Author Archives: torbjorn

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How do CNC Machine Tools Move?

Only 3 possible motions…

There are really only three ways a standard CNC machine tool moves today: linear motion, arc motion, and what is called rapid motion. To understand these types of motion we should talk a little bit about how machines are made and how they are program. To do this we will first look at the construction of a 3 axis vertical machining center, or milling machine.

For this discussion we will start with the z-axis and the spindle since it is the rotation of the tool by the spindle that makes all of the cutting happen. A typical setup for vertical machining center is to have the tool mounted in a spindle which is aligned with the Z axis of the machine. This spindle is typically attached to a mechanism or “way” that allows vertical motion along the z-axis of the machine. Note that misalignment between the spindle and the z-axis way can lead to error in the finished part.

The typical z-axis drive will be a servo motor connected to a ball screw. Ball screws are really quite fascinating in how they work but for the purpose of this discussion you can imagine it simply like a nut on a bolt or screw. If you remove the threads from each end of the screw and mount the smooth parts in fixed bearing blocks with a nut in between them. The nut will move up and down along the screw as you turn it as long as you don’t allow the nut to rotate. If the spindle is then attached the nut you can turn the screw and make the spindle go up and down. To keep the nut with the spindle attached from rotating you need to attach it to something that is fixed rotationally simply welding it to the back of the machine won’t work. Instead it is attached to a bracket that is intended to slide along a guide rail. This guide rail is typically called the way. A typical axis might have two ways with a ball screw between them.

The x-axis is designed and constructed similarly to the z-axis and is installed orthogonally to the z-axis typically moving from right to left from the operator’s perspective. A y-axis can then be mounted orthogonally to the z and x-axes forming a right hand coordinate system.
Each axis is typically driven by a servo motor. Servo motor control systems, at a minimum, require feedback about position to operate. The typical method for getting this information is to attach a rotary encoder between the servo and the ball screw. This allows the controller to know “where” the spindle or x and y tables “are” at any given time as long as it hasn’t lost track of the encoder pulses which measure rotation of the motors. Because of this machine tools of this construction do not know where they are when they are turned on and will have some type of homing sequence that must be run before running any programs. The homing sequence will move each axis on at a time to the end of its travel where a switch is installed. They will drive the axis slowly across the switch noting the encoder position at the instant the switch makes contact and defining the “zero” or “home” position for this instance of operation.

As to programming: the typical machine tool today is programmed with a text based language that is sort of standardized, and goes by several names. I’ve heard NC-code, G-code, G&M-code, and simply code, or machine code. In this text I will try to stick to the terms “code,” and “g-code.” Several standard have been written over the years but as the technology has been developing so quickly the standards didn’t cover all situations individual machine tool makers wanted to address, so there are a core of “codes” common to most machines but when implementing common macros and canned cycles there can be great variation from one machine tool maker to another.
Why call it G-code or G&M-Code? The answer is simple most lines of code start with either the letter G or M followed by a string of numbers or letters that mean something to the machine tool controller. A typical command for example would be something like “G00 X1.4 Y3.5 Z4.0 F96.” This command tells the machine tool to move the axes as fast as possible (G00) to the Cartesian coordinates X=1.4 Y=3.5 Z=4.0 at the rate of 96 inches per minute (assuming the “English” system of units is being used.) Another common command might be “M03 S12000”. This tells the machine tool controller to start the spindle I the clockwise direction (M03) at 12,000 RPM (S12000). It is important to note that It doesn’t matter what the position of the machine tool axes are when the first command is received the machine tool moves as fast as it can from wherever it is to the programmed end position. Another thing to note is that the S12000 can be omitted if the last spindle command was to spin at 12,000 RPM as Spindle speed is a modal command and will stay in memory until it is changed.

Future posts will include a detailed discussion of Machine tool programming and G and M codes. The above paragraphs are enough information to continue the initial discussion on machine tool motion. As stated above there are only three ways a typical modern CNC tool can be told to move.

  • G01 – linear motion
  • G02 or G03 – arc motion (constant radius)
  • G00 – rapid motion

Let’s look at each in turn

G01 pronounced “gee zero one”

The G01 command is given when the programmer wants the tool to move in a straight line relative to the workpiece at a specified feed rate. This command is typically used when cutting is happen or imminent. The feed rate can be specified on the G01 line or previously in the program as feed like speed is a modal command. No starting point is specified. The machine tool commands the servo motors to move from the current position to the end point specified at the feed rate specified accelerating from the current location and decelerating to stop at the end point.
If motion in only one plane or along one line is desired it is possible to omit endpoint coordinates for the axis or axes that will not need to move. For example if the tool is at X=0.1, Y=3.0, Z=0.01 when the G01 command is given and the desired end point for the move is X=0.1, Y=7.0, Z=0.01, the command G01 Y7.0 is equivalent to the command G01 X0.1 Y7.0 Z0.01 and preferable as it is easy for someone looking at the program to recognize that only motion in the Y direction is called for at this point in the program.

