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Energy use should be normalized against usable parts rendered. Is there any analysis of finished part rejection rates for CNC versus manual methods?

You point out that 7 times more energy is used to produce steel than to machine it. To what extent does using CNC tools allow you to reduce raw material usage? This might be achieved with more complex part designs that are difficult for a human operator to produce, but trivial to a computer reading a 3-D model.

If control and maintenance overhead is a major factor in the energy use of CNC tools shouldn't you include the energy cost for the care and feeding of 3 shifts of human operators for manually-operated machine tools? I know that sounds a bit crass, but in commercial operations that cost is a huge consideration.

Minor Heretic


Matt has a good point: material use efficiency.

This reminds me of a service provided by the operator of a CNC plasma cutter. They had a program that would take a set of part designs and optimize the layout on a rectangular sheet of metal. Minimum cutting waste. At 10:1 material to milling embodied energy it wouldn't take much in the way of savings to tip the scale.

Part of the problem is that we don't pay the true cost of energy, especially electricity. The health costs of power plant emissions, for example, are 1.4 to 3.4 times the retail cost of electricity in the U.S. In some states downwind of a lot of coal plants the health cost is more like 10 times retail. I can't even imagine what China pays (or fails to pay) for the health costs of industrialization.Including the externalized costs would adjust manufacturer attitudes towards efficiency.

Kris De Decker


@ Matt & Minor Heretic

Material use efficiency is a major factor for 3D printing. (Which is far from a useful manufacturing technology today.) But even then, since producing a part using a 3D-printing machine costs 50 to 100 times more electrical energy than producing the same part by injection molding, it remains to be seen if total energy use would be lower.


I don't see how a CNC milling machine would reduce raw material usage in a significant way compared to a manual milling machine, or how a laser cutter would reduce raw material usage in a significant way compared to a CNC punching machine.

If anyone has an analysis that shows the opposite, feel free to post it here. In all the studies I consulted, material use efficiency was not mentioned as an advantage of CNC or non-conventional machine tools.

By the way, you could use exactly the same software program to calculate the optimal layout on a rectangular sheet of metal, and then cut it out using a manual machine, no?

Floris Van Cauwelaert


Thanks for the amazing article. Have to let that marinate a while. Quick question: what if, with renewable energy, we are able take the energy consumption out of the equation? I still feel there could be real opportunity for repair, remanufacturing, creating goods with higher value etc. Secondly, the technology becomes available and cheaper fast, environmentalist have a task of helping to find the most useful applications (and preventing a new wave of gadget-culture). Kind regards, Floris



This rings close to home, as my tiny company builds an open hardware book scanner using CNC techniques. See http://diybookscanner.eu .

Environmentally speaking, I'm not sure we're doing as well as I intend. Producing by CNC in a faraway corner of the EU. This is low power wood CNC work, but still. Shipping directly to individual customers all over the EU. I'm flying to Latvia regularly myself (trains take 44 hours and go through Belarus -> transit visa). We do try to minimise plastic packaging.

Do you happen to know about organisations that offer broad eco-analysis for small companies on a budget? I'm thinking production, shipping, product lifecycle, ...



Great article but only looking at the onsite part of the energy lifecycle is a bit narrow. couple of the more value driven objectives with these fabrication tools is 1. the decentralisation of production which is currently dependent upon shipping materials all across the globe and then parts from different places etc. and 2. production in response to demand rather than our current model which is production as a route to creating demand and which often creates unnecessary surpluses. 3. there are lots of other non energy related stuff like shifting control of production out of the hands of corporations and into the hands of people etc etc..

Better life cycle analysis of full material/energy inputs/outputs are needed and scenario testing etc. its good to be asking these questions though.

I have to say that even if you did a full life cycle analysis i still think that localised digital production would be more carbon/energy intensive than most mass produced long supply chains but the analysis would help understand when its most appropriate.

Mr. Downer


This is a FANTASTIC article, and we need more of this sort of analysis as these new tools come on line, because once they are adopted en masse it will be too late.

In my line of work (architecture) these tools promise to "liberate" design thru making previously difficult forms (compound curves, etc.) much easier to produce - but no one is asking, at what cost?

Specifically, if embodied energies are multiplied orders of magnitude, with a concurrent rise in demand for novelty for novelty's sake (see, for example, the ungodly & unnecessary variety of tennis shoes as one glimpse into this phenomenae) things like flat glass, straight rolled steel, and other relatively low-embodied production technologies may come to be seen as inferior by criteria that are wholly uninformed by energy and resource concerns.

I imagine there are realms where laser sintering, for example, can actually result in a net energy savings, but we as designers should remain cognizant of the demands so thoughtfully described in this piece, and be careful what we wish for in terms of "freedom": a world depleted of resources so that humans can "play with form" will be a truly pathetic end, and about as damning of indictment possible for the relatively small cadre entrusted with the creation and maintenance of the built environment.

Andrew Langford


Interesting - I am a small scale shoemaker making mostly standard sizes and fittings but about one third of production is made-to-measure(m-t-m). It is these that I am trying to bring down in cost as, it is not only rich people who have feet that don't fit standards (!).

Building the lasts (the formers over which boots and shoes are made) is one challenge - starting with a standard last I add patches of leather held down with masking tape. This may take upwards of an hour per foot(these patches get stripped off the last at the finish and, whilst they can be saved for future use, they are not easy to re-attach and get a good result.

Then comes the pattern cutting - again, working out from standard patterns helps but I can't use the standard pastry-cutter press knives and my cutting press to cut the leather - this has to be done by hand. Making patterns and hand cutting adds another couple of hours to the process.

