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The tenons and mortises assemble frames and solid wood frames. The accuracy of their execution determines the correct alignment of the pieces and the strength of the whole. If tenons can be made in many ways, the mortises require a specific machine.

Chisel mortiser: how it works

To assemble solid wood elements, the tenon and mortise assembly is the most common technique. It makes it possible to connect two perpendicular pieces (or forming an angle of at least 45°) with the maximum efficiency.

Composition of a mortiser

The mortiser: well held tenons: tenons

1Head down lever
2Engine
3Chuck access door
4Tightening the spindle (chisel)
5Hollow chisel and wick
6Mobile table
7Lateral movement of the table
8Front moving the table

The mortiser: well held tenons: machine

9Chisel and wick Ø 6 mm
10Chisel and bit Ø 12 mm
11Chisel and bit Ø 16 mm
12Chisel of Ø 20 mm
13Bit of Ø 20 mm
14Diamond sharpening cone
15Diamond plate

Mortise tenons: precise joints

Formerly, these assemblies were systematically pegged, that is traversed by a slightly conical piece intended to tighten the post (the male part) in its mortise (the female part). There was no glue that could withstand the stresses on the structure.
Today, ankles are no longer needed, provided you use a suitable glue and machine assemblies accurately. The main difficulty lies in the manufacture of mortises.
Because if cutting the tenons (with hand saw, band saw or circular, to the top...) is quite simple, making mortises by hand with a chisel or a chisel is a tedious task.
The classic machines of the industry are directly inspired by hand-digging gestures; these are the vibrating chisel mortars, single or triple (Maka, Alternax). Designed for mass production, these complex machines perform well, but are difficult to adjust.

The mortiser, a tool specially created for DIYers

For DIYers, manufacturers of wood combined then imagined an appendix composed of a mandrel for mortising drill bit and a mobile table to be added at the end of the jointer shaft. Uncomfortable to set up and store, often inaccurate and does not allow to sharpen the mortises, this equipment was gradually abandoned in favor of the independent mortisers square chisel (or mortiser with wick and hollow chisel), which are a great success, including from artisans, since their introduction on the French market.
The mortiser is used to make square holes. In succession, they form a mortise of the desired length, whose width depends on the diameter of the wick, the latter being equal to the square section of the chisel.

Wick and square chisel: an efficient duo

To square the holes, the rotating bit is placed in a hollow chisel, which remains fixed. The four faces of the chisel are sharpened in order to slice the wood as and when drilling. To do this, the bit slightly protrudes (1 to 2 mm) from the cutting edges.
Wick and chisel are fixed on the head of the machine, whose vertical stroke is controlled by a large lever. The chips are evacuated through a light, made on one side of the chisel.
Wick and chisel sets are not standardized. The diameter of the chisel fitting and the length of the bit with its shank may vary from model to model, and often the shanks are cut with a hacksaw to achieve the desired length.
When installing the drill bit assembly, a wedge or wooden panel should always be placed on the cast iron table of the machine. This is to preserve the sharpness of tools in case of shock.
For safety, it is preferable to leave in place this wedge under the part mortise. It then serves as a martyr hold if the mortises open, voluntarily or by accident (depth stop unsettled).
If the adjustment of the stop is necessary, one can dispense with the stops which regulate the lateral displacement of the table and the length of the mortises, provided to make a preliminary layout on the piece.

To size well its mortises

For optimum strength of the assembly, the width of the mortises must not exceed one third of the thickness of the workpiece.
Take into account the inevitable unevenness of the bottom of the mortises, by providing a variable margin according to the machines: about 5 mm between the length of the tenons and the depth of the mortises for the chisel with square chisel, 2 mm for the false tenons reported (Festool ).
Chain mortising machines machining rounded corners, it is better to round or bevel tenons accordingly.

