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  • Clamping plate to the mill table.

    Gents,

    I have owned a RF45 clone milling machine for about 5 months now, it has been a steep learning curve.

    One problem that continues to occur with me trying to mill a 15mm thick plate that is too big to fit in the vice.

    I use my clamps and run my small indexable cutter along the work piece then remove the clamps, rotate the plate, re clamp and cut again. This always results in an uneven finish and variations in thickness.

    I think that I am missing a very simple solution to this?

    I appreciate your input and solution to this problem fellers.

    Mike

  • #2
    One way to solve the problem is to make the unmilled plate oversize. Use the margins to clamp the plate to the table. Either bolts in to T-nuts through drilled holes in the margins or clamps on the margins. When you are done, cut the margins off.

    Usually when milling a large surface one uses a large cutter. Least expensive cutter would be a fly cutter. This should help you mill the face in one setup. Fly cutters, when setup correctly will leave a very nice finish on the work.

    There are many other methods for clamping oversize work:
    Double sided tape, but NOT the stuff for hanging pictures but the real industrial stuff that is made for work holding.
    Edge clamps.
    Two piece vises.
    Magnetic chucks.

    The other thing you have to watch for is warpage in your part as you take the skin off of one side. One would think that, if a mill table is near perfectly flat, then clamping and unclamping a piece of material shouldn't introduce any error in Z. The reality is that once a piece is clamped and the skin is milled off of one side and then unclamped the part tends to become convex on the milled side. This is especially the case with cold rolled and extruded materials and becomes more pronounced as the part gets larger in surface that is milled and thinner in cross section.
    There are tricks to deal with and minimize warping. One way is to buy stress relieved material. More expensive and sometimes not available for your particular spec. It will not eliminate warping 100% (nothing does.)
    Another way is to mill a little off of each side, say: 0.5mm off one side and it warps. Flip the part and mill another 0.5mm off the other side. There are specific procedures on how to minimize the warp and amounts to cut.... just do a search for "warping" and you will find plenty of posts discussing it.

    -DU-

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    • #3
      how big are these plates? Lots of ways....but if you are milling the entire surface of a large plate, say in steel, the best solution may be to get the thickness you need or redesign to a standard thickness. Milling large plates is less common mill work and carries some challenges - like you've facing as well as not having the work warp and getting a decent finish.

      there are devices like miti bites or vises where each jaw is separate and is bolted to the table....these can hold large pieces without anything fouling the top. Leapfrogging the clamps or holding by making use of any counter bored holes need in the plate are also done.

      for extremely light milling, you can some use double sided tape or a mag chuck with fences (I said light!). I've soft soldered work to pieces that can be clamped - ie you could soft solder to a bunch of bars (size to suit) that stick out each side and strap clamp on those. here's a pick showing the idea - in this case its clamped to a faceplate but the principal is the same (ring was in two pieces so couldn't be chucked)

      Last edited by Mcgyver; 05-23-2012, 09:16 AM.
      .

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      • #4
        Lots of problems in import mills. I know because I have one and have used others.

        First, the table is not necessarily flat. You may be clamping it at different angles each time.

        The column is not necessarily square to the table's movements (notice I said the table's movements, not top). Do check this and correct as needed.

        Finally, are the gibs either locked down if that axis is not moving for the cut or tightened properly if that axis is moving. Any outboard weight can tilt the table if the gibs are loose. Any movement can rotate the table about a vertical axis if the gibs are loose. Always lock any axis that is not actually needed for the cut in progress.

        All of this applies to US made mills too, but probably not as much so.
        Paul A.

        Make it fit.
        You can't win and there is a penalty for trying!

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        • #5
          depending on your vise you may be able to take the vise jaws (actual hardened jaw "plates" ) off and move them to the "outside" of the vise jaws (fixed and movable portions). look at the milling vise and see if there are tapped hols on the rear and front of the fixed and movable jaws and if these match up with the tapped holes in you removable (plates) jaws. (clear as mud I know )
          regards

          3t

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          • #6
            Well thank you very much fellers.