My standard soles don't fit, of course, so I either use oversize units and throw away considerable waste or hand-cut again - this is tough to do and not good for hands and arms.

I had been thinking to 3D print lasts, use photo imaging to get to the patterns and then use CAD controlled laser cutting for leather and sole patterns (or, maybe, 3D print soles so as to allow me to make 'bumper' soles like those you'd see on many walking sandals - Merril, for example - these days).

I'd not expect this to be a solo operation but one owned by a connected network of shoemakers.

As far as your energy analysis is concerned I'd imagine that, whilst the 'machining' might be super energy intensive the whole life picture (locally made shoes that fit, can be repaired, are comfortable and not a mega price - you may not know that 30% of folk don't wear out their shoes but break them by spliting out the sides because the shoes don't fit - shoes that fit last 8 to 10 years a pair with resoling every 2 years) still looks better regards ecology than importing Chinese made (child labor?) throw-away jobbies ....

Would love to do the analysis in detail but time is pressing ...



Great article, thank you very much. Someone mentionned the energy cost of a human person. Just to get a feel here is my attempt to compute - at least an order of magnitude of - the average power spent during a day with light body work:

3000 kcal / 24 hours converted to watts, assuming 4.2 J per calorie:

4.2 * 3e6 / (24 * 3600) = 145.8 W

Even when considering peaks during the actual work, this average remains ridiculously small compared to the kW values discussed here.



Mmm however you have to grow and bring the food and water to the person, which may add quite a bit.

Kris De Decker


@ G

People have to eat whether they are operating machines or not. Unless the aim is to make a world ruled by machines, and to exterminate all humans, the energy required to feed the human operator is of no significance at all.

Kris De Decker


@ ShaneHughes

Concerning your three points:

1. "the decentralisation of production which is currently dependent upon shipping materials all across the globe and then parts from different places etc."

But you still need to ship raw materials... Digital fabrication differs from digital information technology in that sense. I agree that the current logistics of global production wastes energy. But you don't need digital machine tools to solve that. You could perfectly obtain a more decentralized production with non-automated machine tools.

2. "production in response to demand rather than our current model which is production as a route to creating demand and which often creates unnecessary surpluses."

Maybe, but at the same time the new possibilities offered by digital technology will create new demand.

3. "there are lots of other non energy related stuff like shifting control of production out of the hands of corporations and into the hands of people etc etc.."

We have been able to make everything ourselves for decades, using hand-operated machine tools. These tools are cheaper to buy, cheaper to operate, and can actually do more useful things. If you want to shift control of production into the hands of people, you should support tool libraries, hackerspaces, and makerspaces, and especially those that focus on more conventional tools and less on digital machines.

Kris De Decker


@ Floris

It's more realistic to operate human-controlled machine tools on renewable energy, because they require much less power. The potential of renewable energy is limited, for many reasons. That's why it is so important to move towards technology that is less powerful, not more powerful.

Roland Smith


The article states that “CNC machine tools can convert a digital design into an object with the click of a mouse, which means the production process is completely automated.”

As a mechanical engineer who has operated manual lathes and mills and has programmed CNC mills I can state that unfortunately, this is far from the truth. To make something on a CNC mill, someone has to make a 3D CAD model first. This then has to be converted into machine code for a specific CNC machine with the help of a CAM program. While this software can perform the drudgery of generating toolpaths, it is up to the operator of the CAM program to select the surfaces to be milled in a single operation, the milling strategy, what tool to use for it and the milling parameters. This requires considerable insight and experience. Any new CAM programmer generally manages to ruin at least one spindle (which can easily run in the tens of thousands of dollars).

There are some key differences between manual and CNC machines that has been overlooked in this article. CNC machines are capable of making parts that are hard or impossible to make on a manually controlled milling machine. An operator on a manual machine can only move one axis at a time, while a CNC controlled machine can move three or more axes simultaneously. The only pre-CNC machines that come close to that capability are copy milling machines, where a template guided the movements of the machines in generally two axes simultaneously. But that is hardly a “manually” operated machine. A second point is that CNC milling machines are generally capable of much tighter tolerances than a manually operated machine. For relatively small parts (say up to 50 cm) that can be milled from a sufficiently stiff material in a single clamping, I tend not to bother with making elaborate drawings anymore or spend much time about specifying tolerances. A well-maintened CNC mill is capable of delivering tolerances in the 0.05 mm order over such a part.

The comparison of the four machines listed in the table is one of apples and oranges. A machine with a 22 kW spindle (power for “material removal operations”) has different capabilities and is used for different parts than a mchine with a 2 kW or 6 kW spindle. It is like comparing a scooter to a truck.

For a company that owns a milling machine in the western world, in general the most expensive part (expressed in hourly rate, which includes electricity costs for the machine) is the operator. So the trend driven by economics is to use the machines unmanned as much as possible.

Amos Blanton


"A fully automated machine will always consume more energy than a semi-automated machine. So, choosing fewer automated manufacturing technologies should be at least part of the solution."

I think this statement is an oversimplification. It may be true that the difference in energy costs between the two methodologies is high now, but much of that difference may be a result of our current culture of extravagance towards energy usage. A Raspberry PI computer, at approx. 2 watts under load, should be more than capable of handling the computational requirements of most CNC machines (They just aren't doing very computationally intensive work.) So if the energy costs at idle are high, it's most likely down to manufacturers not seeing a clear cost / benefit advantage to minimizing idle power consumption.

I suspect that if most of these machines were designed for an environment in which energy cost was a larger factor of total cost, they would be much more efficient - at least at idle.

