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  • Milling a flat plate?

    I have a piece of aluminum that's 6" x 10" x .250". It has some deep scratches in it. And I think it isn't flat. So how to clamp it down and get it milled off flat.

    You can see in the pic what I am talking about. The shaft is binding just a bit when I tighten the bolts all the way down. I think the base is not flat. Didn't check it yet to verify. But I want to clean it up anyways.

    [IMG][/IMG]

    So how to clamp it down so when you move one set of clamps it doesn't flex? BTW I don't have a 6" vise.

    Any ideas?

    Edit: I just seen this post. These would work perfect. Post #2021 http://bbs.homeshopmachinist.net/thr...-Tools/page203


    Menessis
    Last edited by Menessis; 02-13-2015, 08:55 PM.

  • #2
    Toe clamps maybe?
    .....

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    • #3
      Harold Hall has a couple takes on how to do it, some a little simpler.

      http://www.homews.co.uk/page108.html

      These are about as simple as it gets

      http://www.homews.co.uk/page157.html
      Last edited by R.Bolte.Jr; 02-13-2015, 10:04 PM.
      "Never bring a caliper to a mic fight"

      Comment


      • #4
        Mitee-Bite products are very good: http://www.miteebite.com/images/prod...slot_kit_2.jpg

        Comment


        • #5
          I might try a slightly different approach. Wet-dry sandpaper taped to a surface plate, lap your plate flat.
          Or use double-sided tape and stick it down on a surface grinder table and grind it flat both sides.
          Or learn to scrape, blue it up and get to scraping.

          metalmagpie

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          • #6
            I would use hot glue to glue the sucker to another plate and take light passes with a face mill or fly cutter and flatten it. Heat the plate up to release the glue and flip over. It is going to be incredibly hard to clamp the plate without flexing it otherwise.

            Mitee-bite sells some thermal adhesive saturated paper just for this.

            Comment


            • #7
              It was made as flat plate - ie uniform thickness and probably fairly flat too. Machining has relieved stresses and caused a warp. Taking a skim of one side will likely upset it further. Possibly a cut on both sides would even this out. However I suggest you first measure the warp on a surface plate and then at least try bending it back.
              BTW the way to clamp it without inducing a bend from clamping is to rest it on 3 points not 4 or more.
              Last edited by Baz; 02-14-2015, 04:06 PM.

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              • #8
                Lapping it flat with sandpaper is easier said than done. What usually happens is you get a high spot in the center and the edges are lower. Ask me how I know. You can rough it in this way, but if you want it truly flat, you need to use some further method.



                Originally posted by metalmagpie View Post
                I might try a slightly different approach. Wet-dry sandpaper taped to a surface plate, lap your plate flat.
                Or use double-sided tape and stick it down on a surface grinder table and grind it flat both sides.
                Or learn to scrape, blue it up and get to scraping.

                metalmagpie
                Paul A.

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

                Comment


                • #9
                  Is it flat - or not?

                  If not - why not try and straighten it to an acceptable level of straightness?

                  "Milling" the plate will make it thinner and weaker and more likely to warp again - the more so if the plate has surface stresses.

                  Can you be sure that the plate will be straight when the clamps are released after milling?

                  The plate should be "shimmed" (under the clamps at least as well as any "up bow") in its existing state as if clamped without shimming the plate may distort under clamping and "spring back" when the clamps are released after machining.
                  Last edited by oldtiffie; 02-14-2015, 07:13 PM.

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                  • #10
                    I had to build a 4' square heated press, ordered a plate of 3/4 Ali plate, fitted elements, hairpin square section to the back, the plate wasn't flat for long.
                    I quickly gathered I should have ordered cast plate, changed to cast plate no problem, stayed flat.
                    Tried to recover the rolled plate, figured it could be salvaged, no chance, took the skin off, oops it's curved, turned it over took a skim, oops it's dished now, cut it up, tried smaller bits, same problem, more distortion, gave up!
                    I still have a bit of it I use to practice weld on, still learning btw!
                    In the shop we used a vacuum bed to some effect to hold Ali plate, we used to oil it first then stick it on the perforated backer, provided there were edge blocks it held ok while machining.
                    Mark

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                    • #11
                      Considering you are relying on this plate to maintain shaft alignment, the first thing I would look into is bolting a couple of stiffeners lengthwise along each side
                      of that slot.

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                      • #12
                        I did a project once where I used a combination of tooling plate, regular plate, and flat bar. The tooling plate stayed flat, the regular plate didn't, and the flat bar was fairly flat but not a uniform thickness across the width. I had the same problem- to clamp the pieces for milling, then assuring that the milled faces were actually flat. What I did was use 5 min epoxy directly onto the mill table in as many spots as possible to support the plate. A drop at each spot, then drop the plate onto it and walk away for awhile. I made sure to use a sort of toe clamp at the corners, and placed them only where there was a drop of epoxy cured between the table and the plate. Milled the surface, removing one toe clamp at a time as I passed over that corner. With the whole surface done, I heated the piece with a torch and gently pried it off with a chisel. The epoxy was actually pretty easy to remove from the table and the plate. I didn't clean and degrease before so it had little change to stick anyway. It did stick long enough to get the job done.

                        I did this as a three part process. One side milled, plate turned over and the other side done, then turned over again for the final pass on what would become the important surface.
                        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
                          If you look at that toe clamp, you will see that it goes downward as well as toward the workpiece. So it is also exerting downward pressure which may bow it and that will be released when the clamp is released.



                          Originally posted by KiddZimaHater View Post
                          Toe clamps maybe?
                          .....
                          Paul A.

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

                          Comment


                          • #14
                            Is it not flat or does it have a small twist? Either would cause binding.

                            A very light flycut on both side might help if it isn't "flat", but if the plate has a twist then clamping it down would pull the twist out, only to have it reappear when the clamps are released.

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                            • #15
                              1/4 in seem too thin to expect it to maintain your shaft alignment. That said, look into a piece of ground plat from Mc Masrer Carr. You can get it ground all over or just top and bottom. Whatever you're building looks good . Bob.

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