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Thread: Trying to relate my understanding of grinding to the theory

  1. #1
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    Trying to relate my understanding of grinding to the theory

    I'm trying to apply the practical side of what I know about grinding to the theoretical side...

    So what I know at present about the theory is:

    Newtons third law of motion: for ever action there is an equal and opposite reaction. So as a piece of steel is pushed into a grinding wheel, the grinding wheel pushes back. The faster the wheel is spinning the larger the force it pushes back with...

    Friction: Can't put together a formula regarding this, far too complex for me. But what I do know is the amount of force used to push the steel into the grinding wheel will create friction, which creates heat... The factors that are hard to quantify are the coarseness of the wheel, the coefficient of friction of the steel and the surface speed of the grinding wheel.

    Another principal that I don't have any idea where to look for but understand and can describe is: Have ever seen a milling machine in action. I've watched gouges being milled at the Sorby factory and to mill the flute they use a 6" dia. cutter spinning at a very low rpm and it rips (for lack of a better word) large chunks of metal out of the emerging flute in a very controlled manner in one pass leaving a fairly nice finish in the process... If you were to try increase the rpm you'd end up destroying the milling wheel and the piece being milled and probably the machine. But keep those rpms low and it's incredible how much steel can be removed. But I have no idea how to describe such a process in a theoretical way. Any ideas

    What else am I missing.
    Sent from the bathtub on my Samsung Galaxy(C)S5 with waterproof Lifeproof Case(C), and spell check turned off!

  2. #2
    Hi Brian,

    Quote Originally Posted by Brian Ashton View Post
    Newtons third law of motion: for ever action there is an equal and opposite reaction. So as a piece of steel is pushed into a grinding wheel, the grinding wheel pushes back. The faster the wheel is spinning the larger the force it pushes back with...
    The force it pushes back with doesn't depend on speed of the wheel, in context of Newton's law you quote. It only pushes back as hard as you are pushing it. If it wasn't pushing back as hard, your grinder would experience acceleration in direction of resulting force, ie, it would slide away from you.

    Quote Originally Posted by Brian Ashton View Post
    What else am I missing.
    I think you would need to study materials science, Newton's laws won't let you meaningfully model interactions you are interested in.

  3. #3
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    Damit Jim . . . I'm just a simple country doctor . . .
    When you push toward the grinding wheel it is "pushing" the work down against the tool rest.
    Don't try to understand it . . . it's magic.

    What else am I missing.
    One of these.
    Sharpening is Facetating.
    Good enough is good enough
    But
    Better is Better.

  4. #4
    Brian, what is the purpose of your question? I don't see how it relates to woodworking.

    I had to edit this post after realizing this sounds like a snotty remark. I'm such seat of the pants wood worker, I don't use grinding wheels unless I buy a rusty and pitted tool somewhere. After removing the damage, the blade will never see a grinder or belt sander again. I don't even know what angles I sharpen to. My blades cut wood into feathery shavings if that's what I need. No calculations or measurements or theory required. Different strokes for different folks.
    Last edited by Richard Hutchings; 03-22-2015 at 8:07 AM.

  5. #5
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    The wheel doesn't push back. It would have to be moving forward to push back. It spins but is stationary.

    The coarseness is important to metal removal rate,as everyone knows.

    The cutter milling the flutes revolves slowly as is necessary to keep from dulling the cutting edge from friction against tool steel,which is hard to cut. Any machinist has to learn cutting speeds for different steels and materials or his cutting tools will be destroyed,or if cutting too slow,the work will take too long to be profitable,and he will soon lose his job.

    I do not know what you are driving at,actually!
    Last edited by george wilson; 03-22-2015 at 9:36 AM.

  6. #6
    "The wheel doesn't push back. It would have to be moving forward to push back."

    This is not the way of physics.

    Metod

  7. #7
    Your question is "What else am I missing?" A big unbounded question, I'd say.

    There are lots of general textbooks on this topic that can illuminate some of the principles that you may have not yet discovered.

    Take for example this:

    http://books.google.com/books?id=FRI...page&q&f=false

    Just use the PAGE DOWN key on you keyboard and browse the (abridged) book.

    Google Books and the publisher are nice enough to offer you a large portion of the book for personal review. Luckily the first part of such books offer pretty good coverage of known basics. The basic theory and principles you seem to be looking for, that is.

  8. #8
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    "That is not the way of physics"? That is exactly the way,actually. The wheel is spinning,but it would have to be moving towards the operator in order to "push back". Spinning has nothing to do with it pushing back. Think about it.

    As Winton said,the wheel would push the tool down against the tool rest do to spinning,and the friction,but not back,towards the operator.
    Last edited by george wilson; 03-22-2015 at 12:20 PM.

  9. #9
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    Yes, the wheel certainly does push back. If it did not then it would do nothing

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    This seems like another nonsense thread sprinkled with erroneous assumptions that will end up with petty arguments about the transference of rotational motion via friction.

    It isn't worth the time it takes to get upset nor to get my old college physics book off the shelf to site laws of physics that will be ignored, refuted or complained about due to their technical nature.

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  11. #11
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    On your one day off you tell SWMBO you are going to the local tool store. She mentions you have honey do's to finish around the house today before her mother comes over.
    Now THAT is your equal and opposite for you . . . every thing else is . . .

    Oh for cripe sakes this is silly.
    Look . . .
    Equal and opposite means the source of the energy, you, is pushing against the wheel which for all intents and purposes is stationary other than some extremely slight play in the bearings of the grinder.