Jeremy Faludi


This's an impressively-researched article. However, I have to argue they came to the wrong conclusion in a couple places:

First, I've actually read the Dahmus & Gutowski paper they cited on CNC mill energy use, and the conclusion they came to is _not_ the conclusion Dahmus & Gutowski came to. Their main conclusion was that even the biggest CNC milling energy use was much smaller than the embodied energy of the materials being cut. They say, "the embodied energy per cubic centimeter of input material is around 590 kJ/cm3, or 40 to 120 times larger than the material removal energies" for aluminum, and around 25x for steel. …So at that point, who cares what the CNC machine is doing?

Second, the author's claim that "Automated machine tools can never become as energy efficient as their hand-controlled counterparts" is just not true. By his own quote of their data, "the human controlled machine requires 6.2 kJ of energy to remove one cubic centimetre of material, while the CNC milling machines require 4.8 to 7.1 kJ of energy". (And the manual operation number's not counting the environmental impacts of a person commuting to work, requiring extra factory floor space, etc.) So CNC is sometimes better, sometimes worse.

Third, he says increasing productivity won't help environmental impacts, "power use increases as the material removal rate does." But he's forgetting his earlier quote that 85% of the power use was the same whether the machines are running or not—therefore making more parts in the same time will lower eco-impacts per part, even if you double the 15% of machine power used by the actual cutting. He worries about idle time, but then quotes "these types of machines are often operated 24 hours per day and are idling less than 10% of their total life time."

Fourth (or, second part of third), he argues "an increase of the production rate also implies an increase in material use," which is not necessarily so—faster production can just as easily mean fewer tools producing the same number of parts. Smaller factories, and more shared factories ("contract manufacturers"). It, in fact, encourages manufacturing to use the Zipcar business model—the product service system.

A more accurate conclusion for the CNC part of the article would be, "it's not what you do, it's the way that you do it."

However, his conclusions about laser cutting vs. stamping look pretty sound. And he's right that because energy is cheap, people don't work to conserve it very much. It's a low priority compared to cost & quality. He's also right that when it becomes easier / cheaper to make anything, people make more of it.

Chris Hall


Interesting post Kris, and I've also found the follow up comments informative.

I also thought the chart comparing energy use between machines was apples and oranges. A CNC machining center with 22kW at the spindle is a very different animal than the other ones to which it was compared.

The elephant in the room though, alluded to in places in this article, revolves around social factors. As David F. Noble described in considerable detail in his work "Forces of Production: A Social History of Industrial Automation", the move away from shop floor control of machine tool production, now to the point of 'lights-out' manufacturing, was quite deliberate. Management very much wanted that control. At every juncture of machine development where there was a choice between a CNC system that required more shop floor operator input, and one that required less, the choice was invariably towards the system that required less shop floor operator oversight.

You cannot reduce the issue of machine development simply to an equation regarding relative efficiencies of energy usage. Less energy intensiveness is a definite plus, however it does not hold sway in the question over what technologies move forward and which do not.

Even if we're all in agreement that skilled work (operating a manual milling machine or lathe, say) is better for people than unskilled work (i.e., loading materials in and out of CNC machining centers), that manually-operated machines have some advantages over CNC-based ones in terms of energy intensiveness, at the end of the day it is social factors (who controls production?) that have bigger sway.

And if we reverted to a more human-intensive development of skilled operators and lower energy machining practices, where would these operators come from? Our educational system is not producing them. Every young person is supposed to go to college and get a job in the financial sector or other white collar pursuit.

Jason Olshefsky


I was appreciative of the attention to detail in this article, but was resistant to any negative view of CNC as I frequently call upon shops to use CNC to build parts for my company. While I don't think CNC is wholesale condemned, I think it gets undeserved attention: like several other commentators, I think it's the social behavior that is at fault, not the tool. An analogy would be to blame the hammer since one person can injure another—it's not the tool, it's the operator. For CNC, it's the culture of creating artificial demand, planned obsolescence, demanding cheapness, and other socially-egregious practices.

Nonetheless, it is another factor for me to consider when deciding how to get things manufactured. As it stands now, I think I am firmly on socially-conscious ground in requesting parts only when needed (reducing wasteful production), using recyclable materials (for end-of-life either through wear or damage), and attempting to find shops that implement good labor practices (fair pay, safe environment, and unionization where needed). I'll add to that considerations of energy efficiency: for parts that could be made on manual machines or by CNC, I'll favor manual machining.

Kris De Decker


@ Roland Smith (#14) and Chris Hall (#17)

You both say that "the comparison of the four machines listed in the table is one of apples and oranges". In a sense that is true, although it is rather a comparison of different kinds of apples. But you are missing the point. (Which might be my own mistake for not being clear enough).

The researchers who composed the table wanted to show the consequences of different levels of automation. And then you see that the difference in total power use is much larger than the difference in spindle power. For example, while the spindle power of the most automated machine is only 11 times higher than that of the manual machine, total power use is 67 times higher. The trend is towards more automation (regardless of the spindle power) and that is what makes digital manufacturing so power hungry.

Kris De Decker


@ Amos Blanton (#15)

The power use of the computer is not the problem. If you check the figures in the Dahmus and Gutowski paper, you will see that the power use of computers and fans is only between 6 and 13% of total power use. The auxiliary functions -- performed by human workers in manual machines -- require much more power.

Kris De Decker


@ Jeremy Faludi (#16)

I cite the conclusions of the Dahmus & Gutowski report below:

"This environmental analysis of machining highlights a few important points. From the energy analysis of the material removal process, it is clear that the actual cutting energy can be quite small when compared to the total energy required during material removal..."

