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  • How much jaw lift is too much?

    My question tonight is just like the title says, when tightening a milling vise, how much lift in the movable jaw is considered too much? The vise i picked up for my mini mill is on the, err, 'frugal' side, and ive noticed that when placing a piece on parallels the side contacting the movable jaw lifts about 5 thou as measured by my iffy dial indicator. Personally i think its a little higher of a number. Doesnt seem like much, but it does bugger things up when im trying to mill down bar stock to a consistent dimension

    So, is this normal to see in a mill vise? Are the Kurt style vises subject to the same problem, or would i see better results if i were to make the switch. Shars sells a decent looking 3 inch kurt style im eyeing, but it would be rather pointless if i were to drop the money and find out that the new vise would have the same problem.

    For reference, my present vise is the 3 inch mill vise that Little Machine Shop sells:
    http://littlemachineshop.com/product...ory=1963256912

    And this is the one im thinking about getting:
    http://www.shars.com/3-x-2-95-lock-d...g-machine-vise

  • #2
    Those vises always have jaw lift, because there has to be clearance for the jaws to slide, and they're manufactured to a price point (that's very low compared to their mechanical complexity). You should still be able to get reasonable results in most cases where you're doing things like milling down stock square, using a soft face or deadblow hammer to seat the stock back down onto the parallels as you tighten the vise. It's a necessary part of using such a vise.

    Kurt clones take up a lot of table real estate for their size, but don't open very far either. You'll quickly grow frustrated that such a large vise only opens 3 inches. Yes, you can swap the jaws around to the outer faces for larger plate work, but that's extra setup, and 3 inches isn't a very large vise - that mini Kurt only opens half an inch wider than the vise you already have - meaning you'll be doing it often. They're also not a 'standard' item, so the quality will be variable and largely unknown until you've got it in your hands.

    On a mini-mill type machine, I would look at a screwless toolmakers vise before one of those mini-Kurt clones. This vise opens 60% more than the mini-Kurt, although it doesn't have replaceable jaws, or external jaw mounts - neither of which are features you might need on a mini-mill. By and large, they're also manufactured to very good parallelism and squareness tolerances, regardless of where they're bought from, and the jaw hold-down feature is very effective if you understand how to use it (the closer you can get the screw to parallel, the better). And if you ever decide to move up to a big boy mill, the vise will have a second life as an insert vise.

    http://www.shars.com/products/toolho...oolmakers-vise

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    • #3
      I'm getting 0.0025 to 0.005 mm on a Kurt.

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      • #4
        Got jaw lift? Locate a U-clamp, stud, and heel block over the jaw to force it back down. PITA as in more set-up hassle but it works.

        The relics we apprentices had to contend with popped up a visible amount on tightening. Those vises were 20 years old, veterans of WW II and many round the clock war emergencies. They were in their last stages of wear, suited only for us apprentices and other low forms of life. If you didn't clamp the jaw down, work you were trying to square up took on the look of a polygon.

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        • #5
          Put a length of steel round rod maybe 0.25 dia. horizontally between the workpiece and the movable jaw. As the jaw lifts the rod will roll downward and push the work against the vice base

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          • #6
            Parallels, and a dead blow hammer?

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            • #7
              Get yourself a dead blow hammer. They look like a mallet but the head is filled lead shot or sand so they impart their energy to what you are
              striking instead of bouncing back at you. I picked this one up at Lowes a couple of years ago for $25:

              Snug the vise up a little. You will need to learn how hard to strike the part to get it to seat back down onto the parallel. Use just enough force
              to get it to seat, this is a case where more is not better. Try to ensure that the face of the hammer strikes flat against your part. I usually
              strike the part slightly off center closer to the movable jaw. Once seated make sure you didn't lift it off the other parallel. Then continue
              to snug and seat the part until you feel the vise is tight enough.
              Location: Long Island, N.Y.

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              • #8
                Dead blow hammer for the win!

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                • #9
                  With the Kurt style and copies you can limit the amount of lift by tightening the setscrew in the middle of the movable jaw. You can remove the jaw by backing out the same screw. Many people know this, but many don't.
                  Kansas City area

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                  • #10
                    MOST vises lift a little and you can see this by the fact that typically the parallels shift easily. But after tapping the work piece down with a dead blow or lead hammer the parallels are pinched in place. That assures you that the work is down correctly.

                    I suspect that the proper Kurt style does a good job of holding the work down well. But the cheaper (as in affordable for home shop use) Kurt "style" vise I bought needed some tuning and smoothing in that angled face clamp down area to give it a more Kurt like operation. But it still lifts with thinner items held high on the jaws. So out comes the dead blow to deal with that.

