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Simple compound angle drilling jig

Author: Mark Salusbury
Photos: Mark Salusbury
Illustration: Len Churchill
Published: October 2024
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If compound angles leave you scratching your head instead of boring holes, this simple and accurate drilling jig is the perfect solution.

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  • DIFFICULTY
    2/5
  • LENGTH/TIME
    2/5
  • COST
    1/5

A common fixture in a machinist’s shop, a sine plate is a jig fixture that’s used at boring, grinding or milling machines to support stock when it’s being machined at critical sin­gle or compound angles where zero tolerance is demanded. Here’s how to easily make something similar and use it for woodworking at a drill press to bore angled mortises or holes in flat stock or holes perpendicular to the surface of angled parts. A compound angle drilling jig is a real asset when making stools, chairs or tables, or any time when one part has to be joined to another at an angle.

T-Track Dadoes
Salusbury machined two dadoes in the top section so he could install T-track that will assist in holding workpieces in place.

angle drilling jig

Shallow Rebates
Machine rebates in the edges of the plates to let the piano hinges into the plates. This allows them to pivot at exactly their edges.

angle drilling jig

Double Check
Salusbury is about to machine a round mortise at 7° in the underside of a tabletop. A digital angle gauge will go a long way to ensuring your angles are correct.

angle drilling jig

Start with three squares

Begin by precisely cutting three 10″ × 10″ squares of 3/4″ or thicker solid core plywood (Baltic birch is the best choice), labelling them A (top), B (centre) and C (bottom). Stack the squares (plates) flush on all edges and mark the exact centre across each edge face for future reference.

Pivot points

The set needs to pivot to set angles; one pair of plates, left to right, and the second pair front to back. The centre Plate B is com­mon to both pairs.

Cut two 10″ lengths of piano hinge. Cut rebates the exact same thickness and width as the leaf of the hinge along the plates edges where hinges will be applied. In terms of the width, it will be half the hinges’ overall width when opened.

Stack Plates B and C flat so their hinge areas align and clamp them in a vise, hinge areas up. Check that all edges are flush and the plates are tightly together. Place the hinge, barrel outward, within the hinge rebates and flush with the ends of the plates. Centre punch and drill for 1″ flathead screws. After vacuuming away the swarf, install the screws, then set this pair aside.

Take Plate A to the router table and rout two equally spaced dadoes (centred 3-5/16″ in from each edge of the plate) parallel to the edge you’ve rebated to mount the hinge. Each dado should be a precise fit for a 10″ length of 1/4″ T-slot track to accept hold-downs. Mine are 3/8″ deep and 3/4″ wide so the track seats flush with the plate surface once epoxied in place.

Take Plate A back to your bench and marry it with Plate B, again in a vise. Repeat the steps to join Plates A and B so all three plates are united and hinged left to right and front to back.

Bore two handle holes

At the drill press, bore one hole centrally on each edge opposite the hinge on both Plates A and B to insert a pin or dowel so it’s easier to lift and separate each pair of plates when adjusting and setting angles. Seat and/or glue the dowel or pin in place.

At this stage I disassemble the plate set totally and seal all sur­faces, except the T-track dadoes, with shellac. I protect the dadoes with painter’s tape until the shellac is tacky, then remove it.
After the shellac is dry and you’ve crisply masked off the ends and edges of the dadoes to protect against squeeze-out, mix and spread epoxy along the outer sides of the T-track and the bottom of each dado. Install each section of T-track within a dado with the ends flush with the plate’s edges. With the plate on a flat surface, I place a dowel or rod greater in diameter than the track slot’s width so the slot cradles the dowel or rod. Then add a flat piece of stock or plywood on top to distribute about 40 pounds of weight, pressing the track down into the epoxy to set overnight.

The next day, remove the painter’s tape and any squeeze-out, then rejoin the plate set.

Precision set-up aids

A digital angle gauge (Wixey or equivalent), a small spirit level (often called a torpedo level) and/or a circular/bullseye level make checking for correct angles easy. Additionally, make wedges of the angle you want to bore using a tapering jig at your table saw. These can be inserted between the plates for fast, repeatable set-ups. Playing cards are great for shimming to perfect a set-up, while squares of double-sided tape are helpful to hold a set-up if needed.

Set-up is easy

Place the plate set on a drill press table with T-tracks facing upward. Put the object to be bored on top of the plate set. Choose the angle to be bored and elevate one or both pairs of plates via shims or wedges to create that angle. Rotate and/or reposition either the plate set or the part to be bored to achieve a perfect set-up.

Clamp the plate set to the drill press table, then the part to be bored to the plate set via the hold-downs. Double check your set-up, set the drill’s depth stop to limit the depth of the hole to be bored and bore the hole.

And that’s the hole story. Uplifting, isn’t it?

Angle drilling jig

Angle drilling jig


MARK SALUSBURY - [email protected]

Son of a craftsman father and artist mother, Mark Salus­bury was introduced to skilled creativity at an early age. He has explored all forms of woodworking professionally and casually since the 1970s.

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