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Surface grinding 10" X 48" mill table

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  • Surface grinding 10" X 48" mill table

    I've never had anything large ground on a surface grinder so I'm not sure what to look for that will tell me the grinder knows what he is doing during setup or questions to ask the grinder to determine if he knows how to give a precision grind. I found a local shop that has a surface grinder capable of grinding this mill table which would save me several hundred dollars shipping costs and several weeks time. My questions are:

    1. I believe about 0.060" needs to come off so what should I look for during setup? Assuming they will let me observe the grinding operation.
    2. What questions should I ask before committing to having the shop do the grind?
    3. What else should I be considering before and after the grind? The table belongs to a 1997 Wells Index CNC5 with 831 hours it. The machine in general looks to be in very nice condition, except for the table of course, as you can see from the photos. I will address the Centroid M400 controls when I get farther along with the mechanical issues.




  • #2
    I may not know what I'm talking about sometimes
    but why not mill it yourself on the machine ?
    set a 3 inch wide face mill and let the machine do passes up and down until the surface is clean

    It cant be hard as you have cut it once yourself and you will be assured of accuracy

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    • #3
      Chances are you will drop of the table and they will call you when it is done. .060 is a lot to take off grinding, they may mill it flat and then finish grind.

      Yeah, the table looks like crap but it really wont stop you from doing any work with it. Since it is CNC put a fixture plate on it and use it like it is. I use a fixture plate from Stevens Engineering.

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      • #4
        Originally posted by IanParkin View Post
        I may not know what I'm talking about sometimes
        but why not mill it yourself on the machine ?
        set a 3 inch wide face mill and let the machine do passes up and down until the surface is clean

        It cant be hard as you have cut it once yourself and you will be assured of accuracy

        Because you will end up with a table that is just as flat as the ways are and who knows what that will be like.

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        • #5
          Originally posted by macona View Post
          Because you will end up with a table that is just as flat as the ways are and who knows what that will be like.
          Perhaps a meet-half-way solution would work? Use the mill itself to machine the table somewhere close, within the limits of its own accuracy, then have the outside firm grind off the remainder accurately... I suspect grinding .060" or more off the table would be a lot of work, and they would charge accordingly.
          Last edited by Euph0ny; 02-09-2016, 06:38 AM. Reason: kant spel

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          • #6
            Chances are milling/grinding just the top will release some residual stress in the table and you'll end up with a piece that is less flat than before.

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            • #7
              Hope this answers some of your questions.
              A typical job shop isn't going to take much time to explain anything to you, and due to a number of reasons, probably won't let you witness (insurance at the top of the list). Many guys will get insulted if you ask questions about a set up if it comes across as telling them how to do their job, but will probably take your money for grinding 1/16".
              Without specified results (tolerance) you'll get what you get...what condition is the grinder in, anyway?

              An ethical outfit will want to do both sides per post #6. A responsible set up will be fussy, and the majority of the cost. That will be two set-ups, but no scraping.
              At 800 hours those ways are probably pristine. Why not just fill the gouges and scrape? Or use a top plate.
              If you're doing small NASA parts right on the deck those plane deviations affect then maybe a dress is warranted.

              A reputable outfit, mid-Atlantic would be around $400 min., you haul. No fitting.

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              • #8
                Like mentioned, both sides will have to be done and I am pretty sure the guys doing it do 1 side, flip, and then flip again. At the very least I would find a shop experienced in machine tool rebuilding, not just someone with a grinder big enough to do it.

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                • #9
                  That table may look pretty crappy but if it were mine I would very likely leave it as it. Take a file and knock off the high spots and put a vise on it. There is plenty of original table left to support a vise properly. If you need to mill something like a plate it won't matter either. Consider it a cosmetic defect and move along with your project. I give you this advice with almost 40 years in the tool and die trade.

                  Brian
                  OPEN EYES, OPEN EARS, OPEN MIND

                  THINK HARDER

                  BETTER TO HAVE TOOLS YOU DON'T NEED THAN TO NEED TOOLS YOU DON'T HAVE

                  MY NAME IS BRIAN AND I AM A TOOLOHOLIC

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                  • #10
                    +1 for the fixture plate. Money better spent.

                    You have to admire how someone managed to make those cuts in one pass though. Where were the clamps in that setup?

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                    • #11
                      another leave it vote. weird things can happen taking a broad wide cut like that.

                      I think you'd be asked to leave if you walked in asking all kinds of questions on how they're are going to do it and telling them you want to watch. Its probably going to be a larger shop to have a grinder that big, but regardless, none of them want to work for individuals, especially ones who want to look over their shoulders. small dollars, big pain.

                      IF you did want to have it done, approach it like a commercial shop would....whatever result you want has to be written down, finish, tolerance, etc. you agree on a price and you pay it if the results are achieved - things aren't left to judgement, they're spelled out. You don't hang around, you come get it in 3 days or whatever. You are also going to have to figure out how the wear comes into it, and what you want the flatness relative or parallel to given whatever wear there might be.
                      .

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                      • #12
                        I set mine up and recut it. Only a light cut but I discovered it was bowed length wise. I cant remember the amount but I think it was around 10 thou. Had to recut the dovetail and scrap. A lot of work.i felt better that the table was parallel again but doubt it is needed.

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                        • #13
                          What kind of underside does your table has? If it is dovetailed, the job shop isn't going to do anything other than grind off that 0.06" as requested and that's it. If it is flat, then regrinding that surface too would be easy and guarantee flatness of the overall table (permitting their machine is in good condition and not a see-saw).

                          If it were me, I would mill that table top down close enough insitu, then mill chamfers again on the top of the T-slots and then send it off for grinding. That way the time required to grind that thing drops from 2 hours to few minutes (disregarding setup time).
                          Amount of experience is in direct proportion to the value of broken equipment.

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                          • #14
                            If you grind .060 off the top only your going to end up with a potato chip, in my shop that would be planed on the top, then the the ways, then the top again, and then scraped in flat and parallel, $1,500.00 minimum. Good luck and just leave it alone.

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                            • #15
                              Definitely, DO NOT mill or grind the table. Doing so may open up a can of worms making the table worse. Appearance doesn't mean anything, you have plenty of original undamaged areas to assure nice clamping of fixtures and workpieces.

                              My first new CNC mill's table still has a milled slot I put in it. It made me sick. But, the lesson I learned was not to trust collets to hold end mills in heavy cutting. The cutting forces tended to pull the cutter out lowering it into the table.


                              The idea of milling before grinding.....I don't think my machines will reach the extreme ends of the table anyway, unless a very large diameter cutter was used.

                              I know of a grinding shop that does high precision work with Blanchard's easily capable of this job. The owner is very careful in explaining potential problems with grinding jobs of this type, but he's unusual in this respect. Most shops would just slap it onto the table and go for it (buyer beware).

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