Shop Operations: A fresh look at 1-2-3 blocks

Simply put, a 1-2-3 block is a common shop setup tool usually made of hardened steel that measures 1″ thick × 2″ wide × 3″ long. Machinists use the blocks for myriad machine and inspection setup tasks.

The blocks are accurately ground to size and orthogonal geometry, within 0.0002″ (5µm), with the intention of trusting them as de facto shop floor setup standards without regard to delicacy when performing setups.

Many machinists fondly remember their early training or apprenticeships when they made 1-2-3 blocks from scratch under the watchful eye of a master toolmaker. These young machinists carefully machined the blocks oversize, heat-treated them and then ground them to size. They quickly learned that precisely holding size and geometric features to close limits is more challenging than it seems at first glance.

Figure 1 (above). This array of 1-2-3 blocks shows some of the available hole configurations. Figure 2 (below). It would appear that these holes should allow many possible block configurations to be assembled, but the configurations are limited.

All images courtesy of T. Lipton.

One element making a 1-2-3 block so useful is its ability to simultaneously be a work support and a gage. Some toolmakers pride themselves on achieving nearly gage-block accuracy and imparting lapped-surface finishes. It’s critical to harden the blocks for maximum durability on the shop floor.

These blocks typically are riddled with an array of holes, which, depending on the maker’s whim, can be drilled, tapped, counterbored or processed some other way. Sometimes holes are drilled to lighten the blocks. Supposedly, the hole patterns help machinists attach the blocks to machines or connect them to form more elaborate setup aids and fixtures.

The blocks are typically used in pairs, much like parallels. But with clever bolting arrangements, their applications go well beyond that of a common spacer.

Figure 1 shows an array of 1-2-3 blocks with various hole configurations. I will focus on blocks with threaded attachment holes because this is the feature that makes them a universal inspection tool.