Announcement

Collapse
No announcement yet.

Stupid question: What's the big deal about surface grinding?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Stupid question: What's the big deal about surface grinding?

    I know this question will rank way up there as a Retardo Montalban question, but can someone explain to me exactly why surface grinders and surface grinding in general is so important? I see it discussed all the time and I see these really fancy, really expensive surface grinders in use at machine shops (in pictures, videos etc, not in person). But I never really understood why they are so important. If a surface needs to be ground, why not just mill it? Why not turn it on a lathe? Why not plane it down with a shaper? All I can think of is that grinding is appropriate (and necessary) if you're working with really hard metal that will damage or destroy conventional cutting bits made of tool steel. I can see where it would be necessary there. But heck, how often are you making a piece out of tungsten or something similar?

    Another problem I see with grinding is that the grinder wheels are made of granulated stone that wears away as it grinds. I would think the wheel would get slightly smaller with every pass, complicating the matter of getting an even/parallel cut every time. Obviously it's a workable problem, but doesn't this complicate matters when grinding? Confused, and always have been about the whats, whys and wheres of surface grinding.

  • #2
    It's a finishing program that gets very fine surface finishes.
    Mill leaves tool marks and each one will probably be a few tenths. deep
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



    Comment


    • #3
      Grinding heat-treated tool steel.
      Surface finish
      Accuracy
      Making special tooling
      And for making sweet punches:

      Comment


      • #4
        Good question Machine, i don't think i have seen this asked here before.

        Comment


        • #5
          Wheel wear is not as big of an issue as you would think. First, remember that grinding is mostly a finishing process. You are usually taking off thousandths at a time, at most. Also when grinding you do not step over the full width of the wheel, more like .040 to .050 at a time. This way only the leading edge of the stone takes the brunt of the wear. By the time you take a full pass the back edge of the stone has hardly been touched by metal.

          And like the other have said, you can get finishes and tolerances you just cant get on a mill or lathe with a grinding process.

          That being said, I sold my grinder a few months ago. I just never used it and needed the space for the laser cutter. If I need one that badly I can find someone around here, I am sure.

          Comment


          • #6
            finish, accuracy, ability to machine hardened surfaces.

            wheel wear not an issues macona described.

            I've never surface ground tungsten, but done lots of case hardened and hardened tool steel.....but doesn't have to be that, you still get the finish and accuracy advantage with mild steel, cast iron etc.

            Like so much we collect in our shops, do you absolutely have to have one? no, but it sure is nice and mine sees a fair bit of use. Then again I could take up golf and not need anything in my shop....so 'need' doesn't carry the day for anything in my shop. part of the fun for me at least is expanding the capabilities and skills....thats enough of a reason to get one
            Last edited by Mcgyver; 12-22-2012, 11:44 PM.
            .

            Comment


            • #7
              I know this question will rank way up there as a Retardo Montalban question, but can someone explain to me exactly why surface grinders and surface grinding in general is so important? I see it discussed all the time and I see these really fancy, really expensive surface grinders in use at machine shops (in pictures, videos etc, not in person). But I never really understood why they are so important. If a surface needs to be ground, why not just mill it? Why not turn it on a lathe? Why not plane it down with a shaper?
              Not Retardo Montalbon question but one that needs to be answered here from time to time. Grinding is more than a finish and more than a way to cut hard materials. Grinding machines are typically orders of magnitude more accurate than lathes and mills. It is not at all unusual for a grinding machine of recent ( last 50 yrs) to be capable of working to .00001 when new. I have run several machine with .00001 graduations and new machines are even more capable. This why a toolpost grinder is just a pretender in the grinding world. It is no more accurate than the lathe with any other cutting tool. A cylindrical grinder on the other hand should be accurate to a couple of tenths repeatedly.

              All I can think of is that grinding is appropriate (and necessary) if you're working with really hard metal that will damage or destroy conventional cutting bits made of tool steel. I can see where it would be necessary there. But heck, how often are you making a piece out of tungsten or something similar?
              Tungten would rarely be machined in the pure form. It is very commonly alloyed with copper to produce a dense, hard, machinable alloy used in applications varying from rocket engines to darts, yes, those thrown in your favorite pub. Serious cutting of very hard materials is usually left to EDM.
              Another problem I see with grinding is that the grinder wheels are made of granulated stone that wears away as it grinds. I would think the wheel would get slightly smaller with every pass, complicating the matter of getting an even/parallel cut every time. Obviously it's a workable problem, but doesn't this complicate matters when grinding? Confused, and always have been about the whats, whys and wheres of surface grinding.
              Uh ,No. Grinding wheels are most certainly NOT "granulated stone". They are made of various abrasives, bonds, and structures. They are NOT "stone" in any form. Modern abrasives are man made , even most diamond abrasives are man made. The wheel does not get smaller with every pass because the entire wheel is not cutting. The leading edge does the vast majority of the work and does indeed wear. The area behind the leading edge , unworn, finishes the job. As this area wears, as it inevitably will, the next area will bring the part to size. Therefore if a wheel is one inch in width and is cutting in both directions at .1 crossfeed, it will take at least 5 passes in each direction to affect size. In fact if the wheel is properly chosen, it may take many more than that.,
              Last edited by tdmidget; 12-22-2012, 11:47 PM.

