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  • Prep for tramming

    I figured it's about time to check the mill alignment again. It's been awhile. Couldn't find my outer ball bearing race that I use for this, and the indicator mount doesn't allow for the width of my new t-slot gap spanning ring- so-- made a new mount for the indicator and carefully checked the ring to ensure that it's flat, etc. So far, so good.

    Rig it up and check the mill- it's out by about a thou per inch in a diagonal direction. Ok, I need to do some math and place some shims. Re-test, etc.

    Now I'm wondering- the accuracy of it all depends on the head being a nice fit to the column, and all the slides being clean. Since this is a round column mill, that's one of the things I need to clean and lightly oil. I'm sure by now there's some crud trapped between the column and the head. Anybody have a method of getting this all good before tramming?
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    All those things may be variables, but they are a fact of life. HSM mills are not perfectly rigid and not perfectly snug and they do need to be retrammed frequently. Or at least, my little HF mill needs to be retrammed frequently.

    I tram on the workpiece by taking a light cut with the face mill as I sweep the face mill from side to side. When it is trammed, the face mill will cut on both the leading side and the trailing side, and it'll leave a cross-hatched pattern. When it is not trammed, only one side of the face mill will cut and it will leave a semi-circular pattern.

    I dunno how accurate my method is -- I've never checked it any other way -- but face milling is something I do a lot of, so it works for me.

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    • #3
      Couldn't find my outer ball bearing race that I use for this, and the indicator mount doesn't allow for the width of my new t-slot gap spanning ring
      I never understood why some folks are nervous about running a DTI across the T-Slots. Just make sure the pointer is bent in the opposite direction you're sweeping, and it will gently skip off the beveled edges of the T-slots.

      I wasn't able to get a good tram on my Mill/Drill until I carefully cut the paint between the base and the head casting with a razor, scraped out the filler, then loosened the head bolts enough to tilt the head, and thoroughly cleaned out the base with a scraper and mineral spirits.

      Make sure to look for the beer can shims before you do that -- they were little 1/4" x 1/2" slivers on mine.

      Also, when you start getting close to a good tram, you have to keep measuring as you tighten the bolts -- the bolt tension will easily throw the head a couple of tenths.
      Last edited by lazlo; 12-20-2009, 11:52 PM.
      "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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      • #4
        You don't need the ring, it's just nicer when you don't have to worry about the indicator catching. I found a piece that came out of an automatic transmission that I cleaned up and checked- it works great in this application.

        Just today I read about a couple of mills where the column was filled with concrete and rebar to stiffen it. My thought was, yes, stiffen that, but what about the strength and rigidity of the base where the column mounts- one person filled the base as well with concrete.

        My own mill is flexible enough to allow about 3 thou change on the indicator as I push and pull on the head. Seems like a lot to me, when I relate that to a dimension I'm trying to hit. I'd like to be able to stiffen it up significantly, but I think a better option is to upgrade to a better mill (or a real mill as many of you might be thinking). Costs money of course, so for now I'm going to look at the column and if it seems a little thin I might consider filling it.

        Not a worry right now though, I just want to dial it in closer without skipping a step- that being to make sure the head fits the column properly with a metal to metal contact and not a metal to goo to metal contact. I'm thinking the trick here is to use some solvent to wash the column down. I'll crank the head down as far as it can go, then clean the upper part of the column, wet it with solvent, then crank the head up and do the bottom. A couple of times up and down with fresh solvent will hopefully wash the inside of the head a bit as well. A few more times up and down, wiping the column each time, then a few more times with oil to get that sort of infused between the head and the column, Keep wiping down and cranking up and down til it seems I'm not wiping dirt off anymore. That's my plan anyway.

