How to make these Alternative Dovetail Joints (The Knapp Joint)
A hands-on guide to making the Knapp joint — a 19th-century machine-made alternative to dovetails — using a custom spade-bit cutter, a shop-built drill press jig, and a router template. The video covers building every component from scratch and iterating toward a repeatable, clean result in under 10 minutes per joint. ---
Key Concepts
| Concept | Definition |
|---|---|
| Knapp joint (apt joint) | A historical (late 1800s) machine-cut joint using interlocking pins and scalloped recesses; originally used for drawer construction as a faster alternative to dovetails |
| Annealing | Heating steel to cherry red then slow-cooling to soften it for shaping |
| Hardening | Re-heating and quenching in oil to restore hardness |
| Tempering | Watching heat run through the blade and stopping at a deep straw color to achieve the right hardness/toughness balance |
| Spacer width | Controls whether scallops form complete semicircles, overlap, or leave a gap — determines both aesthetics and difficulty of cutting |
| Pattern-following bit | Router bit used with a template to replicate the scalloped profile on the mating piece |
Notes
Custom Cutter Fabrication
- Start with a cheap spade bit
- Anneal: heat to cherry red, cool slowly → soft enough to shape
- Shape with reference to a 10 mm drill bit for correct gap width; keep both cutters as even as possible
- Harden: reheat and quench in vegetable oil
- Temper: watch heat travel to the tip; stop and cool when tip reaches deep straw color
- Grind a slight bevel with 120-grit belt — that's all
- Two cutters do not bend in use despite initial concern
- **Alternative (rejected)**: plug cutter — too narrow, requires two sizes; hole saw + plug cutter combo — too much movement, not centered enough
Drill Press Jig
- Clamp workpiece to the side of the jig, then make the cut
- Problem: drill press had too much lateral play → cuts inaccurate
- Solution: machine a guide bushing in mild steel
- Drilled at 18 mm (no 19 mm bit available), then reamed to 19 mm with a tapered dowel wrapped in sanding belt
- Cutter edge set 4 mm from fence edge
- Score a line with a marking gauge first to reduce chip-out
- Stop block kept simple — clamped rather than using a T-track
- Jig wide enough to clamp the workpiece on either side of the pillar
Spacer / Spacing Logic
- 10 spacer strips accommodate an 8-inch-high drawer side
- **Spacer = cutter width (19 mm)** → complete semicircles
- **Spacer slightly narrower (18 mm, chosen method)** → scallops overlap slightly; easier interior cut, no need to reach dead center
- **Spacer wider than cutter** → scallops separate; leaves a flat between them that needs squaring by hand — could look distinctive
Making the Mating Piece (Pin Side)
- Attach a template, follow with a router bit, then drill pin holes — some hand work in between
- Template accuracy is the main challenge; ~8–9 failed attempts using:
- Printed and scroll-sawn templates
- Dividers + spade bit scoring
- **Successful method**: cut a fresh scalloped sample on scrap → use that as a physical guide to build the template
- Found copper pipe that fits the guide perfectly; glued a dowel plug inside each disk
- Filed a flat edge on the inside of each disk where they overlap
- Glued disks to a plywood backer using 5-minute epoxy while pressed into the guide; checked sides square to ends
- Added a second thin-ply layer over the top with epoxy + wood glue for rigidity
- Drilled center holes in disks with a Forstner bit → use as pin-location guides on the workpiece
Routing the Mating Piece
- Clamp template to workpiece; eyeball edges parallel — one clamp is sufficient
- Optional: glue sandpaper under template for grip (added after one slip)
- Added a fence to one side of template for repeatable registration
- Use a **6 mm / ¼" pattern-following bit** on a router table (preferred over handheld trimmer — no speed control on trimmer)
- Bit almost reaches into the points; small remnant left
- Use a countersink bit to relieve edges slightly → helps joint close
- **Cleaning between scallops**:
- Original method: skew chisel or any chisel/knife; undercutting slightly is fine
- **Improved method**: No. 7 sweep gouge — radius close enough to the disk radius; a couple of taps per scallop, then clean up with the gouge again
- Changed from 10 mm Forstner to 10 mm brad-point for pin holes → eliminated tight fit
Results & Refinements
- Hardwood combinations tested: silky oak + camphor laurel, black wattle + Oregon
- Complete joint takes **under 10 minutes** once workflow is established
- Plane caused tear-out on one piece → finished on belt sander instead
- Scaling up: template is size-specific; make a new template for wider joints using the original as a reference — new template in 12 mm ply
Actionable Takeaways
- Anneal, shape, harden, and temper a cheap spade bit rather than sourcing a specialty cutter
- Ream an undersized hole with a sanding-wrapped tapered dowel when the exact drill size isn't available
- Use an actual test cut (not a drawing) as the master reference when building the template — it's the most accurate starting point
- Set spacers to 18 mm (1 mm under cutter diameter) so scallops overlap slightly, making the interior cut easier
- Add a fence to the router template for fast, consistent workpiece registration
- Switch to a brad-point bit for pin holes if a Forstner leaves them too tight
- Use a No. 7 sweep gouge for cleaning between scallops — faster and cleaner than a chisel
- If scaling the joint, build a new template using the original rather than trying to extend or modify it
- Consider reducing pin diameter from 10 mm to 9 mm for a slightly easier fit
Quotes Worth Keeping
If you want the scallops to be complete semi-circles then the width of the spacer will be the same as the width of the cutter.
I must have made about eight or nine of these with no success.
It takes less than 10 minutes to make the complete joint.