GB2204828A - Dovetail cutter - Google Patents

Abstract

A machine which incorporates a standard router to cut dovetail joints in wood. The boards to be jointed are releaseably fixed upright to a bar 5 which slides beneath a router mounted at 10. The sliding bar is locked in place, and the router with dovetail bit is drawn forward to form a cut in the end of the board 1. When the first board 1 is cut with dovetails, it is replaced in a second position (as shown) on the bar, and the second board 2 is put in place of the first to make the pins. The cutter is changed, and adjusted to depth, and the corresponding pins are cut in the second board to correlate with the dovetails in the first board. A turntable 16 is positioned so that the router moves at an angle to the Y-axis. The exact position of the the pins is accurately determined by the position of the dovetail cuts in the first board, the dovetail cuts in the board 1 being successively aligned with a marker block 20 at position 21. The boards 1, 2 are held on the sliding bar 5 by fixed fences 8 and cam operated movable fences 7. The machine may be used for rebating or grooving. In a modification, the machine may have two routers for cutting the boards 1, 2 simultaneously. <IMAGE>

Description

DOVETAIL CUTTER This invention relates principally to a machine for quickly and accurately making dovetail joints in timber In addition to its use as a dovetailer, the machine also cuts halving joints, rebating, and grooving, but dovetails are among the most difficult of all joints to execute well, and this dovetail cutter brings craftsmen's dovetails-within the ambit of most woodworking enthusiasts.

Proper dovetails are not generally used on commercial work because they are not economic. Now, relatively unskilled labour can be employed to do work previously only attempted by skilled people, with a considerable saving in time.

There are machines in existence which work on the principle of guiding the dovetail bit of a router into a series of regularly spaced slots.

The dovetail bit cuts both boards at once. Dovetail and pin are identical, which gives an unmistakable machined appearance to the work, the only acceptable joint is the lapped dovetail, as the bottom of the tail is rounded and not square, and it is not inherently a very strong joint.

The Dovetail Cutter does not have these disadvantages. It can produce proper full dovetails identical to the traditional dovetail. In addition the spacing may be as the operator wishes, and the pins, and the tails may be wide or narrow as required. The Dovetail cutter can also work extremely small (1/4") say for drawers in cabinet work whereas the dovetail Jig needs at least " timber to function.

HOW IT WORKS The operation is simple (See Fig.1). The work is fixed vertically against a sliding bar(1.2), and a dovetail router bit is drawn horizontally through the board end to make the dovetail slots, moving the bar between each cut.

The cut board is then placed in a second position on the bar (1.1) against a marker. The second board is offered up to the router, the cutter changed, and the pins cut in relation to the dovetail cuts in the first board, which is used as a template. This time the turntable is used and the cuts are made at an angle accross the top of the board.

As in hand-cut work, the pins can be cut in any position along the board that the operator wishes. This is often essential, when making boxes, for example, where a saw cut is made between the box and the lid, or for drawers where the placing of the front tails differs from the back ones.

No marking out is necessary. Accuracy comes from the machine, and the cut timber. One decides the positioning of the pins, and everything follows.

For the 90 degree cut of the tails, several boards can be cut at once, saving time and preventing breakout.

The depth of the dovetails is limited by the size of the dovetail bit available. However,there is no limit to the thickness of board which can be jointed, as a rebated dovetail joint can be easily made by sliding the board across the locked router bit.

THE MACHINE The machine is wall-mounted for a firm fixing, and to save workshop space, and so that it can be placed at any height to process any length of board. The machine can theoretically be any size, to work any width.

The Sliding Bar The sliding bar (see Fig 1.4) is aligned with its face on the X-axis.

The inside face of the work is placed against it and the face of the bar is therefore datum.

It is held along its top and bottom edges by two fixed guides (1.5), mitred in section, which fit into mitred section grooves in the Bar.

(see Fig. 2: section of Sliding Bar) The method of sliding the bar can be more or less sophisticated. It can be moved manually, or racked along with wheel and worm, or a wire and drum system (1.9). It is important that the bar does not move once the position is set.

