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  • Round column mill guide bar alignment

    Ok, all you fine gentlemen still here? Good- I am starting to build the guide bar setup that will allow raising and lowering the head of the mill without losing position. Basically there will be a guide bar parallel to and in the same plane as the column. Parallel is easy, basically a pair of spacers cut to the same length is used. In the same plane is a bit more difficult.

    So far what I've done is extend the elevation crank shaft and surrounded it with a steel box. One side of this box will have a brace to another part of the head, and the other side will have something that will ride the guide bar. The crank handle ends up being about 8 inches further to the left than it was before, but otherwise its operation isn't affected at all.

    The guide bar will be mounted to the column via a pair of arms with clamps which can be loosened so the bar will swing with the head if I want to rotate it on the column. When I need to use the guide, the clamps would be tightened, then the head can be cranked up and down without losing the alignment. Of course the guide bar has to be in the same plane as the column, otherwise there will be a smooth, but progressive loss of positioning the more you raise or drop the head.

    So that's where I'm at on this last day of the world. I'm looking for a good way to firstly get the bar aligned, and secondly to keep it aligned through the countless times it would be loosened and tightened to the column again.

    I suppose that if the guide bar was rigidly mounted to the arms, it would resist being twisted off-plane, and the mating slide mounted on the crank extension housing would help to keep it 'vertical'. I think this will work, but it's also possible that by some small angular error in machining the guide bar seats that the bar will acquire some small but non-fixable twist. I further suppose that if I were to machine both arms together, then turned one upside down, that the possible error might cancel and I'd end up with the right result. I think this is the way I'm going to approach it. Any other ideas?

    Just to further clarify- if I was to align the guide bar to the column and tighten the clamps permanently, all I'm faced with is aligning the bar once. The head would always ride up and down in the same spot above the base. But I do want to be able to rotate the head on the column as it becomes helpful, which it has many times. This is the remaining 'snag', after which it's just cutting, machining, and assembling parts. Pictures to follow.
    Last edited by darryl; 05-21-2011, 10:49 PM.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    Guide Bar

    That sounds like a good plan. I think if the bushings on the head are 6" or so apart vertically, that should be enough to keep the bar parallel to the column while you tighten the clamps. It will be interesting to see how it turns out.
    Kansas City area

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    • #3
      I've just finished getting a new handle bored to fit the extended shaft. The old handle didn't have enough meat on it to be bored that much, plus it was kinked to one side anyway and would have put the crank even further to the left than this mod put it. So now the mechanicals of the crank extension are done, mounted, and working better than before. Funny how that happens sometimes- in this case partly due to the fact that I added a bushing for the shaft at the end of the extension.

      I used a 2x3 steel tube section for the extension box. The 3 inch dimension is vertical, and I plan to mount the bushings for the guide bar above and below the tube, so that will put the bushings about 5 inches apart. That should be enough to greatly help keep the bar aligned to the column. Two things happen here- one is that the extension box has some wiggle room to allow it to be aligned to the guide bar, and the other is that I can't rely on it initially to align the bar to the column. The guide has to be aligned first, then the extension box gets removed from the elevation mechanism, mating surfaces coated in my best epoxy for this (PC-7), remounted, aligned to the guide, bolts snugged up lightly, then wait. After a full day of cure, I'll tighten the bolts a bit more, then move on to securing the bushings. Before any of this, I'll have to make the connecting arms and clamps for the guide bar.

      I'm happy so far- drilled and tapped everything I needed so far without breaking a tap, and I now have a better place to clamp my work light.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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      • #4
        Here's 2000 words worth- I've temporarily clamped a piece of square tubing to the extension box just to show where the guide bar will be.

        [IMG][/IMG]

        If you look carefully at the right end of the extension, you see two coin sized spots- these are two inch long pieces of half inch rod that have been pressed in, then drilled and tapped so the box can be mounted using bolts from the inside of the elevation mechanism cover. How else, short of welding, can you mount the end of a tubing section to some flat surface- there surely isn't enough thickness in the material to drill and tap into the end of it. The box will be epoxied to the cast cover as I mentioned earlier, and that's as much to fill gaps so I don't crack the cast from tightening the bolts as it is to help keep the parts together as one rigid unit.

        [IMG][/IMG]
        Last edited by darryl; 05-22-2011, 04:56 AM.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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        • #5
          Darryl,

          Cool build man, I also have a round column drill/mill and face the same problems. I have been re-aligning the head with a laser which works ok but is not that accurate. I am anxious to see how you resolve it. Keep the pictures coming. Thanks for posting this.

          Tim

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          • #6
            Use two guide bars just like the ways on my mill. Bore the pairs of holes in the end pieces together. The bars will be parallel, it cannot be otherwise. The end supports will then offer perpendicular surfaces to which you may measure in relation to the vertical column. All that takes is a square.

            The end plates should be screwed together for boring. Alignment on the cross slide is easy by sweeping with a DI mounted in the chuck. You can also do the same on the mill instead of the lathe.

            Free software for calculating bolt circles and similar: Click Here

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            • #7
              Funny, every round column I see,including mine,the belt gaurd is long gone.

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              • #8
                Not real clear on what you are doing here. Does the whole column rotate?

