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Thread: Leg vise experiences?

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  1. #1
    Join Date
    Jan 2019
    Location
    Fairbanks AK
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    1,566

    Leg vise experiences?

    I just ordered from Lake Erie and Anchora Yacht Services, have a couple or four weeks to get my act together.

    My main questions regard the chop.

    I am seeing a lot of folks using 12/4 stock, but then trimming the top of the chop back to half an inch or so so they can get at the workpiece. Is 12/4 really neccessary? If I really need 12/4 I will probably have to glue it up. One 8/4 glued to one 4/4 should put me in the ballpark. Is there a compelling reason I couldn't or shouldn't build the chop up to 12/4 thickness to match the thickness or depth of my benchtop, about the top 4 inches of the chop, and then run 8/4 down to the floor?

    Is maple just traditional, or does it have a specific advantage over white oak or hickory? Weight maybe? I have been buying 8/4 in all three species lately for turning projects, I am leaning towards finding a piece of 8/4 that I can get some turning pieces out of and then use the not suitable for turning remainder as the chop.

    I can visulaize the install, I feel darn good about it; but I would like to hear from folks that have been using them a while.

    "I made my chop out of 8/4 butternut/white pine / figured walnut 25 years ago and it is great" is a valid data point. If I really need to glue up 12/4 from floor to bench top I would rather do it right the first time. "I started with an 8/4 chop but it flexed when I did ___ so I had to make a new 12/4 chop" also valid data point.

    The other thing is I am old enough and wise enough to ask all y'all, what am I not asking that I should be asking? I recognize I don't know what I don't know.

    Thanks in advance.

  2. #2
    Join Date
    Sep 2008
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    N. Idaho
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    Hi Scott,

    I have an elm chop that's probably 12/4, but that's because I got it from a friend, along with the wood for the base of my bench for the best price (free). I also have the Anchora chain and think it works great (there are some picks of the install in a thread I did of the bench build started nearly 10 years ago). From a structural standpoint 2x pine would probably be sufficient because the lever arms in the vice are short. So I would say pick anything that will suit your eye and wallet. I'm not sure what I would have done if paying for wood...

    Best of luck!
    "You can observe a lot just by watching."
    --Yogi Berra

  3. #3
    Join Date
    Jan 2019
    Location
    Fairbanks AK
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    Thanks Chris, I am leaning towards 12/4 because I ass/u/me the ones before us needed it for something; but I will have to special order it and count on the order filler in the lower 48 to send me a good piece. My local guy carries 8/4 and under, he has a little bit of Brazilian something in 16/4 but it is more than $25/ bf. I will go look for your bench build.

  4. #4
    Join Date
    Apr 2019
    Location
    Madison, Wisconsin
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    283
    Hi Scott,

    While I don’t have any experience with a leg vise to offer, I can tell you the following. All else about the geometry and materials being equal, the stiffness will go as thickness cubed, so 3 inches thickness will be over 3 times as stiff as 2 inches. The experience of others, as you indicate, seems to suggest the extra stiffness is a good thing.

    I don’t see any reason you couldn’t laminate pieces together to get the greater thickness if you go that route.

  5. #5
    Join Date
    Mar 2015
    Location
    SE Michigan
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    3,222
    My leg vise chop is 6/4 hard maple, which is 1/4” thicker than what Chris Schwarz shows in his Roubo bench plans. If it’s ever flexed, I haven’t noticed. It has plenty of holding power.

  6. #6
    My chop is 8/4 walnut and works fine.

    The leg vise works best when the fulcrum is slightly wider than the thickness of the held piece. So taper your chop or plan your chain install accordingly.

    Leg vise handles are lower than other vise types. While a lower handle implies greater holding power and leverage and depth capacity, it means more stooping. As I am getting older, the stooping is really wearing on me. The vise is plenty strong and I could have gone a couple inches higher with my handle without sacrificing power noticeably.

    If you are planning to use it to edge plane, a makeshift deadman on the other front leg is a godsend.