            The plate is 250mmx250mm x 15mm thick. The suggestion of not cutting to final size until after milling is a 'why didn't I think of that' solution.

            I have done the tramming and have managed to get the table flat to .003mm over the 150mm indicator sweep.

            I have started on a fly cutter today, got the body machined and 60 degree hole drilled through for a HSS cutter also installed a set screw. Will tackle the taper on the shank this afternoon. This should give me a decent size cut when finished.

            Don't know how to solder yet, will have to learn that too; the setup shown by McGyver is a flash looking one and I hope to do the same Embarrassingly, my vice does indeed have the ability to change the jaws around to hold larger work, only worked this out due to 3t's suggestion. We live and learn.

            Thanks,

            Mike

            Comment


            • #7
              Put the plate on a magnetic chuck - with stops/fences - "belly-up" for the first cut - on the mill table.

              Align the chuck to the mill table as for a mill vise.

              If the mill "Y" is not big enough, rotate the job on the magentic chuck or rotate the magnetic chuck on the mill table.

              Fly-cutter is ideal.

              Hasten slowly.

              Comment


              • #8
                I've done something almost identical on my RF45 and I ended up using counter-bored holes for some bolts with wide but shallow heads. They were advertised as 'coach bolts' and the heads were slotted.

                I found clamping the plate to the table was difficult as it was eager to move.

                The counterbores could be filled if desired. In my case it didn't matter.

                Comment


                • #9
                  Originally posted by mikerolly
                  I have done the tramming and have managed to get the table flat to .003mm over the 150mm indicator sweep.
                  Hopefully you mean you got the head square to the table. Either way... 0.003mm in 150mm is roughly 0.0002" in 6", which would be amazingly good.

                  I have started on a fly cutter today, got the body machined and 60 degree hole drilled through for a HSS cutter also installed a set screw. Will tackle the taper on the shank this afternoon. This should give me a decent size cut when finished.
                  While it is great to make your own tooling (flycutters are incredibly inexpensive to buy) it is a good idea to follow industry practices. I would put at least two set screws (most use 3+) for securing the cutting bit. The cutting bit gets an awful lot of hammering and one just isn't going to hang on for long. Especially if the cutting bit is round (it will want to twist.)

                  For surfacing a 250mm square piece of work as a facing operation on a lathe is fine if your lathe swings more than 14" (360mm) and can accept a few holes for anchoring it to a faceplate. Or go larger on the workpiece and anchor/clamp on the excess... but then you need a bigger lathe still. The finish and flatness, however, can be damn near perfect.

                  Unfortunately the first lessons having to do with warpage can be expensive. It can also vary in amount and type from material to material (and even from batch to batch.) Either way... as has been mentioned there are ways to overcome the problem and plan around it once you are aware of it. There is just no easy one-size-fits-all method to minimize it.

                  -DU-

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                  • #10
                    I've used a 'trick' to do that, which involves drilling mounting holes in the plate. The holes go where they will center in the T-slots. You tap the holes, then use a bolt from the bottom. The bolt gets a washer which fits the slot, then the bolt is cut to length so it doesn't protrude up past the surface, then the end of the bolt gets a slot cut into it so you can bring it 'up' with a screwdriver.

                    Because this isn't the tightest mounting method, you can always clamp some stops to the mill table to prevent the plate from moving sideways from the cutting forces. The stops would be thinner than the plate so they don't get eaten by the cutter.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                    • #11
                      Originally posted by Void
                      Hopefully you mean you got the head square to the table. Either way... 0.003mm in 150mm is roughly 0.0002" in 6", which would be amazingly good.

                      -DU-
                      Yes, I noticed that as well.

                      Perhaps the OP had a typo and meant 0.03mm in 150mm which is about 0.0012" in 6" which is pretty good for most stuff I do on my HF-45 mill.0.0012 in 6 is 1 in 0.0002 or 2 tenths in an inch.

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