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                • #9
                  I have been re-aligning the head with a laser which works ok but is not that accurate
                  There is a real easy way to get much better accuracy with the laser. I presume you are shining from the head to the base. Fix the laser to the head and shine it on the farthest wall you can and make a mark there. That will be an order of magnitude better, at least, as long as the mill doesn't move on it's stand or bench.
                  Free software for calculating bolt circles and similar: Click Here

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                  • #10
                    Originally posted by tdmidget
                    Not real clear on what you are doing here. Does the whole column rotate?
                    No the col. doesn't rotate the head rotates on the col. when being raised or lowered, sort of the same problem as using a drill press and moving the table up and down.
                    I like Evans idea of using two guide bars instead of one, but I'm not the guy doing the work

                    Steve

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                    • #11
                      Why not pin the rack to the column, accurately of course.
                      The shortest distance between two points is a circle of infinite diameter.

                      Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

                      Southwestern Ontario. Canada

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                      • #12
                        There's been a few mentions now of pinning the rack to the column. To start with, there has to be some clearance for the head to be able to slide up and down past the rack. That clearance is in a groove at the top and bottom of the head casting adjacent to the column. My column is about 4 inches diameter, so the groove is about 2 inches from the central axis. Go out to the spindle, and you have roughly a 5 to 1 increase in the side play, so if the groove has say 2 thou of play, the best you could hope for at the spindle is to be within 10 thou. Completely non-acceptable. On my mill, the grooves for the rack to slide in have about 10 to 15 thou of play, so that would put the best case scenario at the spindle to about 50 thou. You can eyeball far better than that. Pinning the rack to the column also prevents being able to swing the head on the column. If all I wanted was an accurate ride up and down, some of these potential problems would be gone. I don't think there's any case where pinning the rack and relying on it for alignment is going to work well enough to be worth the effort.

                        Anyway, Evan's suggestion is along the lines of what I came up with while trying to sleep last night. The bores to hold the guide bar must be square to the arms holding the bar, and the big end of the arms must also be machined squarely so they will extend out from the column in good alignment. I'm going to machine all the bosses on the lathe, then tie the bosses together with some flat sheet material on both sides. Each boss will have the bore and one flat side machined intrinsically accurately, and the other flat side will come very close as long as my faceplate doesn't wobble, which it doesn't. With these parts accurately made, the assembly should square up perfectly.

                        I wanted to mention one other thing- the middle pulley stack is on the right side of the mill. It takes up about 4 or 5 inches of vertical space, so if I had designed to put my arms and guide bar on that side, I'd lose that much vertical travel. As it is, the belt cover will lose me an inch or two on the left side, and I'm probably going to cut out a section of the cover so I can get that back. Seems this mod was destined to be on the left side.

                        Now that I'm clear on how to proceed, I'm back in the workshop. More pics later. Thanks guys.
                        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                        • #13
                          What about a bar that's parallel to the column in both directions, attached to the mill base in a fairly rigid way. Then mount an idicator to the head, so it can bear on the bar in a position that's easy to see. Set the indicator to zero when it bears against the bar, then move the head up or down to the new height you want. You can then rotate it around the column, till you get the same zero reading on the indicator and things should be perfectly aligned at the new height. The big advantage over a guide that holds the head rigidly in alignment, is that you can't over power the guide.
                          Last edited by Robin R; 03-17-2015, 04:00 PM.

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                          • #14
                            Not a bad idea, Robin. A guide bar that's fixed in place which you measure against. Could be finicky with the gauge, though. You'd probably have to dedicate a caliper to it, and mount the caliper to a slider on the bar, denoting an exact spot on the head casting to measure to. I can see that working reasonably well.

                            I have all along been considering the effects of flexing of the guide bar. I don't know how it will translate in actual usage, but I guess I'm going to be the guinea pic here. The bushing that rides the bar doesn't have to go completely around it, so that leaves the potential to add some bracing to the back side of it. Just a strip of flat bar on edge would offer a fair amount of stiffness.

                            I'm going to leave myself the option to disconnect from the guide, in case there's an application where the guide would get in the way of a large workpiece. So far, I've lost 1/8 inch in throat capacity, so nothing there basically, but also I've lost about 5/8 inch off the bottom of the head travel, the room taken up by the bottom arm. I don't recall ever having to crank the head that low, so I'm probably not going to miss any capacity there anyway. At the top I'm replacing the column cap with the upper arm, so no loss there. I can't recall ever needing the full height capacity either, so nothing will change for me there.

                            Well, back to it for a bit, then I'm taking a coffee and pie break. Pumpkin, mmm
                            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                            • #15
                              More work done today on this- here's an overall showing the guide bar mounted.

                              [IMG][/IMG]

                              Here's a close-up of the lower arm. I've used solid pvc to make the bushings to press-fit the bar into, plus make the spacer that half-surrounds the column. The gaps between the steel plates will be filled with pvc also, which will enhance the rigidity of the arms. Both arms have the gap where the rack fits, and this will help keep the rack from skewing when you rotate the head on the column.

                              [IMG][/IMG]

                              This shows the simple strap clamp that tightens the arms to the column. One refinement will be a pair of threaded handles that will take the place of the nut, which is temporary.

                              [IMG][/IMG]

                              When tightened, the arms are held tightly enough to the column that they don't shift with any reasonable force applied out at the guide bar. I will need to rely on the bushings that ride the bar to keep the bar aligned with the column- it doesn't take much to twist it when the clamps are loosened. Filling the gaps between the sheet steel pieces will help with this, but I can tell it won't prevent some small amount of twisting. I'll be transferring that job to the bushings that ride the bar (which aren't made yet), and I'll be spacing the bushings about 9 inches apart. That's the longest I can make that without interfering with the full range of height adjustment. So, that's my next step- the bushing holder.
                              Last edited by darryl; 05-24-2011, 02:25 AM.
                              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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