A stop block is a device that limits the travel of a saw when it is being used to cut an object. Variations of the stop block are also used when drilling an object to prevent the drill bit from going too far into the material. Typically constructed of a plastic or aluminum material, a home-built version of a stop block can be made by cutting a piece of wood to the correct measurement and affixing it to the saw cradle. Many different types of power tools come from the manufacturer with a stop block attached to the tool itself. This type of stop is typically adjustable and easily set by tightening a set screw against the tool's framework.
Often, a stop block is used when making a repetitive cut along the length of a stock where all of the cuts are to be the same length and depth. This allows the worker to make the several identical cuts in a rapid manner by simply sliding the material along a fence and pulling the saw into the material. This is especially effective on a radial arm saw where the saw is easily pushed and pulled into the stock. This is particularly useful when cutting a number of pieces at a specific length. The stop can be placed on the tray of the saw and the stock pushed tightly against the stop and cut to length.
In many cases, a pair of locking pliers or a clamp will be used to fix the stop in place on the cutting bench. Due to vibration and the possibility of contact with the material being cut, exact measurements should be taken periodically to assure that the stop has not shifted its position. In precision cutting with a wooden stop, the stop should be checked every now and then to ensure that the force of pushing material has not altered the stop's profile, which would also alter the cutting length. Using a hard wood stop block will aid in eliminating this potential problem.
When using a stop block in a metal working project such as welding, a steel block is commonly used due to the ability to tack weld the stop in place on the welding bench. Similarly, the block can be clamped to the lathe bed to prevent the tool rest from moving past the intended point on the lathe. For small projects on table saws and other tools that use a metal material rest, a magnetic stop block can be quickly applied and removed when needed.