Housing Joints and Grooves archive
Monday 6 June 2011
John Bullar explores a bread and butter joint
A housing joint is the name given to a slot running across a piece of wood so the edge of another piece fits into it. It is also sometimes called a trench or dado joint. The joint appears in so much joinery, and is particularly prevalent in panelled doors and carcass furniture. So mastering this joint opens up a whole range of joinery options!
A housing generally runs across the grain whereas a similar slot is usually called a groove when it runs with the grain. The difference between a housing and a groove is very little - in fact if you are using manufactured material such as plywood with grain in both directions, or MDF with no grain at all, a groove and
a housing amount to the same thing. If you are working with solid wood, the distinction becomes more important because of the need to consider seasonal movements, as this article will explain.
One of the commonest places furniture makers use grooved joints is to secure the base panels in drawers. If the drawer sides are thick enough to take a groove, a simple slot around the lower inside edge will take a slide-in panel and allow it to move with
the seasons. If the drawer sides are made thin, there will be â€˜drawer slipsâ€™ glued inside with grooves in them
Hand grooved jointsTraditional cabinet work is done with hand planes. These may seem slow, but for the fine furniture maker they have some significant advantages over electric routers - they are quiet, they leave a smooth surface without ripples, and the shavings are large and easy to collect. Perhaps the biggest advantage is that they are finely controllable without risk of damage caused by accidental slip-ups.
A plough plane has three adjustable blades fitted to cut grooves or housings. The main one cuts away at the base of the trench, while the other two slice the sides. Adjustable fences and stops control both the position and depth of the groove
The edge of a panel often needs to be thinned down to fit a housing. The rebate plane has two cutting edges to cut a rebate or rabbet along the edge of a panel. The main blade slices underneath while a small â€˜nickerâ€™ blade at the side cuts into the edge to stop it tearing
Portable routerStep 5
Handheld routers provide speed and power for cutting housings and grooves. However, they are notorious for drifting off course, so they always need to be firmly guided. You can make an L-shaped guide for the router with a lip along one edge to locate it. This will clamp against a board while you route across it at right angles
With the router unplugged and the cutter just level with the router sole, position both router and L shaped guide so the housing slot will cross the board exactly where you want it to
Now clamp the L shaped guide firmly against the board so it cannot move or wobble. Use the router plunger to make a clean stop to the housing slot, then cut the slot with the router pressed firmly against the guide. For a deep slot, make several passes of the router, each a few millimetres deeper than the last
Whenever possible, for locating the position of a housing, use direct marking from one piece of wood against another. This avoids the inaccuracy associated with making measurements and any risk of getting the numbers wrong
Router tableStep 9
Compared to a portable router, the router table provides larger surfaces to guide the wood. The dovetailed housing joint has sloping sides, making it a more secure joint than the straight sided trench housing. However, it needs to be cut in one pass with good accuracy, so the router table makes this more practical
Cutting sloping edges on the end of a board to fit a dovetailed housing is a tricky task. A high fence on the router table makes it more workable. If you are making a number of these joints, it would be better to make a jig to guide the wood
The dovetail sectioned end on the board has to match the section of the housing slot. It also has to be even all the way along so the joint does not jam while you assemble it, but closes tightly without wobble
It pays to make a trial joint on scrap first to check the joint slides firmly together. Be prepared to cut the end off, adjust the settings, and remake the trial joint until the fit is really good. With the router table adjusted, all the joints' halves are cut one after another before the setting is lost
Assembling jointsStep 13
Trial fit housing joints without any glue to make sure they are
a snug fit. If the joint is dovetail sectioned, it needs to be slid
in from one end. If it is straight-sided, it can be pressed together without sliding
Because the housing runs across the grain, wood movement, which changes the width of the boards with seasonal moisture, does not create any tension in the joint - both pieces of wood will move together. This means it can safely be glued all the way along and then clamped to set at a right angle
Panel edgesStep 15
Previously, in issue 50 of this magazine, we saw how the stile and rail joint, or scribed joint, can be used to form the corner joint of a door frame. Here we will look at how it also forms a groove
to hold the panel in place. The joint is cut on the router table with a specially shaped cutter set
With the corner joints pressed together, the scribed joint forms a continuous slot, ready to receive the corner of a panel and hold it in position
The edge of the panel itself is fielded, again using a large cutter on the router table. This provides the thinned-down edge needed to accept the edge of the panel into its groove. A selection of elegant profiles or simple chamfers is available depending of the style of project you are working on
Gluing panelsSolid wood panels traditionally float in their frames - in other words, they are unglued and allowed to slide around freely. This avoids tension between the long grain of the frame and the end grain of the panel as the panel width changes seasonally with moisture levels. Neglecting this precaution would result in split panels and twisted frames.
The snag with floating panels is they rattle annoyingly in dry weather and move to one side of the frame. It is possible to avoid this by partly gluing solid wood panels in their grooves at the centre points of the end grain only. This fixes the panels centrally, while allowing the edges to slide in their slots with the seasons
When the frame is assembled and the panel edge slotted
neatly into its groove, the edges of the panel are slightly narrower than the edges of the frame joint. As a rule of thumb, allow for
a maximum movement of 3% in the panel width. Frames, of course, need to be glued-up securely at the corners. Extra care is needed here to avoid any glue contacting the panel where it could lead to splitting â€“ waxing panel corners avoids this. I hope you find this article helpful in clarifying the main points to be considered when using groove and housing joints in your projects.