The Application of Mortise and Tenon Joints in Building a Playhouse
Mortise and tenon joints are the most commonly used means of joining parts of wooden structures—from heavy playhouse frames to small pieces of furniture. Doweled joints are an extension of the method used today mainly because of convenience in manufacturing processes.
Doweling adapts better to quantity production as the joints can be made easier by machines. For individual craftsmanship, mortise and tenon joints are preferred in many situations. Both methods of joining should have adequate strength for their purpose.
Doweling adapts better to quantity production as the joints can be made easier by machines. For individual craftsmanship, mortise and tenon joints are preferred in many situations. Both methods of joining should have adequate strength for their purpose.
As with any type of joint, a good fit is an important contribution to strength, and in quantity production accuracy is more easily achieved in doweling than in tenoning. In the many variations of the mortise and tenon joint, the tenon is a tongue cut on the end of one piece to fit into the mortise, which is a hole cut to match in the other part.
In nearly all assemblies the grain is lengthwise in the tenon and across the mortise. The side grain in the mortise comes against the side grain in the tenon, which is best for glue to get a good grip.
Only a small area in a joint includes end grain in one part, so the lesser glue strength there is not important. The idea behind the mortise and tenon joint goes back into history.
Early man tapered the end of one piece of wood to go into a hole in another piece. Similar ideas can still be seen in field fences, where the tapered ends of rails go into holes in the posts. More carefully shaped joints followed, and a form of mortise and tenon joint recognizable as similar to ours can be seen in drawings of early Egyptian furniture.
These days, there are effective glues, but those who utilized mortise and tenon joints back in the early days, had to depend simply on the tight fit. Other approaches are depended upon such as the usage of pegs together with wedges in order to ensure the tightness of the joints.
Tenons are basically rectangular in section and usually have squared corners, although there may be some rounding. The mortise cavity is cut to match. If the projecting piece is round, even if it is cut in the solid wood, as it often is in turned work, it is better described as a dowel, although most dowels are loose.
In nearly all assemblies the grain is lengthwise in the tenon and across the mortise. The side grain in the mortise comes against the side grain in the tenon, which is best for glue to get a good grip.
Only a small area in a joint includes end grain in one part, so the lesser glue strength there is not important. The idea behind the mortise and tenon joint goes back into history.
Early man tapered the end of one piece of wood to go into a hole in another piece. Similar ideas can still be seen in field fences, where the tapered ends of rails go into holes in the posts. More carefully shaped joints followed, and a form of mortise and tenon joint recognizable as similar to ours can be seen in drawings of early Egyptian furniture.
These days, there are effective glues, but those who utilized mortise and tenon joints back in the early days, had to depend simply on the tight fit. Other approaches are depended upon such as the usage of pegs together with wedges in order to ensure the tightness of the joints.
Tenons are basically rectangular in section and usually have squared corners, although there may be some rounding. The mortise cavity is cut to match. If the projecting piece is round, even if it is cut in the solid wood, as it often is in turned work, it is better described as a dowel, although most dowels are loose.
Through Mortise and Tenon
If two parts of similar thickness are to be joined in the simplest manner, the tenon goes right through the mortised piece. In this case it is common for the tenon to be one-third the thickness of the wood. It is convenient if the mortise is made the same as the width of the chisel used for cutting it.
Slight variations are permissible to suit this, although too thin a tenon would be weak. At one time mortises were chopped out completely by chisel. Even with the more common method of drilling away most of the waste, though, there has to be some squaring of the shape with a chisel.
The width of both the tenon and the mortise should be gauged at the same setting of a marking gauge, with the limit lines squared around the mortised piece so marking is on both sides. The length of the tenon is marked with knife-cut lines. Leave a little excess length on the tenon to be trimmed level later.
Gauging can be with two settings of an ordinary marking gauge, but special mortise gauges mark both lines at the same time. Usually a brass inset in the stem carries the second pin, so it can be adjusted in relation to the fixed pin to suit the width to be gauged. The stock is set and locked to give the distance from the edge.
The two-pin mortise gauge has the advantage that the distance between the pins can be maintained even if you have to move the stock to suit wood of different thicknesses. Some mortise gauges are attractive in rosewood and brass with screw adjustments. A simple gauge is just as effective, and you can make one with wedges instead of screws.
A wooden playhouse craftsman does not make trial assemblies of mortise and tenon joints. Pushing together and pulling apart tends to wear the surfaces and loosen the joint. It is better to rely on the accuracy of marking out and cutting, so the first assembly is the last and the joint is as good a fit as it can be. If a trail is deemed necessary, do not enter the tenon fully into the mortise.
If the mortised part is wider than the tenoned piece, as it usually is when a rail goes into a table or chair leg, the tenon can be made wider to give a stronger joint. If less is cut away from the rail end, that part is not weakened as much.
It is not common to make the tennon more than half the width of the rail, unless the other part is considerably wider and only a token shouldering of the rail end is needed to locate it.
Slight variations are permissible to suit this, although too thin a tenon would be weak. At one time mortises were chopped out completely by chisel. Even with the more common method of drilling away most of the waste, though, there has to be some squaring of the shape with a chisel.
The width of both the tenon and the mortise should be gauged at the same setting of a marking gauge, with the limit lines squared around the mortised piece so marking is on both sides. The length of the tenon is marked with knife-cut lines. Leave a little excess length on the tenon to be trimmed level later.
Gauging can be with two settings of an ordinary marking gauge, but special mortise gauges mark both lines at the same time. Usually a brass inset in the stem carries the second pin, so it can be adjusted in relation to the fixed pin to suit the width to be gauged. The stock is set and locked to give the distance from the edge.
