This adjustable miter clamp lets you clamp four corners at the same time when building picture frames or cabinet front frames. The miter clamp is built from scrap pieces of 3/4" plywood, and is tightened with a single handscrew or bar clamp. The miter clamp adjusts to fit a variety of frame sizes.

For very large or very small frames, build additional miter clamps scaled to fit the frames.

Key	Pieces	Size and description
A	4	3/4" clamp arms, 1 1/2" × 16"
B	2	3/4" crossbars, 1 1/2" × 5"
C	4	3/4" corner blocks, 2 1/2" square

1. Draw a line lengthwise down the center of each miter clamp arm (A), using a framing square as a guide.

2. Mark locations for drill holes every 1" along the centerline on each arm. Drill a hole through the arm at each mark, using a 1/4" bit.

3. Draw a line lengthwise down the center of each cross bar (B). Mark two points on each centerline, 3/4" from the ends of the cross bar. Drill holes at each marked point, using a 1/4" bit.

4. Draw a pair of diagonal lines across each corner block (C). On each block, mark a pivot point on one of the diagonal lines, 3/4" from one corner. Drill a hole at the pivot point, using a 1/4" bit. Drill another hole where diagonal lines intersect, using a 3/4" bit.

5. Find the midpoint of each side of the corner block, and use these points to mark perpendicular lines across the block. Using the lines as a guide, cut away the corner that is opposite from the pivot point.

6. Assemble the four-corner miter clamp by loosely joining the parts with machine screws, washers, and wing nuts. Use the miter clamp.