Parallel devices for leg vises (ii): The Croix de St. Pierre

The “Croix de St. Pierre” or “St. Peter’s Cross”.

In fig. 243 the Croix de St. Pierre, its manner of action, and the mode of fixing it, is shown in a section of the bench and bench-vice, which affords the most convenient method of exhibiting these points clearly and intelligibly. In this figure, A represents the bench-top, B the bench-front, C the bench-leg, opposite to which the bench-vice D is placed, E the bench-screw, and F the block at the back of the bench-leg, perforated by a female screw, in which the bench-screw E works.

PDfig243It will be noticed that in this figure, the cheek of the bench-vice, instead of being about the depth of the board which forms the bench-front or a little deeper, as in the ordinary carpenter’s bench, is long and comparatively narrow, extending downwards nearly to the ground. It is, moreover, placed exactly opposite the leg of the bench, so that the bars which form the cross may be conveniently attached to both bench and bench-vice, and work in a suitable manner.

The Croix de St. Pierre is nothing more than two flat bars of iron of equal length connected at the centre of each by a pin, G, about which they freely turn. For the reception of the bars, two deep grooves, H and K, are cut in the bench-leg and cheek of the bench-vice, exactly opposite each other, and of the width of the two bars placed together or just a trifle more. The ends L and M of the bars are fastened by pins running through the bench-leg and bench-cheek respectively. The other ends N and O are left free, and work up and down the bottom of the grooves, which may be lined, if desired, with a piece of iron plate cut to fit them exactly.

Now, as the bars are secured at the upper end of each and fastened together in the centre, it is manifest that they will act in the same manner as a pair of scissors, and that when the ends L and M are pushed apart or drawn together the ends N and O will be pushed apart or drawn together in like manner. When the bench-cheek is close to and touching the bench-front and leg, the ends N and O of the bars will touch the ends of the grooves; but as the screw is turned so as to bring the cheek outwards, the ends L and M are drawn apart, and the ends N and O follow the course of the dotted lines, exerting an outward thrust, the one on the bench-leg and the other on the bench-cheek, and preserving perfect parallelism between the faces of the two.

When the screw is turned in the opposite effect is produced, but it may be necessary to assist the return of the bench-cheek by a little gentle pressure at the bottom, which might be applied with the foot. This would be rendered unnecessary if the free ends of the bars were contrived so as to work in a groove similar to that employed for the rack of a window-blind, as shown in section at P.

NOTES: This classic method of parallelizing a leg-vice has been resurrected, and made popular, by Benchcrafted, in the guise of the Crisscross (albeit in the context of the complete vise, the wooden screw is sometimes replaced with a metal one).

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