Manual vs CNC grinding machine: guide to choosing

Choosing between a manual grinding machine and a CNC grinding machine does not just mean comparing two technologies or two price bands. The correct question is another:
for the tools, volumes and organisation of your workshop, is a manual or a CNC suitable?

A manual machine can still be adapted in simple, consolidated and well-manned production contexts by experienced personnel. However, when the complexity of the tools, the use of hard metal, the need to obtain repeatable results or the difficulty in transferring skills from one operator to another increase, CNC becomes a more solid and future-oriented choice.

Editing: Cuoghi Grinding Machines

This in-depth study has been developed starting from the technical and commercial experience gained by Cuoghi Tool Grinding Machines in the design, use and training on manual and CNC grinding machines, integrating the cases and needs found directly at the customer workshops.

What to know before choosing: Manual grinding machine or CNC grinding machine?

A manual grinding machine may suffice when working mainly with simple HSS drill bits, the quantities are limited and the company already has an expert operator. It can also be immediate for the occasional grinding of a single standard tool.

A CNC grinding machine, on the other hand, is more suitable when you need to reproduce modern geometries, work tools in hard metal, manage the same sets of tools or reduce dependence on the manual skills of a single person.

For many workshops, the choice is not only about what they have to grind today. It is also necessary to assess how the tools, processed materials, production volumes and skills available in the company will change in the coming years.

Comparison of manual and CNC grinding machine

Criterion	Manual grinding machine	CNC grinding machine
Initial investment	Generally lower	Higher, but to be assessed on the overall cost of the process
Operator	Requires experience and manual skill	More software-driven process
Repeatability	It depends on the person performing the grinding	Elevated even by changing operator
Single simple tool	It can be more immediate	Affordable if the program is already available
Series of identical tools	Requires the continuous presence of the operator	Greater efficiency and consistency
Complex geometry	Limited possibilities	Greater ability to reproduce
Hard metal	Only manageable in applications and with specific machines	Preferred solution for modern tools and high performance
Operator time	Operator engaged during the entire process	Possibility of carrying out other activities during the cycle
Memory of machining	Know-how remains above all in the experience of the operator	Programs and parameters can be stored and recalled
Future evolution	Suitable for stable and limited needs	More flexible than tooling evolution

The first criterion: which tools you need to grind
When a manual grinding machine is enough
When CNC becomes the most effective choice
HSS and hard metal: what changes in grinding
Accuracy and repeatability
grinding times and productivity
Skills and training of the operators
The most common faults
Four- or five-axis CNC grinding machine
How to evaluate costs and convenience
Three practical scenarios of choice
Which Cuoghi grinding machine to consider
Manual or CNC: the questions to ask

The first criterion: which tools should you grind?

The price of the machine is important, but it should not be the first element to consider.

The starting point must be the type of tool:

what material you need to grind;
what geometries you must reproduce;
how important it is to maintain the performance of the original tool;
how many variants you need to manage;
how often the same work is repeated.

A standard HSS drill bit, used in carpentry or in traditional machining, has different requirements than a modern hard metal drill bit used with high speeds and advances.

Similarly, grinding the head of a cutter is not equivalent to completely reconstructing its external and internal geometry.

Therefore, it is not the CNC that is always better: it is the tool to be worked on that determines how important the technology of the machine becomes.

The main difference is in the ability to reproduce the geometry. A modern tool is designed with angles, clearances, thinning and profiles that directly affect the behaviour during processing. If grinding modifies them excessively, the tool can continue to cut, but not necessarily with the performance for which it was purchased.

When a manual grinding machine is enough

The manual grinding machine maintains a precise role, even if today its field of application is more limited than in the past.

It can be a consistent choice when:

the workshop mainly uses standard HSS drill bits;
the tools have simple and consolidated geometries;
the number of grindings is limited;
above all, occasional interventions are carried out;
there is already an operator with good experience;
the production process is not destined to change in the short term;
the initial cost represents the main constraint.

A typical case is that of some mechanical structural work. In certain processes on sheets and profiles, traditional HSS drill bits are still used, also because more rigid and fragile tools may not be suitable for the working conditions.

In situations of this type, a machine such as the APE 40 UP can effectively respond to the needs of the workshop without introducing a non-essential level of automation.

The machine is not always the limit

A very experienced operator can achieve high level results with a manual grinding machine. The problem is that the quality of the process remains strongly linked to its experience.