(this refers to the high power use during idling, a consequence of automation)

"Another important point is that the energy involved in the material production process can, in some cases, dominate the energy involved in the material removal process..."

You mention only the last conclusion, and you don't seem to understand its implications. You say: "So at that point, who cares what the CNC machine is doing?" The answer is that CNC machines have high power use when idling, which means that increasing the production rate is a way to lower the energy use per produced part. However, by increasing the production rate, you increase total energy use in a significant way, precisely because of the reasons you mention.

The rest of your comment shows that you are totally misunderstanding this.

You also write: "Faster production can just as easily mean fewer tools producing the same numer of parts".

That's entirely correct. But unfortunately, that's not what's happening. And as several people have noted, this is not a technological problem. The paradox of energy efficiency, whether it applies to machine tools or other technology, could be easily solved. But it can only happen through political decisions or, more likely, because of constraints on the energy supply.



What about additive manufacturing like 3D printing? -I read an article that showed even though it is highly automated it uses less energy and has less emissions than conventional manufacturing. See https://www.academia.edu/4685670/Environmental_Life_Cycle_Analysis_of_Distributed_3-D_Printing_and_Conventional_Manufacturing_of_Polymer_Products

Kris De Decker


@ Ryan,

Thanks for the link. Unfortunately, the article is behind a paywall.

From the abstract I learn that the conclusions of the study are the opposite from those in the book chapter that I linked to in comment #3, which says that electricity use is 50 to 100 times higher for 3D-printing compared to injection molding: http://www.livescience.com/38323-is-3d-printing-eco-friendly.html

This would mean that all sustainability gains are the consequence of not having to ship the products overseas, but if that is the case 3D-printing is only more sustainable because we have chosen to set up our factories on the other side of the world. If we would produce plastic parts where we consume them, injection molding would use less energy than 3D-printing.

Anyways, I can't say who is right because I did not read the original reports (I could not find the orginal study mentioned in the book chapter either).

3D-printing requires another article. Some blogs have linked to my article saying that I make a sustainability analysis of 3D-printing, but I don't even mention it.

Roland Smith


@Kris (#19)

Your point carries the implicit assumption that the power of the rest of the machine should go in lock-step with the spindle power.

That is incorrect because it overlooks the fact that spindle power generally correlates with the working size of the machine. The size of the machine in turn correlates in a non-lineair manner to power requirements.

Consider that if the beam carrying the y-axis on a gantry machine is twice as long, it requires eight times the bending stiffness to give the same deflection (error) given a certain load. This is fundamental mechanics.
Stiffness is a product of material properties (Young's Modulus) and the second area moment of the cross section of the beam. A stiffer beam (made of the same material) will have to use more material.

Therefore moving and especially accellerating such a beam at the same rate as the smaller one will generally require more than twice the power.

This is in a nutshell why the comparison is one of apples and oranges.

Kris De Decker


Roland (#24),

You write: "Your point carries the implicit assumption that the power of the rest of the machine should go in lock-step with the spindle power."

In my comment (#19) I write that this is not the case:

"The researchers who composed the table wanted to show the consequences of different levels of automation. And then you see that the difference in total power use is much larger than the difference in spindle power. For example, while the spindle power of the most automated machine is only 11 times higher than that of the manual machine, total power use is 67 times higher. The trend is towards more automation (regardless of the spindle power) and that is what makes digital manufacturing so power hungry."

One thing remains unclear to me, maybe you could help. You say it's the working size of the machine that determines spindle power, but the source I refer to in the article says it's the working speed of the machine:

"Higher production rates require stiff mechanical systems with the capability to absorb arising inertia forces. As a consequence, the masses of the machine structure, such as moving machine components, have to be increased. This, in turn, require motors with high torque output which are able to increase the forces needed during acceleration and deceleration." [16]

Roland Smith


Kris (#25)

The sentence "And then you see that the difference in total power use is much
larger than the difference in spindle power" carries the implicit assumption
that this is unusual for the total power to grow at a faster rate than the
spindle power.

Further on you write "You say it's the working size of the machine that
determines spindle power". This is not what I said: "spindle power *generally
correlates* with the working size of the machine". To *correlate* is not to

I'l try to explain in more detail.

The spindle is the motor on a milling machine that turns the actual cutting
tool, OK? The power of the spindle puts an upper limit on the material
removal rate
. On most machines, the spindle is electronically controlled
to run at a set speed. If it is not removing material, it only uses a fraction
of that total power (just enough to overcome friction in the bearings and air

If the spindle is moving w.r.t. the workpiece, this is called the feed
speed. The depth of the cutting tool into the workpiece is the cut
.The combination of feed speed, cut depth and tool diameter gives the
material removal rate. This in turn determines the necessary spindle power.

If you program the machine to move too fast or with too great a cut depth, Bad
Things will happen. The tool might break, the spindle might overheat or the
machine might just grind to a halt. (On a modern CNC machine, the controller
stops the machine if it senses that any of the motors is using too much

For this reason alone, the spindle seldomly runs at full power or even near to
it. Only when doing the first rough cuts you might come near it, but even then
one tries to keep a safety margin.

If the tool is cutting away material, this causes a force on the tool trying
to stop it from feeding. This force acts on via the spindle on the other parts
of the machine. If the parts of the machine are not sufficiently stiff, the
tool will be deflected too much from its intended path and the dimensions of
the cut will not be accurate. This is one of the reasons why the finishing
step (the last bit of material to be removed from a surface) is done with a
relatively small cutting depth, removing only a little bit of material. This
will give the best accuracy and the best surface quality.

