Intro to Grinding Methods, Machines and Tools

April 16, 2021 11:00 am

Grinding is a widely used abrasive finishing process. Did you know grinding machines have been around for centuries? Well, not the electric ones but the ones that are powered via a pedal. 

Oftentimes grinding operations are compartmentalized by machinists and considered separate from typical cutting processes used in  machine shops. This is most likely for a couple reasons, one being that grinding operations are quite often mistaken as a rubbing process and not a cutting one. Also, grinding is a cutting process that actually creates a smooth finish, unlike the other processes in the category that create unsmooth surfaces. 

There are a variety of machines and tools that perform grinding operations. Read on to learn more about the different methods that are used to get the job done along with some books to check out if you’re interested in deepening your grinding knowledge.

How grinding works 

Grinding is used to finish workpieces so that they meet the required surface finish quality. It rids unwanted material from the workpiece, like any rough texture that remains from previous machining applications. 

Grinding machines or tools use an abrasive wheel to remove metal from the workpiece. When the wheel rotates, it cuts material off the workpiece by cutting. The amount of material removal is dependent on factors like abrasive material and grit selection. The video below explains how to select the right abrasive. 

 

Grinding is a pretty diverse segment of machining, as the amount of material removal varies. Depending on the grinding attachment and project, both miniscule and larger amounts of material can be removed. For example, grinding can be used to either produce fine finishes or work in larger production environments to rough out large volumes of metal. Grinders can also be used to sharpen tools as seen in the video below. 

 

 

Grinding methods

There are different ways to accomplish your grinding operations. Several factors to consider are workpiece size, shape and features along with the production quantity. Machine tools are a larger investment whereas handheld tools are more affordable. 

Grinding machine tools 

Belt grinders are versatile and used for different applications like finishing, deburring and stock removal.
Bench grinders are connected to a workbench or some type of floor stand. Depending on the type of wheel, a bench grinder can be used for all sorts of finishing applications.
Cylindrical grinders are great for achieving superior surface finishes. They are able to remove the finest pieces of material. They can also be used to shape the outside of an object. These grinders are most frequently used when manufacturing a cam or crankshaft.
Surface grinders are considered the most common grinding method. They are very precise tools that use a rotating wheel held in place by a vise. The vise then moves back and forth under the abrasive wheel.
Tool and cutter grinders are very versatile tools that can host a variety of different grinding operations, like surfaces and other complex shapes. 

Grinding hand tools

A die grinder is a high-speed rotary tool that is typically powered by compressed air. The tool has a small-diameter abrasive bit that rotates to get the job done. Check out Choosing the Right Air Die Grinder for more information and some recommended models.
Angle grinders are also abrasive hand tools. Unlike die grinders, however, they run electrically. Learn more about angle grinders and some recommended models in our article Top 5 Angle Grinders Recommended by the Practical Machinist Community

There are also more specialized grinding tools, for example gear grinders which are specific to gear manufacturing, or jig grinders, which have a variety of uses but are most commonly used for jigs, dies, and fixtures. 

Coolant use when grinding

Whether or not coolant is necessary for your grinding application will depend on how much heat is generated. For example, high precision grinding machines like cylindrical and surface grinders generate so little heat that using coolant isn’t necessary. 

Grinding fluid can even increase the material removal rate without subjecting the workpiece to damage. The best fluids to use in this case are water-soluble chemical fluids and oils, synthetic oils and petroleum oils. 

Check out our article How to Select and Maintain Machine Coolant for more information about cutting fluids to make sure you are selecting the correct one. 

Learn more about grinding operations

Grinding technology has come a long way and the industry has a growing need for qualified professionals. But how do you learn about grinding? And where can you learn more about it? Check out some of these handpicked books to either get you started or deepen your knowledge. 

If you’re interested in a broader resource that have some sections on grinding topics, check out 5 Machining Books to Keep on Hand and 15 Timeless Books Every Machinist Should Have.

Handbook of Machining with Grinding Wheels

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Handbook of Machining with Grinding Wheels highlights important industry developments that can improve part quality, higher productivity, and lower costs. The book is divided into two parts, beginning with an explanation of grinding behavior and ending with a focus on new and emerging industrial applications.