  7. #7
    Join Date
    Apr 2019
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    Quote Originally Posted by Prashun Patel View Post
    While a lower handle implies greater holding power and leverage and depth capacity, it means more stooping. As I am getting older, the stooping is really wearing on me. The vise is plenty strong and I could have gone a couple inches higher with my handle without sacrificing power noticeably.
    Hi Prashun,

    You have part of that backwards.

    In any statics situation (i.e. when things aren’t moving, such as when you have something clamped in the vise) the sum of all forces and the sum of all torques must be zero.

    This indicates that the total force applied by the screw is shared between your workpiece and the base, with the sharing determined by how far each is from the screw. Force times distance for each (the work and the base) must be equal, so if the screw is closer to the work the force on the work must be greater because the distance is smaller.

    Therefore, a higher screw increases the clamping power but reduces the capacity.

  8. #8
    Scott,

    I've used chops made of 12/4 and ones made of 8/4 with a 4/4 lamination, functionally there is no difference. At that thickness wood used makes almost no never mind, pick something cheep and/or looks good.

    ken

    P.S. On the portable benches I've used 8/4 Red Oak or Beech chops with no problem.
    Last edited by ken hatch; 01-15-2021 at 10:40 AM.

  9. #9
    Michael, then I've had it wrong all this time. The screw should be as high as one can stomach in terms of sacrificing depth.

  10. #10
    Join Date
    Apr 2019
    Location
    Madison, Wisconsin
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    Quote Originally Posted by Prashun Patel View Post
    Michael, then I've had it wrong all this time. The screw should be as high as one can stomach in terms of sacrificing depth.
    Prashun,

    Not necessarily; by the time the screw is 3/4 of the way up the chop, you're already getting at least 3/4 of the screw's total force on your workpiece (more if you have the work low in the vise rather than at the toe). A few inches up or down on a typical leg vise height won't make much difference in clamping force (but will have some effect).

    Placement of the screw will have more effect on comfort and capacity than on clamping force.

    There are definitely diminishing returns as you raise it higher and higher. I'd say, rather, that one should place the screw as one judges based on the tradeoff between convenience/comfort, clamping force capability, and capacity. Where the "right" placement ends up seems to involve too many factors to make a recommendation without knowing about the person and their work.

    Then, there's the relationship between chop thickness, toe-in angle, and flex that can limit the maximum practical clamping force independent of the screw, say if toe-in becomes toe-out due to too much force applied for the chop design. Deflection is going to be based on the ratio of length to thickness (modified by width) and will also depend on screw placement. I can go into more detail if it's helpful.

  11. #11
    Nice. Thanks. I don’t know bout your fancy math . I just know my old back don’t like stopping. The leg vise is easily the most powerful of my vises and I suspect up or down it will be plenty strong.

  12. #12
    Join Date
    Apr 2019
    Location
    Madison, Wisconsin
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    It appears you already knew the most relevant information, then.

    Should you choose to adjust your setup, you now also know that you won't compromise on clamping force.

  13. #13
    Join Date
    Mar 2012
    Location
    Mid coast Maine
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    477
    Here are are some real world numbers on what one of my leg vises is capable off. If you can’t see the dial it is 1600 PSI.

    5A9E2373-6DC3-4EDE-A17B-D18FEA91BE8B.jpeg

    In answer to your problem Scott of the top of the jaw opening up, there is an adjusting nut at the end of the chain that makes it easy to dial in just the right amount of toe in so at full pressure the jaw is possible.
    full disclosure I am the vender of the chain kit. I’m just here to answer questions, I hope that is ok.
    Jim
    Ancora Yacht Service

  14. #14
    Join Date
    Jan 2019
    Location
    Fairbanks AK
    Posts
    1,566
    A couple items and then I will have to leave this be for a few days.

    I have written down on my Monday to do list the phone number for NELMA so I can order the grading guide for northeast and great lakes USA. Can't do beam calculations without knowing what grade lumber you are using. Local to me none of the hardwood from the NEMLA area has grade stamps on it. Hopefully the person I get on the phone can tell me how to find the grading rules that are supposedly free .pdfs on the website, I couldn't find them.

