www.mot.be | The continental jiggers

THE CONTINENTAL JIGGERS

G. Vanlaer

zie ook ID-DOC, "koetsenmakersgroefschaaf"

Introduction

Prior to the last century, tools were often made individually to user's requirements, largely based on ideas circulated by word of mouth, and consequently they varied from area to area.

Specific variations and adaptations would also be made to allow for specialist work in particular branches of trades. The routers are certainly some of those tools.

Defined by R.A.Salaman (R.A. Salaman. Dictionary of woodworking tools) as a tool used for 'routing out' a depression in a surface of the work, the term 'router' covers a lot of tools having in fact the same characteristics: a wooden stock, about 14 to 17 in long, with the ends shaped to serve as handles. The cutters are either bedded in the stock itself like a plane iron or in a special fitting screwed to it.

All of them have the same appearance except the so called Continental type jigger . This last one has a S-shaped stock and very special cutters. Normally made in pairs for working on either hand, they are used for finishing grooves for taking a panel or glass. For this purpose a groove was first cut with a plough plane to the required depth as close as possible to the finished outline; then, when the work-piece was mounted (in carriage frames, carts or vans) and adjustment was necessary, the continental jigger was used to give the final touch.

Two definitions have been found, one by R.A. Salaman and one by Whelan, the latter being far more adequate to describe this specific tool :

By - R.A. Salaman - A jigger made in France and Sweden (known also as a Coachmaker's Plow or Grooving Router) has an S-shaped stock with the cutter mounted at one end, leaving the lower curve to be used as a handle.The cutters are about 1/4 in square and held by a closely fitted steel wedge which follows the same curve as the cutter. (R.A. Salaman , page 393)
By - J. H. Whelan - It is a stock in the form of the old S or an integral sign. The cutter is held on one end with the cutting edge in the center of the S, the other end of the stock forming the hand- grip. The area beside the cutting edge is plated and serves as the fence. The cutter and wedge are both curved ... sometimes called in English a French coachmaker's plow. (J.H. Whelan, page 360)

In view of these facts I intend to give detailed drawings of the jigger itself and specific technical informations about the cutters, the cutting angles and other useful caracteristics.

Three models are to my disposal:

A: Continental Jigger - 18th century
B: Continental Jigger - 20th century
C: Continental Jigger - 19th century

Continental Jigger - 18th century

Particularities

Cutter and wedge : The cutter and wedge are two fine pieces of engineering. They are both made out of steel, shaped in circular arcs, mating closely along the curve. But the most important feature of those two pieces is their profil (see figure below). Everything is done to prevent lateral sliding. All the metalwork must be of a very high order of accuracy.

Distance between the groove and the work edge : There is no mechanical part to adjust the distance between the groove and the work edge. This distance can be slightly adjusted by inserting one or more layers of leather as shown below. Since the screw c is holding the fence and the layers of leather, the latter can be maximum 7 mm thick with the actual screw. The maximum distance bet- tween the fence and the groove is 11 mm.

The cutter and the cutting angles : It is absurd to pretend to make full grooves from beginning to the end with this tool. It will be used to make corrections or small adaptations. In that case, the blade will be adjusted to remove thin cuts. The force needed to bend the shaving will be smaller and the tool will be more easy to control.

Pitch angle: 60 °. Is defined between the tangent on the inside curve of the cutter at the cutting edge and the wood surface.
Clearance angle: 25 °.
Sharpness angle: 35 °. The shaving slides up the face of the cutter and exits from the plane through the exit channel or eye hole. It works perfectly.
roll angle during shaving:

The roll angle during shaving must be less than 7° in case of a flat groove. If the angle is more than 7°, the tool kicks at point x or y and the cutter looses contact with the groove. If the working surface is lightly concave, the maximum roll angle becomes rapidly less than 2°.

For a straight piece of wood , the fence must be in full contact with the wood. If it doesn't, the distance between the edge and the groove will vary (effect of a yaw rotation).

If the piece of wood is concave, the distance between the edge of the piece of wood and the fence will decrease :

This is due to the fact that the face e - f of the fence is straight (like on the model we have). In the catalog of FERON & Cie, la forge royale probably dated from 1927, there are two figures of a continental jigger (page 43). Fig. 709 shows a picture front face (equivalent of figure 1 of this article) and fig. 710, the rear face (equivalent of figure 3 of this article). Both figures are 42 mm in height (small but very clear). Just behind are two small drawings (8 by 9 mm) not at the same scale. They represent fences with a curved convex e-f face like shown this:

Fitted on a continental jigger, used to make a groove on a concave piece of wood, handle by a skilled man. The result will be a groove at constant distance from the edge. (The distance c-d will be constant.)

Continental Jigger - 20th century

This jigger was made in 1999 by myself. It is the same model as the previous one. It's a pièce unique. The biggest difference lies in the fact that the cutter and the wedge are straight and theirs profiles reduced to a minimum of complexity.

Particularities

Cutter and wedge: The cutter and wedge are both made of steel.They are straight, mating closely along each other and with the groove made in the metal frame, holding them, as compared to the previous jigger but no groove is made in the cutter itself (see figure 5). Their profiles are very simple (see figure below). There is no lateral sliding possible. All the metalwork must also be of a very high order of accuracy.

Distance between the groove and the work edge : No difference exists between this model and the previous one. A piece of leather of max. 5 mm thick could be inserted between stock and fence with the actuel screw. The maximum distance between the fence and the groove is 10 mm.
The cutter and the cutting angles : The pitch and the clearance angles are defined by the user. It differs from the previous one where the pitch angle has is a fixed value of 60°.

Impact of the roll angle during shaving : There are no differences between this model and the previous one.
Yaw angle during shaving : There are no differences between this model and the previous one.

Continental Jigger - 19th century

The maker and previous owner was a coachmaker by the name of G. Darras. This special example was discovered in 1991 together with 4 other routers.

Particularities

Cutter and wedge: The cutter is made of a simple steel plate correctly shaped to form the cutter, fixed on the stock by 4 simple wood screws.It is 1,1 mm thick. No wedge is needed, no adjustment is possible!
Distance between the groove and the work edge : The distance between the fence and the groove is not adjustable and has a fixed value of 6,8 mm.
The cutter and the cutting angles:

The cutter is made of a tiny steel plate, fixed on the stock by 4 screws. The cut out made on the lower side presents two cutting edges: one for each direction of shaving. The pitch angle is defined by the shape of the cut out. The clearance angle by the radius of the part of circle defining the lower 1,1 mm side of the cutter and by the distance between the 2 cutting edges.

The roll angle during shaving must be less than 1° in case of a flat groove. If the angle is more than 1°, the tool kicks at point x or y and the cutter looses contact with the groove. The working process of such tool is too sharp. That's why it 's very difficult to work with.

The modified cutter

BIBLIOGRAPHY (only the most important books used for this work, in alphabetical order)

Johan DAVID - L' outil - 1997
Jean Noël MOURET - Les outils de nos ancêtres - 1993
G.A.NORMAN - Hovelens historie - 1954
R.A.SALAMAN - Dictionary of woodworking tools - 1989/2
John WHELAN - The wooden plane
(catalog) Féron et Cie. A la forge royale. Fabrique d' outils montés à travailler le bois - reprint, july 1981

ACKNOWLEDGEMENTS

I want to acknowledge my debt to Marijke Wienen, assistant researcher at the Museum voor de Oudere Technieken for her role as Candide and for undertaking the final critical reading of the text.

In expressing my gratitude to this helper, I want to make it clear that the final presentation of both fact and opinion, including any possible mistakes, is my responsability alone.