The operator must recognize the initial geometry, set the machine correctly, check the removal and repeat the movements consistently. This capability builds over time and is not automatically transferable to a colleague.

The machine can then still be fully functional, but become unusable when those who know it leave the company.

In our experience it happens that workshops equipped with manual grinding machines purchased many years before require new training after the retirement of the traditional operator. The machine is present, but the know-how necessary to use it is no longer available.

This is a cost that is rarely considered at the time of purchase.

When CNC becomes the most effective and future-oriented choice

The switch to CNC becomes rational when the needs of the workshop can no longer depend on the manual sensitivity of a single person.

The conditions that make CNC particularly suitable are:

regular use of hard metal tools;
geometries that have evolved or are different from one another;
need to obtain uniformly ground tools;
processing of small or large batches;
frequent change of operators;
difficulty in finding already specialised personnel;
there is a need to archive and recall work;
expected growth in tool variety or value.

In these cases, the CNC is not only a more modern way of carrying out the same operation. It changes the way grinding is organised within the company.

The process does not remain in the operator’s memory

With a CNC machine, the parameters used for a tool can be saved and recalled for subsequent cycles.

When you have to grind a drill bit from the same range, but with a different diameter, it is not always necessary to start from scratch. You can duplicate an already validated program and edit the necessary parameters.

In this way, part of the know-how becomes the company’s heritage and does not remain exclusively in the hand of the grinding machine.

Technical experience continues to be important: you need to understand the tool, select the correct grinding wheel and check the result. However, once the process is defined, its repetition is less exposed to the differences between one operator and the other.

The choice must also consider future needs

A company that today uses almost exclusively HSS drill bits might consider a manual machine sufficient.

Before purchasing, however, you should ask yourself if, in the medium term, you will switch to hard metal tools or to more advanced geometries.

The risk is not to buy a manual machine incapable of carrying out the immediate work. The risk is to realize after a few months that the machine purchased meets today’s needs, but not the one towards which the workshop is already moving.

We met companies who, after purchasing a manual, saw a four-axis CNC machine in operation at a customer or supplier and recognised that this would be the right solution for their process. In some cases, the switch to CNC took place when the manual was still almost new.

Saving on the initial investment is not convenient when it leads to supporting two investments in succession.

HSS and hard metal: what changes in grinding?

HSS drill bits continue to be used in numerous applications. They are generally less expensive, tolerate heavy working conditions and, when the geometry is simple, can be re-ground with good results even on manual machines.

Hard metal tools, on the other hand, have different performance and costs. They allow you to work with high cutting parameters and, precisely for this reason, require precise geometry.

The point is not to establish whether a manual machine can physically grind hard metal. Some specific machines can do this.

The question to ask is:

does the grinding manage to reproduce a geometry close enough to the original one to maintain the performance of the tool?

If the geometry is simplified, it may be necessary to reduce speed and feed to avoid premature wear or breakage. This way, part of the advantage for which the hard metal had been chosen is lost.

For this reason, when hard metal represents a structural component of production and not an occasional use, the CNC machine normally becomes the most consistent solution.

Accuracy and repeatability are not the same thing

A manual machine used by an expert operator can produce an accurate tool.

The question changes when it is necessary to obtain:

the same result on ten, fifty or one hundred tools;
the same geometry on different days;
a uniform result even if the operator changes;
a verifiable and reproducible process.

This is where the repeatability of the CNC takes on greater value.

On a manual machine, two operators can interpret or perform the same grinding in a slightly different way. The same operator can also produce variations between the beginning and the end of a series.

With the CNC, once the program, the grinding wheel and the positioning have been verified, the cycle is repeated according to the same parameters.

Repeatability produces benefits that go beyond the visual quality of the drill bit:

more uniform behaviour when drilling;
greater predictability of the duration;
waste reduction;
less need for corrections;
greater stability of the production process.

For a workshop manager or production manager, this value may be more important than the speed of the single cycle.

grinding times and productivity: is CNC getting increasingly fast?

Not necessarily.

If only one simple HSS drill bit needs to be ground and there is no dedicated program yet, an experienced operator can finish the job on a manual before a new CNC cycle is set.

This observation is important because it avoids an unrealistic comparison.

However, when the program is already available or the tools to be ground are more than one, the advantage of the CNC machine grows rapidly.

