Corner Joints Variations

Corner Joints Variations:
Deciding which joint to use in cabinet and box construction relies on a number of different factors. Colin Sullivan tackles the problem and comes up with five variations that don’t require machining.

Nothing is more critical than good preparation. The joint is likely to fail if the material is not square and true in the first place. The majority of corner joints require a lap of some sort. Even a lap dovetail joint must have a perfectly square edge on the pins. Without exception all of the joints mentioned in this article have a structural integrity that is not completely dependant on other carcass components for their strength.
These joints will allow you to finish your sides flush or create a stepped shoulder to suit and incorporate decorative features like chamfers and mouldings. Simple they may be, but each one is a real test of your  hand tool skills requiring clean lines and square faces. 

The right kit
The following traditional joints can all be made with a rebate plane and a grooving plane and therefore avoids the need for a biscuit jointer, Domino or router. Like all hand tools the sharper the better. In which case you may want to have a shoulder plane on standby if this is your first foray into using a rebate plane. For rebates on display a skew blade is recommended especially when working across the grain, Veritas produce such a plane but it is very expensive. 

Loose tongue and groove joints
These are a simple, but very effective way of jointing a corner. Once the grooving plane has been set so that the cutter is in the centre of the board there’s no need for further adjustment. Always work from the finished face of the boards so that they are flush when assembled. This makes things easier for clamping and reduces the amount of cleaning up required after gluing up. Plywood is the most convenient material to use for the tongue as it is stable in both directions.

Good for
• Small drawers and boxes
Pros
• One setting required on the grooving plane
• Achieves good alignment on assembly
Cons
• Displays large expanse of end-grain
• Tight fitting tongue can pop the end-grain shoulder on glue-up

 

Corner block tongue-and-groove
This is a much stronger corner joint made by using a solid square block of wood tongue-and-grooved into the ends of two boards. These ends effectively become shoulders where they meet the face of the corner post. On solid wood construction this may cause a problem with shrinkage if the grain is aligned with the corner post. Quartersawn timber is dimensionally more stable but can display two types of grain pattern on the visible edges. A contrasting piece of timber could be used here as a detail. The corner piece has to be large enough to take two grooves and avoid them meeting in the middle.

Good for
• Carcass work with extending legs
• Small tool chests
Pros
• One setting required on the grooving plane
• Achieves good alignment on assembly
• Scope for adding detail to external corner
Cons
• Large tongues can weaken the joint
• Tricky to glue up a complete carcass in one go

Corner block grooved and rebated
This is another very strong joint, but it does require a slightly larger piece of wood for the corner post. Working from the face, the groove is set in line with the thickness of the board leaving a good shoulder on the board for stability. The inside corner can be chamfered or given a radius but overworking could have the effect of weakening the joint. However, there’s a generous amount of wood on the outer corner to take any shaping or detailing without significantly reducing strength. The use of a cutting gauge to mark out the rebates on end-grain makes it easier to achieve accurate results.

Good for
• Large scale carcass work
• Wardrobes
• Chests of drawers
• Desks
• Fitted furniture
• Use as middle leg for long carcasses
Pros
• Will accept shaping to the internal and external corners
• Allows for generous shoulders
• Good alignment on assembly and easy to clamp
Cons
• Stub tenons can fracture the corner post under extreme conditions

Simple rebated corner joints
This is a useful joint in cabinet construction. Once again easy to mark out as the thickness of the boards used dictate the position of the groove. Try over-setting the groove a millimetre or so to leave a small overhang to plane or sand off when the joint is assembled. If external dimensions are critical to your construction it can sometimes be beneficial to use the internal face of the carcass as your datum as the wall thickness will not change significantly. The material left behind at the edge of the board after creating the groove is fragile, so care needs to be taken when assembling or testing for a good fit. This type of joint is common on old furniture where the external faces might be veneered to conceal the end-grain.  

Good for
• Small drawers
• Boxes
• Veneered caracasses
Pros
• Easy to mark out
• Attractive at the edges
• Good alignment on assembly
• Easy to clamp
Cons
• Displays large expanse of end-grain
• Easy to fracture female component if fit too tight

Double rebated corner joints
In terms of set-up this has to be the easiest of all the joints so far. Both rebates can be cut from the same setting on the plane. The rebate is exactly half the thickness of the board and equal in both directions. Equal amounts of end-grain are in contact with face material in both directions so the joint is structurally well balanced. This simplicity can quickly become a disadvantage, however, as the boards can be assembled incorrectly with little inkling of anything untoward until it’s too late.

Good for
• Small drawers
• Small boxes
Pros
• One setting on the plane
• Attractive from any angle
• Can be pinned in both directions if necessary
Cons
• Easily mis-matched on assembly

Machine alternative
This is one that I produced on the spindle moulder using multiply. It requires some precise setting up as both glue lines are visible after assembly. I use it frequently on carcass construction where the back of the piece will be visible. Cutting the components from the same board and positioning them in the carcass as they have been cut results in seamless corner joints. Over-set the rebate to create the external lap by a few millimetres and you have the joy of scraping or planing flush to look forward to.

Good for
• All manner of carcass work
Pros
• Seamless corners
Cons
• Large carcasses may require additional bracing to achieve overall carcass strength

Multiply