The shim sham shuffle is actually a well-known tap dance combination and has nothing to do with NAAMS. It was just a fitting title for the topic covered in this blog post. In this post, we will discuss Shims & Spacers from the NAAMS Global Standard Components – Assembly.
Shims are washers or thin strips of material used to align parts, make them fit or reduce wear. Shims are designed to fit in between blocks and fixtures to provide support or reach a dimension required in the assembly. Typically designed in a U shape matter so that they can fit between mounting screws. This shape helps to make them easy to install and remove or replace. Designers will use shims individually or as packs of 5, 6, or 7 pieces. Thicknesses range from 0.25mm to 2mm. Many assemblies require a tolerance to be hit in relation to a length or height, shims allow designers to hit these tolerances. They can be stacked between NAAMS NC blocks, L blocks, or pin retainers.
They come in a variety of sizes and styles. The material is typically very thin so that they can accommodate smaller to larger tolerances. NAAMS specification for the material is an SAE cold rolled steel. Different widths of the shims can have different surface treatments either yellow zinc dichromate, black oxide, or none. Yellow zinc dichromate surface treatment is used for corrosive resistance and acts as an anti-rust primer. Black oxide coating is also for corrosion resistance.
Spacers are pieces of material use to create or maintain a distance between two things. NAAMS spacers are designed for similar purposes as shims but are thicker in dimension. Designers can determine if they require either a shim or spacer in their assembly. It depends on the tolerances they have in their assemblies. Most spacer designs consist of holes and slots instead of open-ended U shapes like the shims. They can come in 3 to 5 hole configurations and thicknesses of up to 7mm. Spacer material can be 1020 SAE Hot Rolled Steel or 1018 SAE Cold Rolled Steel with a black oxide surface treatment.
All assemblies have tolerances to hit and will have concerns about parts wearing out through the life of their machines. Even the smallest parts like shims and spacers play a larger role in the quality of machines and the product they output. Small parts such as these can greatly help an engineer throughout the design phase and even the maintenance phase. One can make the comparison that engineers may have to “shuffle” their design to fit shims (and/or spacers!) between components hoping their assembly will not be a “sham”, hence the NAAMS shim sham shuffle!