CNC Grinding Machine Buyers' Guide - HM

The first step to buying the right CNC grinder machine for metal or non-metal machining is understanding the machine and its basic buying principles. Otherwise, you could settle for less than you bargained. This guide will show you all you need to know to buy the right grinding machine. Let’s get on to it!

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What Is a CNC Grinding Machine

A CNC grinding machine is an automated machine that uses one or more abrasive grinding wheels to remove materials from workpieces. Their use cases include finishing, honing, shaping, and surface treatment for metal parts.

A CNC grinding process follows a pattern or flow whereby the tooling/abrasive wheel head rotates against a workpiece. This rotary pattern removes material through abrasion. As opposed to crushing the material, which we commonly attribute to the term “grinders.” The architecture only gives this CNC machine its unique name.

Classification and Types of CNC Grinding Machines

Every CNC grinder machine falls into one of the following categories or classes. These categories shape their types and possible use cases in the factory. 

The different classes of CNC grinders include:

• Surface and internal grinders: As their name implies, we use a CNC surface grinding machine to finish external workpiece surfaces. On the contrary, we use a CNC internal grinding machine to finish internal surfaces. In technical terms, external surfaces are the outside diameter (OD), while internal surfaces are the inside diameter (ID).
• Precision and rough-finish grinders: Another classification we highly consider is the CNC precision grinding machine or rough-finish grinder. Precision grinders minimize CNC ID or OD grinding machine errors and ensure that the finished workpiece produces the quality the machine shop grinder expects. At the same time, we use rough-finish grinders when we do not prioritize accuracy, like honing, shaping, simple tool shaping, etc.
• Hand and complex grinders: We may hold the workpiece materials as we machine them when using hand grinders. Usually, these workpieces require simple machining processes like honing or rough finishing. Conversely, we do not hold the workpiece when using complex grinders. Instead, we have a work-hold or spindle on which the material rests and passes through the abrasive wheels.
• Centered and centerless grinders: CNC centerless grinding machines have two parallel grinding wheels that rotate in the same direction but at different speeds. In this setup, we rest the workpiece on a fixture or work-hold supporting device, typically in the middle of the rotary wheels. This architecture opposes the traditional centered grinding machinery, where a rotary spindle holds the workpiece at the center.

Moving on, we have different types of grinders based on the abovementioned classes. They include bench, belt, pedestal, jig, tool and cutter, and cylindrical. There are others, too, depending on the CNC machining needs. However, we use these for grinding machinery.

Bench Grinder

A bench grinder is a hand grinder mounted on workbenches or benchtops. Often, these types of grinders don’t produce finishes as perfect as many other grinders, including its closest lookalike, pedestal grinders. For this reason, many factories use it for minor activities like honing or finishing cutting tool edges and shaping simple workpiece materials to be welded.

Pedestal Grinders

Instead of workbenches, pedestal grinders are mounted on bigger pedestals, giving them their characteristic name. Pedestal grinders have similar purposes to bench grinders. However, they finish materials better than bench grinders. Perhaps their complexity is why they best bench grinders.

Cylindrical Grinders

We use a CNC cylindrical grinder machine to shape the surface or OD of cylindrical or round workpiece materials. As a centered grinding machine, the workpiece is fixed on a spindle with a central axis of rotation. The abrasive wheel works on the material from the sides in various axes.

Like jig grinders, a CNC cylindrical grinding machine can shape materials of any size and perform grinding with repeatable accuracy. This also makes it an excellent CNC camshaft grinding machine.

Belt Grinders

A belt grinder is a belt designed like a motorcycle wheel. This belt is coated with abrasive, resembling sandpaper. We often use this type of grinder to remove simple burrs and edges, clean lathe tools, and shape and polish workpieces.

Sometimes, we merge belt grinders with another abrasive wheel to form a centerless belt grinder. Also, belt grinders may possess different forms or customization depending on the need. Popular examples include manual belt grinders, stroke belt grinders, platen belt grinders, etc.

Drill Grinder Machines

We use CNC drill grinding machines to make holes in workpieces. This grinding is a CNC ID grinding machine used to sharpen fluted drill bits and twisted drill lathe cutting tools in the factory. 

