How to Measure an Air Shaft?

When measuring an existing shaft for replacement, the first question you should ask before measuring the shaft is: Do you have a drawing of this shaft?

If so, please verify the accuracy of the drawing. Shafts can be altered and the drawing doesn’t always match. If a drawing is not available, please continue.

Using a measuring tape and digital caliper while following a few basic instructions allow you to acquire measurements and create a sketch which will be adequate for our engineers to use as the basis for a CAD drawing. The measuring tools need to be accurate.

Tape measures can be periodically checked with a caliper.  Try to avoid ‘bows’ in the tape while measuring by laying the tape flat on the shaft.  Beginning the measurement at the 1″ tick helps avoid any inaccuracies that may have developed between the ‘lip’ at the end of the tape. Sometimes the ‘lip’ can be altered when the tape automatically snaps back into position after you’ve completed a task. Remember to subtract one inch when doing so. Steps 1 thru 7 require a measuring tape.

Step 1: Measure the total length of the existing shaft. You may find that using a straight edge on the end of the shaft allows for a more accurate measurement. Do not include attachments such as gears, couplings, or other items which will not be provided with the shaft. This may require that you request that the bearing, gear or coupling be removed so that you can see the ‘naked’ shaft.

Goldenrod will provide a quotation for the shaft only. If you would like pricing on ancillary items, we can provide and install a gear, coupling, or bearing for an additional charge. Please provide all part numbers.

Step 2:  Locate the position of the roll (web area) relative to shaft and load bearing centers (explained in Step 4).

Step 3: Determine maximum body length. This is achieved by measuring the distance between the machine frames, allowing for roll clearance including side adjustment, if any. Note: The body should be as long as practical without interfering with machine frames or bearings.  Note: Also provide information as to how the shaft is placed in and taken out of the machine.  If placed in the machine with lifting hooks for example, where do the hooks make contact with the shaft?  Does the rewind shaft roll out onto a lifting table?

Step 4:  Measure the distance (length) between the bearing centers  where the shaft ends rest in the machine. Note: The BC dimension is the basis for all shaft stress and load calculations.  It is required on all data sheets, sketches, or drawings. Also, as mentioned in Step 3, note the inside to inside frame dimension of the machine.

Step 5:  Show overall lengths of journals and the length of each individual step.  Remember, the sum of all the components must equal the overall length (OAL) of the shaft.  Always measure the overall length twice.

Step 6:  Show position of drive/brake connector and dimensions.  This could be a keyway, slot, flat area, square, pin at 90 degrees to the journal, or other mechanism.

Step 7:  Show position of air valve(s).  Please note if valve location shown is critical or if it is possible for Goldenrod engineering can choose placement of valve.  Also indicate if the shaft has a large air valve (a little larger than a dime) or small/mini air valve.

Step 8 and 9 requires a digital caliper. (Many machines today will be assembled using metric measurements.  Find a caliper that can display values in both metric and standard increments).

Step 8:  Measure journal diameter at bearing area: NOTE: Bearings need to be held in place or retained.  There is typically a shoulder on one side of the bearing and a snap ring or lock nut on the other.  If there are two bearings side by side, please indicate.

When bearings assembled on journal are not able to be removed:  Measure O.D. X I.D. x width and name the bearing manufacturer and bearing number (even if customer is providing bearing).  The journal diameter can then be determined from the bearing manufacturer’s specifications book.

When the shaft runs on bearings or if the bearing surface is mounted on machine:  Provide verbal description of load bearing area on machine and length or bearing area (wear area) on shaft journal.  Allow for sidelay adjustment of shaft in machine.

With bearing assemblies:  Provide sketch showing all dimensions of bearing housings and describe the item holding the bearing in place (nut and washer, or snap ring.)  Please note any dimensions which can not be changed to ensure proper shaft operation. Note: If you are using Safety Chucks, try to identify make and model number.

Step 9:  Measure journal diameters.

Steps 10 and 11 require both a measuring tape and digital caliper.

Step 10:  Measure journal options such as keyways, pinholes, tapers, etc.  Keyways: Measure the length, depth and width of the keyway.  Also indicate position of keyway on journal.  The keyway can be open ended, meaning they begin at some point on the journal and continue all the way to the end; or the can be closed, meaning that the entire keyway is located somewhere on the journal.  Pinholes should be measure for diameter and placement in reference to some identifiable location on the shaft – i.e. ‘end of journal’, etc.  Tapers: measure the beginning of the taper, the end of the taper and the width of the taper.  This will allow our engineering to determine the angle of the taper.

Step 11:  Measure the width of the load bearing surfaces. Identify the material from which the bearing surface is made; i.e. roller bearings, bronze, plastic, or other.  Note: If the shaft is supported by cam followers, the journals are heat treated or ‘hardened’.  Many times you can tell if the journal is heat treated by trying to scratch it with the hardened points of you caliper.  If you cannot plainly see the scratches, it is hardened.

Some manufacturing plants have spare shafts available for you to measure at any time.  Others have only one shaft which will be in use almost constantly.  It is advisable to inquire when setting up your appointment as to when a shaft will be available to measure so that you waste little time to perform this task.

HELPFUL HINT!  Keyways, pinholes, tapers, and slots wear with use and may be difficult to measure because their shapes are distorted.  When this occurs, you will want to examine this part of the shaft thoroughly to find any original areas to measure, or measure its mating part (pin, chuck, key, etc.).  A brief discussion with the department supervisor or maintenance man may provide clues, a replacement part, or a sketch or drawing they have made in order to make replacements.