G02 pronounced “gee zero two”

G02 like G01 is typically used when the programmer intends for the tool to be in contact with the workpiece, i.e. when cutting is happening, or when the tool is entering or exiting the workpiece material these entry and exit moves are typically called lead in and lead out or entry and exit respectively. G02 commands the machine to move from its current location to a specified endpoint like G01, but instead of interpolating a straight line the servo motor controllers are commanded to interpolate a constant radius arc motion. To this end the programmer must specify the desired end point of the motion, and a radius to define the arc. There are a couple of common ways to define the radius those will be discussed in future posts on programming. The command “G02 X1. Y1. R1.” tells the controller to move the tool from where ever it is to the point X=1.0 Y=1.0 Z= (whatever it is at the start) along an arc with a 1 inch radius (again assuming the English system of units.)

It is important to note that if the straight-line distance from the current position to the commanded end point is less than 2 times the radius the command will fail generating an error code on the machine controller.

It is possible to make arcs in the x/y plane, the x/z plane, or the y/z plane but you need to tell the machine controller which plane you want to arc in. There will be more discussion on this in posts on programming.

G03 pronounced “gee zero three”

G03 acts just like G02 except the arc is counter clockwise.

G00 pronounced “gee zero zero”

The G00 command is typically used for positioning the tool and is not usually used when the tool is intended to be in contact with the workpiece. It is used for moves to and from the tool change location and moves or “links” from the end of one cutting operation to the start of another.
G00 motion is called rapid motion and it’s goal is typically to waste as little time as possible performing non value-added motion. For setup operations and proving out (testing) programs most machine tools will have a rapid override command that allows the operator to decrease the full speed rapid to some percentage of the machines full speed capability. Operators should know something about the machine when selecting rapid overrides; I regularly use machines that move at about 600 inches per minute at full speed rapid, and another that moves at 2000 inches per minute. Twenty five percent rapid 2000 in/min machine is almost equal to full speed rapid on a 600 in/min machine.

The other thing operators and programmers should be aware of is the fact that many engineers are lazy and the easiest way to implement rapid motion in the machine controller does not allow the tool to move in a straight line from the current point to the programmed end point. The path the tool will take is predictable, but not a straight line! (By “easiest” I mean the way that requires the least math and thus the least processing resources)

dogleg rapid

The easiest way to implement rapid motion is to command each axis independently, but simultaneously. For the command “G00 X10.0 Y4.0 Z-3.5” the controller looks at the end point for x and compares it with the current x position if they are not the same it starts the x-axis motor spinning at full speed in the correct direction continually checking if it has reached the correct value. When the current position equals the desired end position the x-axis motor is stopped. At the same time the controller is moving the y and z axis servo motors checking their current positions and the commanded end positions stopping each servo when its axis has reached the commanded position.

Many of the most modern controllers have options that will disable dogleg rapid but it is best for programmers and operators to know that the machine they are using today probably moves this way.


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What’s the cost of changing a lightbulb

I went to school with a lot of people that were good at math. Walking home to my apartment one afternoon of my senior year I noticed a for sale sign in front of a house. It was a three family house like almost all of the others in the neighborhood. Very similar, in fact, to the one I was renting an apartment in at that time. When I got home I called the number on the sign just to see how much a house like that cost.

Being good at math myself it was easy to understand that rent from one of the apartments was probably enough to pay the mortgage, leaving one to live in and another to live off. I didn’t buy that house but it wasn’t long before I was on the path to becoming a slum lord in a college neighborhood. Early in my real estate career I didn’t have a lot of disposable income and spent a lot of time shopping in discount stores following the save a buck style of accounting popular with slumlords and accounting departments at companies around the world. A box of six light bulbs for a buck, you bet that was in my cart.

After 15 years and at least 100 tenants I’ve divested myself of all of my residential rental properties and would never consider buying a cheap light bulb again. Why you ask. What’s the cost of changing that cheap light bulb? I can tell you from experience it’s a lot more that the $0.17 I paid for it at the discount store.

The cost of changing a light bulb is the cost of the interruption of dinner with friends and family when you get a phone call from an angry tenant who cannot see to put their key in the lock. They are especially angry because the light has been out for weeks and you haven’t done anything about it. There is no point reminding them that you don’t go visit them every evening and if they don’t tell you they light is out you don’t know.

