Trying to relate my understanding of grinding to the theory

[Brian Ashton]

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.

[Marko Milisavljevic]

Hi Brian,


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.


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.

[Winton Applegate]

Damit Jim . . . I'm just a simple country doctor (https://www.youtube.com/watch?v=MULMbqQ9LJ8) . . .
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. (http://www.sharpeningsupplies.com/Shapton-Professional-120-P507.aspx)

[Richard Hutchings]

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.

[george wilson]

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!:)

[Metod Alif]

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

This is not the way of physics.

Metod

[Bob Woodburn]

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=FRI3AgAAQBAJ&printsec=frontcover#v=onepage&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.

[george wilson]

"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.

[Pat Barry]

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

[Jim Koepke]

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

[Winton Applegate]

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 :rolleyes:

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.

[Winton Applegate]

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 (http://en.wikipedia.org/wiki/CERN) and not all this God Particle (http://en.wikipedia.org/wiki/Higgs_boson) business.

Can't you just picture it ?
:D:p:confused::eek::(
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.

[Jim Matthews]

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.

[Winton Applegate]

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.

[Pat Barry]

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

[Steve Voigt]

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


The relevant measurements are cutting speed and surface feet/minute, not rpm. For example, with a HSS end mill, 1" diameter, I'd probably run a mill at around 400 rpm. Your 6" cutter would run 6 times slower, which is near of the bottom of the range of a bridgeport-style mill.



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.
…
The wheel of the grinder is repelled away from you as you push against it

That's a really good explanation. The usual example in physics books is pushing against a wall.


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
I was just about to go dig out a an old textbook and scan a page, then I read your post. Thanks for talking me off the ledge. :p

[Winton Applegate]

its not really clear what you want
he wants what we all want . . . an excuse to sit on the couch and consume more madeline cookies and coffee rather than go to the shop and make all them nice sharp tools dull again.

[John Gornall]

I once worked as an engineer testing metal cutting tools. The key point in grinding is that the heat generated is directly proportional to the amount of metal removed. Remove a lot of metal in a short time makes things hot. The speed of the wheel doesn't matter. A fast wheel, however, allows you to remove material faster generating more heat in a shorter time causing temperature to rise fast. A fast wheel with a controlled, light cut will not overheat your tool. Many grinding wheels cut better at higher speeds.

[Winton Applegate]

John,


Many grinding wheels cut better at higher speeds.
I'm not disputing that but merely wondering . . . why that is.
Is it a centrifugal force thing where the fast wheel is able to shed swarf better or is it that the grains of abrasive are more effectively fractured exposing sharp edges more readily ?
etc. ?

[Jim Koepke]

I'm not disputing that but merely wondering . . . why that is.

The faster a wheel is turning the more "length" of its contact area is being presented to an object touching the wheel in a given period of time.

As an example, a wheel with a circumference of 24" at 1 rpm is presenting 24" of surface to a point in contact to the wheel. The same wheel at 2 rpm is presenting 48" of surface to the same contact point.

jtk

[george wilson]

supposing you tell me how the wheel is pushing back,when it has no forward movement ? Do you feel a physical sensation of the wheel pushing back against you? The force exerted is straight down,unless you are holding the tool well above the center line of the wheel. Then,from friction,it can push back some,but not a lot. I never have in over 60 years of using a grinder. It really doesn't even kick back like a buffer can(very easily),because the tool doesn't get "tangled in the wheel like it can in the soft fabric of a buffer wheel.