Larger machines are generally meant for larger workpieces. Larger workpieces
generally means more material to be removed. If you have two cubes, and second
one has sides twice as large as the first one, the second cube will have 8
times the volume of the first cube. Hence the tendency to have larger spindles
on larger machines.

Now for the rest of the movements. On both "manual" and CNC machines, the
spindle can be moved by electric motors with respect to the workpiece
along three orthogonal directions called "axes". On a manual machine, there
are also handwheels for moving the axes but those are generally not
used for feeding, only for setting dimensions. Hand feeding isn't very fast
nor accurate. On a manual machine, usually only one axis at a time can
use the power feed. On a CNC machine, generally all axes can move
simultaneously, hence the term "5-axis simultaneous CNC". This is what gives
the CNC machine the unique capabilities that a manual machine doesn't have. On
a manual machine, the feed direction is always parallel to one of the axes. A
CNC machine can basically feed in any direction. This is another reason why
this is a comparison between apples and oranges. A lot of parts that are
trivial to make on a CNC machine are impossible to make on a manual machine.
Try making a 3D curved surface on a manual machine. This capability comes at a
cost, of course; you're running three or five motors simultaneously instead of
one. This will use more power.

However if you were to restrict a CNC machine to the capabilities of a similar
manual" machine (same size, same spindle power, same feed rate, only feed one
axis at a time) the power use of both would also be similar.

There is another reason why smaller machines use much less power than big ones;
there is not enough room for the moving pieces to accellerate to a high speed
before they come to the end of the movement range and have to decellerate.

For all these reasons, the power requirements of a machine (both
"manual" and CNC) of size X will tend to be proportional to X^C
rather than X*C (where C is a constant).

John Fisher


Someone may have mentioned this, if so sorry, but the units used in the chart of comparative energy use are incorrect. the correct unit is Kwh kilowatt hours, not Kw.

For instance a 6700W spindle head in a CNC center may only move for a few seconds, as the processes are much much faster than a manual machines. So -just making up numbers - a 1 second CNC cut at 5000W is 5000 W/seconds or .0013 Kwh where a 20 second manual cut on a spindle at 1000W is .005 Kwh.

Also the CNC works much much faster than a manual system, so you have to figure out the energy per part cost.

That said, its perfectly true that there are motors and computers in the CNC that don't even exist in the manual machine, where some movements are powered by breakfast and lunch. However fewer employees also means fewer car trips and less energy overhead.

Life-cycle costs are a big headache!



This article is terrible. So many things wrong. I work as a tech in one of the largest job machine shops on the west coast.

As one other has said, just because you have a spindle rated at 108hp (like we do) does not mean it draws anywhere near that much power. I dont think we have ever had that spindle close to that point. It only draws as much power as the load requires.

This applied to lasers too, one of our lasers is 4.4kw but is rarely ran at that power. Material type and thickness determines power setting. Along with our two lasers we have two cnc punches. They are crazy fast and kind of fun to watch but they also require a lot of maintenance and tooling is rather expensive. Plus you really need a tool shop to keep the tools sharp. Then there is setup, a laser you can just send the file down that is generated from a cad file, you can also program at the station with it's build in cad software. Enter the parameters of the material and how many you want and go. The punch is a different story. You need special tooling for anything but the most basic of designs. And you need someone to set the machine up. The punch does do things that the laser cant do, like raised tabs, louvers, and countersunk holes.

"We've been able to produce everything locally for decades using hand-controlled machine tools. Digital tools only allow us to produce more and faster. "

Nom just no. Before we had cnc lathes we had screw machines, tracer lathes, and turret lathes. These are what we used for production of any decent quantity of parts. They take time to set up but once you do it is basically pull a lever and go. The screw machines will run unattended as long as you have stock feeding it. "Lights out" operations existed before "Digital".

Before cnc mills we had tracer mills. These are single or multi spindle machines that used hydraulic or air powered tracers to copy 2 and 3d parts from a master making multiple parts at a time. They even had these set up with 4th axis attachments to do very complex shapes like turbine wheels.

Production has almost never been on traditional manual mills and lathes. Manual machines in production shops were mostly found to support or repair the production machines and build and maintain tools and dies. Manual machines were and are still found in small shops like oil field shops and home shops too. Even there they are being replaced with cnc.

Many people thing CNC is only good for production, it is also good for one offs. Many machine have what is called "conversational" where you can design and run a part right at the machine. You can also enter manual commands from the MDI.

Manual machined parts mean a lot more scrapped parts from things like manual goofs or just not being in tolerance. You probably loose more money here than any place else, especially on a multi op piece.

The author seems to think you can just take a design and pop it out with no one to attend to it. It does not work like that. Sorry. Most parts are multi op parts. Stock is prepared, fixtures are designed and built, multiple machines are used, debur, finishing, etc. That is why this "manufacturing a click away" will never happen. You can easily design a fancy part, that does not mean it can be made. It takes programmers to program the part and select tooling and to figure out how the heck they are going to make it. Then you need to figure out how you are going to hold the part down, this often requires fixturing.

The author really need to spend some time in a modern machine shop to see how things work before he writes an article trying to trash it.

Mario Stoltz


Hello Kris,

Thanks a lot for another insightful article. As indicated by some of the answers from industry specialists, this is in fact a very complex topic, especially as it is closely linked to items like productivity, overall industrial production, embedded energy and the like. Not an easy task to cmopletely separate one item of the equation.

