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Thread: Leg vise question

  1. #1
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    Leg vise question

    Anyone build one using the crossed metal strips at the bottom (St Petter's Cross?) to keep the jaws parallel? Any pictures or details?

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    Quote Originally Posted by Jerome Hanby View Post
    Anyone build one using the crossed metal strips at the bottom (St Petter's Cross?) to keep the jaws parallel? Any pictures or details?
    I recall Jameel Abraham mentioning three or four years ago that he was experimenting with the form, but there was never any followup.

    I suppose you have seen the illustration of "La Croix de St. Pierre" from The Amateur Carpenter and Builder. Here's a brief Schwarz blog post about it.

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    Although the St. Peter's cross is a cool mechanism, I've never seen the need for one on a leg vise. A leg vise operates much like a gigantic wooden screw clamp, in that the jaws don't have to be parallel for it to work well. All you need is for the pin in the parallel guide to be set in a position slightly wider than the thickness of the board you are clamping in the vise. As long as the holes on the parallel guide are spaced closely enough (mine are effectively spaced in 1/2" increments), you won't need a mechanism to keep the chop parallel with the leg. Just move the pin to the best position for your board.

    In fact, it's the ability of the leg vise chop to rack slightly back and forth that gives it so much holding power.

  4. #4
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    Same two pieces of information I've been able to find. I see comments that this is a great idea but no evidence that anyone has done it <g>. I'm thinking about building a mockup and trying it. What I was thinking is to secure the metal cross pieces in the middle (like a pair of scissors). Securing the metal strips at the top. Cutting vertical slots in the two wooden pieces and connecting the metal strip ends with a rod through the slot. This is using two "crosses", one on each side of the vise.

    Quote Originally Posted by Andrae Covington View Post
    I recall Jameel Abraham mentioning three or four years ago that he was experimenting with the form, but there was never any followup.

    I suppose you have seen the illustration of "La Croix de St. Pierre" from The Amateur Carpenter and Builder. Here's a brief Schwarz blog post about it.

  5. #5
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    If I'm going to be stooping down to adjust a pin, then I won't be building a leg vise. No criticism, I just know myself and having to do that would tick me off every time I had to do it... Besides, anyone could build that, you don't see folks building the "cross". Same with the Nyquist Tail vise. And, you don't see many shoulder vises anymore. I think I'm detecting a theme here since I'm already planning to do the shoulder and tail vise and talking about the leg.

    Quote Originally Posted by Wilbur Pan View Post
    Although the St. Peter's cross is a cool mechanism, I've never seen the need for one on a leg vise. A leg vise operates much like a gigantic wooden screw clamp, in that the jaws don't have to be parallel for it to work well. All you need is for the pin in the parallel guide to be set in a position slightly wider than the thickness of the board you are clamping in the vise. As long as the holes on the parallel guide are spaced closely enough (mine are effectively spaced in 1/2" increments), you won't need a mechanism to keep the chop parallel with the leg. Just move the pin to the best position for your board.

    In fact, it's the ability of the leg vise chop to rack slightly back and forth that gives it so much holding power.

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    I was interested in doing this as well before I ordered my BC leg vise. From what I read, you need to use some fairly stout iron because of the force exerted by the screw. I found one web page where a guy had made them from aluminum, and the vise bent the aluminum. Norm Vandal's bench in Landis' book has one, and it has some general details on how it was done.
    Last edited by Justin Green; 03-27-2012 at 9:11 AM.

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    Quote Originally Posted by Justin Green View Post
    I was interested in doing this as well before I ordered my BC leg vise. From what I read, you need to use some fairly stout iron because of the force exerted by the screw. I found one web page where a guy had made them from aluminum, and the vise bent the aluminum. Norm Vandal's bench in Landis' book has one, and it has some general details on how it was done.
    Thanks for the information. All the discussion of leg vises fired up after I had already bought and read that book and I never thought to look for "old" information. I'll dig that book out tonight. I'll probably use some wooden slats in my mockup. Once I have it worked out, I'll look for better material. Seems like the stock I bought for my shoulder plane sole (yet another project where I haven't actually gotten past the gathering phase) wasn't super expensive, I bet it would work well.