    I did do a beam calculation with a 5x5 inch hickory timber. For beams and stringers, hickory, (american) beech and birch all use the same table. So imagine a select structural grade hickory beam 5x5 inches and three feet long. Set two anvils on your driveway so the outside edges are three feet apart, set the beam across them. Set one of your hands on one of the anvils and under the beam. Have a friend lower a Toyota Corrola or similar 2800 pound item on the beam 12 inches down from the end of the beam over your hand, 24 inches from the other end, a point load. The beam will not fail, and will only deflect 0.029 inches.

    I don't know of anyone using a chop five inches thick. At some amount of force the threads on the screw and nut will fail.

    All: Please keep your data points coming. "My chop is 2.5 inch thick maple, four inches wide at the floor, 12 inches wide at the benchtop, no issues" is all I really need.

    Michael B:

    There are many things timber framers are willing to do if an engineer trusted by both the builders and the building inspector signs off on the blueprint, but the timberframers would not attempt if an engineer hadn't signed off. I am not a timberframer. I did spend most of my free time last winter learning about it. And this beam is an unusual situation in the load comes and goes and comes and goes, much more rapidly then seasonal snow load.

    I have to get the grading book in, find reasonable design values for material I can get, and I have to leave the through hole for the vise screw out of the beam width. If the chop is two inches wide at the bottom stop block and the through hole for the vise screw is two inches on center there is no beam, from a timber framers perspective.

    In say 2-3 weeks I should be able to write up reasonable beam calcs, makes sense to start with hard maple. When I get to the end of all that you or anyone else who feels qualified is cordially invited to look it over and say because of x, y, and z this item is actually 30-50-200% stronger than calculated.

    Jim R:

    Your posts come up in my search results here often, glad you are still around. I have wanted a wood screw face vise since I used one in Junior High shop class, and can finally justify it as my current vise wracks too much to do the thing I am trying to do now. My suspicion is the AYS chain system on the parallel guide is going to meet 75-90% of my needs. I saw a new thing recently since I last watched all the leg vise videos on you tube. If you were to interent search "Jay Bates leg vise" and kick over to the "videos" tab of your search results you should find a 22 minute video near the top of your results. If you open that and pause it six seconds in you will see a wedge on the floor that will probably tell you all you need to know.

    I am planning to do both, just run the AYS chain system routinely (It is still, after eight years, good enough for Derek Cohen for heaven's sake), and have the system from Jay Bates video ready to go.

  15. #15
    Join Date
    Apr 2019
    Location
    Madison, Wisconsin
    Posts
    283
    Hi Scott,

    When designing based on acceptable levels of deflection, strength becomes a non-issue unless you’re using very stiff and brittle materials (think ceramics). Far more important is the elastic modulus and the geometry. If, however, you want to order the grading guide and run the calculations for your own edification, I won’t try to dissuade you.

    For the screw, there will be a pull-out strength based on the effective shear area of the threads; that said, it’s not as simple as the calculations might lead you to believe. Going by just the shear area formula, one would conclude that more threads engagement is always better. However, as long as the screw maker has done their job properly and in the case that the material of the screw and threaded hole are identical you’ll generally get very close to maximum strength on a coarse thread with 4-5 threads engagement (more for fine threads). This is because the materials deform under load (the screw stretches, for example) and the first 4-5 threads end up taking most of the load (highest load on the first thread, less on the second, and so on).

    The screw is unlikely to be able to apply a large enough load to break any reasonable chop design, particularly if the chop has been designed for appropriate stiffness. This includes under cyclic loading as well as static loading. Put another way, I’d recommend you design the chop for the stiffness you want and let the strength take care of itself.

    If I understand your goal correctly, you’re interested in whether you can get away with using locally available lumber for a high-performance chop rather than ordering something. I am confident that you can; I am willing to help.

    Michael

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