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Re: [mill_drill] Re: Round Column Mill Anti-rotation Modification

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  • Bruce Johnson
    Hello Martin, Its Bruce Johnson, and I too considered the anti-rotation problem for a round column mill about five months ago soon after acquiring an RF-31, my
    Message 1 of 44 , Jan 1, 2011
      Hello Martin,

      Its Bruce Johnson, and I too considered the anti-rotation problem for a
      round column mill about five months ago soon after acquiring an RF-31, my
      first mill. I was advised by a local career machinist of 35 plus years of
      experience, to stay away from the round column due to the lack of
      repeatablity to index a center as you move the head up and down the column
      and he suggested I look into a small knee mill, maybe a Millrite or
      Clausing. I talked to a few more people, and a Rockwell was added to my
      prospective list. Then I started looking at the spindles and decided the
      preponderance of tooling available, (I had zip) was much greater for the R8
      spindle and the power of the Taiwan made machines was about double, and yet
      the prices were about one half on the used market. I then gave some thought
      as to what I might be making on the machine of my choice and what accuracy I
      would need. The answer was that as a newbie, accuracy was down on the list,
      and most things that I machine on my lathe that I have owned for 30 years
      are just repairs for other tools, simple turnings and bushings, etc. On the
      other hand, a resonable counter bore on a mill with decent concenticity was
      desirable. The amount of time spent on a machine was also a factor in the
      trade-offs. I kept asking myself, will I really need this parameter or
      feature in the near future.

      I decided to look into pinning the gear rack onto the column as a start,
      because I had heard just about what you heard, not to many details, and no
      data as to the end result from people who had tried this, and I figured that
      I could always move the work relative to the head to get bye for my needs.
      But in the back of my mind, I had the capability of the traditional flexible
      head movement of the smaller American made machines still imprinted. The
      result was I decided to try and come up with a modification that would let
      me keep my center for the majority of the time, but for that rare occation
      when I needed to rotate the head around the column axis, I wanted something
      that was semi-permanent and the roll pins to attach the rack to the column
      were not the solution for a couple of reasons: The first was difficulty
      getting them in and out, and secondly, I was not getting the rigidity of the
      rack against the column to maintain linearity and parallelism with the
      column axis. I did try several different combinations of pins with a
      countersunk screws on the top and bottom of the rack close to the teeth.
      This was an improvement but I still had to remove three pins equally spaced
      between the top and bottom screws.
      I then had a breakthrough and tried allen drive set screws where the three
      pins had been and clamped the rack tight while tapping through BOTH rack and
      column. I left a very small amount of material in the column thickness so
      the screws would bottom out and not drop into the column ( my column is
      still empty but I plan to fill to increase rigidity). The set screws have
      to be the right length, so that the top of the screws are just below the
      bottom of the gear teeth, and centered on the width of the rack. I had to
      do a little careful fillng on the head of one screw to match the gear tooth
      profile. I had previously measured the width of the rack at several points
      and as I recall, it was less than .001 inch over the length of the rack and
      straight using my best straightedge. Now I have 5 screws to pull using the
      same allen-T wrench and the head now swivels as it did before. You do have
      to crank the head up and down during the process to get at the center three
      The next task was to design a better method for the head to " track" the
      gear rack. I noticed two important things as I looked at the dimensions of
      the rack and the way the head moves against the rack. The sides of the
      rack are not flat and the head travels against one side of the rack due to
      gravity and the head weight against the sloped gear teeth. The notch at the
      bottom of the head which is considerably wider than the rack is what makes
      contact with the rack side on my machine. I essentially decided to close
      this gap using a copper bar that is slightly crowned at the rack contact
      point (side) which decreases friction and it is mounted on the adjustable
      ring on the top of the head. The bar is slotted down the center allowing
      for contact adjusting pressure using two allen head cap screws and washers.
      I chose the copper since I did not want to gall the gear rack sides and I
      had it "on hand"-Any semi-soft metal would work most likely. Rack and bar
      were lubed on contact sides and on rack teeth.

      Your roller idea on a flat ground surface may be a better method over the
      long haul and should take out some column to rack error for the Z-axis but
      my method is a cheaper fix, another example of cost vs. accuracy. Speaking
      of accuracy, the bad news is I have yet to take the final data as personal
      problems and bad weather have stalled my hobbie time. When I finish, I will
      release some pictures to the group and may in the future make some direct
      comparisons between the RF and a Clausing 8520 which I have access to. Oh,
      definitely torque the head bolts using a torque wrench and use the same
      sequence each time. I would be interested to see the variation between
      machines in regard to the bolts and any differences due to the roller
      contact. I would appreciate an update on your progress if you decide to go
      ahead, and remember, where there is a will-there is a way! Best regards,
      .original Message -----
      From: "Martin Kennedy" <martin@...>
      To: <mill_drill@yahoogroups.com>
      Sent: Friday, December 31, 2010 03:33 PM
      Subject: Re: [mill_drill] Re: Round Column Mill Anti-rotation Modification