The Fixed Fence and the Cammed Fence The timber is held on the bar against the Fixed Fence (1.8) by a moveabled Cammed Fence. (see Fig.3) The Cammed Fence slides in a channel in the bar (2.2) in such a way that the board can be offered up to it and quickly, and firmly locked into place; the cam (3.3) pushing the fence (3.4) against the work. Teeth in the channel (3.2 and 2.3) meshing with dogs (3.1) on the cam plate (3.4)prevent it slipping away from the work as the cam (3.4) tightens. As there is a lot of swapping around of boards, they need to be placed quickly, and loosened instantly the cam is slackened, releasing the board. One manifestation of the cam has the fence (3.5) formed behind the cam so that it is pulled away.

The Cam Clamp used independantly The cam-clamp slides in the channel of the bar (2.2). The profile of the channel can be cut by a standard router bit. This means that this type of clamp can be used as a clamp independantly of the Cutter, using a rail cut with bit to match the profile of the channel. The rail can be cut using the machine so that the machine can cut its own clamps in any length of timber This is important as it is necessary to glue up as soon as the joints are cut to avoid problems with timber movement.

Router plate Any make of good quality router is used. The router is mounted (at 1.10) on a plate (1.11) which can be pulled forward, sliding between two Router Plate Guides (1.12). A locking mechanism (1.13) on the guides fixes the router for grooving and rebating.

A Keeper (1.14)on the guides allows the bit to travel forward through the work to a given position (for lapped dovetails > .

Turntable The Router Plate Guides are fixed to the Turntable (1.16) allowing the router to be drawn forward at an angle, either to the right or to the left (N-right N-left) It can be set at a prescribed angle against a Pin (1.17) placed in the Baseplate (1.18), or the pin can go through the guide into the baseplate to fix it. Therefore at 90 degrees it can make the dovetail cut or rout a straight groove, or it can swivel between stops to allow quick changes between left and right cuts, for making the pins.

Waste can be cut away with a sweeping action of the Router between these stops. This is to clear areas between the pins. Clearing is done in a clockwise direction to avoid breakout Base Plate The turntable is set in the Baseplate (1.18). The Baseplate itself can be moved forwards and backwards on the Y-axis with the rack and pinion (1.19). This alters the distance from the centre of the turntable circle C to the face of the bar. (This is evident from Fig 4.2) For cutting dovetail pins at a given angle, the further forward C is, the wider is the spread of the left and right cuts at the face of the board against the bar (at datum), and vice versa.

The accuracy of the pins can be very finely adjusted (with 1.19), giving a tight fit for softwoods and a precise fit for hardwoods, leaving room for the glue.

The Marker There are two positions on the bar for the the timber. A Cutter Position (1,1) and a Marker Position (1.2).

To make the Marker (1.20), a block is placed in the housing immediately behind the bar in the Cutter Position and a slot is routed into it with the dovetail bit. This block is taken out and fixed into the housing behind the Bar in the Marker Position. (1.21 shows the block in Marker Position) It is used to determine the exact position of the cuts for the pins. A block is made for each bit size.p From darker to the Cutter and from Fence to Fence are equidistant < see Pig 4), so a dovetail placed against the Darker Block (4.1) will correspond exactly to the position for the pin in the Cutter Position (4.3). As the dovetails are moved against the Darker Block so each pin position will be nicely placed.

Locating the exact line-up between the two dovetail cuts of board and marker is easy for large dovetails because it can be felt with the finger. A light behind the block makes the line-up visible, or a feeler stick the exact size of the dovetail gives positive mechanical positioning.

CUTTING DOVETAILS Dovetails are cut first, using the dovetail bit. The turntable is fixed at 90 degrees (Y-axis), and the correct depth is set. A blank board is set in the marker position and the dovetails are marked on it. The first mark is set against the Marker Block, and the dovetail is cut in the board in the Cutter Position. The bar is slid along to correspond the next mark against the Marker, the next cut is made, and so on until all are done. Maybe four or six boards can be cut at once depending on the thickness of the timber.

A board with dovetails is then placed in the Marker Position (Fig. 4. 1/2), so that the cut dovetails can match exactly the slot in the Marker Block. This board is used as a template for the corresponding pins.

Cutting the Pins The bit is changed to a straight bit, and set to depth (4.5). The turntable is freed, and stops placed in the base for the angle of the dovetail in use. The router can now swing left to the correct angle, and right (N-left and N-right) behind the bar, and be drawn forward through the work, thus making the pin.