[John Gornall]

I would have a piece of steel turning on the lathe. Instruments were hooked up to measure temperatures and motor amperage. I would vary the speed of the lathe and find the cutting speed using the least amps. Then watch the temperature in the cutting tool. Then see the life of the cutting edge. Looking for a compromise of these elements to give cost effectiveness including down time for tool changes. I would decide the best cutting speed. For example cutting mild steel with high speed steel I would suggest 100 ft per minute. Simplified, if drilling I would go 4 x 100 (cutting speed) divided by bit diameter so drilling in mild steel with a 1/4" high speed bit is 1600 rpm. The smaller the bit the faster to get up to cutting speed at the cutting edge. At the time I was testing carbides came online and tests told me to hurry these into production. What I'm getting to is that every cutting tool has an optimum speed. Grinding wheels used to have their recommended speed written on them - don't seem to any more. Oneway the lathe company sells wheels specially designed for 1750 and 3450 rpm. They used to recommend the high speed but have let that go - internet wisdom overrules these days.o

[Pat Barry]

supposing you tell me how the wheel is pushing back,when it has no forward movement ? Do you feel a physical sensation of the wheel pushing back against you? The force exerted is straight down,unless you are holding the tool well above the center line of the wheel. Then,from friction,it can push back some,but not a lot. I never have in over 60 years of using a grinder. It really doesn't even kick back like a buffer can(very easily),because the tool doesn't get "tangled in the wheel like it can in the soft fabric of a buffer wheel.
First George, a question, do you apply pressure to the tool into the wheel as it is being ground? Maybe just an ounce or so? Of course you do, you have to apply some force. Newtons law says the wheel pushes back equally. Its the law. We just abide by it. We can't help but abide by it. Its not like the speed limit law which we all sometimes don't abide by.

[Winton Applegate]

Pat,
Steady on . . . lets say the grind wheel blocks a trust but does not advance.
Yes ?

[Winton Applegate]

Jim,
So it is a simple matter of surface feet per minute.
I was thinking along the lines of trading out surface feet per minute for feed rate and comparing the over all quality of cut, stone life, end production rate.

of the

grinding wheels cut better
I was focussing on the BETTER rather than just faster, cooler, what have you.

[Pat Barry]

Pat,
Steady on . . . lets say the grind wheel blocks a trust but does not advance.
Yes ?
I don't understand what you are saying but I do trust that law.

[Winton Applegate]

Then see the life of the cutting edge. Looking for a compromise of these elements to give cost effectiveness including down time for tool changes. I would decide the best cutting speed

Kind of the way I go about choosing a plane blade angle. Well loosely . . . OK very loosely.

Anyway I get it the high speed is better for steel and I enjoyed hearing about HOW you determined the best tool use.

I am still interested in your opinion (or knowledge) of why the higher speed was better for the stones. What actually happened between the work and the stone (or after the surface of the stone left the work) at higher speeds.

[John Gornall]

Set up a piece of wood for edge planning. Set the plane and make a few strokes to be sure all is smooth. Now do a stroke as slow as you can go and still cut wood - a hard push. Then do a stroke at real planing speed - seems easy. A plane cutting wood has a "best" speed. This is true for all cutting tools. A grinding wheel is a whole bunch of cutting edges glued together. It's a complicated cutting tool. Grinding wheels do not cut steel better at higher speeds - some do, some don't. A grinding wheel is designed for a specific job. The grits in a wheel have characteristics like any blade - what is the cutting angle? It's not regular like a plane blade because the grits are stacked randomly. The wheels are made using grits, binder, density and other traits to do the job required. You should choose a wheel suited to your wood working tools. Follow the manufacturers recommendation. And test speeds if you can. I have a variable speed grinder - 1725 to 3450. With a new tool or a new wheel I try the range of speeds to see what works for me. I like an 80 grit blue wheel at 3450 for most chisels - gives a nice smooth, even grind but needs good hands. And for wood lathe tools I usually use 60 grit at 1725 - not so fussy.

Extremes

- when I drill steel or wood with a 1/16th HSS bit I use an air drill at 10,000 rpm

- Paper mill rolls 30 feet long and 30 inch diameter being ground. The roll is spinning on a roll turning lathe. The grinding wheel is 24+ inches in diameter. All moving fast. The roll is ground to plus or minus .0001 (3 zeros) and crowned a few thou from end to end. .