                    For a mini mill I really like the suggestion from the other guys to use a screwless vise. These style vises naturally lock downwards and while you might still need to rap the work down they do provide a smaller size vise to use on the smaller machine. And in fact LMS has THIS MODEL ON CLEAROUT just now. At the $65 price I might even suggest buying two so you can set up the pair of them to use for longer work pieces similar to what Joe Pieczynski shows in some of his You Tube videos. The nice thing is that these use up FAR less table area than the Kurt style you are considering. And not only is it around 3 inches shorter but it also does not have the lead screw stub sticking out to snag on you or get in the way of the hand wheel for the table.

                    Another advantage of the screwless LMS vise is that if needed it can be set up on it's side and clamped to the table to better hold items vertically that need something done on the ends. Try THAT with a Kurt style with anything other than a rather large and bulky angle plate in addition to the vise.
                    Chilliwack BC, Canada

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                    • #11
                      Personally I prefer the CNC style vise http://littlemachineshop.com/product...ory=1963256912 that pulls down the movable jaw but has machined sides and hold down slots. Can be installed at an angle like a swivel vise, without the height. Can be laid on its side. No jaw lift. Four jaw positions allow you hold large plates on the outside positions. I ussually keep a taller set of jaws on the outside so there is no need to remove the inside jaws for plates. Easy to clamp these vises to a tilt table too.

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                      • #12
                        Gary, other than the price I really like that option. All those advantages for positioning and in a size which is in tune with a mini mill. And as we always say in time worry over the price, if it's not totally outlandish, fades as we smile each time we use it.
                        Chilliwack BC, Canada

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                        • #13
                          This drawing attempts to illustrate the jaw rising problem:



                          With a thin part being held at the top of the jaws, as the vise is tightened if the moveable jaw has any clearance in it's mounting the top edge of that jaw stops moving when it contacts the part, but the bottom edge continues to move toward the fixed jaw. This causes the movable jaw to rotate and it then rests on the bed of the vise on it's rear edge only. The front edge lifts and so does the face of that jaw and the part being held by it.

                          This jaw rise problem only occurs when a thin part is gripped at the top of the vise jaws, often with it sitting on parallels. If the part is seated down on the bed of the vise, it will not rise or, at least, the amount of rise will be minimal. So, if you can do your work with the part down on the bed of the vise, you will eliminate much of this problem.

                          There have been different solutions to this problem. Most involve better control of the angle of the movable jaw or a downward motion of that jaw when it is tightened. Oh, and there is always the brute force method of using a dead blow hammer.

                          Several features have been used to control the angle of the movable jaw:

                          1. Longer jaw length - most of the high end milling vises use this, often combined with other features.

                          2. A tightening motion that is at a downward angle - the most notable example of this is the "screw-less machinist vise".

                          3. Various devices that impart a downward motion to the movable jaw as it is tightened with a horizontal screw. These are usually hidden inside the vise. This is a feature that is often combined with the longer jaw I mentioned in #1 above.

                          4. A plate that attaches to the movable jaw and rides on horizontal surfaces below the vise bed.

                          5. An additional, round guide rod that is below and between the rails of the vise bed.

                          In my opinion, the best of these methods are the Kurt which uses #1 and #3 and the "screwless" machinists vises which use #2. Both of these seem to work very well. The others are often used on low quality vises that are not made to tight tolerances and perhaps for that reason, do not seem to work very well.

                          I have not yet been able to afford a Kurt or similar quality milling vise but I so have a somewhat larger "screwless" machinists vise that I use for most precision work on the mill.

                          BTW, that term "screwless" is somewhat misleading. These vises do have screws, they are just a lot shorter and not easily visible.
                          Paul A.
                          SE Texas

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

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                          • #14
                            Not to argue too much with an industry standard practice of hammering a part down with a dead blow hammer, but if you look at my drawing above and imagine what happens when this is done, you may come to the conclusion that this practice is not the best.

                            If you hammer the part down as it is trying to rotate, it will still be sitting against a tilted jaw. Now, that hammering may also bring the moveable jaw down somewhat. So the part will be held by it's bottom edge while the top edge is somewhat loose. And the moveable jaw will be in a somewhat unstable position as it really wanted to be rotated more with the pressure applied by the screw. So there is a chance that the vibration of making a cut could cause the moveable jaw to rotate again and that will lift the part again. I do use this technique, but I also look for signs of the part moving as I cut.
                            Paul A.
                            SE Texas

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

                            Comment


                            • #15
                              Originally posted by BCRider View Post
                              Gary, other than the price I really like that option. All those advantages for positioning and in a size which is in tune with a mini mill. And as we always say in time worry over the price, if it's not totally outlandish, fades as we smile each time we use it.
                              I know what you mean so I bought 2 which made me feel better somehow. Another thing I do a lot of work in soft jaws, steel or aluminum. Soft jaws can be more accurate, you take a pass on a step of a few thosandths and it is dead true. We carve up softjaws while milling when they are in the way. Make oversize jaw blocks so you can trim them multiple times.

                              A little trick. Cut a step on the bottom of each jaw so they don't sit on the vise body. Then you can clean up the whole jaw surface using a long endmill right in the vise.

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