              Comment


              • #8
                Originally posted by Machine View Post
                I know .....
                Another problem I see with grinding is that the grinder wheels are made of granulated stone that wears away as it grinds. I would think the wheel would get slightly smaller with every pass, complicating the matter of getting an even/parallel cut every time. Obviously it's a workable problem, but doesn't this complicate matters when grinding? Confused, and always have been about the whats, whys and wheres of surface grinding.
                Years ago, I used to worry about the same thing with all cutting tools. I mean, if you start to turn a diameter with a single point tool, it will wear while you are cutting. Wouldn't the end of the cut have a larger diameter than the start? Well, it dies wear. But in practice, it is not a real problem unless you are taking really heavy cut and then you are probably going to see other problems that will completely hide any small differences in diameter.

                In short, theory says yes, but practice says it is so minimal that you need not worry.

                Grinding wheels take very small amounts off in one pass and the wear on the wheel is very slight. Like others have already pointed out, the wheel cuts mostly on the leading edge and is wide enough to allow you to finish the job before the wear reaches too far in. And you should dress the wheel before this happens.
                Paul A.
                SE Texas

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

                Comment


                • #9
                  You can have a diamond point mounted on the grinder table that the wheel goes over, This dressed the wheel to a known size and makes it 'flat', So you can know your wheel is true and what exact size it is. Thats one of the reasons surface grinding wheels don't have accuracy problems as they wear, They can be easily 'resharpened' to flat (Or even to a shape!) every few passes while still on the machine.
                  Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

                  Comment


                  • #10
                    Select the surface finish/texture you require and use the range of processing (grinding included) and take notice of the "machinability" (including "hardness") required for the job.

                    http://en.wikipedia.org/wiki/Surface_finish

                    http://www.roymech.co.uk/Useful_Tabl...in_Values.html

                    http://www.google.com.au/#hl=en&tbo=...w=1920&bih=846

                    Comment


                    • #11
                      It is not a dumb question. The surface grinder is one of the least understood machines in a shop usually. The reason is that most people don't know what to do with it. There is the making of things very flat to an accurate thickness. Then there is form grinding where you shape the wheel with a special diamond dresser to make angles, a concave or convex radius, or a combination with the angles being tangent to the curves. There is also tool & cutter grinding with the correct fixtures, and making dowel pins and step pins with a spin jig. Also you can turn down the shank of an end mill or tap if you need to cut deeper than the flutes allow. You can grind special shaped punches and dies for punch press dies. You can make any shape or size of rotary broach. You can sharpen a reamer or make it a special size and/or turn a pilot on the end.
                      The list goes on and on but you get the idea, it's not just for making things flat. I would hate to try to run a shop without a surface grinder.

                      Comment


                      • #12
                        If you ever take a freshly milled surface to a grinder, you may notice that the small looking ridges left by the milling cutter are easily 0.02 to 0.2 mm deep, even a finish cut with a sharp tool leaves around 0.01 to 0.05 mm. And the block you milled on both sides to get it flat and/or even thickness - well, it isn't flat nor even most probably, if done in a vise.

                        If you want good sliding surfaces, the ground finish is good for that as it bears loads very well.

                        And sure the grinding wheel will eventually wear down, but as has been said, it takes some time and grinding to do that. On some machines (like CNC and automated manual machines) there is a wheel dressing unit, basically one slide with a hydraulic or electric feed that moves a diamond across the wheel to dress it. For example, on a Johansson automatic grinder I can set how much the diamond will dress and how often (like 0.005 mm off after 0.1 mm of grinding). The machine drops the Y axis (the wheel) the same amount as I dress, so the wheel stays in the same place relative to the workpiece.

                        If the wheel wears more than expected (wrong wheel type, lots of rough grinding), then the part will be oversized. But, there is an easy fix: Just grind more
                        Amount of experience is in direct proportion to the value of broken equipment.

                        Comment


                        • #13
                          Thank you for asking this question. Now I have to go buy a surface grinder. I don't want any of you guys coming into my shop and noting that there is no surface grinder and thinking to yourself....hmm, no surface grinder in sight. This guy is just a farmer working to farmer tolerances.

                          Can anyone recommend a grinder for my use? I am in Germany so probably a European will need to answer this question. Maybe Jaako!

                          I have thought recently that a surface grinder should be my next acquisition maybe just before the CNC plasma table.
                          Location: The Black Forest in Germany

                          How to become a millionaire: Start out with 10 million and take up machining as a hobby!

                          Comment


                          • #14
                            Ive been looking at this in anticipation, and as elsewhere my surface grinder was hiab'd off the truck yesterday.
                            Besides making things flat and smooth (very useful to me) like clutch plate steels and shims etc, I have a jig to hold mill tooling for sharpening at defininate angles to use it to touch up some very blunt big endmill's, and I'm on the hunt for a spindexer to mount on it to make hard round things smaller.
                            I already want to take my straight drill shanks to collet sizes so I can hold them all in standard collets.
                            I'm sure the list will grow when its under power and in place!

                            Comment


                            • #15
                              Originally posted by Black Forest View Post
                              Thank you for asking this question. Now I have to go buy a surface grinder. I don't want any of you guys coming into my shop and noting that there is no surface grinder and thinking to yourself....hmm, no surface grinder in sight. This guy is just a farmer working to farmer tolerances.

                              Can anyone recommend a grinder for my use? I am in Germany so probably a European will need to answer this question. Maybe Jaako!

                              I have thought recently that a surface grinder should be my next acquisition maybe just before the CNC plasma table.
                              You are just too funny!

                              Clearly you have identified a problem (no surface grinder) and are heading to a solution. Look for a good MŲ†gerle, Jung, Blohm, Schaudt or other good German, Swiss or Austrian machine.

                              Happy Christmas BF!

                              Comment

                              Working...
                              X