[Marko Milisavljevic]

supposing you tell me how the wheel is pushing back,when it has no forward movement ?

When you lean against a wall, or stand on your deck, are you pushing it? How, when you have no forward motion? You don't have to be in motion to exert force. Newton basically said that when you apply force to something (by standing on it, leaning against it, hitting it), there will be equal reaction. Reaction could take a number of forms - object could simply apply equal force back at you (like you leaning on a wall), or accelerate away from you (like you leaning against a cart), or some combination. This is idealized - there is also friction and other issues that you would have to calculate if you were modelling something specific. It is a bit of a mental leap to think that an immobile object is applying a force to you, but if you distrust me here is a set of experiments you could enjoy:

1) Take a nice soft piece of pine (to keep it woodworking-related) and whack yourself on the forehead with it. There will be a bruise on your head, and a dent in pine. Both experienced force.
2) After that heals up, take another piece of pine, lean it against a wall and run into it with your forehead. Again, there will be a bruise on your head and a dent in pine. Pretty much the same outcome, except this time you reversed roles as to what was moving and what was stationary.
3) After that heals up, take yet another piece of pine, and put it and your head into a large vise. Squeeze it slowly and gently, but make sure you stop before you hear cracking. If you hear cracking you went too far - hopefully the board will still be in one piece. Again, your head will have a bruise and pine will have a dent, even though this time you were both stationary.

[greg Forster]

Definitely not something I should be reading at 5AM Monday morning

[Richard Hutchings]

Can't wait until my shoulder heals so I can do some woodworking when I wake up. I can't believe I'm following some of this. More popcorn please. Carry on.

[Pat Barry]

When you lean against a wall, or stand on your deck, are you pushing it? How, when you have no forward motion? You don't have to be in motion to exert force. Newton basically said that when you apply force to something (by standing on it, leaning against it, hitting it), there will be equal reaction. Reaction could take a number of forms - object could simply apply equal force back at you (like you leaning on a wall), or accelerate away from you (like you leaning against a cart), or some combination. This is idealized - there is also friction and other issues that you would have to calculate if you were modelling something specific. It is a bit of a mental leap to think that an immobile object is applying a force to you, but if you distrust me here is a set of experiments you could enjoy:

1) Take a nice soft piece of pine (to keep it woodworking-related) and whack yourself on the forehead with it. There will be a bruise on your head, and a dent in pine. Both experienced force.
2) After that heals up, take another piece of pine, lean it against a wall and run into it with your forehead. Again, there will be a bruise on your head and a dent in pine. Pretty much the same outcome, except this time you reversed roles as to what was moving and what was stationary.
3) After that heals up, take yet another piece of pine, and put it and your head into a large vise. Squeeze it slowly and gently, but make sure you stop before you hear cracking. If you hear cracking you went too far - hopefully the board will still be in one piece. Again, your head will have a bruise and pine will have a dent, even though this time you were both stationary.

LOL - this is educational

[george wilson]

You may as well be "pushing" against a stationary rock. The rock doesn't push back. It is just there,and too heavy to move. You HAVE to push against the grinding wheel to get it to cut into the steel. You are getting confused about something.

This whole thing is rather silly.:)

[bridger berdel]

And most of the coathangers in the world would disappear...

[Marko Milisavljevic]

Imagine the wall was on rails with a giant spring behind it. You lean against it, wall moves until the spring compresses enough and it comes to stop, with you still leaning on it. Is it pushing you now? I think you'd agree it is, yet your body can't tell the difference - it is still feeling the same pressure against it, stationary or sprung wall. Through magic of Newton's third law, even a stationary object that can't initiate the pushing is pushing back when you push on it. It instantly stops pushing when you stop pushing. Like watching yourself in a mirror.

[george wilson]

Actually,I really don't care about this topic enough to waste any more time on it!!:)

As Jim said,it's one of those that goes nowhere and gets everyone upset.