Jig Grinders

A CNC jig grinding machine is a CNC vertical grinding machine for high-precision and high-speed grinding. We usually use this machine to grind the ID and OD of workpieces with varying diameters or shapes more accurately than many other grinders. This makes the jig grinder an excellent CNC crankshaft grinding machine.

Tool and Cutter Grinders

A CNC tool and cutter grinding machine serves one purpose: to sharpen or hone milling and lathe cutting tools used by a CNC grinding machine operator. They are versatile tools used for workpieces with complex shapes and sizes. This contributes to their simple or complex customization. The complex types are usually the CNC tool grinding machines automatically controlled by 3D computer-aided manufacturing.

Centerless Grinding Machines

Although we touched on these earlier while classifying CNC grinders, we’ll add a few more. Centerless grinders are unique. We have three types: thru-feed, in-feed, and end-feed grinders. 

• In the thru-feed (or through-feed) centerless grinding process, we pass or feed the workpiece through the grinding wheel. As a result, the workpiece passes from one point of both wheels to another.
• In the end-feed process, we pass the material in the axial direction. As a result, the material moves back and forth through the center of the two wheels. There is usually a stop at which the workpiece rests and continues the process again.
• The infeed process uses a quite different and complex approach because of the type of workpiece material. Usually, these materials have different shapes or diameters. Because of this, infeed grinders are often customized to serve materials of different diameters.

Features of a CNC Grinder Machine

Every CNC grinding machine has at least one of the following features. The goal is to enable you to identify any grinding machine by its features or properties. Some CNC grinding machine specifications include:

Grinding Wheels

The most dominant feature of a grinding machine is the wheels. The wheel head acts on the workpiece, shaping or finishing it as desired or programmed in the CNC software or computer-aided designs (CAD).

Electric Motor

The electric motor converts the electrical energy in the grinding machine to mechanical energy to speed up the grinding process. As a result, electric motors ensure that we have adequate torque and power to facilitate CNC grinding.

Spindle

This is an essential feature of centered CNC grinding machines. It’s what distinguishes them from the centerless types. A spindle holds the cylindrical workpiece in position during machining and ensures it freely rotates or moves at the axis.

Work Rest

In centerless grinders, we use the work rest instead of a spindle. This work rest is adjustable and replaceable, depending on the need and machine customization.

Coolant

Finally, another prominent feature of most grinding machines is the coolant. The coolant of the setup comprises 

• A fluid (Petroleum-based, semi-synthetic, soluble, or oil-based): This fluid is usually recycled within the setup, ensuring constant lubrication, heat control, and reduced friction.
• A pipe or nozzle that showers the fluid on the machined workpiece. 
• And a tank holding the fluid. 

Workbench or Pedestal

A workbench or pedestal is a special table or surface where we mount the grinding machine. Workbenches are common with pedestal and benchtop grinders.

Essential Factors to Consider When Choosing CNC Grinding Machines

Ensure you keep the following in mind when choosing your CNC grinding machine. They’d guide you to choose right and on budget.

1. Workpiece Type

Before anything else, you have to know your materials. You do not want to use grinding tools meant for woodwork or glass machining for metallic materials. A good understanding of your workpiece material will give insight into the type of grinding machine to choose or buy. 

2. The Type of Grinding Machine

The next box to check is the type of grinding machine to choose. But before that, you should clarify your purpose for selecting the grinding machine you have in mind. 

Different grinding machines serve different purposes. And the type of machine you choose must align with the machined materials.

The versatile or complex grinding machines usually cost more. So, if you’re on a budget, ensure you know why you need the machine so you do not buy or choose an undesired grinding machine.

3. Grinding Wheel Type, Size, and Material Composition

Once you’ve settled on the purpose of the grinding machine and the kind that serves such purpose, you can pick the wheels with the best abrasives or abrasion capacity. Abrasives are what finish or shape materials. So, the type of abrasive on the wheel must depend on the grinding purpose and workpiece material type.

3. Ease of Machine Part Replacement or Maintenance

Another way to choose right is by confirming how easy it is to replace or maintain machine parts when faulty. That is the only way to ensure a longer-lasting CNC grinding machine.

4. Budget and Pricing

To stay within budget, you must consider the workpiece material and the purpose of the grinding machine. Considering these factors will help keep you in line with your budget. You’d know which machines to go for and have a specific pricing in mind. 