The operator can:

retrieve the program;
change the few required parameters;
positioning the tool;
start the cycle;
engage in other activities.

On a manual machine, on the other hand, it must remain engaged during the entire grinding.

The value of hidden time

In some workshops, CNC grinding machines are placed next to machines with longer processing cycles.

While the main machine is working, the operator prepares or starts grinding other tools.

The grinding machine cycle time does not disappear, but is superimposed on a time during which the person would still be engaged in another process.

This use in hidden time allows you to:

increase the number of activities managed by the same operator;
prepare the necessary tools for the following cycles;
reduce unproductive times;
using the machine without creating a dedicated full-time workstation.

Therefore, to assess productivity, it is not enough to compare how many minutes the grinding wheel takes.

It is also necessary to measure how long the operator must remain in front of the machine.

Skills and training: does a CNC require a more specialised operator?

It is one of the most common objections, but the answer depends on the type of CNC.

A four-axis machine designed for in-house use in the workshop may be easier to learn than you would imagine if you’ve never worked with a numerically controlled grinding machine.

After the initial training, the operator can begin to manage the usual machining, especially when the machine is prepared using the customer’s real tools and programs consistent with his needs.

Full mastery requires practice, in particular when expanding the types of tools to be machined. However, this is different from having to develop the manual skills of an experienced grinding machine for years.

A five-axis CNC presents greater possibilities, but also a more articulated programming. It must be evaluated when the complexity of the tools justifies the higher level of control.

Training must start from the customer’s tools

During start-up it is not enough to explain the general controls of the machine.

It is useful to:

analyse the drill bits and tools actually used;
recognise the different geometries;
prepare dedicated programs or macros;
check which parameters to modify;
explain how to check the result;
clarify which grinding wheels to use.

The goal is not to teach the operator to apply the same standard grinding to each drill bit. It is to put it in a position to recognize the differences and reproduce, as far as possible, the correct geometry.

The most common faults on manual and CNC grinding machines

Automation reduces some errors, but does not eliminate the need to work carefully.

Typical errors in manual grinding

Among the most frequent errors are:

insufficient tightening of the tool;
excessive removal in a single passage;
overheating of the material;
failure to reproduce the original geometry;
differences between one cutting edge and the other;
application of the same grinding to different tools.

Too aggressive removal can overheat or “burn” the tool, reducing its performance during processing.

Typical CNC grinding errors

On a CNC the errors are generally different:

selection of an unsuitable program;
insertion of incoherent parameters;
assembly of a grinding wheel different from the one indicated in the program;
incorrect identification of the tool;
insufficient control of the initial geometry.

The sensor and the software can intercept some dimensional inconsistencies and interrupt the cycle.

However, they cannot know that a grinding wheel has been physically mounted that is different from the one provided.

The CNC controls the process, but always works on the basis of the information and tools provided to it.

Four- or five-axis CNC grinding machine?

After determining that CNC is the most suitable solution, a second choice remains: four or five axes.

When a four-axis CNC is enough

A four-axis machine such as the MAC 20 or MAC 26 is designed for companies that want to manage HSS and hard metal drill bits in-house, as well as specific machining on milling cutters, taps, countersinks, reamers and other tools.

The electronic probe allows the tool to be detected and positioned, while the programs can be stored and recalled for subsequent cycles.

For many workshops this is the most balanced solution between investment, operational simplicity and grinding capacity.

When five axes are needed

A five-axis CNC such as META is indicated when it is necessary to work more complex geometries or intervene on several parts of the same tool.

A milling cutter, for example, may require machining on the head, on the outer diameter and inside the groove. When it is necessary to completely reconstruct geometries of this type, the five axes expand the possibilities compared to a machine designed mainly for grinding drill bits and for operations more limited to milling cutters.

The choice of the five axes must therefore derive from the tools to be machined, not from the idea that a greater number of axes is automatically better for any workshop.

How to evaluate the costs and convenience of the investment

There is no number of monthly tools beyond which CNC automatically becomes convenient.

Two companies that grind the same number of drill bits can come to different conclusions.

The convenience depends on:

value of tools;
material and geometries;
re-grinding frequency;
operator’s hourly cost;
time during which the machine must be manned;
need to maintain spare tools;
urgency with which the tool must return to production;
cost of errors;
expected growth of the workshop;
specialised personnel are available.