        Another option which can work for me is to hoist the head assembly right off the column, then clean both well before reassembly. This won't be hard because I already have a hoist in place made just for lifting the mill. Maybe it's overkill to go to this extent, but it is time for a thorough cleaning anyway.
        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
          Patience

          Originally posted by darryl
          I figured it's about time to check the mill alignment again. It's been awhile. Couldn't find my outer ball bearing race that I use for this, and the indicator mount doesn't allow for the width of my new t-slot gap spanning ring- so-- made a new mount for the indicator and carefully checked the ring to ensure that it's flat, etc. So far, so good.

          Rig it up and check the mill- it's out by about a thou per inch in a diagonal direction. Ok, I need to do some math and place some shims. Re-test, etc.

          Now I'm wondering- the accuracy of it all depends on the head being a nice fit to the column, and all the slides being clean. Since this is a round column mill, that's one of the things I need to clean and lightly oil. I'm sure by now there's some crud trapped between the column and the head. Anybody have a method of getting this all good before tramming?
          Darryl.

          You do need to correct that tram. I prefer about 0.002" (0.004" at a pinch) over 8" - job dependent.

          There no need or use to tramming by adjusting the column unless you really do want the column precisely square to the mill table. That job is a PITA on a round column mill and not much better on a square-column dove-tail mill and rarely justified on either mill.

          When the milling head is clamped to the round (or square) column mill, the milling-head and column are one unit for all practical purposes.

          Most milling is done with the milling-head clamped to the column - irrespective of whether the quill is clamped to the milling-head or not.

          The quill should be clamped to the milling head for/during tramming.

          I presume that the milling-head is adjustable for "tilt" (left-right) and not for "nod" (forward/back).

          I loosen my milling-head tilt bolts and adjust tilt directly. I adjust nod by inserting shims between the tilting head and the milling head.

          Its a bit frustrating at first but as you get used to it you will get better at it.

          Its a wise move to check your tram every time you raise/lower and/or swing your milling head on the round column - if the job justifies it.

          So, minimise the number of times you raise/lower swing the milling head and you will be OK.

          If/when you raise/lower the milling head, keep its axis pointing to/at the same place on the mill table (within about 10 degrees should be OK) - by "eye" will do.

          With a bit of care and patience you can do very well on a round-column mill.

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          • #6
            Well, I just finished going through it all. This mill has no tilt or nod capability, so I have no choice but to shim the base of the column. I did as I thought to do, cleaned the column, ran it up and down, cleaning the exposed portion of the column each time. It wasn't as gunked up as I thought it might be, so that went easily and I finished with a clean oily rag wipedown.

            The base bolts were pretty tight but I got them out and did the rock and shim thing until I had about an inch of space between the base and the - base. Cleaned it all up, did the rock and shim removal thing until I had the base back down without any shims, then tested it. As I expected, it was out worse than before- same as when I first got it.

            Once I got over the brain cramp about it being out both ways, I went left/right first. Error of about 3 thou corrected by placing 6 thou shims front and back on one side, then nod corrected by placing shims left and right (at the front in this case), equal thicknesses- 4 thou it turned out to be. Tested a few times during tightening of the bolts. Final outcome- I could have used another half thou for the nod adjustment. As it stands it's within less than a half thou front to back, and it's a guess as to whether there's any change at all left/right. That's over 6 inches. I'm happy with that.

            Now- what can I do about the flex? It doesn't take much to move the dial +- 1 thou, considerably more force to move the dial another thou each way, then it's pretty solid after that. It's not a function of the base bolts, since I checked this flex with the bolts snug but not tight, then again with them fully tight. My hunch is that it's not the column flexing that much. I believe it's the machines base. Anybody ever played with this- I'd be happy to hear of your experiences. As OT suggested, this is going to be the same for any mill with a column and base, round or dovetail.

            Ok, as I was musing about how to find the source of this flex, I had an idea- there's a pair of bolts behind the table where the flexible shield bolts to. They are on the casting that has the column on it. I bolted an angle bracket under one bolt, then clamped a piece of bar to that such that it extends over the table. Clamping an indicator to the side of that bar, I could measure the deflection from bar to table. I get pretty much the same deflection there as I was reading from the spindle to table. That tells me my hunch was right- most of the flex is not in the column itself, but further down.