Before that, do market research to know the current prices of the grinding machines you want. Or, better still, you could request a quote from a reputable dealer.

5. Reputation of the Manufacturer or Supplier

The reputation of the CNC grinding machine manufacturer precedes them. This is why buying products with social proof or recommendations is important. Don’t just buy any product with shiny or glamorous features; ensure that the promises are as-is when you begin to use the machine.

6. Ease of Use and Understanding of Machine

Of all the other considerations, make you know how to control and manage the machine you choose. Otherwise, buy those with handy manuals and easy controls or usage. It will save so much stress and even the cost of hiring a professional when you could’ve easily done the job yourself.

7. The Level of Precision Grinding You Need

As mentioned earlier, different grinding machine classes have different purposes and needs. Do you need a high-precision grinding? Or is a rough-finishing or honing you need? You must be clear about the level of precision grinding you need. This will depend on the workpiece material and what your machining expectations are.

8. Coolant System

Coolant are another essential component of CNC grinder machines. They ensure that the heat capacity of the system remains constant. Also, they remove the chipped materials from the workpiece and wheel head.

You must choose the type of coolant you use carefully. Fortunately, we have different kinds, varying in cost and purpose. They are petroleum or synthetic coolants, soluble coolants, oil-based coolants, and hybrid coolants. For instance, a soluble coolant would be great if the material you’re machining has gummy petroleum residues.

Additional reading:
What is CNC Machining? 3 Axis | 4 Axis | 5 Axis - RGBSI Blog

For more CNC shaft turning machineinformation, please contact us. We will provide professional answers.

9. Automation features of the machine

As CNC grinding machines, we must always remember the automation and computerized components. As modern-day machining tools, we must consider their compatibility with the tools at our disposal.

Different manufacturers may have different software that is not compatible with one another. You must ensure these coasts are clear before replacing damaged CNC machine parts or automation features. 

How Much Does a CNC Grinder Cost

To crown the information we’ve realized in this guide, let’s see the CNC grinding machine price estimate. 

Note that we cannot give a specific price for CNC grinders due to the fluctuating global market and currencies. However, we can estimate their prices based on their use and functionalities.

• CNC cylindrical grinding machine price: Used CNC cylindrical grinding machines are commonly available. Their high supply may contribute to their lower prices. Their prices start from $2,000 for simple cylindrical grinding machines to over $50,000 for complex CNC types.
• Bench grinders price: These grinders are simple and readily available. You could get them between $80 and $, depending on the quality and brand. 
• Belt grinding machine price: Belt grinders, like bench grinders, are simple machines. However, their prices begin at $500 for simple grinders and over $10,000 for complex ones like the CNC centerless belt grinders.
• Pedestal grinding machine price: You could get a pedestal grinding machine from $250 for second-hand grinding machines to $2,000 for higher types.
• Jig grinding machine price: We often hire or rent jig grinding machines due to their high prices. But if you need a custom jig grinder for grinding needs, then you should budget above $100,000 
• CNC tool and cutter grinding machine price: These are simple machines. Nevertheless, there are bigger and more complex CNC types. You’d find prices between $400 to over $5,000.

Conclusion

CNC grinding machines may be similar in use case but have strikingly different purposes. Without careful consideration, you may choose a CNC machine for grinding for the wrong reasons. 

Hopefully, this CNC grinding machine buyers’ guide has shown you everything you need to know to make the right choice, including the potential prices of respective grinding machines.

Centerless grinders are the unsung heroes of the machining world, providing key advantages in roundness, diameter and surface finish that aren’t achievable with lathes and mills.

Despite the critical role it plays in metalworking, centerless grinding is often only faintly understood. Common misperceptions abound that can have a material impact on your part quality and overall productivity.

To demystify the process, here are seven basic principles related to centerless grinders.

1. Deceptive simplicity combined with peerless precision.

Centerless grinding works thanks to a few basic principles of physics.

A grinding wheel and a regulating wheel hold the workpiece in place on a stationary work rest throughout the grinding process. The workpiece is held in place by the pressure of the rotating grinding wheel and the smaller-diameter regulating wheel, with the centerline of the workpiece sitting higher than that centerlines of the two wheels.

