Flanges & Yokes

BTI engineers and manufactures a complete line of manual, semi-automatic, and fully automatic precision measurement and testing equipment for flanges, yokes, and related assemblies and components

Flanges and yokes are small machined parts that decide whether a much larger assembly runs smoothly. A companion flange, a weld yoke or a slip yoke locates the driveshaft to the transmission and the axle, and any eccentricity it carries becomes runout and unbalance in a rotor several feet long.

Balance Technology Inc. builds balancing and dimensional measurement equipment for companion flanges, weld yokes, slip yokes, tube yokes and the end fittings used in driveline assemblies.

Small Part, Large Consequence

The mass of a yoke is trivial next to the driveshaft it joins, which leads people to discount it. What matters is not the mass but the geometry: the pilot diameter and the flange face locate the shaft, and an error there tilts or offsets the entire assembly.

A pilot machined eccentric to the bore by a small amount produces runout at the far end of the shaft that is larger than the original error, because the shaft amplifies an angular misalignment over its length. The same logic applies to a flange face that is not square to the axis.

Where the Unbalance Comes From

These are machined forgings and castings, and the dominant sources are machining offset — the bore, pilot and face not concentric with one another — and the asymmetry designed into the part. Bolt hole patterns, grease fittings, keyways, splines and clamping ears are all deliberate departures from rotational symmetry, and they have to be accounted for rather than corrected away.

Forging flash variation and core shift in castings add a distributed contribution that machining does not remove.

Component or Assembly

Both approaches are used and they answer different questions. Balancing yokes and flanges as components catches parts that are out of family before they are welded or bolted into a shaft, which is cheap and prevents scrapping a finished assembly. Balancing the driveshaft assembly controls what the vehicle actually receives.

Production practice on a driveline usually does both: component control as a gate, assembly balance as acceptance. The component stage matters most where the assembly correction range is limited, because a yoke that arrives badly out of family can consume the entire weight budget on the shaft.

Correction

Material removal by drilling or milling on the flange face, the outside diameter or a designed boss is the usual method. The constraints are that the pilot, the bore, the bearing seats and the face must not be touched — those are locating surfaces — and that section thickness limits what can safely be taken from the rest.

Setting the Tolerance

Tolerances follow ISO 21940-11 from a balance quality grade, the component mass and the service speed. Because a yoke is light and runs at driveshaft speed, the permissible residual is small in absolute terms, and tooling contribution becomes a meaningful share of the budget. BTI publishes a free ISO 21940-11 balance tolerance calculator with the method behind it — grade selection, the permissible unbalance formula, plane allocation, and a worked example.

Runout Is the Other Half

Balance and runout are separate characteristics, and on these parts runout is frequently the more consequential. Pilot concentricity, face squareness, bore-to-pilot relationship and spline condition all need gauging in their own right. A line that measures balance and not geometry will pass yokes that cause driveline vibration no balancing can fix.

What Else Gets Measured

Flange and yoke lines commonly combine balancing with dimensional gauging of bore, pilot, face and bolt pattern, runout and squareness measurement, spline gauging, hardness testing, and crack detection on forgings.

Equipment Configurations

Layouts range from single manual stations through to automated cells combining gauging, balancing and correction, and vary to accommodate any production rate. For platform selection across the full range, see BTI balancing machines.

Related applications include driveshafts, axles and RDU components and transmission components.