image129Mortise and Tenon joints:

Mortise and Tenon joints of different varieties are standard method of joining two pieces of Wood when ‘~’, ‘X’ or ‘T’ joints are to be formed. One piece is given a rectangular slot (Female), known as mortise and other piece is given a projected male end to fit the rectangular slot, known as Tenon. Tenon is formed by cutting out 5/16th width of the wood piece from both sides of the batten up to a specified length and keeping 3/8th width of piece intact (depending upon the extent to which it is to penetrate the mortise of the corresponding piece). Similarly the mortise is formed by chiseling out 3/8th width of the piece or equal to the width of the Tenon, to a specified length (depending upon the extent to which the Tenon is to penetrate and to be accommodated). In some joints an additional key is provided, also known as haunch on top/bottom side. The joint formed by fitting the two is called a ‘Mortise and Tennon’ joint. The various joints are described from (a) to (k) in following paras.

Halved Joints: There are simpler joints but strengthened with wood screws, like halved joints and miter joints. Here the end to be joined is cut at 45 degrees, for half the width of the piece, and a matching cut on the corresponding piece. Various joints ‘~’, ‘X’ or ‘T’ can be formed by these joints also. The draw back in these joints is that these are eccentric to the point of application of load, in case of vertical door/window frames and are liable to show weakness under specific load conditions and are therefore not used. These are however used in packing cases, picture frames etc.

Commonly used Mortise and Tenon Joints are described below,

Through Hunched Mortise & Tenon: The length of the Tenon is equal to the width of the other piece to be joined, such that the Tenon fully pierces the mortise and gets exposed on the other end, and is called a through ‘M&T’ joint. Additionally a haunch is provided at the top and is called ‘Through Mortise and Tenon Joint’ The purpose of the haunch is to prevent the joint becoming ‘bridled’ as it reduces the tendency of the Tenon cupping and thus avoiding the frame joint lose the right angle, after some usage. These types of joints are commonly used for door/ window frames and for paneled doors/windows.

Secret Hunched Mortise and Tenon: This is similar to the through hunched ‘M&T” joint except that the secret haunch is achieved by cutting it at 45 degrees. This is needed for instance when the top of the frame is exposed such as a cane seat on a stool, etc. This is normally used in furniture work and not used in building doors/windows.

Secret Hunched Stub Mortise and Tenon: Here the length of the mortise is less than the width of the piece receiving c it in the Mortise. Similarly the mortise is not chiseled through, thus the end grain of the Tenon is hidden and not coming through. Here also a haunch is provided which is not visible. It is prudent in all cabinet work to have a small shoulder top and bottom of say 2 to 3 mm to hide any ‘blemishes’ that may be exposed on cutting the mortise.

Corner Rail to Leg: This joint is used in joining the leg of a chair, stool or table. The M & T joint is a variation of c) above but in three dimensions. The meeting Tenon’s are mitered to gain the maximum length. Note that it is also ‘hunched’ to prevent the joint becoming ‘bridled’. A lower rail batten would not need the haunch.

Corner or `L’ Bridle: Here both the mortise and Tenon are cut through and jointed. This is comparatively a weaker joint and adopted for light use furniture and crude work.

Corner or `L’ Dovetailed Bridle: This is similar to above but stronger due to dovetail joint. Some chair seat are done like this.

`T’ Bridle: This is very commonly used for joining Stile of door/window to mid-rail in case of paneled doors, glazed doors, or even wires net doors. The mid leg in a half round table jointed like this.

Halved and Miter Jointsimage130

Corner Halved or `L’ Joint: With countersunk screws to reinforce it. It is used for packing cases, carcasses quality work, etc.

`T’ Halved Joint: for a ‘T’ joint required in packing cases etc. this joint is used. The cut is made at 45 degrees in both the pieces, for half the width, matching each other. This joint can also be prepared for ‘X’ joint, where both pieces of battens can be continued.

Mitered Corner Joint: Both the pieces are cut at 45 degrees for full depth, and joined with glue and wood screws. This joint hides end grain, suitable for table top moldings and picture frames, etc. where very less loads may be required to be taken by the joint.

Halved Corner Miter Joint: One piece is cut for half width at 45 degrees and the other piece is cut through at 45 degrees but half width is retained to join with the other piece. This is used where the end grain may be hidden joint on at least one face. This is stronger than Simple miter joint.

Other types of ‘T’ Joints

image132Butt joint: Here the two pieces are often nailed with round headed nails from the horizontal batten, in a dovetail’ fashion. This is called askew’ or tosh’ nailing. This is very Low quality carpentry and is only used for temporary work like shuttering etc.

Square Through Housing: Somewhat better than (l) above. Often strengthened with nails as above.

