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Surface grinder troubles - won't grind the chuck flat

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  • Surface grinder troubles - won't grind the chuck flat

    Hi folks,

    I have a small Eagle manual surface grinder, and last week decided to skim the vice jaws on my mill. Afterwards I checked them and discovered they were sloping from top to bottom by about a thou (and also bent, but that's another issue!).

    I decided to skim the mag chuck as it was in bad condition from when I got the grinder, so I covered it in WD40 and using an alum wheel took half thou's off until it was clean. The surface finish came out immaculate and it was cold to the touch throughout.

    Trouble is when I then attach an indicator to the spindle and move the table around I find the chuck is 2 thou higher on the left than the right, and 2 thou higher on the operator's side than the rear!

    Any idea what could be causing this? As stated the surface finish was really good, the gibs on the knee are in my opinion 'about right' (much tighter and the knee jerks/jumps as it's cranked up), and I was only taking half thou cuts. The machine is pretty much level, not perfect but within a thou or so.

    Cheers,
    Rich

  • #2
    I feel like I'm grasping at straws to explain away 2 thou with this.....but....sounds like what's being ground, in this case the chuck, isn't being supported and is flexing away from the wheel.....or heat is distorting things temporarily. Did you completely spark out? Even if it doesn't feel warm, you are putting energy into it, cold to the touch doesn't mean it isn't much warmer than when you started. Furthermore, based on its construction/geometry, who knows how it will change shape as it grows from the energy added. flood would be best so you know its temperature is close to the same start to finish....if you don't have it you might consider adding it, makes a big difference imo especially for grinding.

    how well does the chuck mate with the table? maybe slightly grasping at straws here, but if there is debris there, or one surface isn't flat (warped chuck for example), I could see how if the chuck was only contact in a couple a places with a large bridge between the chuck could forced away from the wheel slightly causing those areas to end up high

    I seem to recall installing a chuck involves a skim of the table? I'd start there....take the chuck off and indicate the table, skim in needed. with blue check the fit to the chuck
    Last edited by Mcgyver; 12-21-2012, 10:57 AM.
    .

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    • #3
      Totally agree with Mcgyver on this, seems very strange! Also we used to grind our surface tables with the magnet on. Also when you indicate the table is it in the same location back to front on the slides as when you ground it?
      Tony

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      • #4
        Was the magnet chuck in the on position when you ground it??? It should be when you dress it.

        JL.............

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        • #5
          It doesn’t take much to heat up a chuck and once heated up, they grow a lot. A half thou cut is more than I used to do for cleaning them. I typically would shoot for 1-2 tenths for the cleanup pass and would dress the wheel between every pass. Use a very open wheel for this.

          Also, mark up the chuck with a marker before the finish passes. If all the marks come off while making a .0001” pass, it’s flat. If not, you have some more cranking to do. Take your time and never try to get one more pass out of the wheel before dressing; you can be there all day if you try taking shortcuts.
          George

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          • #6
            Like George said, very small cuts to avoid heat. But also, use a VERY LARGE step feed. When I would grind a chuck in, I would take only 1 or 2 tenths with flood coolant and step feet about 3/4 of the width of the wheel. Hope this helps.

            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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            • #7
              Hi folks,

              The machine is a dry grinder so I don't have flood, but I did cover it in a good layer of WD40 each pass. I also left it for quite a long time to cool down between passes.

              The increments on the hand wheel are only in half thous, I can try to get less but the machine isn't that accurate that I can dial in a tenth reliably.

              I was stepping in about half a wheel width. The magnet was on.

              One thing I'm curious about is the technique for indicating the chuck - The chuck pulls the tip of the indicator which I presume isn't a problem generally speaking, but I wonder if means depending on the strength of the magnet I'm getting different readings? I need to verify the indicator arm rigidity I think.

              Will take another look at everything and let you know what I can find.

              Cheers,
              Rich

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              • #8
                Originally posted by bborr01 View Post
                also, use a VERY LARGE step feed.
                what's the reasons for that? less chance of heat build up per pass?
                .

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                • #9
                  I also use large cross feed steps. Can’t remember if it was beaten in my head by a toolmaker while an apprentice or picked up with time.

                  I think the reason for doing so is that a larger step over will use more of the wheel and spread the build-up over a larger area. A small step means only the leading edge is doing any cutting and the build-up will be concentrated in a smaller area, causing more problems.

