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How much jaw lift is too much?

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  • #31
    Originally posted by garyhlucas View Post
    I think a screwless vise on a minimill is a mistake. A minimill is a very limited machine to begin with. So any accessory you add should expand that capabilty, not limit it even further. As a mechanical designer I spend a lot of time figuring out how to design a part I can hold for machining. With a versatile vise that can hold lots of different size parts and in different ways like softjaws modified to hold a part you are WAY ahead of the game.

    Don't limit your machine further, give it new capability with a proper vise.
    How does a 3 inch jaw vise that opens nearly 5 inches (the Shars screwless vise), give up anything in capability to a 3 inch Kurt-clone that opens only 3 inches? We're talking about a machine that has 5 inches of y-travel, not a Bridgeport.

    I mean, you aren't even giving up the ability to use soft jaws/machined inserts. You could put two, inch thick aluminium soft-jaw inserts into that screwless vise, and you'd still have the same holding capacity as the Kurt-clone.

    The only thing it gives up is outside-face mounting the jaws, which seems a bit ridiculous on a mini-mill.

    Besides, look at the massive tradeoff hidden in the details of that Shars Kurt-clone:

    Accurate to 0.002” per 4” on squareness and 0.006” per 4” on parallelism without base
    I had a mill vise that was out of parallel with the base 0.002" over 4 inches, and I can tell you, even that was frustrating enough to cause me to replace it.

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    • #32
      As an apprentice we all made "Hold Down Strips" for doing thin work in the vise These are a stepped "Staircase" style of strip about 5/8" thick by about 3/4" wide front to back. The back face has a 3 degree angle to ensure the strips push the work down in use. I still use mine 55 years on.

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      • #33
        The screwless vises are designed for surface grinding and similar precision operations that do not require high gripping power. They do not have the gripping power of a milling machine vise. The reason a milling machine vise is called a milling machine vise is that it is designed with the gripping power and (hopefully) accuracy required for that application.
        Jim H.

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        • #34
          How much jaw lift is too much depends on the part tolerance
          that you are trying to achieve. Simple answer.

          -Doozer
          DZER

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          • #35
            This picture from arceurotrade shows a good view of the holddown mechanism:

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            • #36
              Life and machining are both a series of compromises. Cost vs. quality or utility is one of them. There is a famous saying, "I can do it fast. I can do it cheap. I can do it well. Choose any TWO." Picking a vise for a milling machine is one of these compromises.

              Recommendations against using a screwless vise for milling? Sure there are. A professional machinist will probably go for a Kurt or similar vise every time. He is not paying for it, his company is. He is not considering the cost, just the utility. And, in truth, in a professional shop with all costs (like labor) included, the more expensive tool may very well be the overall cheapest.

              Others have talked about the way that Kurt and other expensive vises generate the downward force needed to keep the movable jaw from rising. And yes, that force must come from somewhere. The closing force is divided between holding the part and keeping the jaw down. This is true for the Kurts as well as the screwless style. The screwless vises simply have the screw, yes they do have a screw, at about a 45 degree angle so it pulls both in and down. Simple but effective. It works, I can attest to that. I have not used one, but I am sure the Kurt design also works.

              The Kurts are simply larger and have a bigger screw. The screwless ones are probably limited to about a 5/16" or 3/8" diameter screw. So the Kurts can apply more force and the fraction of that force that is directed to holding the part is likewise greater. I am sure that if Kurt made a two inch vise with the same mechanism, it would also have a smaller screw and less holding power. And you are NOT going to put a 5" or 6" vise on a mini-mill. It just won't fit. I have my doubts about the 4" Kurt fitting. So the holding power of those larger vises is simply not a consideration here.

              I have and have been using a screwless on my RF-45 style Grizzly mill and have never had a part slip. But I do not take 1/2" hogging cuts either.

              Price, size, holding power, precision: all of these are part of the compromise you must make.



              Originally posted by epicfail48 View Post
              Now i remember why i saw recommendations against using a screwless vise! Ive seen cautions against them because they dont hold work as securely as a traditional vise due to splitting the clamping force between sideways and down, any truth to that? I dont want to risk launching a part across the room while im trying to mill a slot. Has anybody running a screwless had a problem with work slipping under milling or drilling operations?
              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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              • #37
                Thanks for all the advice guys! I ended up ordering the Shars screwless vise SunGod linked too, it showed up today and i got it mounted this evening:


                Had to mill out some holddowns, felt kinda cruel using the old vise to make the parts for its replacement. Kinda like making an employee train his replacement. Havent got the chance to do any real testing, but my initial impressions are putting me in the camp of people who believe that a screwless vise may be the best option for a mini mill. The first thing i noticed was the build quality, it feels a lot more solid than the first vise, despite being about the same price. The movable jaw moved smoothly, but with no play, the jaws locked up with no lift (yay!), and everything just felt solid. A few pretty sharp corners, but nothing worth complaining about. For the price i can tolerate stoning off a few burrs myself.

