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Table locks,,, when and why

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  • Table locks,,, when and why

    I actually really havent used my locks much on my little jet 8 by 36, one of the reasons is i havnt gone godzilla crazy with cuts yet, here's my two part question, I can see useing the locks for Y when feeding with X on heavy stuff but if its not heavy work is it not more accurate to leave the locks out of it ---- i mean even with properly ajusted gibs a couple of X locks will move the table back some, or for something like a rotary table --- you get everything centered with your RT and then go off center for say a bolt hole pattern or something ---- after this wouldnt it be a no no to lock your X and Y on your mill table, sure it would give more stability but it would also change position,,, all tables move when locked No? I know mine does yet my gibs are properly adjusted, there will always be oil room that gets squished out esp. with thick vactra.... A DRO also will not catch this because of the way the scales are mounted have no change on the table position even though the table will shift, so you center and then lock --- things change but that doesnt register on your scales...
    Lets hear it

  • #2
    Mine doesnt have locks JRouche
    My old yahoo group. Bridgeport Mill Group

    https://groups.yahoo.com/neo/groups/...port_mill/info

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    • #3
      Just checked deflection, Y --- .001 X --- .003 and .004 if i really clamp down hard on both X locks, typically X will show more due to it being longer so more deviation and oil surface area that has to be squished out plus two table locks to force it over... this would be more than enuff to mess up the majority of the parts im building for my cranks --- yet my X gibs actually stick slightly because im a little on the snug side with them...

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      • #4
        I know it's a slightly larger machine, but...

        My Bridgeport originally had a different (optional?) style of locks that won't move when you lock them down. I still have the one on the X axis, but not the Y, becase first, it was part of the Y axis scale mount on the old optical readout, and second, because some neanderthal broke the clamp in the mill's previous life.

        So I have the unmoving lock on the X, but on the Y, I've learned to watch the DRO and do a little "proceedure" when I'm locking the Y. Basically, I "overshoot" the target position by about .001", then back up to the correct position, then crank back in the original direction so I take about half of the backlash out of the Y lead screw. It may sound silly, but I know my machine, and this process works for me.

        I'll go take a picture of how the X lock works so you can see how it's done. It probably wouldn't be so hard to make one for just about any mill.

        -Mark
        The curse of having precise measuring tools is being able to actually see how imperfect everything is.

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        • #5
          Here you go. This is the X table lock. There's a rail mounted using the front T-slot, and the clamp is a special kind of C-clamp. Half a turn of the lever locks it down just fine.



          A closer view shows that there is a little plate isolating the screw from the rail it locks down on:



          Now, looking at the front of the clamp, you can see the holes for the alignment pins in the little plate. The pins are in the little plate, and having them align with the holes in the clamp means that the only motion of the plate is the downward clamping, and no side-to-side motion is transmitted from the clamping screw.



          Interestingly enough, the clamp screw is just a socket head screw, and the lever just screws into the side of the "knob" that's fastened to the socket head screw using a set screw 90 degrees out from where the lever screws into the knob.

          -Mark
          The curse of having precise measuring tools is being able to actually see how imperfect everything is.

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          • #6
            Don't lock 'em unless you need the rigidity to control chatter. The latter sounds to me like roughing, where the accuracy will be less important. Don't lock 'em if accuracy is paramount.

            Best,

            BW
            ---------------------------------------------------

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            • #7
              Cool Bob, I guess maybe iv been doing things right after all for a change, Wirecutter --- that is an interesting lock, maybe not quite as rigid but it does allow you to lock without change, i think that if you know your machine as well as you do then what your doing with the Y axis is maybe even better, I think if you had the same setup on Y as you did on X that it would be great for most aplications but the table would still be free floating in its X and Y gibs therefore might introduce chatter while boring or such, still you can tell they were trying to get around an inherent problem, thanks for sharing the pics...

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              • #8
                Well, I lock the "unmoving" axis as a matter of habit, unless I'm doing a lot of drilling or other "light work". I normally keep the gibs pretty snug, but it's an older machine with some wear, so it gets a little tight at the far ends of the Y axis.

                I'm really diggin' the new DRO, and it shows me just how much things move when working. Mostly, it shows me when I accidentally bump one of the cranks.

                -Mark
                The curse of having precise measuring tools is being able to actually see how imperfect everything is.

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                • #9
                  Originally posted by A.K. Boomer
                  Wirecutter --- that is an interesting lock, maybe not quite as rigid but it does allow you to lock without change,
                  It doesn't look as rigid as it seems to be - it works great for my use. I wouldn't mind having the one that used to be on the Y axis, but it won't work with my DRO installation. We all make do...

                  -Mark
                  The curse of having precise measuring tools is being able to actually see how imperfect everything is.