To determine the exact fit for the type of wood used, a test is made with a narrow piece of scrap. A dovetail in the dovetailed board is placed against the slot in the marker block, and the test piece is placed in the cutter position. Two cuts are made on N-right and N-left without moving the bar, making the two sides of the pin.

If the resultant pin is too snall the baseplate is brought forward, and if too large the plate is moved away, and the process retried until the fit is exact. This setting is then kept for all work with that cutter.

The proper board for the pins is now offered up to the Cutter Position.

The bar is slid along to correspond the first dovetail to the Marker Block. At this position a cut on N-right alone will make the corresponding pin on the edge of the board (4.6 > .

The board is slid to the next dovetail position. The pin is again cut, making N-right first, then N-left. The waste is then removed between the cut just made and the N-right cut of the previous pin (4.7). This is repeated until all the pins are cut.

The two boards, dovetails and pins will now fit with a firm push.

LAPPED DOVETAILS Lapped dovetails are made in the same manner as the ordinary dovetails, but the pins are made with the Keeper in place on the Router Plate Guides, to prevent the bit travelling forward though the board beyond the depth of the dovetail. They have rounded corners which need to be squared up with a chisel later, using the routed cuts as guide.

Figure 5 shows the sequence of cuts.

OTHER JOINTS Mitred dovetails can be formed using the Keeper in place for the dovetail as well as the pin. The router is then run along the top of the board to form a square rebate on both, and the remaining nib is mitred with a conical router bit. The rounded corners are squared up using a chisel as before.

Using a straight router bit, halving joints and comb joints can be made.

Slots can be cut by holding the work beneath the router, and drawing the router across it.

By fixing the router, grooves can be routed for panels and lids and bottoms. This means that the whole drawer, with dovetails, and lapped dovetails, as well as grooves for the drawer bottom can be fashioned on the one machine. Rebates can be made for fielded panels, inlay, and many other uses.

Limitations on the depth of the dovetail are imposed only by the size of the router bit and the power of the router. However,there is no limit to the thickness of board to be jointed, as a rebated dovetail joint can be easily made by sliding the board across the locked router, or using a radial arm saw to rebate the board.

DOUBLE CUTTER VERSION A version can be made with two cutters. The marker is replaced by a second router on a baseplate, but without a turntable. One cutter has the dovetail bit which first cuts the tails, and immediately the pins are made without moving the bar.

This has the following advantages: 1. That the two cuts would follow each other allowing no time for the wood to move.

2. That time would be saved by not having to change the cutter blade between cutting dovetail and pin.

3. Hairline accuracy is possible, as the exact position would be given for the pin cut direct from the dovetail cut, without the operator having to judge it.

4. Accuracy is further maintained as the depths of cut could be kept set throughout the cutting, and not altered on change of cutter.

It is a very simple matter to link the two routers and the bar so that the hand action can be performed mechanically, so that they cut simultaneously, further reducing the cutting time.

Claims (7)

1. A Machine which makes proper craftsmanlike dovetail joints.

comprising a sliding bar which can hold timber vertically so that it may be cut and shaped by a router.

2. A machine as claimed in 1 where the sliding bar may hoid boards of timber in two basic positions: a cutter position where they are cut, and a marker position where they are held to form a guide for the cutter.

3. A machine as claimed in 1 and 2 whereby the router is guided across the end of the timber at a prescribed angle. The angle can be varied by a turntable arrangement to suit different dovetail angles,

4. A machine as claimed in 1,2 and 3 but where the centre point of the turntable can be altered so that when it is cutting at an angle, the thickness of pin so formed can be altered.

5. A machine as claimed in 1S2,3 whereby the distance between the two fence positions on the bar is equal to the distance between marker and cutter so that the position of a cut in one piece placed against the marker can be corresponded with a cut in the other piece in the cutter position.

6. A machine as claimed in 1, in which the board of timber are held in place against. a sliding bar by a cam with dogs fitting into a toothed rack to prevent slippage so designed to prevent movement of the boards during cutting. Moreover that this cam should have a use as a clamp independant of the dovetail machine.

7. A machine as claimed in 1 through to 6 and as a development thereof whereby there are two routers incorporated in the one machine. with one replacing the marker. One router can be set with a dovetail bit to cut dovetails, and the other router can be set with a straight bit for cutting pins.