Chris Schwarz's Blog

St. Peter’s Cross: Keeps the Jaw of Your Leg Vise Parallel

The Croix de St. Pierre, from page 211 of “The Amateur Carpenter and Builder” from the early 20th century. Image courtesy of Gary Roberts.

One of the biggest complaints about leg vises is having to engage some sort of secondary mechanism to keep the jaw parallel as you advance it and to act as a pivot point when squeezing the work. I have a bar in my tail vise that is bored with a series of holes. By moving a steel pin into the correct hole I can control the parallelism of the jaw and set the jaw for different thicknesses. I’m so used to it that I don’t think much about it and it has become part of the natural rhythm of my work.

However, if you don’t like stooping, you won’t like having to do this.

One solution, which is presumably French, is called “Croix de St. Pierre.” I’ve seen it in action on a commercial leg vise and it is ingenious. It is, essentially, two flat pieces of steel that are joined by a hinge in the center, much like scissors, forming an “X” shape. At the top of the X, one end is attached to the bench; the other to the jaw of the vise. The two ends at the bottom run in grooves in the jaw and leg of the bench. The scissors action of the X keeps the jaws parallel as you work.

I’ve always meant to make one of these devices myself for a leg vise, but I’ve always been satisfied with the occasional stoop to move the steel pin.

– Christopher Schwarz

9 thoughts on “St. Peter’s Cross: Keeps the Jaw of Your Leg Vise Parallel

  1. Dino Dimas

    A variation of the Veritas Twin Screw Vise mounted sideways on the chop would work better.

  2. Tom Holloway

    There’s something strange about calling this "X" cross the St. Peter’s cross. Google and Christian iconography will make clear that St. Peter was crucified upside down, with a cross having the crossbar close to the bottom, and the center post vertical. The "X" cross is associated with St. Andrew (patron of Scotland).
    As for a way to keep a leg vise parallel, I’d have to see it work, to believe it. I do think the "P" inset in the plan is a sort of "T" track devide for the lower points of the ‘X" to slide in.

  3. J.C. Collier

    Sweet! I never knew what this device was called although I had seen one on a bench in FW years ago. I found one on eBay and bought it. It’s only the leg with the x axis limbs and it came with a 2.5" diameter x 24" length wooden bench screw and nut. The leg is interesting as it was obviously rebuilt-up as time went on, reinforced/stiffened with newer material while the St. Peter’s Cross appears original to the device.

  4. Gary Roberts

    Le Croix de St. Pierre was an inverted cross. There are various stories, but the one that is repeated most often is the St. Pierre did not feel worthy of crucification (by the Romans) on the same type of cross that was used for Christ. So he was crucified on an inverted cross. If you can image what the crossed bars on this vise will look like when the vise is closed, you can see that they form an inverted cross.

  5. Patrick Lund

    A person could maybe put a screw at the bottom of the leg vise and connect it a chain to the top screw, much like the Veritas twin screw bench vise turned 90 degrees.
    It would be a complicated setup however.

  6. Wendell Wilkerson

    Can you explain what the picture labeled P is depicting? It almost looks like T-track. Is that what the loose ends of the device are suppose to slide up and down in? You know what’s more tempting than changing the parallel guide for a Croix de St. Pierre? Using a wooden vise screw instead of the metal one. There is just something really cool about a vise with wooden screw.

    Wendell

  7. Curt Seeliger

    Landis’ "Workbench book" includes an example of this setup. I don’t recall the owner’s name, but I do recall he wasn’t happy with it — it was a lot of work, and the result was unstable.

  8. Karl Rookey

    Ingenious. The name sounds religious, but I suspect it is a joke that plays on the inventor’s last name. Do you know any more about it?
    Also, I had immediately had the same thought that Louis had of creating a metal wear plate for the moving part of the cross, but on looking more closely, I’m suspecting the item labelled P shows a track in which the bottom section is meant to ride?

  9. Louis Bois

    French?!? Ov coursss eet eez!!! Eet’s eegeeneeous!!!

    I wonder if you’d need some sort of wear plate at the base of the mortise to avoid grinding into the wood over time? I know I’d probably put something there. Thoughts?

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