Home Shop Machining/Equipment/Reference Tools

Reference Tools for Home Shop Machinists
Before any of this will make sense, it's important to understand relative verses absolute accuracy. At one time in history, the carpenters building a house would make a story-stick. This stick would have marks saying doors were this wide, the ceilings were this high, and so on. It didn't matter where exactly those marks were so long as the person making the door and the person making the door frame used the same stick, or at least a decent copy of it. This is relative accuracy. However, in an age where the door is made in a factory, with the hinges and handles made in another, and even prebuilt door frames made somewhere else, that story-stick is going to have to get around. Thus, we invented absolute measurements, measurements against a fixed, repeatable standard.

In a home shop environment, if a person makes a part and then that same person makes a second part to fit, absolute accuracy is not that important. The two parts could be perfectly machined to match each other to a very, very high degree of accuracy, but yet have no relation to any outside standard. On the other hand, if some pre-machined outside part is going to be used, say a bearing, then absolute accuracy becomes important. Many times, that pre-machined part can be used as the standard that everything else is based on. Other times, references become important.

A reference is something that is known to a specific standard of accuracy. A shop's measurement tools are then calibrated against this standard or they are used to directly layout the work.

Surface Plate
A surface plate is likely the most common standard reference used in a Home Shop environment. They are used to: It is not uncommon to use a thick plate of glass as a substitute if that's all that can be had.
 * Check for flatness of an edge
 * Layout parts using height gauges

Gauge Blocks
Gauge block sets are blocks of metal that can be stacked together to get very precise lengths. They are used to:
 * Make a set length to compare with
 * Used to set up a Sine Bar measurement

Gauge Pins
Gauge pins are sets of cylinders that have a known circumference. They are used to:
 * See if a hole is the right size

Sine Bars
Sine bars, in conjunction with gauge blocks and a surface plate, are used to set precisely calculated angles.

Squares
Squares are used to check whether something is at 90 degrees to a reference plane. They come in multiple styles such as:

Machinist square

Cylindrical square