[Brian Ashton]

supposing you tell me how the wheel is pushing back,when it has no forward movement ? Do you feel a physical sensation of the wheel pushing back against you? The force exerted is straight down,unless you are holding the tool well above the center line of the wheel. Then,from friction,it can push back some,but not a lot. I never have in over 60 years of using a grinder. It really doesn't even kick back like a buffer can(very easily),because the tool doesn't get "tangled in the wheel like it can in the soft fabric of a buffer wheel.

One of the reasons I concluded that newtons 3rd law of motion was at play was by using the example of a motor boat in water. As the boat moves through the water it pushes against the water which intern pushes back causing the boat to rise out of the water. The water is obviously stationary but due to the curve in the hull and speed of the boat it is still pushing back on the moving boat. This I believe is also happening, in a similar way, at the grinding wheel in that as an individual granule of grit on the wheel cuts into and scores the steel it pushes the steel back. The user pushing the steels is pushing at an equal force towards the wheel, thus holding it stationary.

Someone was asking why this is in woodworking... It wasn't explained but it relates to grinding edge tools.

@Jim K. Sorry you think this is a BS thread but one thing is for sure I was putting out the discussion cause I wanted to tap into the wealth of knowledge that exists here and try to develop an understanding of the grinding process. I don't belong to any other forums anywhere so here is where it gets posted. Not sure how this would become a ridiculous debate like sharpening threads simply because this is about understanding the physics behind a process, not a my sharpening method is better than yours pissing contest. If you have ideas I'd certainly like to here them. Ultimately I'm hopping to get a couple nuggets of info that will help to give me a clearer picture on what s taking place or a direction as to where I can do some exploring.

[Brian Ashton]

Hi Brian,



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.



I think you would need to study materials science, Newton's laws won't let you meaningfully model interactions you are interested in.

I gave an example earlier of a boat moving through water that I think is similar to what's taking place at the grinding wheel. If the boat rises out of the water relative to the boats speed doesn't newtons law apply to some degree? I.e. the boat pushes against the water, the water pushes back...

Maybe my understanding of material science is off but isn't that the study of developing new materials. Im not sure how the grinding process relates to such a field.

[Brian Ashton]

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.

At some point as you say you use a grinding wheel for your woodwork tools...

I'm interested in being interested. It's a circular logic that drives me.

[Brian Ashton]

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=FRI3AgAAQBAJ&printsec=frontcover#v=onepage&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.

Thx! that's a great reference. That should give me a couple hours of reading to do

[Brian Ashton]

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

What I'm trying to gain an understanding of is a method of grinding that I'm sure isn't a new technique but more a forgotten one. This type of grinding relates specifically to putting a bevel on a piece of heat sensitive tool steel or carbon steel by hand. The usual rhetoric everyone espouses is you need to grind at a high speed if you want to remove material quickly... What I've found is the opposite. I've been grinding my tools at about 500 - 600rpms for about 25 years and always knew it was an extremely effective way of not burning a tool... I also had the inclination that it was also faster at removing material. For more than 15 years I never tried to verify it though because I didn't actually care about that. It wasn't till about 8 years ago that I mentioned it on a forum and the supposed experts all burred up and said I was out to lunch... At that time I thought maybe I'm mistaken so I put it to the test to see if what I was thinking was actually taking place. At the time I thought it might be 10% faster, maybe more maybe less I didn't really know. What I found to my total surprise was that I could remove material at about 40% faster without ever getting close to overheating the tip of the tool. I repeated the process a number of times with the same result. When the odd naysayer came over and dared to challenge me on it I showed them, with the same results each time. Couple years ago I mentioned it here with the same reaction from the "experts." Nowadays I don't give a rat ring if anyone believes it or not, my only goal is to understand the process for myself.