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                  • #10
                    Conventional wisdom, especially with a vertical mill, is to lock any axis not being used. That also includes the quill.

                    The end mill exerts a surprising amount of force, and even with everything locked, will produce a "C" shaped slot due to flex imposed by the cutting forces.

                    If the table is allowed to float around under these forces, results will be unpredictable, and accuracy will suffer, not to mention finish, and the tendency to destroy endmills in the process.

                    If extreme accuracy is required, an undersized cut should be taken, measured, the table moved the needed amount and retightened and finish cut taken.
                    Jim H.

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                    • #11
                      I have DRO that I keep set to .001" tolerance on the display. My enco mini mill will only go out .001" when the gibs are tightened which since I have a DRO I just stop .001" short then it tightens to spot on .000" For my mini mill with .000" display resolution I have not yet seen the numbers change on the locked axis's while doing a cut. Although the biggest part I've milled so far is only 12"x6" approximately. But, a few times I have neglected the lock down usually with unfortunate results. I remember once it went off by .01", but the z axis is the killer, if you dont lock that on my machine it just lifts all the way up.
                      “It was not til Leibniz and Newton, by the discovery of the differential calculus, had dispelled the ancient darkness which enveloped the conception of the infinite, and had clearly established the conception of the continuous and continuous change, that a full and productive application of the newly found mechanical conceptions made any progressâ€‌

                      Hermann von Helmholtz (1821-1894)

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                      • #12
                        Originally posted by JCHannum
                        Conventional wisdom, especially with a vertical mill, is to lock any axis not being used. That also includes the quill.

                        The end mill exerts a surprising amount of force, and even with everything locked, will produce a "C" shaped slot due to flex imposed by the cutting forces.

                        If the table is allowed to float around under these forces, results will be unpredictable, and accuracy will suffer, not to mention finish, and the tendency to destroy endmills in the process.

                        If extreme accuracy is required, an undersized cut should be taken, measured, the table moved the needed amount and retightened and finish cut taken.
                        For my mill (IH), the big win is in locking the gibs when roughing and to pretty much always lock the Z where possible. A lot of these Asian mills have quite a bit of slop in the quill, and things can really get to bouncing and chattering if that axis isn't locked durings cuts (unless the cut requires Z-Axis motion, of course!).

                        For finish cuts, taken a little more shallow, I don't notice much advantage in locking the gibs. The big win there is to climb mill rather than conventional milling. There the difference is huge and obvious both in how the handwheel feeds (it feels "happier/smoother" climb milling) and how the surface finish turns out. If you haven't played with this, it's really easy, just cut in both directions and I'll bet you see a pronounced difference one way versus the other. I actually taped a diagram to the side of my mill head for a while until I could tell which was which without thinking about it.

                        Once you get used to these differences in feel, it also becomes obvious to the touch and sight when the head is not quite in tram (DOH! I hate when I discover that after beginning a cut!).

                        Best,

                        BW
                        ---------------------------------------------------

                        http://www.cnccookbook.com/index.htm
                        Try G-Wizard Machinist's Calculator for free:
                        http://www.cnccookbook.com/CCGWizard.html

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                        • #13
                          I was recently roughing some pockets in cast iron, 1" EM, .125 doc and a pretty good feed. If I didn't lock the Y axis it would self feed out 25 thousandths when I engaged the X. Made for a oddly shaped pocket if I wasn't careful when changing direction. I always lock the quill when it's not moving, I've had the quill pulled down as well as having tools pull themselves out of holders when the helix decided to act as a screw. I've never had the table pulled up, but I'm sure that it's just a matter of time...

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                          • #14
                            That self feed may have been the "table suck in" that can happen if you wind up climb milling through a direction change. I wonder, but you do want to keep an eye out if you reverse direction and be aware when you are climb milling.

                            Best,

                            BW
                            ---------------------------------------------------

                            http://www.cnccookbook.com/index.htm
                            Try G-Wizard Machinist's Calculator for free:
                            http://www.cnccookbook.com/CCGWizard.html

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                            • #15
                              I have a little bench top at home and alway lock the unused axises. <sp?> The bigger one at work I rarely lock. The mass of the table and its rigidity makes a big difference.

                              On the little one, the problem for me is lack of mass and slop in the feed. If I am going round the outside of something, the milling will move the table as I start on the opposite side. The quill also has slop so I will lock it nearly always. If I need to move in the Z, I have the option to almost lock it, makes the z motion stiff but reduces chatter.

                              It also is so small that the "column" lacks in rigidity so locking the Z helps eliminate chatter and lets me take a more vicious cut.

                              So why do I have the small toy at home? It costs a whole lot less and fits in the shoebox workshop and if it really cant handle it I can take the job to my work's workshop and grovel.
                              Murphy was an optimist

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