Stopped Housing: The stop or clap’ is to give a better view.

Dovetailed Housing: To increase the strength of the joint in pulling dovetail joint is provided. This joint also has to be strengthened with nails or screws.

Stopped or ‘Lapped’ Housing or ‘Dado’: This joint is a variation of (n) for fixing planks, shelving or partitions, etc. It may be vertical or horizontal.

Stopped or ‘Lapped’ Dovetailed (single or double) Housing or ‘Dado’: This is a variation of (o) for fixing of planks etc. and has greater strength in pulling. It is also to be strengthened with wood screws, nails.

Splice Joints: These are used to extend the members, mainly thin members like planks or scimage133antlings where the joint would be hidden under lamination. The joint in is stronger than in as it provides more surface area for gluing.

image134Procedure for Correct Wood Working (Making a frame): The drawing supplied will be finished dimensions. Prepare an estimate of the material required based on the cutting lengths and the other
dimensions like width and thickness also should have tolerance for planning etc. Cutting lengths are obtained by adding the sawing allowance (3-4 mm for every cut) but something additional which would be required to be cut at the time of fitting the joints.

Do not mark out all individual lengths on the length of timber and then cut off like onion slices or like sausage. Measure, mark and cut off individually otherwise you will get a cumulative error. When you have cut out the members from the dimensions given in the Cutting List, lay out the members in the same arrangements as their positions shown in the scaled drawing. Always position the members in this way whenever you need to consider the next move. It helps to ‘see’ what you need to do next.image137

A ‘Face mark’ is drawn on the width of the wood in the direction of the ‘Face edge’ which is drawn on the corresponding edge of the member, and is a drawn as a large ‘X’. Use a HB pencil to draw details such as this. The Face and Edge Mark is very important and is always used to measure, mark and work from.

The Horizontal and Vertical members are now brought together and clamped or held in the vice so that the dimensions and joint positions may be
marked as one, on all similar members.

From the Scaled drawing or Rod, determine the joint positions and mark these on the face edge while the members are still held together in the vice or clamps.

The actual line of the joint, where it is cut or joins is called the shoulder line. Always measure from the same point, say top or left of the frame. Use a marking knife or at least a sharp H2 pencil to draw shoulder lines. It is good practice to use the jointing member itself to determine the width and not a ruler or scale. First of all make a small mark to transfer the measurement and then with carpenters’ square, complete the shoulder line across all the members so they are marked the same.

When all members have been treated in this way, remove from clamp, and taking each member in turn, with the carpenters’ square, complete the ‘squaring’ all round. Take care to ensure that the stock of the square is always against either a face mark or face edge mark or the ‘square’ may not meet.

Now that all members are marked or ‘set-out’, arrange the timber in the manner of the complete frame and identify each joint with a ‘figure or ‘letter’ so you may re-construct the frame in the same position from time to time for checking. Note that the ‘waste’ area has been neatly ‘hatched’ with a HB pencil.

Check that the lay-out and dimensions are the same as the drawing. After marking out all the pieces, the members shall look as seen in fig:image141

Next step is to gauge the width of the mortise and Tenon’s. The thickness of the Tenon’s should be approx. 3/8th of the width of the material to be jointed (some carpenters take 1/3d the width, but 3/8th is stronger and should be adopted). From this select the nearest mortise chisel to this size.

Take your Mortise Gauge to the Chisel you have selected and set the points as close to the thickness of the chisel as you can determine. If you cannot get gauge to exact chisel width then edge slightly on the smaller size rather than larger. This way the Tenon will fit inside the mortise. If the Tenon is gauged slightly larger it will not fit at all or will be too tight and need trimming. The joint should be loose enough to adjust and fit without driving the entire adhesive out. If the joint has to be hammered home, it is too tight. On the other hand it should not be so loose to allow excessive movement away from its original shoulder positions. Most good adhesives will easily ‘gap-fill’ up to say 1 to 11/2 mm’s. To use the gauge you should hold the timber firmly in your hand or in a vice. The gauge should be forced against the face side with the points of the gauge ‘trailing’ in order that they should not ‘dig-in’.

Do not press too deep at first otherwise the points tend to follow the grain of the timber and it will be difficult to gauge a straight line. Better to make two or three attempts until you reach the right amount of depth. A sharp pencil following the scribed lines will improve the sighting.

Scribe the mortise and Tenon gauge lines between the full shoulder lengths and where there is a corner joint, all the way through the waste area to the end.