My understanding at this point is:

There's an inverse relationship between how much a single piece of grit on a grinding wheel can dig into a steel surface and rip out a strip of material and the speed at which it's moving. I.e. The faster the grain of grit is traveling across the surface of the steel the less it can dig in and therefore the less material it can remove, unless much more force is applied to push the steel into the grinding wheel. This is where I think Newtons 3rd law of motion applies.


But the problem to this is the harder you push the faster the steel heats up... which leads to... The two surfaces rubbing hard together is increasing the heat in the steel which is our main problem in grinding and the primary reason I made a slow speed grinder... This is where I'm wanting to get a better understanding of how to put together a formula that would for the most part explain what's taking place. It's pretty clear now, after thumbing through the two reference documents mentioned that such a task is very complex.

The heat transfer coefficiency of the steel also plays an important part in that it draws the heat building up away. When using a high speed grinder the steel isn't able to draw away the heat fast enough and it over heats relatively quickly as we all know. Whereas a slow speed grinder generates heat at a much slower rate, which allows the steel to deal with it much more efficiently.

So these are three factors I've identified that I think are taking place. How they interact and produce a good result is what I think I happened upon a couple decades ago. The lower rpm of the grinder allows each granule of the grinding wheel to dig much deeper and remove a much larger volume of material with each pass. While at the same time, the heat from the friction builds up much more slowly because the heat generated is related to velocity. To add to this, because the heat buildup is slower the steel is able to draw much of that heat away from the tip. This allows me to dwell much longer on the wheel which intern allows me to remove even more material... Culminating in a much more rapid removal of material compared to the common grinding methodology preached by all the experts.

[Richard Hutchings]

Why didn't you say that in the first place.:rolleyes: Now I need to get a slow speed grinder.:mad:

[Brian Ashton]

Why didn't you say that in the first place.:rolleyes: Now I need to get a slow speed grinder.:mad:


I was hoping less was more in this case

If you have a lathe and can find a mandrel that attaches to the outboard side (or you don't mind pulling it off all the time on the inboard side) you have a slow speed grinder.

[Richard Hutchings]

Good idea. Thanks Brian.

[Pat Barry]

It's a circular logic that drives me.
Brian, I do think that this "circular logic', by definition, will lead you no where and leave you frustrated. Its best to reorient your logic in a linear fashion that takes you toward a solution.

[george wilson]

Just grind your tool!!!!!:):):)

[Brian Ashton]

Brian, I do think that this "circular logic', by definition, will lead you no where and leave you frustrated. Its best to reorient your logic in a linear fashion that takes you toward a solution.


Hey, you're the one who wanted more details... :)

[Brian Ashton]

Just grind your tool!!!!!:):):)

There's a t shirt in there somewhere. Stay calm and grind your tool. Or how bout, Shut up and grind your tool

[Bob Woodburn]

Brian, below (indented) is a brief verbal sketch of the relevant characteristics of a grinding wheel quoted from : http://en.wikipedia.org/wiki/Grinding_wheel

Given a wheel specification defining all five characteristics below, manufacturers generally recommend a range of speed and feed and depth of cut (the latter 2 comprising what is being called here force or pressure). Speed is typically stated in wheel circumference feet per minute.

I assume the manufacturer's recommendation is an attempt to optimize the desired metal removal rate, final finish, heat effects, wheel wear, frequency of dressings needed, and so on and so forth for industrial processes.

A woodworker forming bevel edges that are meant to have durability may focus on heat effects and require absolute minimal pressures in the hope of minimizing plastic deformation and burrs at the edge. Fast metal removal at an edge may not be a goal.

I hope you can see that it is meaningless when generalizations are made about wheel speed alone, without stating the five characteristics of the wheel at issue and stating which grinding results one is trying to optimize and which are irrelevant.

If you want the best opinion about why your wheel works the way it does at low speed, you should talk with the manufacturer. I'd be interested to know what their experts have to say.


"There are five characteristics of a cutting wheel: material, grain size, wheel grade, grain spacing, and bond type. They will be indicated by codes on the wheel's label.
Abrasive Grain, the actual abrasive, is selected according to the hardness of the material being cut.




