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Using the vice jaw on the rear.

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  • Using the vice jaw on the rear.

    Hey guys,

    I'm working on machining a plate that's too wide for my normal jaws so I have put the moveable jaw on the rear of the sliding section. My question though was, since the force is now acting to rip the jaw out of the 3/8-16 threads should I ease up a bit on the clamping pressure? Makes me a little nervous cause I know that thing can develop a crazy amount of force.

    First operation is to drill some pilot holes so no need to mash it but then I have to spiral mill the final holes since there is only 1/8" clearance over the top of the vice, not enough for the big drills to break all the way though so I don't want the plate to get loose either.

  • #2
    Vise Jaws

    I have used my vise that way numerous times. Although the bolts on mine are 1/2" I'm sure grade 8 3/8" SHCS will do fine. You should be able to hold the part very solid without cranking on the vise handle with all your weight.
    Just a firm cinch up should be plenty.
    Kansas City area


    • #3
      Cool, I was just curious if I was worried about nothing and people normally just cranked the snot out of them or if that's a great way to rip the threads out. I try not to tighten the vice like a gorilla normally anyway. Figure if it requires that much force to keep in place then you have something else wrong. I can't take monster cuts anyway. Its just here I'm only getting a 1/8" bite on the workpiece so I felt a little nervous about not really cranking down.


      • #4
        I tighten my mill vise all the time with a little 6 inch spinner handle. The big long 15 inch handle that came with my vise has lived up on the shelf behind my mill for many years now. I don't think I have used it but just a few times while I made my short spinner handle. There is little reason to be cranking those vises so tight you crack your walnuts. They produce pretty good clamping force with just a snug and a thump with the palm of your hand.


        • #5
          I would add some thick washers to the 3/8-16 bolts holding it in place. Make them as large as will fit. Actually you could make plates using some 1/4" thick steel stock (or thicker even) for them. Just cut some rectangles that will fit and drill 13/64" holes for a close fit (close for washers anyway). You will probably have to use longer bolts to ensure sufficient thread engagement. I would suggest SHCS.

          These plates/washers will distribute the clamping force over a greater area which will lower the stresses at the small area that the original screws/screw holes would have produced. This will help prevent bending or cracking the vise jaw.

          And, as Toolguy said, do not use excessive force.
          Paul A.
          SE Texas

          And if you look REAL close at an analog signal,
          You will find that it has discrete steps.


          • #6
            Nah! Don't worry about it. If you're tightening your vise enough to threaten its strength you're overdoing it. Tighten the vise enough to hold the work without distorting it or threatening the vise. Light cuts on delicate work use a light touch. Heavier cuts, proportionately more.

            Same thing with clamps and step blocks, drawbars, and anything else in the trade. Semipermanent fastenters in assemblies like attachment bolts for stressed parts like head bolts etc torque to 90% of yield strength is the norm. Frequently revised set-up and service access attachments need a more selective, attuned technique. With experience comes judgement.

            So. Back to the origianal question: When using the hard liners on the back side of the jaws, have regard for the strength of the attachment bolts and the elasticity of the grip; otherwise procede. You might slip a feeler between the liner and jaw. If there's more than a thou or two either ease the grip or snug up the attachment screws.

            BTW, a quibble: the fixed and movable workholding parts on a vise are the "jaws." The hardened plates attached to them to take the wear are "jaw liners". Most everyone calls them "jaws" including me. But when referring to specific parts and differentiating between them you gotta get technical and use the right names to avoid confusion.
            Last edited by Forrest Addy; 12-20-2011, 07:58 PM.


            • #7
              Just running rough numbers reveals that you would need about 140 pounds of force on a 16 inch (long) vice wrench to reach yield on two 3/8 " Grade 8 screws.
              You make the call, but it looks like no problem to me
              Those two screws will take about 5 tons of force ..if they are grade 8 ( DIN 10.9)
              Green Bay, WI


              • #8
                Alright, I'll quit my worrying then! I'll note the terminology now too. Thanks for all the input.