      > Thanks to all for the suggestions!
      > I have not heard much to give me hope that I can successfully modify the
      > mill as I described. I was never positive that it'd work, and everything
      > I've read makes me even less certain that it could work.
      > Of course, as much as I'd like it, buying a new $10k CNC mill to replace
      > one I already have is not much of an option! It would certainly fix one
      > problem (the mill) and lead to another (the wife).
      > I've tried the laser trick and a string on the far (20' away) wall in
      > the past without much success. I don't think it's very accurate, and
      > it's definitely not easy to do - I can't see that far to see if the
      > laser is on the string, and end up running back and forth as I torque
      > the head bolts. The diameter of the laser is relatively large at that
      > distance, and that's where the inaccuracy comes in.
      > I'm aware of the limitation of my round column mill. Thoroughly. But you
      > have to work with what you have. I plan my operations, but setting up
      > the mill for different operations like a chucked reamer and then milling
      > at the maximum extent of the quill is not a good idea. Sometimes you
      > just have to move the head between operations.
      > I do like the suggestion of the camera. I had not heard of this before.
      > I found the web page that describes it and allows download of the
      > software "CentreCam" http://www.miketreth.mistral.co.uk/centrecam.htm
      > I'm going to build one and see how it works. I just need to find an
      > appropriate webcam to buy. I think that building the holder would be
      > simpler than modifying heavy mill iron! Accuracy for the camera is
      > claimed at 1 thousandth or so, which is plenty close. There's already a
      > computer and monitor sitting right next to the mill to drive the CNC, so
      > I would not need to buy much stuff.
      > On 12/31/2010 9:15 AM, draggingsteel wrote:
      >> I cant imagine the column ever being repeatable. Loosening and
      >> tightening the bolts will make a considerable change every time. The
      >> idea on pinning the rack to the column might help but even if the
      >> sides were ground and you ran guides along them, the loosening the
      >> head would negate all efforts. Do you plan on cncing the head or the
      >> quill? The reason you dont see it done much is probably due to the
      >> extra complications. If you used Arnie's/Zarzul/Wildhorse Innovations
      >> camera that mounts in the spindle, you could form a reference point on
      >> the table. Find and center your reference point, lock the head and
      >> switch to the tool of choice. I have seen lasers used aiming at a
      >> place on the other side of a room. That might get you close but that
      >> would be about it.
      >> --- In mill_drill@yahoogroups.com
      >> <mailto:mill_drill%40yahoogroups.com>, Martin Kennedy <martin@...> wrote:
      >> >
      >> > I'd like to modify my round column CNC mill so that the head will not
      >> > rotate and lose my center when raising or lowering the head. I looked
      >> > on-line for modifications, and although I found people that mentioned
      >> > them, no one had any details on how they were done or how well they
      >> worked.
      >> >
      >> > I'm thinking about pinning the rack on the round column, and then using
      >> > a surface grinder to make the rack very flat on the sides and parallel
      >> > to the column. I'd then modify the head to include some ball bearing
      >> > rollers that press up against the sides of the rack, similar to the
      >> > arrangement on a band saw. (These are on an eccentric bolt so that the
      >> > rollers can be snugged up against the saw.)
      >> >
      >> > I think that one of the potential problems is around the two bolts on
      >> > the back of the head that clamp onto the round column. If I leave them
      >> > slightly loose so that I can move the head up and down, then there will
      >> > be play in the head. If I loosen them, move the head, and then tighten
      >> > them, they may cause some small movement of the head even with the
      >> > modifications above.
      >> >
      >> > Has anyone done a modification on a round column mill to reduce or
      >> > eliminate head rotation, and how has it worked?
      >> >
      > ------------------------------------
      > Yahoo! Groups Links
    • Bryan
      My G1005 lay in someones garage floor in pieces for years and was covered in paint spatters. I used Goof Off to remove it from the whole machine. The labels
      Message 44 of 44 , Feb 5, 2011
        My G1005 lay in someones garage floor in pieces for years and was covered in paint spatters. I used Goof Off to remove it from the whole machine. The labels survived with no wear and tear.
        The only place it didn't all come off was the black plastic around the on off switch.


        --- In mill_drill@yahoogroups.com, Paul Alciatore <palciatore@...> wrote:
        > It is hard to tell what kinds of original and
        > "over" paint are there. Paint remover may remove both.
        > I would first try gentle scraping with something
        > like a fingernail or a plastic implement. If the
        > surface of the original paint was not properly
        > cleaned and prepared, it may flake off. After
        > that I would try paint remover applied for a
        > short interval. Perhaps you can control the
        > depth of removal by the time you allow it to soak
        > in. But this will probably not leave a nice
        > finish. Some form of abrasive polish may improve it.
        > In the end, chances are you will need to replace
        > all or part of the original paint. Break out the
        > artist brushes. The above suggestions may allow
        > you to match the original colors.
        > Paul A.
        > At 06:38 PM 2/4/2011, you wrote:
        > >
        > >
        > >I have an older piece of equipment that's been painted a time or two.
        > >One of the paint jobs covered up the emblems/nameplates on the machine.
        > >Has anyone had any luck removing the overpaint on a nameplate, while not
        > >removing the original paint on the nameplate?
        > >
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