Choose, Use, Store Shims Properly
Jane Alexander | January 25, 2018
Shims are crucial in efficiently achieving precision shaft alignment. Proper choice, use, and storage of these items are key.
Tom Shelton of VibrAlign (vibralign.com, Richmond, VA) provided some important tips in a recent post on the company’s blog.
• Always use new, clean shims. The cost of new stock is minimal when compared to the cost of extra downtime caused by an inefficient precision-alignment process.
• Improper storage and re-use of old shim stock can contribute to soft foot. Dirt, debris, bent shims, and inconsistent thickness of cheap carbon-steel shims can drive up costs from lost time.
• Shims for a given alignment should be of the correct size and the same size. They should be made of stainless steel, a material that can withstand the compression created by a machine’s mass and clamping force of hold-down bolts. Never combine multiple shim sizes or materials in the same stack.
• When selecting the shim size (A, B, C, or D, for example), choose that which offers the most contact between the foot and base and has the proper slot size for clearance around the hold-down bolts of the movable machine.
• Be mindful of the position of shim stacks in relation to hold-down bolts. Maintain clearance between the shim and bolt to prevent damage to the stack (bent shim) or bolt threads. A bent shim can induce soft foot where soft foot doesn’t actually exist.
On a Related Note: Handle Alignment Tools with Care
Although precision measuring equipment is typically made for industrial settings, it should be handled with care. Important rules to keep in mind:
• Keep precision tools in their original cases. Environmental effects from improper long-term storage can be detrimental to this equipment.
• Don’t overlook routine maintenance. Calibration should be performed annually or, at a minimum, every other year.
• Casually throwing dial indicator sets into a box or drawer can damage mounting brackets and cause hysteresis (internal friction) in the indicators.
• Regarding laser shaft-alignment systems, remember that dirty sensors (laser and detector lens) can lead to non-repeatable measurement results. All system components should be stored properly in the carrying case to protect them from damage. EP