The purchase cost is only part of the calculation

To correctly compare manual and CNC it is useful to consider the total cost of the process:

investment in the machine + operator time + training + consumables + waste + unavailability of tools + risk related to loss of skills.

A manual machine has a lower initial price, but may require a more constant presence of the operator and expertise that is difficult to replace.

A CNC requires a greater investment, but can reduce:

the time monitored;
the differences between the operators;
tools discarded due to incorrect grinding;
the need to outsource some work;
the times necessary to make the tool available.

The economic distance between a professional manual and a four-axis CNC can also be less decisive than it appears when compared to the total cost of tools and production.

Quantity or immediate availability?

A company can justify a CNC because it grinds many drill bits every day. Another may grind a few, but need a specific tool to be available immediately.

In the second case, the value is not represented by the absolute number of grindings, but by the cost of a stopped production machine or a delayed delivery.

For this reason, the return on investment should not be calculated only by dividing the price of the machine by the average cost of outsourced re-grinding.

Three practical choice scenarios

Scenario 1: structural work with standard HSS drill bits

The company mainly processes sheet metal and profiles. It uses traditional HSS drill bits, performs occasional grinding and already has an experienced person.

In this case, a manual grinding machine may be enough. The process is stable, the geometries are simple and the CNC would risk being underused.

The assessment must change if the operator near the boarding house is the only one who knows the machine or if the workshop plans to modify tools and machining.

Scenario 2: workshop using hard metal drill bits

The company uses modern tools, needs uniform results and wants to regrind in-house without building a specialised structure.

In this case, a four-axis CNC is normally the most consistent choice.

It allows you to work with memorable programs, reduce dependence on manual skill and manage grinding during other production activities.

Scenario 3: company that processes milling cutters and complex geometries

The company must intervene not only on the milling cutter head, but also on the external diameter, on the grooves or on special geometries.

A four-axis CNC could cover only part of the process. When it is necessary to manage the tool completely, it is advisable to evaluate a five-axis CNC.

In this scenario, buying a simpler machine just to reduce the initial investment risks leaving some of the work outsourced anyway.

Which Cuoghi grinding machine to evaluate?

APE 40 UP

To consider for:

HSS twist drill bits;
taps and countersinks;
traditional geometries;
workshops with manual skills already present;
occasional grinding or contained quantities.

Discover the APE 40 UP manual grinding machine

MAC 20 or MAC 26

To consider for:

HSS and hard metal drill bits;
management of modern geometries;
repeatable programs;
reduction of dependence on the operator;
in-house grinding integrated into the production department;
specific machining on milling cutters, taps, countersinks and reamers.

Discover the MAC 20 four-axis CNC grinding machine

Discover the MAC 26 four-axis CNC grinding machine

Manual or CNC: the questions to ask yourself before buying

Before you choose, please collect the following information:

What tools do you need to grind?
Do you predominantly use HSS, hard metal or both?
Do you have to reproduce standard or complex geometries?
Do you occasionally grind individual tools or repetitive sets?
Does the result have to remain the same even if the operator changes?
Do you already have experienced manual grinding personnel?
What would happen if that person left the company?
How much does the operator’s time spent on the machine cost?
How important is it to have the tool immediately available?
Do you plan to increase the use of hard metal?
Do you just have to work specific drill bits and parts of the milling cutters or do you have to rebuild complete tools?
Will the machine chosen today still be suitable in five years’ time?

If needs are simple, stable and already managed by competent personnel, a manual can continue to be a rational choice.

On the other hand, when the complexity of the tools, the request for repeatability, the value of the operating time or the risk of losing in-house skills increase, CNC is normally the most effective solution.

Conclusion: do not choose only on the basis of price

A manual grinding machine and a CNC do not simply perform the same job with a different level of automation.

The manual retains value in simple and consolidated processes. The CNC, on the other hand, makes grinding more repeatable, transferable and consistent with the evolution of modern tools.

The final question should therefore not be:

“Which machine costs less?”

but:

“What machine allows me to correctly manage today’s tools without restricting tomorrow’s workshop?”

To find the right solution, it is necessary to start from the real tools, materials, geometries and production organisation.

Contact Cuoghi Tool Grinding Machines and describe the tools you need to handle: we will evaluate together if your needs require a manual machine, a four-axis CNC or a five-axis solution.

Manual or CNC grinding machine: differences and selection criteria