Which tool is most accurate for making the preparatory setup for milling an angle on a workpiece?

The sine bar is utilized for precise angle measurement and setup in milling because it provides a means to create a specific angle based on the height of its pins and the workpiece's surface. The sine bar leverages the sine principle, meaning that the angle can be accurately defined by the ratio of the opposite side (height) to the hypotenuse, allowing for high precision when setting angles for machining processes.

This tool is particularly effective in achieving accurate angles because it allows the machinist to establish the correct height using gauge blocks, which can provide repeatable positioning of the workpiece when milling. Its design facilitates the setup of angles minimalizing potential errors that might arise during cutting.

Using alternatives may offer some degree of angle establishment, but they generally lack the same level of precision. For example, a machinist square is primarily used for checking and establishing 90-degree angles, and while the combination set can measure various angles, it’s less specialized in providing the precise setup needed for angled milling. Similarly, the angle set is useful for specific angle measurements but may not provide the same accuracy and adaptability as utilizing a sine bar in conjunction with gauge blocks for precise setups.