While I feel that you may be reacting a bit harshly to some of the comments, I am fully with you that there is no way we can come to a sustainable future for our societies and our planet by relying on computerized control and fully automated machines.

...which leads slowly to my point. Some of the comments indicate the advantage that NC and CNC machines yield much higher precision than available in manual machines, and from my own (limited) experience I can support that. Also, as indicated - many parts not previously manageable can be manufactured.

The second bit is positive, as it can lead to simpler and lighter construction, potentially reducing embodied energy. By the way, this is also one potential benefit of computer designed construction in general - in the old days, strength of parts could only be estimated and ample safety margins were added, leading to excess embodied energy. With computer aided design, strength of parts can be computed with more adequate margin, leading to lighter construction. This has the potential for lower embodied energy, although this is not automatic of course.

The "higher precision comes for free" bit however is poisonous, I would think. Rather than simplifying a design / construction and focusing on the important bits (i.e. an intelligent construction where only very few dimensions need to be tight), computer aided design lures the designers and constructors into a world where every part has an assumed very high precision (because that is what it looks like on the computer screen).

Rather than start with what is easily available at minimal cost, effort or embodied energy, this approach may lead to over-designed constructions. I would think that the world where we need to go is a world where computer-aided design and modeling helps create designs that are optimized to be self-aligning or easily aligned, and where low tolerances are either not relevant or reduced to very few points/areas. This is what constructors should strive for, if they want to help make our world-as-we-know-it sustainable to more generations, rather than help the world shake us off.

Kind regards,

kris de decker


@ John (#27): please read the article

@ macona (#28): thank you for all the details. You write: "Just because you have a spindle rated at 108hp (like we do) does not mean it draws anywhere near that much power. I dont think we have ever had that spindle close to that point. It only draws as much power as the load requires."

Of course, but the same goes for the manual machines. Comparing the energy use of machine tools at maximum spindle power is how researchers investigate these issues.

@ Mario (#29) and macona: I think the comments show that the article can be improved. The analysis of the laser cutter is not disputed, but the story of CNC machines is indeed complex and I did not manage to make my point entirely clear.

Mario Stoltz


One question that really interests me as a general takeaway.

my gut feeling would be that in pre-industrial production (by smiths and craftspeople), most energy in the system was embodied energy of the materials. I would think that the energy embodied in the manufacturing tools and their operation was small compared to the embodied energy of the materials. This is as most tools did not have a lot of wear. Those tools that did easily wear or break were small and easily replaced.

With industrialization, the ratio between "tool energy" and "material energy" started to change. Embodied energy of the tools (real machines for the first time in history = larger, heavier, much more complex) and the engery for their operation (steam power) was fairly high. Of course, productivity also rose steeply. Still (again - gut feeling only) I would assume that the tools were mostly built to last and thus the embodied energy of the materials was still higher than that of the tools and their operation. This is indicated by the fact that many such old machines have worked for 50+ years and some are still operational even today.

With modern manufacturing, I would not be sure of the result. Embodied energy of tools (like 5-axis CNC machining centers) and energy for their operation is considerable. The lifetime of such a manufacturing station is maybe 10 or 20 years, or less? I cannot imagine that they any of those operational today are still around in 2050. For the production of non-metal components, we predominantly use power tools rather than manual tools. Also these have a shorter lifetime and higher embodied energy than any manual tools. On the other hand, their productivity is also higher.
At the same time, the materials that we use in construction nearly all have higher embodied energy than classical materials. We use light metal alloys or plastic composites rather than wood. Nearly none of the semi-finished materials we typically use can be provided without a factory that processes them in large machines; this is true even for the wood-based materials (plywood, chipboard, MDF).

Two questions remain:

1) how has the ratio of manufacturing energy to material (embodied) energy developed, and especially for modern-day production, is it really higher than the historical average or not - taking into account the productivity increase?

2) how are we looking in terms of the general embodied energy in the things that we use and in which we live and work today? Here, the answer is clear. Embodied energy in anything that humans manufacture in the first and second world has exploded and is exponentially higher than the embodied energy of the things that our ancestors have used. This alone is enough to kill humanity if we do not change it. This is where our real problem is.

kris de decker


@ Mario,

I have numbers that confirm your gut feeling.

In general, energy consumption during the use phase dominates total machine tool energy use, reflecting both the high energy use during the use phase and the long life expectancy of machine tools. However, while the average lifetime expectancy of human-controlled machine tools amounts to 18.6 years, the average lifetime of a CNC machine tool is only 9.5 years.

Source: [12], page 26 and further. http://www.ecomachinetools.eu/typo/reports.html?file=tl_files/pdf/EuP_Lot5_Task2_August2012_FINAL.pdf

The numbers concern metal working machine tools in general. The document also has figures for other types of machine tools and for individual types of metal working machine tools.

Roland Smith


@Mario (#31)

There are a couple of reasons old machines last a long time.

As macona mentions, manual machines are generally used in supporting jobs, not series
production. So they see relatively little use and don't wear much.

A second reason is that back in the day, machine frames were generally made from cast iron using sand molds because that was the only viable way to make such complicated pieces in series. Since cast iron has limitations on wall thickness (wall thickness generally needs to be >5 mm for cast iron) these frames were generally way heavier and more sturdy than they needed to be.

A reason why modern CNC machines don't last that long is that computer technology is still evolving. We have a 3D computer controlled measuring machine built in the 1980s. It's original computer was a box about 50 cm cubed stacked full of custom made circuit boards. When that computer broke down a couple of years ago, the components needed to repair it had been out of production for over a decade. So that computer was replaced by a standard laptop running a much more capable piece of software. On this measuring machine this was a good option. For techical reasons this is generally not a viable option for a CNC milling machine.



