COPING & MITERING TIPS

What is Coping?

"...the action of shaping by means of cutting trim to conform to the face profile into which it will butt".

To install trim easily and professionally, cope and/or mitre the inside and outside corners. When mouldings are properly installed, they add character and value to your home or project.

You'll need these tools:

  • Mitre Box
  • Back Saw
  • Coping Saw
  • C-Clamp
  • Fine Sandpaper
  • Utility Knife
  • 2-Sided Carpet Tape
  • Hammer
  • Nail Punch Set
  • Measuring Tape
  • Compass Set

Why Cope an Inside Corner?

Although an inside corner of any room may appear to be 90° (and was 90° when originally constructed), humidity changes and house settling will result in corners not remaining a true 90°. For example, if two pieces of trim were cut at 45° each but the corner angle was now 91° or 92°, the two pieces would not fit properly. By coping a mitre for an inside cut, this problem is eliminated.

When installing crown, baseboard or chair rail mouldings, most cuts are inside corners and coping will be necessary. Here's how to do it:

Inside Corner Coping

  1. Start with the wall first seen upon entering the room.  Cut the moulding the full length of the room, making a square cut at each end. Put the trim in place.
  2. The next cut will have to butt into the face of the piece just installed. Do this by cutting a 45° mitre as you normally would. Be sure to place the trim in your mitre box in the same position it will be on the wall.
  3. To have this trim fit the face profile, the mitred part of this 45° cut will have to be removed.  Use a pencil to outline the face profile to make an easier sight line to be cut. (see fig. 2)
  4. Cut the shaded area off with a coping saw (fig. 2 and 3). It should be done at an angle greater than 90°.
  5. Place the moulding against the face of the adjacent piece. If there are areas needing further adjustment, mark them with a pencil. Using sandpaper and/or a utility knife, remove the necessary high spots.
  6. Continue around the room in this matter until complete.

Outside Corner Coping

  1. When cutting an outside mitre, be sure to have the face of the moulding facing you.
  2. Hold the moulding in the mitre box in the same position as it will be placed on the wall.
  3. Precise angles can be cut with an electric mitre saw. To find the exact angle of an outside corner, place a blank piece of paper on the ceiling or floor against the wall. Then place another piece of paper on the ceiling or floor of the wall around which the trim is to go. Be sure to have both pieces of paper extend past the corner far enough to overlap. (see fig. 4)
  4. Take a compass and place the point on it at the intersection of the inside corner (fig. 5). From this point, draw a circle from the edge of one page to the edge of the other. (fig. 4)
  5. Now, place the point of the compass at the point where the pencil hit the edge of the page. Extend the compass and draw a small arc. Repeat this at the edge of the other page, making sure that the arcs intersect. (fig. 6)
  6. Draw a line from the inside corner through the center of the intersection of the two arcs. Use a protractor t measure the true angle (fig. 7).

Tips & Ideas

  • To help hold the trim more securely in the mitre box, use 2-sided carpet tape and secure a piece of sandpaper to the bottom of the mitre box.

  • Use a C-clamp to help hold the trim and keep it from slipping when you cut.

  • To prevent chipping the trim's face, only cut on the down stroke.

  • Before nailing the trim in place, put a bead of adhesive caulking on the back.

  • Practice coping a mitre on a sample piece of trim before making the actual cuts.