Aluminum Oxide (http://en.wikipedia.org/wiki/Aluminum_Oxide) (A)


Silicon Carbide (http://en.wikipedia.org/wiki/Silicon_Carbide) (S)


Ceramic (http://en.wikipedia.org/wiki/Ceramic) (C)


Diamond (http://en.wikipedia.org/wiki/Diamond) (D, MD, SD)



Cubic Boron Nitride (http://en.wikipedia.org/wiki/Cubic_Boron_Nitride) (B)



Grinding wheels with diamond or Cubic Boron Nitride (CBN) grains are called superabrasives. Grinding wheels with Aluminum Oxide (corundum), Silicon Carbide or Ceramic grains are called conventional abrasives.
Grain size, from 8 (coarsest) 1200 (finest), determines the physical size of the abrasive grains in the wheel. A larger grain will cut freely, allowing fast cutting but poor surface finish. Ultra-fine grain sizes are for precision finish work.
Wheel grade, from A (soft) to Z (hard), determines how tightly the bond holds the abrasive. Grade affects almost all considerations of grinding, such as wheel speed, coolant flow, maximum and minimum feed rates, and grinding depth.
Grain spacing, or structure, from 1 (densest) to 16 (least dense). Density is the ratio of bond and abrasive to air space. A less-dense wheel will cut freely, and has a large effect on surface finish. It is also able to take a deeper or wider cut with less coolant, as the chip clearance on the wheel is greater.
Wheel bond, how the wheel holds the abrasives, affects finish, coolant, and minimum/maximum wheel speed.



Vitrified (V)


Resinoid (B)


Silicate (S)


Shellac (E)


Rubber (R)


Metal (M)


Oxychloride (O)"

[Pat Barry]

It might be an interesting science project to study grinding force versus wheel type versus RPM versus blade hardness versus grinding angle, etc but I do think this would require quite a lot of expensive instrumentation and well designed experiments to gather useful data. At the end of the day you will still have tradeoffs to consider and no clear cut single best method. I do not think and ground shaking discoveries are to come of this however and I therefore kinda like George's pragmatic approach to "Just grind your tool!!! :) :) :)" those might be great words to live by and recall for future discussions

[Brian Ashton]

It might be an interesting science project to study grinding force versus wheel type versus RPM versus blade hardness versus grinding angle, etc but I do think this would require quite a lot of expensive instrumentation and well designed experiments to gather useful data. At the end of the day you will still have tradeoffs to consider and no clear cut single best method. I do not think and ground shaking discoveries are to come of this however and I therefore kinda like George's pragmatic approach to "just grind your too :) :) :)" those might be great words to live by and recall for future discussions

Not entirely sure why you think I'm trying to break new ground. I certainly have no desire to do any rigorous study that's for sure. I'm also not trying to find or convey that I have found the holy grail of grinding. This is my method, I have no interest in spreading the gospel just want to know why it works the way it does. At present I've gone as far as my limited knowledge will take me so I was looking for some other perspectives and or guidance as to where to look further. I already said it's probably a process that's been forgotten and I just happened to stumble on it again. When it comes to putting a bevel on a piece of steel by hand I doubt there is anything new to discover that hasn't been learned over the past 400 or so years. All I'm doing is something that I like to do - learn. Learning is one of those spices of life. Maybe you think I'm obsessing over this or something but I can assure you I maybe think about it once every couple years. It's like I have all these pots of interesting ideas that are simmering away on the back burner. Every once in a while I pull the lid off one and give it a bit of a stir... At this moment I'm simply trying to adding a bit of flavour and seeing what comes of it. When I've satisfied my curiosity I'll put it back on the back burner and maybe revisit it again in a couple years, maybe sooner, maybe never.

Anyways I've had a few good posts, thx guys, that I can ferret out and ruminate over. Watch this space in about 2 years.