“Setting the right height of the work rest is critical to ensuring the correct placement of the workpiece to achieve the necessary roundness and diameter tolerances,” said Dan Geddes, president of GCH Tool Group.

Once grinding begins, the difference in the two wheels’ rotating speeds determines the speed of the removal rate.

“The greater the difference, the faster the removal,” Geddes said. “Furthermore, since no fixturing is needed, centerless grinders require a simplified setup and allow quicker turnaround times.”

Their fast load time, in turn, means centerless grinders operate virtually continuously compared to other forms of machining, he said.

Despite this simplicity, centerless grinders are well-suited for finishing the outside diameter of small cylindrical metal parts requiring tight tolerances. Because they can grind consistently at high speeds, these grinders also are ideal for high-volume applications that require high levels of precision.

“Examples include applications in the medical, aerospace, military and automotive industries,” Geddes said.

2. Where machining ends, centerless grinding begins.

Centerless grinders address the limitations of machining related to dimensions, materials and surface finishes. Basically, centerless grinding takes up where machining leaves off.

“Centerless grinders save the day when it comes to parts that are out of round from a turning machine,” Geddes said. If the part diameter is too small for turning or its center can’t be mounted, centerless grinding can achieve the necessary roundness.

Furthermore, because centerless grinders create no axial thrust on the workpiece, they’re well-suited to grind long pieces of brittle materials that would distort on a lathe or mill.

3. Choosy grinders choose the right wheel.

It’s critical to select the grinding wheel that works well for both the material being ground and the type of finish desired. Wheels are available with different:

• Diameters
• Thicknesses
• Grit sizes
• Grains

“Grit size has a direct impact on the surface finish,” Geddes said. “The smaller the grit, the finer the finish will be.”

Grain types include superabrasives like cubic boron nitride (CBN) or polycrystalline diamond, which provide important benefits like prolonged sharpness, high thermal conductivity and superior durability.

4. Getting the right angle.

Angles and roundness don’t sound like they’d go together, but the proper roundness and tolerance of a workpiece depends on the angles at which the wheels contact the part.

Uneven wear, tapering and reduced wheel life can result if the angle of the regulating wheel is too acute. If the regulating wheel is nearly parallel with the grinding wheel, parts can stall between the wheels or crash.

The angle of the workpiece rest blade also needs to be just right to ensure proper grinding. The width of the grinding wheel is a deciding factor in what that angle should be, with larger wheels generally requiring smaller angles.

5. Cool it for the best results.

Centerless grinding creates a lot of heat, and coolant is needed to remove heat from critical components of a centerless grinder.

Pressurized coolant keeps the grinding wheel at the appropriate temperature, so it won’t crack or blister. The coolant also prevents heat from returning to the workpiece, an important factor since high temperatures can make it difficult to hold roundness and straightness tolerances.

For 24/7 operations, a chiller might be needed to remove heat from the coolant and other fluids, Geddes said. “A coolant filtration system is also useful as it removes swarf and keeps the coolant free of grinding medium particles.”

6. Different feeding methods for different jobs.

There’s one main difference between the two most common forms of centerless grinding: the way in which the workpieces are fed through the grinders.

For parts like gear shafts that have complex shapes, in-feed grinding is the usual choice. In this method, the grinding and regulating wheels need to be dressed to match the part profile, and the work rest must be tooled to match, as well.

For parts with consistent roundness, through-feed grinding is normally used. Driven by a slight angle applied to the regulating wheel relative to the grinding wheel, the workpiece moves along the work rest between the two wheels.

7. Adaptability is the key.

Some centerless grinders have been around for decades. But that doesn’t mean they’re headed for the scrap heap. Centerless grinders are well-suited for upgrades and retrofits, like automation and loaders, electronic machine controls or a servo-drive transmission.

“New technologies allow older centerless grinders to adapt to today’s production demands,” Geddes said. “Upgrades allow these machines to perform better than new.”

Other options include:

• Electronically controlled diamond advance
• Servo infeed systems
• Single screw swivel adjustment

Bonus Tip: Experience matters.

While the basic concept of centerless grinding is simple, there are a variety of critical actions – for instance, properly setting the angles of the wheels and work rest or selecting the right grinding wheel – that have a material impact on the final product.

It’s important to find a partner that not only has extensive experience with centerless grinders but also has a clear understanding of your production needs.