Target your needs well before investing in a mortising machine

Choosing a square chisel mortiser depends primarily on the diameter of the tools you intend to use. The basic models do not allow to dig beyond a width of 12 mm. The most powerful can go up to 25 mm wide.
The squaring of square chisel holes is done by manually operating the main lever, larger diameters require more force. The possibility of turning the head or tilting is also a factor. Just as the capacity of the mechanism of movement of the table, clamping parts, or the maximum section of parts that can be mortised (which depends in particular on the length of travel of the head on the rack of the column).
Finally, an excellent sharpening of the chisel is essential. It can be done using a special tool (a diamond cone) or by a professional.

The price of mortisers

For an efficient machine beyond a diameter of 12 mm, it takes no less than 700 €. For structural work, it is possible to rent a chain mortiser for 90 € / day.
But the fixed machines, too heavy, are not rented.

Chain mortiser or oscillating wick?

• Traditionally, carpenters use a chain mortiser (A and B) to make large square mortises. This powerful machine operates as a chainsaw mounted in a vertical and lateral guide device, flanged on the workpiece to be machined. Compared to the machine presented here, this device produces less precise mortises when at their surface state, and slightly greased by the lubrication of the chain. This may interfere with bonding (mortise and tenon frame assemblies are rarely glued, and often pegged).
• There is another process inspired by oscillating wick industrial mortisers used in carpentry (to make chairs, armchairs...) which further simplifies the implementation of mortises. It is a power tool for making mortises with rounded edges of high precision (C). The process called Domino (Festool) proposes wooden "pigeons" to be inserted in these mortises, to dig on the two parts of the assembly. This forms a false post, which greatly facilitates the implementation of this type of assembly.

Machining of chain mortiseuss

Machining of chain mortising machines (A) are impressive: up to 50 mm wide and 155 mm deep.

Chain mortising machine

As a chain, the tool makes it possible to make mortises on pieces of framework. The machine is clamped on the piece (B).

milling machines with dominoes or false tenons

The Domino milling machine (C) is a portable oscillating wick mortiser. It avoids the manufacture of tenons.

How to use a chisel mortiser

Using a chisel mortiser

Built of cast iron, the square chisel mortiser is very heavy. It must be securely attached to the workbench or the support supplied by the manufacturer.

to mount a lock

Insert the wick into the corresponding square chime and hold it firmly.
Be careful not to get hurt because the tips are very sharp.

Attach a chisel bit to a mortiser

Brace and tighten the chisel. The wick should preferably rest on a hold.
Advance the table and its guide as far as possible against the chisel to adjust its parallelism.

pick up a lock of mortise chisel

Raise the bit tightly in the chuck before clamping it. It must exceed slightly the edge of the chisel. Otherwise, remove it and cut the stem.

clamp a piece to mortise

Clamp the piece to be slotted, then move the table to center the chisel on the route of the mortise (previously executed) at one of its ends.

adjustment of the depth stops of a mortiser

Adjust the stops that determine the depth and length of the mortise.
Its width being given by the diameter of the wick, the section of the chisel is identical to the latter.

dig the wood with a mortiser

To avoid jamming and heating tools, dig in successive passes, the evacuation of chips through the light is always on the side where the work began.

dig the wood with a mortiser

Turn the lever on and off.
Start by digging on the side where the light of the china is. This technique avoids the heating of the tool.

move the table of a mortiser

The lateral displacement of the table, which determines the length of the mortises, is done by operating, depending on the model, either a steering wheel or a lever.

head of a mortiser

The head of the machine includes a single-phase motor and carries the tools.
It slides between two adjustable stops on a cast iron rack (Scheppach).

clamping the parts of a mortiser

The clamping device of the parts on the table can be single screw or quick clamping. The latter saves precious time for handling parts (Scheppach).

Pivot of a mortising head

The head pivots 180° on some machines. This is very useful for embedding a mortise lock in the edge of a door for example.

use a martyr wedge with a mortiser

A roller shop maid to hold the room and a martyred wedge to protect the wick, the chisel and the table are often indispensable.

sharpening a chisel

Sharpen the chisels using a diamond-specific sharpening cone for this purpose. There are manual models or to mount on a drill, with a slow speed.

eliminate the morfil of a chisel

A diamond plate removes the morfil that forms during sharpening. For locks, use a water stone or a file.


Video Instruction: Quick & Easy Mortises