    Docket that on the chalk board for the moment (and I don't mean a fulcrum point).
    The opposite reaction is at the base of you, more than likely your feet, against the floor. You push against the immovable grinder and your feet push in the opposite direction against the floor which hopefully is also for all intents and purposes immovable. Of course then one has to, in the formula, enter the belly slosh rebound factor, BSR we call it, often over looked except in the highest echelons of sharpening higher mathematics . . .
    . . . fortunately, dear reader, that is precisely where you have beached your self

    now back to the first comment on the chalk board.
    The wheel of the grinder is repelled away from you as you push against it, it reaches the limit of the play in the bearings, very quickly, and rebounds back toward the work only to begin another voyage. I suppose if the work was smooth and the grinding wheel was smooth and the force being applied against it were perfectly steady, and there were zero play in the grinder bearings there wouldn't be all this gymnastics.

    As far as not caring about actual numerical angles of the cutting tools to grind to that is perfectly acceptable as long as one is experienced enough to know how to correct the edge (in which direction relative to the plane of the blade/bed of the tool) when the cut is not optimal for the material being cut.
    ANGLES MEARLY PROVIDE A LANGUAGE WITH WHICH TO COMMUNICATE ONES WISDOM TO ANOTHER. (dammed handy matter of fact).

    I think the main thing to know . . . that I have come to appreciate from reading this forum . . . is that really sharp and coarse grinding wheel grit cuts faster and COOOOOLER than finer grit that is all rounded over and causing friction.
    That sounds perfectly, blitheringly, cross eyed, badger spit, obvious . . .
    doesn't it ?

    The way to achieve it though, when one buys a plane ol' grinder off the shelf at the big box store may not be so obvious.

    The coarse wheel is too fine and it is too hard and it CAN, in LESS THAN EXPERT hands heat up the blades.

    So I learned to, and I knew this to some degree before I got here (I already had white wheels but too fine) . . . get a much coarser wheel, along the lines of a 40 something grit and select a soft(ish) wheel even going to the pink wheels instead of the white wheels.

    The advantage of that is the wheel is self sharpening faster by wearing away and so it is always very sharp at the cutting grains.

    There is some more of your opposite reaction to put in the formula.
    Last edited by Winton Applegate; 03-22-2015 at 3:06 PM.
    Sharpening is Facetating.
    Good enough is good enough
    But
    Better is Better.

  12. #12
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    Speaking of the more practical application of physics Queenmasteroftheuniverseandbabybunnytrainer just asked me "why is it that when one washes PAIRS of socks when one goes to sort them there are odd numbers and missing entities.
    I think if we were a truly practical and rational life form we would be investigating THAT at CERN and not all this God Particle business.

    Can't you just picture it ?

    They suspend one sock in the particle collider tunnel at CERN and accelerate the other matching sock at near light speed and crash it into the stationary sock (or sock going in the opposite direction if you want to get fancy) . . .
    Given what I know of the realm I currently find myself in (with all of you by the way), this "REALITY" everyone keeps insisting on calling it, . . .

    after the socks collide the researchers would find only that lost set of keys to the motor home we sold last year laying on the floor of the tunnel. Or something along those lines.
    Sharpening is Facetating.
    Good enough is good enough
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    Better is Better.

  13. #13
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    http://astakhov.tripod.com/MC/tool-chip-temp1.pdf

    This has lots of Greek letters and discussion of temperature 'fields'
    all of which is beyond me.

    I'm not sure what you and I need is a physics tutorial,
    I think a more specialized metallurgy primer is in order.

    Steel is very interesting stuff, once the ingot cools.

  14. #14
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    Jim,
    This seems like another nonsense thread sprinkled with erroneous assumptions that will end up with petty arguments about the transference of rotational motion via friction.

    It isn't worth the time it takes to get upset nor to get my old college physics book off the shelf to site laws of physics that will be ignored, refuted or complained about due to their technical nature.
    "Seems like", "seems like",
    that is the only questionable thing you said.

    commmmonnnnn . . .
    All you need is a little espresso and you will be back in the breach wielding your physics book with the best of them.

    what else are we going to have petty arguments about , get upset about, ignored, refute or complain about due to their technical nature ?

    errr . . . I mean . . . talk about.
    Sharpening is Facetating.
    Good enough is good enough
    But
    Better is Better.

  15. #15
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    Quote Originally Posted by Brian Ashton View Post
    I'm trying to apply the practical side of what I know about grinding to the theoretical side...

    So what I know at present about the theory is:

    Newtons third law of motion: for ever action there is an equal and opposite reaction. So as a piece of steel is pushed into a grinding wheel, the grinding wheel pushes back. The faster the wheel is spinning the larger the force it pushes back with...

    Friction: Can't put together a formula regarding this, far too complex for me. But what I do know is the amount of force used to push the steel into the grinding wheel will create friction, which creates heat... The factors that are hard to quantify are the coarseness of the wheel, the coefficient of friction of the steel and the surface speed of the grinding wheel.

    Another principal that I don't have any idea where to look for but understand and can describe is: Have ever seen a milling machine in action. I've watched gouges being milled at the Sorby factory and to mill the flute they use a 6" dia. cutter spinning at a very low rpm and it rips (for lack of a better word) large chunks of metal out of the emerging flute in a very controlled manner in one pass leaving a fairly nice finish in the process... If you were to try increase the rpm you'd end up destroying the milling wheel and the piece being milled and probably the machine. But keep those rpms low and it's incredible how much steel can be removed. But I have no idea how to describe such a process in a theoretical way. Any ideas

    What else am I missing.
    Since we all agree on Newtons law (as proven above by multiple diverse and sometimes inconceivable points), lets figure out what exactly you are trying to figure out Brian? We need more information from you because its not really clear what you want

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