This interruption that ruins your mental peace is not the only cost though. There is additional cost. There is the cost of the trip to your barn to get a ladder and put it in your truck. There is the cost of the cost of going to the home improvement store to get light bulbs because you can never find the ones you got at the discount store. There is the cost of leaning the ladder against the railing of the stairs to reach the offending non-functioning bulb. And of course, there is the cost of sweeping up the glass from the bulb you dropped from the top of the unstable ladder. Not to mention the cost of putting the ladder away and figuring out where you put the original discount bulbs so you can put away the ones that are left over from this job.

At the peak of my rental management business it was really a sideline business for me as I was spending most of my time traveling and consulting for companies like General Motors and Goodyear not to mention the federal court system. For the type of work I was doing I could bill upwards of $2000 per day. Even if you divide the day into 24 hours that’s still almost $85 per hour ($250 per hour if you manage to work only 8 hours.)

Depending on how you do the math it cost me between $170 and $500 to change a lightbulb during those years. The only comparison shopping I do when looking at light bulbs is to find the ones that last the longest.


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My 6th year as an undergrad made me who I am today.

A couple of years ago I attended a graduation party for one of the most amazing students I’ve ever had the privilege to work with. He was wearing a t-shirt that said:

“College – the best 7 years of my life!”

I kidded him about it because I knew that he had not finished in the typical(?) four years and he admitted that it had indeed been seven. Not only that someone gave him the shirt his freshman year.

It made me think back to the end of August 1994 when I was about to begin my 6th year enrolled as an undergraduate engineering student.

I had plenty of excuses and rationalizations for the fact that I wasn’t done but none of them mattered what mattered was that I had no intention of asking my parents for money to pay for this year – a year that should not be – and that I had used up all of the money I made during year four to pay for year five. (I took year four “off” and worked full time.)

With almost no cash and a full course load for two more semesters staring me in the face I signed up for the payment plan offered at the bursar’s office and got a full time job driving a forklift in a warehouse attached to a plastic injection molding company. This was my first experience working directly for a manufacturing company and it was an eye opening experience.

It was also a tiring experience you see I was still taking a full course load and was working second shift five days a week plus taking all the weekend overtime they would give me. Amazingly enough I did not fail all of the classes I took that semester, but I failed enough of them to know that I needed a better plan for the spring.

I still use some of the credit cards I applied for that winter and finished the spring semester passing 12 classes with all As and Bs and almost $35,000 in credit card debit that I was very adept at moving from card to card in rotation.

In one sense, looking back, I can see that I manufactured both my failure that first semester and my success the second. During the first semester I misused my resources my time and my focus. One of the only classes I passed that semester was a class I now teach at that same university and I often wonder if the C that I got was actually a gift from the instructor.

In the spring of 1995 on the other hand success was my only acceptable result and I was able to focus on the things required to pass my classes and manufacture my success.


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Everything You Need to Know About 3d Printing But Don’t Know How to Ask

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http://lmgtfy.com/?q=everything+you+need+to+know+about+3d+printersThey say that the best way to learn about something is to write a book about it. So that’s what I’m setting out to do now. 
     People have been asking me about 3d printing, rapid prototyping, and additive manufacturing for years and I’ve always had answers. But honestly the answers haven’t really satisfied me.
     I remember one time when the father of a prospective student at WPI, the university where I work asked if we had any rapid prototyping capabilities. I knew he meant 3d printing but I rather flippantly answered that an endmill a half of an inch deep and half of an inch over moving through aluminum at 800 inches per minute is rapid, and it is but it wasn’t what he was asking. 
     The world (at least the part of it that I interact with) is very excited about this “new” technology and rightly so, but if all of your information is from TED talks,Tweets and your own opinions then like me there is much you can learn about this technology.
     As I research my book I’ve developed an initial list of questions:

  • What are today’s printers useful for?
  • Which printer manufacturers will be here in 20 years?
  • How many production printers are made with 3d printed parts?
  • How fast can 3d printers create parts
  • What is the fatigue life of a 3d printed part vs a machined part vs a forged part…
  • What materials can I print
  • What is the cost of additive manufacturing vs the more common subtractive manufacturing?
  • When will I be able to ask my printer for “Earl Grey tea, warm” and get it?
     When I learn the answers to these questions and more I’ll write about them here and when I know enough I’ll put the material together into a book we can all use for reference. 

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From Troubled Youth to Well Paid Professional

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How do you go from troubled youth with jail time to Cadillac driving skilled  professional with 8 weeks of training? The trick is to get the right training. 