Where, on the corner joint there is to be a ‘haunch’ continues the scribed lines down to the depth of the haunch, say 12 – 15 mm down. The exact amount can be marked across in the next stage. Remember, failing to haunch a corner mortise and Tenon causes the joint to ‘break-out’ and the joint is then ‘open’ or ‘bridled’. Remember to scribe both edges and to keep the stock of the gauge always against the ‘face mark’ otherwise a ‘step’ will occur in the joint and cause ‘winding’.image142

Tenon’s are scribed between the full shoulder lines and down the end grain to meet with the other side. This allows you to saw down the end grain with a Tenon saw.

Treat all members similarly with the gauge and when complete return the gauge to the tool box.  Place all timbers in their positions and
then consider the next stage.

The joints at the corners that are to be hunched are diminished (made smaller) across the face edge and opposite side. Avoid where possible marking across the face (other than the shoulder lines) because it can create confusion.

The mortise should also be ‘cut-back’ on the inside of the joint where a groove or rebate reduces the width of the Tenon.

image143The Working and Making Joints: The working and making of a i) Shoulder ii) M&T joints iii) ‘T’ and ‘X’ joints in frame iv) ‘T’ and ‘X’ joints in planks v) Simple and dovetailed joints in planks explained in the steps through sketches given below.

Cutting and Cleaning a Shoulder:- The shoulder is a vertical cut in the wood to accommodate another piece of wood. The shoulder in different job conditions is shown in sketch below. The other steps for making a shoulder are a) Sawing a shoulder b) Smoothing or cleaning the shoulder.image145

Mortise and Tenon Joint: Normally the horizontal member is made the Tenon (Male part) and the vertical member the Mortise (Female part). The making of Tenon requires sawing of the Tenon cheeks in 3 steps a) sawing at 45o from side 1, holding the piece angular in vice b) sawing at 45o from side 2, holding the piece angular in vice and c) sawing horizontally down to shoulder. Then the Tenon width is sawn and followed by sawing of shoulders and haunch if provided. The shoulder should be cleaned using special plane or by chisel.

Next the Mortise is cut using Mortise chisel in steps taking little material at a time or the work can be also started by boring/ auguring holes of required depth and later giving it the required shape and size by chisel. Haunch is cut the last, wherever required as shown in sketches below.

 ‘T’ and ‘X’ joints in frame:-‘T’ and ‘X’ joints are very often used for frames and the method for making of both is similar. In ‘~’ joint there is one socket and 1 pin to be joined and in ‘X’ joint two sockets is to be joined.

image147Procedure for making a 7′- Halving:

Shoulders are prepared in the standard way as explained in para Cutting & Cleaning of Shoulders and the detailed procedure is explained in steps through sketch as below.

‘T’ and ‘X’ joints in Planks:-Shelf and cabinet work is normally done using planks and ‘T’ and ‘X’ joints are used for joining just like similar joints for frames. The difference is that joints in planks have to be longer and elaborate to gain enough strength for carrying loads. Simple joist are, i) Escaped bare face dovetailed housing ii) Through housing iii) Stopped common housing iv) Stopped housing with through twin Tenon’s and v) Butt glued dowelled joint. Commonly used are through housing for general work and stopped common housing joints for aesthetic work. The making of stopped common housing is explained in steps through sketch.image151

Procedure for making a stopped common housing joint: Simple `L’ joints:- The Simple `L’ joints in planks can be i) Butt glued and nailed ii) Lap glued and nailed iii) Finger or Box joint iv) through dovetail joint and v) Lap dovetail joint. The strongest and aesthetic joint is dovetailed joint and the steps for making a through dovetailed joint is explained through sketch below.

image153image149image155

Tips for Correct Wood working:

Select timber and cut to nominal size (i.e. plan size plus an allowance for waste on ends.)

Dress one side and one edge as required.

Mark Face Side and Face Edge as shown.

Reduce to required width and thickness as required.

Cramp together all horizontal members together in vice or clamps.

Mark out shoulder positions with a sharp H2 pencil.

Repeat with Vertical members.

Gauge mortise or halving lines.

Mark out with a sharp HB pencil all other details including any haunches and the finished cross section on one end.

Marking and gauging should be completed on all members before proceeding.

Chop out all mortises taking care to exclude the haunch for the time being.

Rip down the grain of the Tenon’s but do not cut off shoulders at this stage.

Prepare square moldings i.e. grooves and rebates.

Prepare round moldings i.e. remainder including any chamfers.

Cut shoulder lines carefully remembering to allow for rebates and any scribing required.

Prepare any miters or scribes.

Fit joints, firstly individually and then as a frame correcting as necessary.

Clean up inside edges and any inaccessible faces.

Prepare and rehearse cramping making sure you have waste padding.

Glue – up and cramp – up. Drive in wedges from outside corners first.

Clean up back of work with smoothing plane.

Clean up front of work.

Cut off waste and clean up edges.