This method of setting bearing clearance is based on Hooke's law: In the elastic range of the material, the system deforms proportional to the applied load (ie Fu003dkx, where ku003delasticity coefficient). This approach assumes that there is little part-to-part variation and that the total system deformation of the assembly is consistent and repeatable under a given load (Figure 9). To determine suitability for a particular system, the dimensional reference condition, the deformation constant, must first be determined. The deformation constant is the (average) system deformation resulting from a known set load applied to the bearing, obtained by testing several trial units. This system deformation is usually measured by measuring the shim gap (Figure 10). The ACRO-SET system constants are then derived. It is equal to adding the required bearing clearance to the set load deflection constant. In production, this constant is added to the amount of shim gap to determine the final shim pack thickness for each unit. Contact a Timken sales engineer for assistance in determining ACRO-SET system constants. Simply use the shim table (Figure 11) when selecting the final shim set thickness for each device. The shim set thickness noted in the table incorporates the effect of the ACRO-SET constant previously determined. Note that with the shim gap measured at two locations 180 apart, the proper shim set size can be easily determined from the shim table. We will use the planetary drive wheel assembly (Figure 10) to illustrate the ACRO-SET method. 1. Determine the set load P by pre-testing and apply this load through two bolts (180 apart). The applied load is proportional to the bolt torque. (In general, apply a higher seating force first, then rotate the bearing to ensure the parts are properly seated before taking ACRO-SET shim clearance measurements). Second gap measurement (180 position), mm The first gap measurement is as follows: (0 position), mm 0.94 0.97 0.97 0.97 0.99 0.97 0.99 0.99 0.99 1.020.71 0.97 0.99 0.99 1.02 1.02 AcrO-SET Method 2. Rotate or oscillating the bearing while applying the set load P and measured Shim clearance, measured first at 0 degrees and then at 180 degrees. 3. Select the appropriate shim set thickness from the shim table, which is equal to the measured gap plus the pre-determined ACRO-SET system constant (derived from pre-tested assemblies). Figure 10 averages the two readings and gives the final thickness of the shim pack. In this case, the shim thickness for the 180 degree position is 0.66, for the 0 degree position is 0.61, and the final shim thickness is 0.97. 4. Install the final shim set and tighten all bolts according to the tightening torque . Special notes for the ACRO-SET method: 1. The seating and setting load of the bearing is usually applied by several bolts (i.e. load u003d NT/(dμ), where: N u003d number of bolts, T u003d torque of bolts, d u003d The diameter of the bolt, μ u003d thread friction coefficient, usually μ u003d 0.17). In general, the applied seating force should be 2-3 times the Ca(90) value of the bearing with the lowest capacity in the system, and the applied set load should be 0.75-1 times its Ca(90) value. 2. Adjustable parts with loose fit. The adjustable position is preferably a loose fit. However, the outer ring and inner ring can also be a tight fit as follows: A. The outer ring is a tight fit to the bushing and the bushing is a loose fit to the housing. B. In the operation of setting bearing clearance, use a standard outer or inner ring with a loose fit (need to compensate for the average tight fit in the ACRO-SET constant). C. Design the tight fit compensation in a specific tool (PROJECTA-SET). 3. Components necessary for the ACRO-SET method, such as housing walls and cover plates, must be produced with consistent dimensions for each part. 4. The design must be such that a set load can be applied to the movable bearing part for adjustment. 5. Bearings must be rotated or swung when the set load is applied. 6. The design must facilitate measuring the clearance of moving parts. 7. The thickness of the actual shim set used should be confirmed. ACRO-SET Method Figure 12. PROJECTA-SET Concept As shown in the diagram, the PROJECTA-SET method is to project the two faces required to measure the spacer size from the hard-to-reach position of the gage to the measurable position. The tapered roller bearing assembly includes the assembly pressed into the lower inner ring of the shaft (B), the upper and lower outer rings, and the upper inner ring is not included. The spacing datum projects the lower inner ring table a known distance (x) (from the end of the shaft). The gage datum projects the upper outer raceway the same distance (x). The upper inner ring in the measuring position. The measuring points (eg dial indicator for small batch measurements, electronic transformer LVDT for high volume measurements) are arranged and preset to indicate the size(s) of the spacer. In this figure, applying a known force to the movable datum (H) to install the upper inner ring on the projected track gauge will give a direct reading of the desired spacer size. In practice, alternatives can be used to meet any special production equipment and requirements (eg, a static datum that moves the head above to apply a measurement load). Typical applications of the ACRO-SET method Examples of where the ACRO-SET method has been successfully applied to tapered roller bearing setting clearance include: manual transaxles, drop box transmissions, agricultural tractor axles, power take-offs, planetary gears , differential and drive pinion shafts, gear reducers, off-road truck and tractor wheels.