[Richard Hutchings]

Thanks to you Brian, I've now given some thought to something that I never would have thunk to think about. I'm going to try to flush it out but I have to say it was interesting.

[Pat Barry]

Not entirely sure why you think I'm trying to break new ground. I certainly have no desire to do any rigorous study that's for sure. I'm also not trying to find or convey that I have found the holy grail of grinding. This is my method, I have no interest in spreading the gospel just want to know why it works the way it does. At present I've gone as far as my limited knowledge will take me so I was looking for some other perspectives and or guidance as to where to look further. I already said it's probably a process that's been forgotten and I just happened to stumble on it again. When it comes to putting a bevel on a piece of steel by hand I doubt there is anything new to discover that hasn't been learned over the past 400 or so years. All I'm doing is something that I like to do - learn. Learning is one of those spices of life. Maybe you think I'm obsessing over this or something but I can assure you I maybe think about it once every couple years. It's like I have all these pots of interesting ideas that are simmering away on the back burner. Every once in a while I pull the lid off one and give it a bit of a stir... At this moment I'm simply trying to adding a bit of flavour and seeing what comes of it. When I've satisfied my curiosity I'll put it back on the back burner and maybe revisit it again in a couple years, maybe sooner, maybe never.

Anyways I've had a few good posts, thx guys, that I can ferret out and ruminate over. Watch this space in about 2 years.
Its been and interesting discussion certainly. I think if you boil it down to making some of the variables in the process fixed and focus on the relationship of speed vs pressure and time and then measure the result in terms of material removed you will find that the formula will be something like speed * time * pressure is proportional to material removal. Therefore, in order to compensate for the faster grinding wheel speed and get the same result on your slower grinding wheel you willl need to increase either time, pressure, or both. Its purely that simple. Temperature of the tool in the grinding conditions is most driven by frictional heating, material thermal conductivity, etc and that in turn is driven by pressure and exposure to the frictional force and therefore that includes both grinding wheel speed and time of pressure application. Again, all of this is well understood by mechanical engineers. The fact that you feel that you can obtain a cooler tool with large amounts of material removal at low speed indicates to me that you probably press very hard for a short period of time. Using this same sort of pressure on the high speed tool will lead to higher tool temperatures unless you compensate by significantly reducing time of pressure application. All the other variables involved (type of grinding medium, coarseness of the medium, wet or dry grinding, tool steel hardness and tool steel material, grinding angle, etc, etc, etc) are also in play in the real world making the process extremely complicated. This is where the school of hard knocks provides the best guidance. If you get acceptable results using the low speed grinding wheel, then great, that's all we are striving for.

[Eric Schubert]

Here's a quick rundown of my understanding of the original questions posed, Brian:

While the wheel isn't actively pushing back against the blade being ground, physics dictates that in order to remain stationary an object must push back with the same amount of force that you are exerting upon it. So your horizontal force against the blade presses it to the wheel. That force is transferred to the wheel, which is transferred to the bearings or wheel mount, which transfers to whatever the grinder is mounted to, and then to the floor/wall. So, imagine the table or bench pushing the grinder back against you pushing the blade to the wheel.

Imagine sliding a box along the ground.

The force of friction of the box sliding along a surface has a relationship to the normal (perpendicular, gravitational) force of the object against the surface and the coefficients of friction of the surfaces in contact. The higher the force of gravity (heavier the object) the more force you use to push and slide the box. The same is true with the blade on the wheel. The higher your force pressing the blade against the wheel, the higher the force of friction being generated that the wheel must overcome to keep spinning at the same speed. This force of friction is tangential to the wheel.

If you are sliding the box at a constant speed, your force equals that of the frictional force. And since your blade does not move, the force you use to push tangentially to the wheel plus any help from the tool rest will equal that of the opposite tangential force of friction.

