Creating identically sized mortises
Some hand-woodworking tasks become a whole lot easier and more accurate when you use a simple guide to help steer the cutting action. A perfect case in point: mortising guides like these two. After you hog out most of the mortise waste at your drill press, these jigs guide your chisel straight down, helping you pare the walls square to the faces and ends of the workpiece. You'll create identically sized mortises and save yourself a lot of time fine-tuning individual tenons.
Select your guide material carefully
Pick the right guides
By gluing up four pieces to create the guide opening, you size it perfectly and create precise 90° corners. Depending on the application, make the end and side guides from hardboard or MDF. Both materials provide smooth edges. Use 1/4" hardboard guides [top drawing] when you need to see into small, shallow mortises such as those used for holding decorative square buttons. For larger, deeper mortises, 3/4" MDF [bottom drawing] provides a broader support surface for the back of your chisel, keeping the tool vertical as you pare the full depth of the walls.
Sizing the guides
Size the side guides to match the length of the mortise. For an MDF jig, the width of the end guides matches the workpiece thickness, and the side guides fit between the mortise and the edge of the workpiece [top photo]. To maximize glue surface for a jig with hardboard guides, cut the end guides to span the workpiece and both cleats [bottom photo].
Assembly come next
Put the pieces together
To help assemble a hardboard jig, find a scrap the same thickness as the mortised workpiece. Clamp the cleats to either side of the scrap so they stand about 1/4" above the edge. Then, one at a time, glue and clamp the hardboard pieces on top of the cleats, ensuring that the opening is square to the cleats and centered on the jig's width.
For an MDF jig, glue and clamp the guides between the cleats.
Using the jigs
Clamp a workpiece with the drilled-out mortise to your bench and align the jig opening with the mortise layout lines. Clamp across the cleats to secure the jig to the workpiece. With a chisel, pare down along the guides, concentrating on keeping the back of the chisel pressed against the guides.
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