You can see more of  Noel’s story at: http://www.cox7.com/launchpoint/shifting-gears

     In the Shifting Gears Episode of Launch Point we told Noel’s story. Noel had been headed down the wrong path but after he learned completed our program where we offer training in partnership with the MassMEP  and Quinsigamond Community College things were looking up.
     In this program we empower people with limited or no manufacturing training or experience to compete for some of the best and highest paying jobs in industry in just 8 weeks.  These 8 weeks are intensive on some of the days the students are in class from 6AM to 4 or 5 PM with just a short break at midday. The trainees learn both soft skills like teamwork and work etiquette and hard skills like CNC Setup and Programming Techniques. They get resume help and interview coaching.
     All of the trainees in Noel’s class had jobs before the class was over, ten of them hired by Siemens before the class even started, hired that is, pending successful completion of the training.
     We have been teaching classes like the one Noel took for most of a decade now and there are dozens of stories as uplifting as this one. When we first met with Jeremy Bout, director and producer of the Launch Point series it was both easy and difficult to choose which one to tell.



     


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manufacturing the future of the world

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It takes a village to raise a child. What does it take to raise village? It takes people coming together sharing resources to meet common needs. This is where manufacturing started. It started with the caveman, who was good at making stone tools and not so good at hunting, making tools and trading them to hunters for food. As villages grew into towns, towns into cities, and now into global villages the scaling factor has always been manufacturing. Throughout all of history and prehistory we have been manufacturing the future of the world.
     What is the future we are manufacturing now with a department of the US government considering changing the official definition of manufacturing to include  “Factoryless Goods Producers” (FGPs) (see It Takes a Factory to Make a Manufacturer.)

The future is what we make of it and if we are not making anything then the future is what someone else makes of it.

   Regardless of your opinion on FGPs please take a moment and consider the question. Designating FGPs as manufacturing companies will certainly improve the “manufacturing numbers,” much like recognizing that McDonalds is really doing assembly and packaging not cooking would. Manufacturing in it’s most fundamental sense is the transformation of raw materials into something someone else wants. It’s those processes that transform the raw materials that actually add value and create wealth and when it comes down to it, it’s really all about wealth.
     Wealth can be found (dug up out of the ground), wealth can be stolen (usually with an army), and wealth can be created (through manufacturing). Other than those three possibilities the only thing we can do is trade it and move it around. The banking industry, the financial markets, the FGPs, and all of the service industries simply serve to move wealth around. If all a society is doing is moving wealth around without any wealth creation it will naturally become highly stratified with the wealthiest people becoming more and more wealthy and the less wealthy becoming poorer and poorer.
     If a society on the other hand is continuously creating new wealth through manufacturing wealth will be unlimited. In a society of unlimited wealth there will be extremely wealthy people but there will also be a strong middle class and there will be real possibilities to move from the poorest classes to the wealthiest classes with hard work and creative thought. Which village would you rather live in, the one with unlimited wealth or the other one?


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no skills gap?

Category : Uncategorized

I won’t say there is no skills gap. In Massachusetts alone right now there are about 250,000 unemployed people and at the same time about 130,000 unfilled jobs with the employers reporting that they cannot find skilled workers. No I won’t say there’s is no gap. There is obviously a gap. The other thing that’s obvious, at least to me, is that the problem isn’t a gap of skill. The solution to a skills gap is always training and we are really good at training. 
     We are really good at training; one program I’m involved with has trained almost 200 people to become operators of computer controlled manufacturing equipment over the past few years. In this program we help long term unemployed people gain highly sought after skills in a very short time. In a period of about 9 weeks we can enable someone who has never been in a manufacturing facility to get a job as a CNC machine tool operator with basic programming and setup skills.
     By the graduation day, for any session of this class, almost every trainee already has a job. The rest typically have one within a few weeks. We’ve even had one local employer hire 10 out of 12 trainees  from a session of the class before it even started.  No training isn’t the problem, we can do training.
     We can do training, but 200 is a drop in the bucket compared to the 130,000 potential jobs out there and that is just considering Massachusetts. When we started this project I assumed that the cost of delivering the training and our ability to fund it would be the limiting factor in the number and frequency of classes we could offer. The actual limit on the other hand has been our ability to sign up qualified candidates.
     Its not that the other 249,800 unemployed people in the state are too stupid to complete our training on the contrary most of the people not applying could fly through the class.
     The primary problem with our class is that people aren’t interested in careers in manufacturing. They think those jobs are dirty and beneath them. They might love to watch Mike Rowe but they don’t want a “Dirty Job”.
     This is especially sad because, although there are dirty jobs in manufacturing, those aren’t the ones the employers are having trouble filling. Hungry people with no skills take those jobs.  The jobs that sit unfilled are good jobs with good salaries.  In the program mentioned above the placement rate is over 90% and and the starting salaries average close to $37,000 per year.  These are well paying jobs in good industries making the things our society needs to exist.  If the problem was simply one of skills we would have crossed it years ago with programs like this one.
     It’s a perception gap not a skills gap that we need to cross.


