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How to Cut an Angled Corner Mat

Angled Corner Mat Figure 1

Figure 1

For a long time some mat cutters came with an impressive accessory known as an “angle plate,” a tool used for marking out and holding mat board for cutting angles other than right angles.  By using it, you could cut octagon-shaped windows, diamonds, triangles or stars – in fact, any shape of window that consists of straight lines.

Angled Corner Mat Figure 2

Figure 2

Not a few owners of mat cutters that didn’t offer an angle plate concluded that they were unable to cut such mats.  But they were wrong.

If you own a mat cutter that has a guide rail, you, too, can cut angled mats, and for a lot less than the cost of a pricey angle plate.

Angled Corner Mat 3

Figure 3

In fact, all you need is a plastic 45/90º triangle (a $2.50 investment at any office supply store) and you’re ready to cut impressive angled mats like the 8-sided mat shown here.  Here’s how.

First, set your mat cutter’s mat guide and mark out four borders of 1¾”.  At this point you’ve defined your window opening in pencil.

Angled Corner Mat Figure 4

Figure 4

Beginning at one corner of the window you’ve just marked, measure out along one of the lines 1¾” and draw a line to intersect the first line (Figure 1).  Then measure down the vertical axis 1¾” and mark another line to intersect (Figure 2).  Each line should be about 3 inches long.  The combination of lines forms a small penciled square.

Align the guide rail of your mat cutter through the box at a 45º angle

Angled Corner Mat Figure 5

Figure 5

from corner to corner (Figure 3).  Mark along the guide rail.  The pencil line will bisect the box at 45º (Figure 4).

Repeat this procedure in each corner, defining the 45º angled corners (Fig. 5).

Place the guide rail in alignment with one of the 45º angles you

Angled Corner Mat Figure 6

Figure 6

marked.  Using the 45/90º triangle, place it so one of the 90º edges is against the guide rail and the other is at a right angle to the guide rail.  Position it so the corner of the triangle is at the corner of the penciled square.

Make a mark along the full length of the 90º side of the triangle (Fig 6).   The line you mark will extend at a right angle to the 45º angle

Angled Corner Mat Figure 7

Figure 7

that bisects the box (Fig 7).  This is the key to the whole technique.  Only by having lines at right angles to the start and stop points of the line can you start and stop the cut in the right places.  You can draw and cut a line at any angle, starting and stopping in the right places, as long as you have lines extending from it at 90º angles.

Angled Corner Mat Figure 8

Figure 8

Position the triangle at the opposite corner of the penciled square and extend a line at a 90º from it.  You now have lines to start and stop from (Fig 8).

Leave the mat under the guide rail and  position the cutting head on the start line.

Insert the blade and begin cutting.  Cut until you reach the stop line (Fig 9).

Angled Corner Mat Figure 9

Figure 9

You have made a cut at 45º  relative to the perimeter edge of the mat (Fig 10).  Repeat this procedure for each of the four angled corners.

Set the mat guide back to 1¾”  and prepare to cut the straight sides of the mat’s window .  Place the mat under the guide rail.  Remember, in each corner there is a penciled box.  Start at

Angled Corner Mat Figure 10

Figure 10

the top line of the penciled box at the top left (Fig 11).  Stop at the bottom line of the same penciled box.   This cut connects with the two angled cuts made earlier (Fig 12).  Repeat for the remaining three sides.

An impressive 8-sided mat results (Figure 13).  Apply the premise of this core technique to cut octagonal mats, triangular mats and even

Angled Corner Mat Figure 11

Figure 11

star shaped mats, all for less than the cost of the instructions that come with an angle plate.  Now that’s versatile and economical.



Angled Corner Mat Figure 12

Figure 12


Angled Corner Mat Figure 13

Figure 13

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