Cutting an accurate miter is only half the battle. Gluing and clamping the joint can be just as challenging. The parts have a tendency to shift as clamp pressure is applied, making it difficult to keep the edges aligned.
This simple miter joint clamping jig solves the problem by supporting both workpieces while three adjustable blocks hold the joint securely during glue-up.
Build the Frame Assembly Jig
The jig starts with a large plywood base that provides a flat surface for supporting the workpieces.
Two triangular clamping blocks hold the pieces from the outside. Each block has a tongue along the bottom that rides in a groove in the base cleat. This allows the blocks to slide into position for different-size assemblies.
Add sandpaper to the contact edge of each block. The extra grip helps prevent the workpieces from slipping when clamping pressure is applied.
A third triangular block provides pressure from the inside of the joint. This block travels along a T-track in the center of the jig and locks in position with a knob.
Together, the three blocks capture the workpieces from both directions and keep the miter aligned.
WOODSMITH TIP: Wax the Jig Before Glue-Up. Before assembling the jig, apply wax to the surfaces where glue squeeze-out might occur. This helps prevent dried glue from bonding the project to the jig.
Clamp the Miter Joint
To use the jig, apply glue to the mitered ends and place both workpieces on the plywood base with the mitered edges pointing toward the bottom of the jig.
Carefully center the joint over the T-track.
Slide the inside clamping block against the workpieces and tighten its knob. Then bring the two outside blocks against the workpieces and secure them with a bar clamp.
Position the bar clamp near the base of the outside clamping blocks. This directs the clamping pressure where it's most effective and helps keep the blocks stable.
With everything tightened, the jig keeps the pieces supported and the miter aligned while the glue dries.
Easier Miter Joint Assembly
The best shop-made jigs solve a specific frustration, and that's exactly what this one does. Instead of trying to hold two slippery mitered ends together while juggling clamps, the jig provides a flat work surface and controlled pressure from several directions.
And because the clamping blocks are adjustable, you can use the same frame assembly jig for a variety of mitered projects.
Take the Frustration Out of Your Next Glue-Up
A good jig makes miter assembly easier, but there are plenty of other ways to get better results at the assembly bench. Explore our clamping and gluing tips and tricks for holding parts securely, keeping assemblies aligned, and avoiding sticky situations.
EXPLORE CLAMPING & GLUING TIPS → These Tricks Can Help You Avoid Sticky Situations