The two-pin mortise gauge has the advantage that the distance between the pins can be maintained even if you have to move the stock to suit wood of different thicknesses. Some mortise gauges are attractive in rosewood and brass with screw adjustments. A simple gauge is just as effective, and you can make one with wedges instead of screws.
A wooden playhouse craftsman does not make trial assemblies of mortise and tenon joints. Pushing together and pulling apart tends to wear the surfaces and loosen the joint. It is better to rely on the accuracy of marking out and cutting, so the first assembly is the last and the joint is as good a fit as it can be. If a trail is deemed necessary, do not enter the tenon fully into the mortise.
If the mortised part is wider than the tenoned piece, as it usually is when a rail goes into a table or chair leg, the tenon can be made wider to give a stronger joint. If less is cut away from the rail end, that part is not weakened as much.
It is not common to make the tennon more than half the width of the rail, unless the other part is considerably wider and only a token shouldering of the rail end is needed to locate it.
Stub Mortise and Tenons
In many places it is better for appearance if the end of the tenon does not show on the outside of the mortised piece. If the joint does not go right through, it is a stub mortise and tenon. The distance the joint goes through depends on the wood sizes and the degree of strength required.
If the mortised piece is a fairly light section, the cavity may have to be cut as far as you can go without breaking out at the far side to allow for a long enough tenon to give strength. In thicker wood you will have to judge how much to go, and this comes from experience.
In most furniture construction a tenon should usually be 1 inch to 1 ½ inches long. In the construction of wooden playhouses, it should be significantly longer depending on which part of the playhouse you are working on.
If the mortised piece is a fairly light section, the cavity may have to be cut as far as you can go without breaking out at the far side to allow for a long enough tenon to give strength. In thicker wood you will have to judge how much to go, and this comes from experience.
In most furniture construction a tenon should usually be 1 inch to 1 ½ inches long. In the construction of wooden playhouses, it should be significantly longer depending on which part of the playhouse you are working on.
The tenon is cut in the same way as for a through joint. The mortise should be deep enough for the tenon not to touch its bottom. When the joint is drawn tight, the shoulders of the tenoned piece must close against the surface of the other piece before the tenon touches bottom.
The area left void there will not affect strength, as that comes from the meeting side grain surfaces. A mortise traditionally, was chopped out with a thick mortise chisel. The thickness was needed for strength in levering out the waste.
For this method, several cuts are made across the grain, but not right to the ends. The waste is levered out prior to another line of cuts at the next level until a sufficient depth is cut and the ends, which have been levered against, are trimmed to length. With a chisel width matching the final width of the mortise, there should be no need for further cuts on the wider surfaces of the mortise.
For very deep mortises there are hooked chisels, called lock mortise chisels, that remove the waste from the bottoms of the mortise, which has first been chopped with a straight chisel. It is more common today to remove most of the waste from a mortise by drilling.
With a depth gauge on the drill or the drill press, you can make a series of holes that overlap and automatically make the mortise the right depth. With a suitable router cutter it is possible to enter like a drill, the move along for the length of the mortise. In both cases the mortise finishes with rounded ends.
They can be squared easily with a chisel to match the usual tenon, and that is normally preferred in individual work. On the mortise is left rounded. The tenon is rounded to suit or even made narrower to avoid the curves. For large mortises to be cut in large numbers—usually for playhouses—a machine with a chain that lowers into the wood is used. It is equipped with cutters and looks something like a chain saw.
One thrust into the wood makes a mortise of the right length and width, but with a rounded bottom, if it is not a joint that goes through. That is not a tool for the individual craftsman, but another tool is driven in the same manner as a drill, using a fairly substantial press.
The outside is square to match the width of the intended mortise. It is hollow and made like four chisels with their bevels inward. Down the center is an auger bit. As the tool is lowered into the wood, the outsides cut out a square and the auger bit removes the waste.
The area left void there will not affect strength, as that comes from the meeting side grain surfaces. A mortise traditionally, was chopped out with a thick mortise chisel. The thickness was needed for strength in levering out the waste.
For this method, several cuts are made across the grain, but not right to the ends. The waste is levered out prior to another line of cuts at the next level until a sufficient depth is cut and the ends, which have been levered against, are trimmed to length. With a chisel width matching the final width of the mortise, there should be no need for further cuts on the wider surfaces of the mortise.
For very deep mortises there are hooked chisels, called lock mortise chisels, that remove the waste from the bottoms of the mortise, which has first been chopped with a straight chisel. It is more common today to remove most of the waste from a mortise by drilling.
With a depth gauge on the drill or the drill press, you can make a series of holes that overlap and automatically make the mortise the right depth. With a suitable router cutter it is possible to enter like a drill, the move along for the length of the mortise. In both cases the mortise finishes with rounded ends.
They can be squared easily with a chisel to match the usual tenon, and that is normally preferred in individual work. On the mortise is left rounded. The tenon is rounded to suit or even made narrower to avoid the curves. For large mortises to be cut in large numbers—usually for playhouses—a machine with a chain that lowers into the wood is used. It is equipped with cutters and looks something like a chain saw.
One thrust into the wood makes a mortise of the right length and width, but with a rounded bottom, if it is not a joint that goes through. That is not a tool for the individual craftsman, but another tool is driven in the same manner as a drill, using a fairly substantial press.
The outside is square to match the width of the intended mortise. It is hollow and made like four chisels with their bevels inward. Down the center is an auger bit. As the tool is lowered into the wood, the outsides cut out a square and the auger bit removes the waste.
The result is a nicely squared hole, and a mortise is made by moving along to make the required number of touching square holes. In both cases standard sizes are produced, so more tools are needed for different sizes. The wooden playhouse craftsman doing individual work will prefer a drill, router, or chisel.