                The next big plus was the height. Not the overall z height though, even though I did gain about 1/2" over the old vise. I'm actually talking about the height of the jaws themselves, the jaws on the old vise were 1" tall (wide? Dunno, top to bottom) whereas the new ones are closer to 2.5"ish. Haven't measured exactly. Anyway, larger jaws=more contact surface which I can only assume is a good thing.

                Overall footprint is pretty nice as well, the new vise is roughly the same footprint as the old, but has larger jaws and more capacity. Hardened surfaces are a plus, as is the fact that the new vise has much higher tolerances than the old. Let's not forget the lack of jaw lift, I'd be remiss if I didn't mention that given the reason for buying it. The only negatives I've come across so far are the aforementioned sharp edges and the fact that adjustment isn't quite as convenient compared to a screw vise. The clamping screw and moving jaw are a little fiddly, the cross bar seems to like getting stuck. Even so though, I can live with that given the advantages

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                • #38
                  I saw a nice bodge for screwless vices. Get a LONG t handle hex wrench to tighten the screw. Loosten the vice but leave the t handle in the screw. The weight cams the screw anchor up into the notches and assists in getting the anchor in the right groove as you tighten the jaw against the workpiece.
                  You can also grab the wrench low and twist it slightly to clear the grooves when opening it.
                  Joe

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                  • #39
                    I bought one of the Chinese milling vices, 5" jaws, opening about 6" from Arceurotrade, see post#35 by ikdor, the Kurt type modification of the hemispherical bearing was instigated by none other than Sir John MBE. The jaw lift is minimal, maybe 0.0005" to 0.001". It was not Kurt quality, but I could afford £100, well worth the money. This size is about the maximum for a drill-mill.

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                    • #41
                      Its common knowledge we ALL love the various vices we use. Its the third hand we always wanted.

                      I have some that don't move at all. Bock 3" double that is as large but not as heavy as my old ass bridgeport vice. The BP vice moved, I have three kurts and I don't even check for movement. I do like most folks do. Dead blow mallet and seat the part. Its just a habit for me, basically automatic. Never thought about it till this discussion.

                      Fun read too. I'm a slow reader. I got through some good ones

                      Where is the fresh sourdough bread and butter I was promised JR

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                      • #42
                        Originally posted by JRouche View Post
                        Its common knowledge we ALL love the various vices we use. Its the third hand we always wanted.

                        I have some that don't move at all. Bock 3" double that is as large but not as heavy as my old ass bridgeport vice. The BP vice moved, I have three kurts and I don't even check for movement. I do like most folks do. Dead blow mallet and seat the part. Its just a habit for me, basically automatic. Never thought about it till this discussion.

                        Fun read too. I'm a slow reader. I got through some good ones

                        Where is the fresh sourdough bread and butter I was promised JR
                        Wrong guy, I promised cookies for not having the popcorn prepared

                        I'm still a little curious how guys manage to wack a part with a dead blow to seat it. I tried it, but I found that if I snugged up the jaws on the part, then tapped and tightened, the tapping was pointless because the subsequent tightening cause the jaws to lift the part. Tightening then tapping was equally pointless because with the jaws tightened to prevent movement while milling, the part doesn't move when you smack it with the dead blow. I just don't get it!

                        Course, doesn't matter any more with that sweet screw less vise still liking it, those sharp edges are a little annoying, but everything else is head and shoulders above my previous vise. Tramming was a pain, but it's under .0005 out. Just for kicks I measure the top of the jaws, turns out the right side is .001 higher than the left. I can live with .001 in 2.5 inches

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                        • #43
                          Like Jim said, screwless vises are grinding vises. They're a pita and don't have the holding power. I picked a D30 recently, (small Kurt) which I don't think are made anymore...which is shame as they'd be the perfect size. Seeing it beside the bigger Kurts made me think it a home made D20 or even D10 might be an interest project for use with a small mill

                          I took 30 posts, but imo Chris's the best answer - holddowns. I've a few Kurts and while great vises even they sometimes benefit from holddowns, especially for small parts that would otherwise have to be held toward the tops of the jaws. If you don't have some, they're highly recommended. Hold downs let old style vises perform as well or perhaps even better than a Kurt....they just take a bit longer to set up so don't have the convenience of the Kurt
                          Last edited by Mcgyver; 07-23-2017, 12:44 PM.
                          in Toronto Ontario - where are you?

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