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  • using a rotary table on a surface grinder

    I have a disc I want to grind on my surface grinder. This disc is 8" in diameter and my grinder is a 6x12. There is so little out there on the use of surface grinders, so I'm unsure if this is a horrible idea or not.

    I have a rotary table and I'm thinking of presenting the disc to the wheel with the rotary table instead of just the x y controls of the grinder.

    Am I way off the mark here?
    Brett Jones...

  • #2
    Sure, it'll work. It will also indicate whether your RT is square to the table. Absolute cleanliness of the table and RT base is a must. You might want to run an indicator down and across your table first. If the table is not flat, the RT won't be flat. When you turn the RT, you'll remove more stock on the high side if both aren't flat or square to each other.

    Comment


    • #3
      Good point about the table being parallel.

      The grinder is in good order and I recently ground in the chuck, so I feel good about that part of the idea.

      I'm kind of curious what the finish pattern is going to look like if I do this.
      Brett Jones...

      Comment


      • #4
        Finish will depend on how you orient the work to the wheel.Parralell the rotation of the work it will look like a concentric ground disc.Right angles to the rotation will leave circular marks and ridges which you probably won't like.

        You might want to rough grind the part flat in the conventional fashion first to get it 90% flat.It's gonna take a lot of turns on the RT handwheel to make a pass
        I just need one more tool,just one!

        Comment


        • #5
          90 degrees - do it

          Brett,
          as your magnetic chuck is "ground in" you should have no problems with centreing the disc on the chuck and grinding a width just a bit less than you can travel between the "Y" slide stops.

          Do it the first time, rotate the job 90 degrees and grind the "wings/ears" that were left off during the first "pass". Just grind it down just a little (say 0.0005" or less) with the final pass being a very light "cut". Then rotate it 90 degrees again and grind that last little bit down so that you leave the merest trace (aka "witness mark") of the previous light grind.

          You will have a sort of a "cross" pattern, but if you do it carefully, it will be very quick and very accurate.

          There should be no need to use the rotary table at all.

          Comment


          • #6
            Using a rotary table

            Of course, there is little or no criticism with the advice given. I would go this way but!

            Aye, here's the rub. You are holding down a disc. How do you propose to keep it down on the surface grinder?
            If you use a magnetic chuck, it is possible to replicate the undersurface of the disc- and if not correct, you might as well, give up. If you haven't a magnetic table, how do you propose holding down your disc?

            I would suspect that you will have to do some very careful 'pressure' ring clamping so that your grinding wheel will not knock the tops off the clamps and bolt heads.

            Forgive me, but I am not being devious or clever or otherwise awkward. I have a baby dividing head( a George Thomas one) and I foolishly left the 4" diameter to plates to heavily corrode. The only way that I can address what seems to be a similar problem is to glue or Araldite each of the three plates onto not a surface grinder but a tool and cutter grinder. I have precious little ' meat' left on the discs which have all the drillings done- and countersunk and all that. I did it all from the bull wheel on the lathe headstock- and I don't want to do it again.

            So, how do WE do it?

            Cheers

            Norm

            Comment


            • #7
              Missed it?

              Norm,
              you may have missed it, but the OP has a good "ground-in" magnetic chuck on his grinder.

              Originally posted by bhjones
              Good point about the table being parallel.

              The grinder is in good order and I recently ground in the chuck, so I feel good about that part of the idea.

              I'm kind of curious what the finish pattern is going to look like if I do this.

              Comment


              • #8
                Rotary Table

                Sorry, Mick, but -well, I have cataracts! I've been ducking the issue!

                OK, we still come to holding down and having to carefully shim. I did muse about using one of mine- and still got to the awkward packing up to avoid the 'pulling down'
                I was toying with putting a thin polyester inteface on and letting it all gel.

                Oh, dear, Mick. I've dumped part of my workshop already

                Cheers

                N

                Comment


                • #9
                  Norm was asking how is he going to hold the work to the rotary table. Good point...

                  Make a vacuum chuck?

                  Comment


                  • #10
                    Packing it in

                    Thanks Norm.

                    The "packing" issue had slipped my mind.

                    For the OP (bhjones):

                    Norm has raised a very good issue here. It is distortion and packing.

                    If anything is distorted, either the chuck will pull it down and when the part is ground and the chuck released the part will "spring back" to its original "out of flat" shape. The other case is where the chuck does not pull the part down but is the part is seated on the chuck on its convex face it may actually "rock" on the chuck under the wheel. Neither outcome is desirable.

                    In both cases, the job, if not flat, should be packed or "shimmed" to be stable as this will give a flat face when the chuck is released.

                    In both - and many other - cases, it is quite possible that there will not be sufficient "grip" and the job may "move" (and "fly like a bullet") if it "lets go".

                    In that (and as far as practical - all) cases, use the "alignment" slips or stops (the slotted rectangular steel strips on the ends and sides of the chuck) to "stop" the job - but have the job "hard up" to the strips.