I'd be curious to know how human energy is factored into the equation. The humans who would be controlling the more efficient machine aren't directly using electricity to function (as a computer controlled machine does) but they consume a ton of other resources indirectly. For example, the humans eat food, drove to the factory, heat their house, fly around the world — all of which consumes energy so you can't just ignore the human energy variable as it is quite significant over a lifetime.



CNC machines are much better than manually operated machines. I know the power consumption for running a CNC machine is much higher but if you look at the time saved by these machines then we can't think of any alternatives. Sometime it is not feasible for small manufacturing companies to afford this high priced machines. For them , manually operated Lathe, milling, drilling, shaper or planer machines are a good choice. And if we talk about the longevity of these CNC machines, then we have to think out of the box. Mechanical, Chemical, Metallurgical engineers have to work together to make a prototype which lasts longer and also less expensive like manually operated machines. This will certainly help the economy. But again if we think about the time saved and quantity of the products that a computer operated machine produces we can't complaint ! And again the power consumption! (off topic) Engineers and scientists please suggest the world to use non-conventional energy sources or renewable energy sources. Thanks

jon banquer


Just came across this site and in general, enjoy your articles. Most of them seem well thought out and documented. However, this one ...

The description of how nc operates is very good, especially for a person who is not in that field. But your conclusions .... mmm, bad boy :)

I don't disagree with you on the social end of things : if I were to start a shop now it would be all manual. But the reasons are not energy-related.

Bona fides : I started and ran a small shop from about 1976 until a couple years ago, so I've actually done production on manual machines. There aren't so many people around now who can make that claim. I also
bought and paid for and did all the accounting for when I went to nc. I'm more of a lathe guy than a miller but the principles are the same ... let me throw out a few things for you to think about :

When I got my first cnc lathe in 1978, I ran the same jobs on it that I'd been doing manually. I'm a decent lathe hand, by the way, so it's not like we're comparing some slouch to a hot-dog cnc machine.

The nc machine was almost exactly ten times faster. So for the exact same quantity of parts you would need ten lathes and ten guys, all eating lunch, pooping, driving to work, parking out front. Ten times the footprint. This is not energy-efficient !

Engine lathe, 6,500 lbs x 10 = 65,000 lbs. One nc lathe, 20,000 lbs (This was in the old days, a new one that size generally runs maybe 12,000 lbs) Energy to produce ?

NC produces way higher quality. The tolerances were better and there were shapes that could only be done with great difficulty (if at all) by hand. Many features simply can't be done by hand. Parts off an nc machine are several orders of magnitude more accurate.

Scrap : on the nc machine I would often scrap the first part because it was easier to just make one, measure it, then change the offsets. Afterwards, unless a tool broke, there was no scrap. In the old days we figured 4% scrap. So if you needed 100 parts, you'd cut up 105 - the last thing you want is to come up one part short on an order so you'd figure the 4%, then add one or two.
Where'd that energy go ? :)

@ Mario & Roland Smith : another reason manual machines last longer is that you simply can't run them hard enough to hurt them. Okay, you *can* hurt them but it's difficult for the human body to withstand the
torrent of blue-hot chips flying off a machine that's
really working. The reason I bought my first nc was because I was sick and tired of chip burns all over my body. Arms, down your shirt, in your ears. You can't enclose a manual machine because you have to get
to the levers. There's another point against manual
machines : the mess everywhere. How much energy does it take to clean up all the chips, and how bad for the world is all the coolant that gets sprayed everywhere uncontained ? This may seem inconsequential
but I'd have to clean out the chip pans at least once a day, often more. NC machines almost all have chip conveyors that (sort-of) dry the chips and dispose of them into barrels. And the oily ones have Roto-Mist oil collectors that filter the coolant out of the enclosure. Without an enclosure you can't do that as very well.Clean the air for the entire shop ... does that take energy ? hint hint ?

I sort of wonder if the people who studied manual machines actually had any manual machines to study : it's been a long time since there were any manual shops. Anything bigger than a Bridgeport is *always* idling. You don't turn the motors on and off. A typical 16" engine lathe will have a 7.5 horspower AC motor that gets turned
on, then it runs. All the functions are controlled by levers and clutches. Any milling machine bigger than a toolroom mill is the same. Manuals idle more than nc. Manuals are *always* idling.

Think of ten 7.5 hp motors running continuously versus one 20 hp plus the two servos (one for each axis), for the same amount of product. I don't think the manual will come out more efficient.

Worse, a lot of production equipment was powered by hydraulics. All the tracer machines, both mill and lathe, ran hydraulic tracers. Let me tell ya, hydraulic systems are not energy efficient ! Nor are they clean. Many larger machines have hydraulics to do the actual work. Not energy-efficient *and* they are always idling at full energy draw, whether they are producing parts or not. The pump is producing 250 psi all the time, not just when doing work.