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why do we engineer?

Category : Uncategorized

Why do we engineer?  We engineer to enable manufacturing!

Why do we manufacture?  We manufacture to enable society!

Our entire society is based on manufacturing,  this process of taking raw materials and turning them into useful goods.  The things we use the things we surround ourselves with even most of the food we eat has been manufactured before we see or touch it.


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Can we make learning videos instead of teaching videos?

I can’t say I’m part of the ME Generation, and with that said, or rather not said, I can say that when I want to know something, unless I’m standing next to someone I’m pretty sure knows the answer, the first thing I do is Google it.  Then I look for a video (preferred) or a web page that explains it to me.  I’m forty three years old, or as I like to call it thirty-thirteen years old.  My generation literally grew up with computers.  I remember the first PCs.  I remember the launch of Macintosh.  I was there when our rich college friends first got PCs with color monitors and the rest of us reminded them that green is a color too.

Now as an engineering professor at a world renowned university my colleges and I regularly lament the fact that our students don’t do the reading and unless we somehow make it required they are likely to skip class in droves. I can tell you emphatically that that it is not their fault!  If we as faculty cannot engage them we deserve to be talking to an empty room and we are doing them and extremely expensive disservice.

So how do we engage them?  I’ve tried things like:

  • in class quizzes,
  • pre-lecture quizzes based on the reading,
  • post-lecture where the answers were only covered in lecture, not in the reading…
None of those things have really seemed to work for and I think it’s for the same reason that although I read almost continuously in high school, on the bus to school, on the bus back from school sitting in bed at night, sitting in the back of the class room,  I don’t think I ever finished one of the books assigned by my English teachers.

What does seem to work is to interact with them, to have a conversation, to ask questions and pull the answers out of them, to give them ownership of he class and its direction and to act as a guide on a journey of learning.  This can be hard to do as you might imagine with a lecture hall full of introverted engineering students.  I’ve been known to resort to throwing candy to (at) students who participate in my ongoing conversation and I’ve made it a habit of showing at least one YouTube video or clip in each class.  It’s these videos that I think are both part of the solution to the problem of engagement and part of the problem itself.

I’ve been using video as a teaching tool for as long as I’ve been teaching, and when I tell my class that they have to watch “my teaching video” —  of me talking about something — if they want to know — what I want them to learn — about that something; it doesn’t matter if the video is any good, I have a captive audience.  This has lead me to “produce” a few good videos and a lot of less good, even bad, videos.

A bad video is much much worse than a bad lecture.  I know from experience that some students will be embarrassed to fall asleep or even zone out in class but will think nothing of falling asleep in front of YouTube or more likely the’ll click on a more interesting video.
A good video can be much better than a good lecture the students can refer back to it they can share it with others they can help spread that knowledge.  A good video is a learning video not a teaching video.

Look for our new learning videos in May

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Do engineers really need to know anything?

Category : Uncategorized

I’m not sure how frequently something needs to be repeated before it becomes cliché but there is a saying that I’ve heard so many times and that I’ve even used in class that I think fits, at least in the limited circles I travel in.

They say: “Engineers don’t need to know anything; they just need to know what book to look in.”

Well OK – That’s a little like saying anyone could be a great chef if they have the right cook book, and by extension must make Google  the world’s greatest engineer. (http://lmgtfy.com/?q=am+i+an+engineer%3F)

I can tell you that as an engineer you do in fact need to be good at using reference materials, and knowing which book to look in certainly speeds the process.  In reality, though, simply owning the books isn’t enough.  You need a clear understanding of the fundamental physics of the situation, to know when you are approaching the edges of those laws, when the things you are doing might even expand those edges; and you need to be really good at solving those pesky word problems from middle school.

Einstein was once asked how many feet are in a mile. Einstein’s reply was “I don’t know, why should I fill my brain with facts I can find in two minutes in any standard reference book?”*
As an engineer you will remember the facts that you use often, as to the others, it is sufficient to understand that they exist, how to find them, and how to use them when you need to.

*(http://www.goodreads.com/quotes/276428-einstein-was-once-asked-how-many-feet-are-in-a)