American Machinist Grinding Book: Modern Machines and Appliances, Methods and Results

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This text is a classic. It was inspired by the columns from the original magazine American Machinist. It provides a thorough description of all the different types of grinding machines and how to take care of them.

Tribology of Abrasive Machining Processes

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Tribology is “the study of friction, wear, lubrication, and the design of bearings; the science of interacting surfaces in relative motion” (Oxford Languages). This book uses the science of tribology to understand, predict and improve abrasive machining processes. In this book, you will find solutions to the most commonly experienced industrial abrasive machining problems such as poor surface quality, rapid wheel wear, vibrations, high process costs and more. 

Turning and Mechanical Manipulation: Abrasive and Other Processes Not Accomplished With Cutting Tools

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This book covers a wide selection of different finishing processes. You will find information about the production of cylindrical, spherical, conical and plane surfaces by abrasion and surface grinding. 

Eco-efficiency of Grinding Processes and Systems

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Eco-efficiency is a term related to sustained growth and development. If you’re interested in how to further optimize your grinding systems and processes, checkout the research in this book. Various combinations of grinding process parameters and system configurations can be evaluated based on the eco-efficiency and this book will assist you in analyzing those economic and environmental impactors.

 

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5 Comments

  • sparky says:

    As a Mold Maker/ Grinder Specialist with over 40 years experience it would take all day to talk about what I have done on the grinder! The surface grinder is a primary machine in the mold shop, but probably only about 10% of my work has been flat work on a surface grinder which you would think is primarily a flat work machine! Diameters, elliptical shapes mixed with multiple angles are just some of the “fancy” stuff we do in the typical plastic injection mold tool shop! I would be happy to answer any questions someone might have about grinding!

  • Yitzy says:

    Hi, I have been searching for someone like you to advise me. I currently am using the Maka swing-chisel mortiser in my shop. It cuts mortises with a specifically profiled chisel which is affixed to it’s oscillating head. I’m trying to figure out the best way to sharpen these chisels, their complex shapes make it impossible to use the conventional sharpening/grinding systems. I had contacted the technicians at Tormek as well as other manufacturers for their input- they were not able to help me. Here is some diagrams of these chisels https://lussault.fr/en/ (this is a French company that manufactures them)

  • Yogesh says:

    What is the best way to grind a 1″ dia shaft with 150″ length and a tolerance on dia of +/-0.001″ and TIR of 0.0005″/foot?

  • Wizard says:

    They forgot to mention rotary grinding, jig grinding, thread grinding, centerless grinding, i.d. grinding, form grinding and then the many CNC grinding applications available today. Grinding is very fascinating indeed and something that even the majority of the most seasoned pros never quite master completely. Nothing more nerve wracking than trying to get the last little bit of taper out of a shaft with very little grind stock left on it, or tolerances of +0, -.00001″

  • Ex St.George TAFE Teacher says:

    Having done a LOT of grinding over my lifetime with close to 60 years of workshop experience, I would like to comment on some of the material presented. Some of it I totally disagree with. Breaking it down we need to divide grinding into either off hand or precision. Off hand is where either the workpiece is held by hand or the grinder is hand held. Lathe tools, chisels, drill bits etc can be ground on off hand machines. Then with precision grinders they can be Cylindrical (plunge, plunge and wipe or traverse), Internal (dedicated or universal in either plain or auto size versions eg. Heald Sizematic. ) Next comes Surface Grinders with different table/spindle configurations (horizontal spindle / horizontal reciprocating table, vertical spindle / horizontal reciprocating table, horizontal spindle / revolving circular table, vertical spindle / revolving circular table with either solid grinding wheels or in the case of vertical spindle machines they also may have segmented wheels that are screwed in to form a wheel head. Next we look at centreless grinding machines that use 2 wheels consisting of a grinding wheel and a regulating or ‘control’ wheel. These wheels generally have a wide face and the operations are either plunge or through grinding. The tilt on the regulating wheel determines the speed of the workpiece past the grinding wheel. Next we have Tool and Cutter Grinders which can also be used to do surface and cylindrical work if the attachments are available. There is another type of grinding that fits in between off hand and precision and it is called ‘Spot Grinding’. Spot Grinding is a scary operation that you thank providence that you still have your fingers after you finish. It is used where the workpiece is too small to grip it by magnets or it is small and non ferrous (hence non magnetic). I have used all of these machines and methods and still remember the 6 monthly periods where the largest tolerance I saw was 0.0001″ .
    Now, where I draw differences in some of the articles…. In the use of coolant when grinding….”For example, high precision grinding machines like cylindrical and surface grinders generate so little heat that using coolant isn’t necessary. ” It is obvious that the writer has never cylindrical ground small diameter soft materials, especially long slender components. Mild Steel will draw itself into the wheel due to the localised heat and I know with valve spools where each land is a different diameter, IF you grind without coolant then the lands will not be concentric. Disbelieve me at your peril. I am prepared to answer any query you may have just send me your email (desirably with a phone number and even though I am in Australia I will call you).
    Those of you who want to have it demystified then these are some things we need to talk about. a) selecting a grinding wheel, b) understanding the code eg 38A 60 K 7 VBE, c) checking the wheel for safe use, d) mounting the wheel and balancing, e) safe switching on, f) NEVER use the sides of the wheel (they are not designed for sideways load), g) ensure workpiece is always moving so as to minimise the possibility of digging holes in the periphery of the wheel. There are others but that is the start point.

    Suggestions for sharpening lathe tools from scratch using HSS. We all have our favourites and mine were Fargersta, ASSAB 17, Bohler 59 and Sandvik so mainly Swedish and German dialects of HSS tool steel. This would be so much easier if I could put this in a diagram but I will try to explain it in words. Essentially we have a prism with the top and bottom rectangles and the sides parallelograms. Let us formalise the geometry of the tool (looking at a Right Hand Turning Tool as the example). I have used exactly the same general proportions on sticks from 5/16″ x 5/16″ through 3/8″, 1/2″, 5/8″, 3/4″ and 1″ and you will have success. Understand that the top left hand corner is the part that will do the cutting. So looking from the top we can grind the end of the tool toward the right hand corner at an angle of around 10 degrees. This is called the end cutting edge angle or ‘trail angle’. As you are producing this angle you tilt the tool back so that it also produces around a 10 degree angle down the side which is known as ‘end clearance’. Use the FULL WIDTH of the wheel face when you are grinding and continually cool the tool to reduce the amount of heat being generated. Next we grind left side face starting at the bottom and working toward the top face to produce about a 10 degree angle. Follow the line of the rectangle so it should be cut away leaving one point in the top left corner. We want only ONE facet per face and you achieve this by hinging the tool from the bottom and up onto the face. This means you cannot hold the toolbit too tightly. This takes a while to get the feel and it takes practice and lots of it. The angle you have now ground is called Side Cutting Edge Angle but most commonly as ‘Approach Angle’ and in this case it is known as a 90 degree approach. Because the tool has been tilted it also produces the side clearance. This leaves us to concentrate on the top of the tool. REMEMBER ANY ANGLE CUT INTO THE TOP IS CALLED ‘RAKE’. Rake can be positive where it is ground toward the right of the cutting edge or negative where it is ground towards the cutting edge. Neutral rake is where the top of the tool is left unground. Finally, you should break the corner of the tip by following the angles formed by the side clearance and the end clearance. You can also oilstone a small radius on the tip but just ensure it follows the angles of the side and end clearance are followed. As a simple rule of thumb just remember that regardless of whether you have used side rake or back rake or a combination of both, RAKE is ALWAYS where the chip bears and all other angles are clearance angles. To conclude this long winded explanation I must advise you that the angles maybe altered depending on the material to be cut. I deliberately did not include grinding lip chip breaker tools but will write a separate instruction on how to do it if there is enough interest. Remember that this is only the start because we need to know how to do feeds and speeds as well. Remember in the long run it is VOLUME of material removed per minute that is the key.
    Hope I am still here for next time guys because I am in Stage 5 End Stage Renal Failure so if you need this info then hit me up before I permanently depart !!

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