            That makes sense to me. There's not as much 'leverage' in the metal in the base to resist flexing as there is in the column. Please find fault in my logic if there is any-

            I guess the next thing to ask is how much deflection would you see on one of those garbage bridgeports? ? Same conditions, indicator mounted to the spindle, rotated towards you, reading to the table.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

            Comment


            • #7
              Well done.

              You've done very well Darryl.

              Any mill in "drill" mode has pretty much the same forces and reactions as a "G" clamp in "clamp" mode does - and it rarely matters.

              In "mill" mode when traveling left/right, the loads and reactions are similar to a "G" clamp that has very little - if any - clamping force but is held along its bottom in a vise and the "nut" (top) end pushed side-ways and both the the top (milling head) and back (column) have torque forces applied which tend to cause "twisting". (There are others but they can be neglected).

              Self-evidently, the greater the forces the greater the deflections - and vice versa.

              So expect larger deflections under heavy cutting loads and less (very little) under light to finishing cuts.

              You will soon learn the limitations and capacities of your machine.

              Just stay within them and you might be pleasantly surprised at just how well you can and will do.

              Comment


              • #8
                Originally posted by darryl
                Now- what can I do about the flex? It doesn't take much to move the dial +- 1 thou, considerably more force to move the dial another thou each way, then it's pretty solid after that.
                It sounds like you have some crud stuck between the base and the head casting. You might shine a flashlight in there and inspect the base of the casting, and the underside of the head casting. I needed a paint scraper to get all the junk out -- there was paint, filler, cosmoline, casting sand, and swarf in the base of mine.

                The round column is surprisingly stiff. The head bolts, on the other hand, are made of Chinese cheese, so a lot of guys replace them with ASTM hanger bolts (grade 5 equivalent), and really crank down on it. I did that, and replaced the base bolts too, and it completely eliminated any twist around the column, or head slip during a cut (which is scary as hell ).
                "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                Comment


                • #9
                  Most of the work I did was to separate the head and column assembly from the bed, so I could get in there and clean it all up. I have done this before, so I wasn't surprised to find it fairly clean. The mounting of the head assembly to the base is pretty solid, and I did test for flexing and movement during tightening of the bolts. Without any shims at all, and with the bolts just snug and with them tight, the flex was the same, so I've ruled out that interface as a source of the problem.

                  I agree, the column is pretty stiff, and with the head fairly low on it to facilitate the indicator, there isn't much flexing to be expected anyway on that short of a section. I thought I might have some play or rocking motion of the head on the column, but there doesn't seem to be any.

                  I remain convinced that the base is flexing. It has a ribbed structure underneath, but it's not boxed in. Boxing it in would stiffen it up significantly. If I was to do an upgrade, I would first lift the head and column assembly off the base, then place four pieces of threaded rod in place of the bolts, epoxying each one into the threads in the base. There would be probably three or four inches of bolt sticking downwards inside the base, and about two inches or so above. I would lower the head assy onto those bolts and run nuts on them fairly snugly (with my shim packs in proper place) to cause an alignment of the threaded pieces to suit the bolting. Once the epoxy has hardened, the next procedure would be to remove the column (I'll just be hoisting it straight upwards and letting it hang there for awhile) and drag the base and stand out. The rest of the job requires turning the base over, with table still in place, and seeing what can be done to make it a boxed in structure. Filling the boxed in cavities would be part of the upgrade. The filling would encapsulate the four threaded rod pieces and fill all gaps where a metal plate or two are used for the boxing in.

                  This isn't likely to cost me more than about thirty bucks or so for materials, just a lot of time and fooling around. The base will obviously become heavier, so I'll have to have a plan in place to muscle the thing around and set it upright again on the stand.
                  Last edited by darryl; 12-21-2009, 09:37 PM.
                  I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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