Another statement that sticks in my craw is the claim that nc machines while idling eat up a lot of energy. I simply don't buy that. You said, " ... the power used handling the workpiece and tools is less than 15% of the total power required. The remaining 85% of the power used by the machine is constant, even when no action takes place." But the point you are missing is, even if this were true, if a company doesn't want to go broke the idle time is infinitesimal. You open the door, take out the part with an air chuck and button push, put in another part, close the door, push "go". Many machines now change parts, too - in just a few seconds. So, for smaller parts, maybe
fifteen seconds every five minutes of machining time. On large parts, the machine can run for *hours* between part changes. The key to making money is "Keep them spindles turning !" and that's what shops

Remember, nc machines are expensive. If a shop has its nc idling a lot, then they will quickly go broke and someone will buy those machines at auction who does *not* leave them idling unproductively :)

Even when idling, I don't buy the claim that they are inefficient. Of course there are always improvements to be made but a 1980 cnc machine was much less efficient than a new one, and the 1980 machine was even
then way more energy efficient than a manual. My electric bills about tripled but I got ten times the volume. Plus back then the electronics required an air conditioner, the transformers gobbled electricity, the motors and servos were all dc. I have no numbers to throw out but I
know that a 2012 machine uses *way* less electricity, even sitting there, than a 1980 machine. I just can't believe this thing about nc not being 'energy efficient'. It goes 180* counter to my real-world experience.

If you remember, in the seventies we had two oil embargoes which jacked up the price of electricity by two and three times. Many of the "authorities" predicted big price increases because of that, but the
machine builders and utilities replaced all their older motors with more efficient ones instead, and we didn't see what the ivory tower 'experts' predicted. The manufacturers and users are not as unconcerned with electricity prices as you think.

Anyway, at least on all my machines, when the spindle is not turning the spindle motor is *off*. Contactor dropped out. No current going through it. That's much more efficient than a 7.5 hp motor continuously turning, yes ? The ballscrew motors as well : if there is a turning force on the screws, then the current delivered to the motors goes up. But with no force, current to the motors is infinitesimal. When they are moving, they eat a lot of electricity - but that's because they move at 400 inches per minute. Try that with a manual machine :)

Another point - nc machines use ballscrews. Manual machines use Acme-thread lead screws. There's a tremendous frictional difference there. Yes, the cnc most likely does use more total energy - but that's because it is moving ten times faser and making ten times as many parts per unit of time.

This is possibly where your analysis went off the rails : what you really need to know is the energy used *per part*. If you did that I am sure that NC machines would clean the floor with manuals.

You bring up lasers. Yes, lasers are energy-intensive. They are also maintenance-intensive and cost a lot. No one who pays the bills likes them because honestly they cost too much and you are right, they eat energy. Pieces of junk, really ... But they are *so* versatile ! (and clean. Punches are not clean, all that stock has to be oiled to be
punched. No one mentioned that to you, right ? Then the oil cleaned off it. Lasers don't need that.) So, let's assume that you have a shop where half the work could be done by punching, but the rest needs a laser. Why would you buy two machines ? Yes, the laser is too expensive and too much hassle to be optimal for the job that's
suitable for punching and it drinks electricity (aka energy) - but *you don't have to buy a second machine !* These machines are not small, either. To handle a 4 x 8 sheet of steel the machine has to be at least twice as big as that, yes ? (The steel moves, not the cutting

So how much energy do you save by not having that second machine, floor space, oil, and operator ? Probably more in one week than the laser will waste by being a high-energy process in its entire lifetime

Don't get me started on "3d printing" -- what a fraud :)

I'm sure I'll think of more holes in your article :) but that's enough for now. I do agree with you about the social side of it - I'd prefer that nc machines were never invented. The throwaway economy filled with cheap junk is anathema to me. But really, nc machines are *not* less energy-efficient than humans. You are mistaken on this one.


Anyhoo, except for this one article, I like your magazine. Some good thinking and analyses there.

best of luck !

Jon B



The line -- "Because energy consumption equals power consumption multiplied by time, in the end a CNC machine might use less energy than a manual milling machine for the processing of a similar part." Pretty much punches a hole in the balance of the article. For what really matters is not how much overall energy is utilized but the imputed Kw per part produced. I would suggest that industry has already figured this out, else-wise they would be at a competitive disadvantage vs their competitors for the energy cost of every part made.

Randy Eckart


@Kris, when you get around to that 3D printing article, you might look into Direct Shell Production Casting technology.


With this method the ceramic molds for metal castings are printed, and then fired and poured with molten metal.

Shapeways has a similar but more direct process where a 420 stainless steel metal powder is 3D printed with binder, and then infused with bronze in an oven for a final composition of 60% steel / 40% bronze.


Compared to direct laser sintering of metal powder, either method should be much more energy efficient. In fact these methods should compare quite well to traditional metal casting technology in terms of energy consumption.



@Kris et Al, A very interesting article and discussion. For anyone who wants to assess eco-efficiency or attempt LCA (life cycle analysis) there are some wonderful free resources at Tech University Delft. Excel spreadsheets of Reputable Idemat data can be down-loaded giving individual eco-indicators (carbon eq, energy intensity etc) and compounded eco-cost data for thousands of materials and processes. http://www.ecocostsvalue.com/EVR/model/theory/5-data.html
The need and approach for LCA are explained elsewhere on the site (click on home page at the top R). A common approach is to calculate the burden per kg of product from its constituent components (materials & processes). The boundary of the analysis can be selected to suit the application from comparison of competing processes to cradle-to-grave life cycle analysis taking account of packing,transport,usage,recycling, disposal etc.
Be very careful when comparing process data ....eg material processed in injection moulding is the mass of part ...for milling it is the material removed (which may be half of the blank mass)...but for sawing,laser or water-jet cutting it is the material removed in the kerf (not material cut away)....you have to keep your brain engaged! Some very quick assessments based on Energy intensity or eco-cost can indicate where the major eco-burdens lie..Find the big ones..assess which are addressable..then go for the low-hanging fruit!



Nothing about a abrasive waterjet, they can even cut a 3D material with great precision and with minimum of a heat deflecting on the material. Please add an article on your take on the matter

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