                    The following links may assist.

                    http://i200.photobucket.com/albums/a...uck_block1.jpg

                    http://i200.photobucket.com/albums/a...uck_block2.jpg

                    http://i200.photobucket.com/albums/a...uck_block3.jpg

                    http://i200.photobucket.com/albums/a...uck_block4.jpg

                    http://i200.photobucket.com/albums/a...uck_block5.jpg

                    Comment


                    • #11
                      Using a rotary table

                      Macona,
                      Your idea is fine but it adds yet another set of tooling and as Mick(OT) rightly reminds us, it does not avoid having a 'flying saucer

                      I was suggesting a rather non engineering solution to anchor the missile down.

                      We have been getting so much here of dangerous practices.
                      One geyser is trying to use a drill to mill, and another is buggering about with a ****ty mill and trying to keep his few remaining coins in his pockets by making a vise whilst i am being bollocked for tool and cutter grinding- 'cos i have built most of the swag----- and I ain't no engineer.

                      I got another sad letter from a very clever engineer who had been flamed because he was criticising unsafe practices.

                      Have the lunatics taken over? Sorry, but it might jolt somebody to think higher than their navels.

                      Rant over

                      Norm

                      Comment


                      • #12
                        Originally posted by aviemoron
                        Of course, there is little or no criticism with the advice given. I would go this way but!

                        Aye, here's the rub. You are holding down a disc. How do you propose to keep it down on the surface grinder?
                        If you use a magnetic chuck, it is possible to replicate the undersurface of the disc- and if not correct, you might as well, give up. If you haven't a magnetic table, how do you propose holding down your disc?

                        I would suspect that you will have to do some very careful 'pressure' ring clamping so that your grinding wheel will not knock the tops off the clamps and bolt heads.

                        Forgive me, but I am not being devious or clever or otherwise awkward. I have a baby dividing head( a George Thomas one) and I foolishly left the 4" diameter to plates to heavily corrode. The only way that I can address what seems to be a similar problem is to glue or Araldite each of the three plates onto not a surface grinder but a tool and cutter grinder. I have precious little ' meat' left on the discs which have all the drillings done- and countersunk and all that. I did it all from the bull wheel on the lathe headstock- and I don't want to do it again.

                        So, how do WE do it?

                        Cheers

                        Norm
                        Norm,
                        How are the dividing plates held on the dividing head? couldnt you use that to hold the plates? My plates are held on with three screws. If I had to do it to mine i would make a backing plate with a slightly raised boss (mimicing the dividing head) with the screw hole tapped in and dowel in the disc stop location. If not on surface grinder the same but to a mandrel. or am I missing something?

                        Comment


                        • #13
                          Dividing heads

                          Derek,
                          Reading between the lines, I suspect that we are exactly on the same wavelength. As I said, there isn't much meat left on any of the little plates/discs and I was facing East and hoping to see( ouch) the next miracle.
                          I'd just missed the first one.

                          You are right, of course but i will have to bite my pride and make new ones.

                          Aren't these lot clever? I worry, we have lost so many over my time here.
                          You can or should buy the books but this is where stuff should come that the writers miss out. Thanks, fellas, for adding to the books. There's them wot writes and them wot does!!!!

                          Norm

                          Comment


                          • #14
                            Cleaning-up

                            Norm,
                            a question - or two.

                            Do you want that/those plates ground or cleaned up.

                            Grinding is the hard way unless essential.

                            If a clean-up is all that is needed why not start with a wire brush and say WD-40 or similar and/or a piece of "wet and dry" paper used "wet") on a flat surface (not too flat - mill table or a bit of thick float glass will do - as will anything similar).

                            There have been any amount of fairly recent threads and posts on removing corrosion/rust etc. Some are very handy and clever.

                            I am more focused on the required outcome as well as alternative means of achieving it than I am wedded to a particular process.

                            [Edit]
                            If I had to grind it on the tool & cutter grinder without a magnetic chuck, I'd seriously consider clamping a 3-jaw chuck to the table and setting up the plate in the chuck using a good dial indicator. Gentle tapping as required will do it well and quickly. Grinding is quick and easy from there on in.
                            [End edit]
                            Last edited by oldtiffie; 10-15-2008, 06:23 AM.

                            Comment


                            • #15
                              Originally posted by bhjones
                              I have a disc I want to grind on my surface grinder. This disc is 8" in diameter and my grinder is a 6x12. There is so little out there on the use of surface grinders, so I'm unsure if this is a horrible idea or not.

                              I have a rotary table and I'm thinking of presenting the disc to the wheel with the rotary table instead of just the x y controls of the grinder.

                              Am I way off the mark here?
                              Long ago when I went to a very experienced machinst with a " I want a..." or a "I want to..." He always wanted the full story on what it was for and why so he could understand which bits needed thought and which bits didnt, which short cut he could use or not...

                              So lets go back and have a few more details on this disc so we can help you all the better.
                              e.g.
                              • The application
                              • the material
                              • How and what the disc is attached to in the application

                              for instance it might be stainless (magnetic chuck no good)
                              it might have holes for bolts in middle in an area that doesnt need grinding
                              It might smooth and flat already
                              It might need grinding on one side or two...

                              Comment

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