Introduction: Make a Nuckle Joint
Articulated wooden joints have all but been replaced by metal hardware these days, but for a touch of class, nothing beats them.
The Nuckle Joint is basically a wooden hinge. The version I demonstrate here allows a full 180 degree movement, with the 'flaps' starting and ending at 90 degrees to each other. It is probably most widely used for the extention legs on fold-out card tables, and for the bracket supports on Pembroke tables.
Step 1: Watch the Video
To enhance your understanding of the process, you might like to watch the YouTube video I made of this very joint.
Step 2: Prepare the Two Pieces
The ends of the two components to be joined, should be prepared the same width and thickness, and 'shot' square on the end.
Step 3: Mark Width of Knuckle
Set a marking gauge to the component thickness, and scribe this around the end of both components. This defines the volume from which the two knuckle halves will be formed.
Step 4: Find Centres
Knife in the diagonals on both of the tops and bottoms of the joint areas. A mitre square should line up perfectly if the previous steps have been followed. The centre of rotation of the knuckle will be where the knife lines intersect.
Step 5: Scribe the Circular Profile
Use a pair of dividers, pivoted about the four cetres, to scribe in the circular profile of the knuckles. The circles should reach, but not overlap, the sides and end of the components.
Step 6: Find the Transition Points
If we cut the knuckles to the full circular profile, they would simply fall off. So we have to transition between the knuckle and the rest of the component, at some point on the circle. To allow the joint to rotate through 180 degrees, with the components aligning at 90 degrees to each other at each extreme, the transition points are most easily positioned at the intersection of the scribed circle and diagonals, furthest from the end (see just above and left of where the pencil is pointing in the photograph).
Use a try-square and marking knife, to knife a line around at this point.
Step 7: Saw to Transition Line
Now saw, in the width of the components, almost down to the transition points. You don't want to saw all the way, because the transition should end up a crisp 90 degree corner (one side a bevel, the other the tangent to the circle), not the blunt end of a saw kerf.
Repeat for the four transition lines.
Step 8: Create Transition Bevel
Use a wide, sharp chisel, together with a block cut at 45 degrees, to pare down to the transition line, on the inbound side of the components.
Step 9: Shape the Knuckle Cylinder to Transition Curve
To shape the knuckle up to the transition, we need to plane down to the scribed circles. Pare one end to the scribed circle, to prevent breakout, before using a shoulder plane to complete the section.
Step 10: Complete the Knucke Cylinder
The ends of the knuckle cylinders can then be planed to the scribed circles. Pare or plane a bevel at the far end before planing, to prevent breakout. A block plane is ideal for this job. Start by planing off the 90 degree corners, then the 135 degree corners that that produces, etc. until the cylinder profile created.
Step 11: Divide and Scribe Individual Knuckles
Divide the length of the knuckle cylinder by five, and scribe around both cylinders using a marking gauge from the face edge (i.e. mark all from the two ends of the cylinders that will eventually mate). Mark the areas that will be waste - two on one component, three on the other.
Step 12: Saw Out the Waste
Sawing in the waste, but right up to the scribe lines, split the knuckle cylinders into five parts. Then sawing at angles, or using a coping or jeweler's saw, remove as much waste as possible.
Step 13: Create the Knuckle 'Sockets'
Carefully pare away the waste below the removed knuckles, creating the negative image of the knuckle - a hollowed, circular section, between the transition lines.
A carving gouge of a similar radius can help to perfect the profile, where access from the ends is possible. And a convex scraper is usefull in the three sections where access is restricted.
Continue to perfect the knuckle 'sockets', until the joint assembles perfectly.
Step 14: Drill for Hinge Pin
With the joint aligned and cramped tightly, drill for the hinge pin, halfway from one side and halfway from the other. The intersection of the diagonals gives the centre point, and a brad point bit makes location easy.
A drill press is ideal to ensure a straight and well aligned hole, but careful boring with a hand drill can surfice.
Step 15: Flush Up the Knuckle
With the hinge pin installed (or as in the photographs, removable pins) the knuckle is flushed up with a file and sandpaper.
Step 16: Job Done!
You're Knucle Joint is complete.
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You can secure the hinge pin with CA glue applied to the top and bottom entry points.
Beeswax on the rubbing surfaces before assembly is a good idea.
A tough hardwood is best (Beech or Birch are great). I used Iroko for this demo, which was a little too spongy/crumbly to work as well as I'd have liked.