How to Properly Measure for a Sheave Replacement

How to properly identify and measure a FLANGE MOUNTED TRACTION SHEAVE replacement.

Being able to measure a sheave is the most critical step in the accurate identification and reproduction of a replacement part. In this case, we’ll focus on one of the most common type of sheaves, the FLANGE MOUNT GEARED TRACTION machine sheave.

In our example here, we are using a Titan I Traction Machine. Let’s walk through this step by step on how we go about identifying this as a FLANGE MOUNT GEARED TRACTION SHEAVE.

Firstly, as you can see, the machine itself is a geared traction machine due to it’s use of a traditional worm and gear transmission and not a direct motor drive as is the case with a gearless machine.

Secondly, the sheave is acting in a traction capacity. That is, it grips the ropes thereby acting on them with a force consistent with the direction of travel of the sheave. Unlike a deflector or non-traction sheave, a traction sheave’s rope grooves will have a geometric profile other than a basic “U” in order to physically “grip” the rope.

Lastly, the sheave is mechanically fastened to the spider assembly directly with fasteners and may also depend on an interference fit as well. This is unlike a hub-mounted sheave, which may involve mechanical fastening and/or a key and keyway, but typically relies on an interference fit directly to a dynamic or static main shaft.

We can now start out by identifying this, and any other similar sheave, as a FLANGE MOUNT GEARED TRACTION SHEAVE.

Let’s walk through the steps to properly

measure this type of sheave.

ROPING CONFIGURATION:

Count the number of rope grooves on the existing sheave. Next determine the rope diameter. If necessary, use a rope gauge supplied by most wire rope manufacturers, a caliper, or a standard sized ground rod to measure. Then measure the groove or rope pitch. This is a commonly misunderstood dimension. It’s simply the distance between the center of one groove to the center of the adjacent groove. It is occasionally called “rope or groove centers”. The easiest means of measuring this, provided there is no damage to the existing rope grooves, is to measure from one edge of the groove to the corresponding edge of the adjacent groove. This is far easier than the precision tooling necessary to determine the exact groove bottom and subsequently the groove centers. Roping configuration is commonly expressed in the following format:

Number of Ropes by Rope Diameter by Groove Pitch. For example, 5 x ½ x 7/8” means the sheave has 5 cables, ½” rope diameter, on 7/8 rope or groove centers.

Now, let’s continue by measuring this sheave’s outside diameter…or “OD”. If one is available, use an outside micrometer for the most accurate readings. Otherwise, use a caliper, rigid scale, or a tape measure to determine the diameter.

Next, measure the face width. This is the distance across the entire face of the sheave. As with the outside diameter, the most accurate measurement will come from an outside micrometer, however, a caliper, rigid scale, or tape measure can be used.

As a side note, many manufactures produced a solid cast spider that integrated the traction sheave into the spider assembly. These solid cast spiders are non-demountable. The following dimensions cannot be measured on a non-demountable assembly.

Let’s measure the bolt circle pitch. This is the distance from one fastening bolt-hole center to the adjacent hole center. By providing this dimension, we can mathematically determine the bolt circle diameter. Next, count the number and size of the mounting bolts. If there are any push off bolts, provide the same measurements and specifications as with the mounting bolts.

Next, let’s measure the bore of the flange. This dimension may be critical and require an inside micrometer or the use of a standard and an outside

micrometer for indirect measurement if there is an interference fit on this surface. We’ll discuss this further in just a moment. Otherwise, a caliper, rigid scale, or tape measure may be used provided the dimension can be provided within a 64th tolerance.

Next, we’ll measure the interference fit of the mounting surface. This is a highly critical dimension and must be measured using a precision inside micrometer, or standard and outside micrometer for indirect measuring. Tolerances for this dimension are commonly +/- 0.0005.

Lastly, we’ll measure the offset of the roping configuration. Use a rigid straight edge and lay or support it across the outside of the sheave face. Now, use a depth micrometer, caliper, rigid scale, or tape measure to determine the distance from the face of the sheave to the mounting surface. If both side result in identical measurements, the sheave is said to be “center mount”. If there is a difference in measurements, it is an “offset” sheave. This offset is frequently expressed in terms of the distance from the outside of the sheave face to the mounting surface only.

News Date: 
Thursday, July 17, 2014