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    Norm Vandal found a set or took a set from another bench, and his are cast iron. I was thinking about lining the grooves in the chop and leg with steel channel and using bearings at the ends of the cross that aren't fixed. So basically all I would have to do is route the channel in the leg and the cross would just screw in as a single unit.

    I'm tempted to mock one up just for fun, since I have a second workbench with unadultered legs...

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    Quote Originally Posted by Jerome Hanby View Post
    If I'm going to be stooping down to adjust a pin, then I won't be building a leg vise. No criticism, I just know myself and having to do that would tick me off every time I had to do it.
    Also in the spirit of no criticism, people worry unnecessarily about moving the pin, I think. In use, I rarely have to move the pin. On my leg vise, there's one position for the pin where the leg vise works well for stock anywhere between 1/2" to 1" thick, which is what I need to clamp in a leg vise well over 95% of the time.

    As far as the effort involved in stooping down, if you can pick up a piece of wood that fell off your bench onto the floor, you can change the pin on a leg vise. If it's really going to be an issue, you can raise the position of the parallel guide, as in the plans for the Benchcrafted vise.

    And if the St. Peter's cross really does keep the chop parallel to the leg, you're going to lose clamping power compared to a leg vise without one. That's just basic physics, and probably why you don't see more leg vises with that mechanism.
    Last edited by Wilbur Pan; 03-27-2012 at 9:43 AM.

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    I have been aware of the cross mechanism for many years,but I doubt it would really manage to keep the jaws QUITE parallel,even if the whole mechanism were made of steel. By that,I mean the "T" slots that the cross arms would run in. It would,I believe,keep the jaws NEARLY in parallel alignment,but,because of slack somewhere,or slight bending of the materials in the cross,would not quite work perfectly,unless it were made with machine tool tolerances,and massive parts.

    If I were to make one,I'd make the tracks out of steel,make the rollers or pins at the ends of the screws fit CLOSELY in the steel tracks,and make the arms of the cross pretty massive,with very little play anywhere,no more than would be necessary to get the mechanism to operate smoothly.

    Even then,I think the jaws would still have enough misalignment that they would not quite properly grasp a thin scraper for sharpening.

    I saw an expensive Ulmia work bench in the furniture conservation shop,that had a long wooden jaw,and an internal chain drive mechanism. Sure enough,when I tested its parallelism with a thin steel scraper,it wouldn't quite hold the scraper snugly at both ends of the scraper,when tried near one end of the vise.

    This is what always happens when wood bearing surfaces are allowed anywhere in the mechanism. The sprockets were likely fastened into the wood jaws,OR had a little play in their bearing surfaces.

    I do not see how there would be any loss of clamping power. It's just that the cross mechanism likely would not stand extreme tightening without flexing somewhere.

    Since the location of the vise screw limits the useful depth of the vise,I agree that raising the parallel guide is the more practical solution. Put a string on the pin to keep from dropping it if bending over is a problem(it's getting to be a problem for me!)
    Last edited by george wilson; 03-27-2012 at 10:31 AM.

  11. #11
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    Thanks George, I think you just saved me a bunch of time. I'm not a fan of the leg vise but this cross thing was intriguing. I trust your evaluation and your method described if you were to make one exceeds what I was willing to do. Think I'll stick to the vises I've already decided on and pour my efforts into doing them as well as I can.

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    Unless you have a good milling machine and lathe,it is best to try something else,really.

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    I believe that LN have a leg vise that acts like a sideways double screw. This does not require a pin.

    Regards from Perth

    Derek

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    Is there any reason why the pin(s) for the bottom piece couldn't be attached to a foot pedal to operate the pin(s)?

    My thought would be to have three pins with springs so that one could be doing the work while the other two float.

    If my memory is working, Harry Strasil was also working on an idea for the sliding bar using a locking set up like is used on F-clamps.

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

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    Quote Originally Posted by george wilson View Post
    Unless you have a good milling machine and lathe,it is best to try something else,really.
    I've got the Gingery books. Maybe I'll revisit this after I build a furnace, lathe, milling machine, etc... <g>

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