Correctly Using a String or Straightedge to Measure Misalignment

Outside of the Gates EZ Align Precision laser Tool, a straightedge and/or a string are commonly used to measure and monitor misalignment in belt drive systems.  Unfortunately, these tools are commonly misused which can result in inaccurate conclusions about the actual drive alignment. 

A straightedge, such as a large ruler or other precision machined edge, should be used to project the orientation of one pulley face with respect to the other.  In other words, the straight edge should be contacting the reference pulley across the entire face of the pulley and be contacting both edges.  This straight edge projection should then be compared to the secondary pulley to determine the severity of the misalignment. 

When utilizing a string to gauge misalignment it is important to ensure that the string is held taught and is contacting the pulley at both edges of the pulley face.  The string then needs to be kept as straight as possible to ensure the most accurate alignment conclusion can be made. 

It is important to verify that the edges of both pulleys are of equal thickness, especially with V-belt sheaves, given if the edges are of different thicknesses the actual riding surfaces of the belt can be misaligned regardless of the edges being aligned.  Therefore, if the edge thicknesses are different, it is necessary to quantify this difference and ensure the pulleys are offset to account for this thickness variation.  Though this method is relatively simple, it can easy be misused and result in misaligned drives with decreased life, performance, and stability. For any additional questions feel free to contact us at ptpasupport@gates.com or 303-744-5800.

When In Doubt....

F = MA Actually, a simple formula that is quite often forgotten or overlooked by designers. The key point to remember is that the appropriate sizing of your belt drive is only as good as the load calculation or estimation used to design it. F = MA

Use of Flanged Sprockets

Guide flanges are needed in order to keep the belt on the sprocket. Due to tracking characteristics, even on the best aligned drives, belts will ride off the edge of the sprockets. Flanges will prevent this belt ride-off. On all drives using stock or made-to-order sprockets, the following conditions should be considered when selecting flanged sprockets:

1. On all two-sprocket drives, the minimum flanging requirements are two flanges on one sprocket or one flange on each sprocket on opposite sides.

2. On drives where the center distance is more than eight times the diameter of the small sprocket, both sprockets should be flanged on both sides.

3. On vertical shaft drives, one sprocket should be flanged on both sides, and all the other sprockets in the system should be flanged on the bottom side only.

4. On drives with more than two sprockets, the minimum flanging requirements are two flanges on every other sprocket or one flange on every sprocket —on alternating sides around the system.

On made-to-order sprockets, flanges must be securely fastened, such as using mechanical fasteners, welding, shrink-fit or other equivalent methods.