts to 0.20 oz-inches or less and we expect our measurement to repeat within ± 0.05 oz-inches. An ounce-inch is the standard balance measurement units that relate to imbalance. (See figure 1A) Balance speed is another key element of driveshaft manufacturing. Your driveshaft should be balanced as close to operating speed as possible. Whatever force (imbalance) is generated at 2,000 RPM
is increased four-fold at 4,000 and nine-fold at 6,000 RPM. Even the smallest imbalance force at slow speed can make your car shake at high speed.
Critical Speed can be reached in any shaft depending on the physical characteristics of the shaft and its speed of rotation. The critical speed of the driveshaft is the point where the first order resonant frequency is excited by the speed of rotation. Avoiding long mathematical equations, it’s the point that the driveshaft starts to “jump rope”. There are several ways to handle the issue of critical speed, such as shaft material, size and design. With something as simple as changing from a steel shaft to a MMC aluminum shaft you could see as much as a 12% increase in critical speed. Items such as balance, balance weight location and joint clearance all have a direct effect on critical speed.
Learn more about the different material choices here.