Here's an illustration:

309956

Flat illustration:
F(n) = normal force (perpendicular)
F(o) = you pushing to slide the box along the surface
F(f) = frictional force working against you sliding the box (varies with F(n) and surface roughness)

Wheel illustration:
F(b) = your force pressing the blade against the wheel
F(n) = the normal component of F(b) on the wheel
F(t) = the tangential component of F(b) on the wheel
F(f) = frictional force on the wheel/blade

Since your force is at an angle as you create the bevel on the blade, break your force down into the normal and tangential components. Only the normal component generates frictional forces. The tangential component is probably a combination of your F(t) pressing against the frictional force and the tool rest holding the blade in place. These forces combine to offset the frictional forces and keep the blade stationary. If these forces do not balance, the blade moves (probably flying across the room somewhere...).

F(f) = F(n) x Coefficient of Sliding Friction

So, let's say you're pushing with 10lbs of force and your coefficient is 0.2, then your frictional force is 2lbs.

The coefficient varies with surface roughness of the two faces in contact with each other. You can often look these values up as a combination of whatever materials you're using and how rough the surfaces are. For instance, the coefficient of friction for dry wood on metal is roughly 0.2. But again, this varies as the texture changes on the surfaces of either the wood or the metal.

Make sure to use the sliding friction coefficients, not the static coefficients. It is harder to get an object started sliding than to keep it sliding. Static coefficients are to calculate the initial force required to get an object moving from a stop, hence the larger coefficient values.

Hopefully this at least helps. If you need further clarification, let me know.

[Eric Schubert]

By the way, I have to add...

Theoretically, the frictional force is purely a function of the normal force and the coefficient of friction. Speed of the box on the flat surface should make no difference whatsoever.

However, in reality, this can change quite a bit with a texture that isn't consistent or that changes as it wears. Or even a very rough texture can dig into the edge or side of an object and cause extra frictional forces to be generated. So, take my post as pure theory that may very with actual, real-world conditions.

Also, since a wheel is round, its opposing force is not necessarily purely tangential. Some of it is normal, as well. (To be normal/perpendicular, you'd have to push directly toward the center of the wheel. Doing so makes grinding very difficult, so we hold the tool we're grinding to the side where the wheel is spinning away from us for safety.) This complicates things.

Now, the heat generated is another matter entirely. This is due to the work being done by the frictional force as it opposes your own forces. Since you're grinding and removing material, heat is also generated as you break the bonds of the molecules of steel or iron from one another. (Just imagine very tiny frictional forces causing more work to be done here, for the sake of simplicity.)

Let's think about the sliding box again. You put work into sliding the box a particular distance. The farther the distance, the more work being done. An equal and opposite amount of work is then done by the frictional force to oppose you. All of this work done by friction goes toward generating heat.

Work = Force x Distance

Force to push the box = 10lbs
Distance = 10ft

Work = 100 lb*ft

How to take that work and calculate change in temperature in a tool is difficult. Some work generates heat in the wheel, some generates heat in the steel, and a small amount is even dissipated into the air around both. You'd need to know the thermal properties for each of them to make that calculation happen.

[george wilson]

And,that and $5.00 will get you a cup of coffee at Starbucks!!!

Just grind the TOOL!!!!!

[Noah Wagener]

" "Isaac Newton, the man who made the brilliant observation that something unimpeded will fall to the ground but never figured out why. His disciples are zeroing in on when." "

Winton, are you suggesting a Shapton 120 could serve as a grinder? Could you compare its speed to the 1,000 and its hardness?

[Tom McMahon]

Unless I missed it, somewhere in this thread has the square area of contact been mentioned. When I was in high school metal shop I was taught to use a wheel with a radiused face to limit the area of contact. Joel from Tools for Working Wood wrote an article about it. https://toolsforworkingwood.com/store/blog/48

[Richard Hutchings]

I am with you George. They're having fun on another level and I still believe it has nothing to do with woodworking. Yet, I still come back to read.


And,that and $5.00 will get you a cup of coffee at Starbucks!!!

Just grind the TOOL!!!!!