                  When grinding the chuck on a dry grinder, I’ve used both WD-40 and Crisco on the chuck, with Crisco being the winner in my opinion. I’ve also used a cold gun (cold air blast) and that helps a bit too. It doesn’t take much to make the chuck worse than what you started with. Keep at it, keep the cuts as light as you can, and keep the wheel dressed and when you dress, dress it deep.
                  George

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                  • #10
                    You all are overlooking what maybe the problem. The machine is worn? There is a real simple test to see if it is your grinding procedure or your machine. Do you own a steel or granite parallel as long as the mag chuck? If you do lay it on the chuck and indicate the middle 2/3's zero or a close as you can get it by using feeler gage under the ends. Use a tenths (.0001") indicator.

                    If the machine is worn then when you feed to the rest of the 1/3 travel the ends will raise. The opposite of the chuck grind. If you think about it the majority of your grinding is probably short and the table and saddle top ends don't get worn, so when you go to dress the chuck or table top they grind low on the edges.

                    Remember when your machine shop instructor told you to move your part around on the chuck or even on your mill vise, he was telling you that because the machine will get even wear. If you don't have a long parallel put your precision level on the chuck and shim it level when the table is centered, then slowly move the table out to the ends and watch the bubble. You will have to stop the movement and let the table come to a rest, which usually is 10 seconds on precision .0005"/12 level.

                    There is also another possibility I have seen in my 40+ years of machine rebuilding and scraping. The spindle bearings are bad or lose and when you near the ends and fall off the end of the chuck the wheel grind deeper and as it rolls up on to the chuck it stabilizes and grinds flatter. When I rebuilt a machine that was a dry machine I either used a air coolant sprayer or a hand pump squirt bottle and dress the wheel very open or coarse. I would also mount a dial indicator on the column and feed down in .0001" to .0002". .0005" with no coolant is to much. Check things out and let us know. I also grind 5 blocks on the machine when I am finished and indicate them on a plate to verify flatness. More on that later if needed. You can write me directly at [email protected] or get my phone number there and call me.
                    Merry Christmas. Rich
                    Last edited by Richard King; 12-21-2012, 11:53 AM.

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                    • #11
                      Originally posted by George Bulliss View Post
                      I think the reason for doing so is that a larger step over will use more of the wheel and spread the build-up over a larger area. A small step means only the leading edge is doing any cutting and the build-up will be concentrated in a smaller area, causing more problems.

                      When grinding the chuck on a dry grinder, I’ve used both WD-40 and Crisco on the chuck, with Crisco being the winner in my opinion. I’ve also used a cold gun (cold air blast) and that helps a bit too. It doesn’t take much to make the chuck worse than what you started with. Keep at it, keep the cuts as light as you can, and keep the wheel dressed and when you dress, dress it deep.
                      You are still taking away the same amount of metal total, so the heat input is the same.

                      The only reason to teach taking wide cuts is speeding up grinding operations and using the whole wheel so that when it clogs, it is clogged full width instead of just the very edge of it.
                      Amount of experience is in direct proportion to the value of broken equipment.

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                      • #12
                        Originally posted by Jaakko Fagerlund View Post
                        You are still taking away the same amount of metal total, so the heat input is the same.

                        The only reason to teach taking wide cuts is speeding up grinding operations and using the whole wheel so that when it clogs, it is clogged full width instead of just the very edge of it.
                        Maybe I'm visualizing this wrong. but isn't the amount of metal being removed the depth of cut X the width of cut, omitting the radius of the wheel?

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                        • #13
                          I hate to point out something simple, but is it a table lube problem. I don't have a table but if it uses a one shot, "floats" the table, and by the end of your cut it is tight?

                          Only something to look at.

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                          • #14
                            Originally posted by Mcgyver View Post
                            what's the reasons for that? less chance of heat build up per pass?
                            The way it was explained to me is that when you take smaller steps, the wheels edge breaks down on each pass and you end up with a dull cutting edge on your wheel before you get all the way across the chuck. Not that the wheel will not cut then but it is just better to have the wheel as sharp as possible for something like this.

                            Another thing is dressing the wheel. Dress with a quick pass over the wheel. Don't dawdle. If you dress too slow it has the same effect as glazing the wheel. And have a sharp diamond dresser. It is amazing how much different a grinding wheel will perform when it is dresses with a sharp diamond instead of a diamond that is all rounded off.

                            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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                            • #15
                              I see a lot of good points mentioned here. Table and colume lube was mentioned in my manual as a possible cause to your problem If the colume is dry it may be sticking when lowered and as you work your way across the chuck surface the head may be dropping slightly.
                              Taking too heavy a cut could result in faster wheel wear so by the time you've worked your way across the chuck the wheel has worn and dulled / loaded resulting in a + indicated surface towards the end of the job.
                              If you have trouble reading in between the half thou graduations of your down feed dial and I know what thats like try mounting a dial on the head and watch it as you feed down. Then let it sit with the machine running and see if any vibration causes the head to settle.
                              As other have said a finish pass shoould be no more than a couple tenths.

                              JL.......................

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