Starrett 505P-7 Miter Protractor: Choose the Right Scale

Trim meeting at a corner can call for a miter joint or a butt joint, and the Starrett 505P-7 gives those jobs different scales. Its inner scale is marked for Miter Cut; its outer scale is for Single Cut. This 7-inch plastic miter protractor lets you take a saw-setting reading at the corner, with the cut type identified on the tool.

Two scales for two kinds of joint

When two pieces will meet with mitered ends, Starrett directs you to the Miter Cut reading and then to the miter saw. The 505P-7 marks that reading on the inner scale. The practical benefit is having a scale intended for that saw setting on the instrument you put against the corner. You can work from the angle the pieces have to meet, instead of assuming that the corner is square.

For a butt joint, Starrett specifies the Single Cut scale. On this model, that is the outer scale. A buyer fitting a piece that will butt against its neighbor has a separate named reading for that task. Having both settings on one instrument is useful when the work includes both kinds of joint.

The two laser-engraved scales have corresponding cut labels printed along the arms. Check the cut name as well as the reading before carrying it to the saw. The arms can fit the corner while you are still looking at the wrong scale; choosing the intended cut remains your part of the job.

Read the corner where the trim will meet

The detail photograph shows two hands holding the 505P-7 inside a corner, with one arm against each surface. Look at the space available for both arms at your own job. The nominal 7-inch size does not guarantee that the tool can sit properly in every recess.

Take the reading at the relevant location. Starrett's crown-molding guide specifically begins by measuring the corner close to the ceiling. A reading taken somewhere more convenient is useful only if it represents the angle the trim must fit. Resolve that placement before moving to the saw.

The scale reading is one part of the setup. Saw adjustment and the position of each workpiece still matter. A trial cut and fit with offcuts is a practical check before you commit the finished material.

Crown molding adds miter and bevel settings

Starrett's two-page crown-molding guide adds steps after you record the inner-scale Miter Cut reading. You also need the molding's spring angle, which the guide says to obtain from its supplier. The published table has columns for 38-degree and 45-degree spring angles.

The inner-scale number becomes an input to that table. For a listed reading, the row under the appropriate spring-angle heading supplies a miter angle and a bevel angle. This gives a buyer using the covered molding and angles a documented route from the corner to both saw adjustments. The dial alone does not supply the complete compound setup.

The guide also distinguishes inside and outside corners, and the left and right pieces. Saw directions, the side of the blade holding the work and the molding edge placed against the fence change across its setup instructions. Keep the actual guide with the job so those placement choices accompany the angles.

If your molding has a different spring angle or your reading has no matching row, the published table does not settle the setup. Obtain instructions for that material and cut before relying on a setting.

Write the cut name beside the reading you take back to the saw. For crown molding, first check that the guide covers the material's spring angle and the recorded reading, then keep its two saw settings with the workpiece instructions. That is the manual setup to plan for when buying the 505P-7 for this kind of work.