Category Archives: Terminology

Tool Runout vs. Tool Deflection – What Are The Differences?

There’s a reason tight tolerance parts cost more time. Yes, I use the word “Cost” because time is money, and it can take a considerable more time to set-up and run a part if the tolerances are closed up. Tool run-out and tool deflection can both be an issue when trying to hold a close tolerance. However, they are not the same thing.


Tool run-out is how far off of the rotating axis the tool is. While in the machine, you want to check just above the bottom of the tool, as that will give you the most accurate reading and is almost always worse than the top of the tool where it goes in the holder. To check it, put an indicator on a vice and touch the tool off of it. Zero it out and then rotate the tool (usually in a counter-clockwise rotation so it doesn’t catch the cutting edge). If there’s run-out, one side of the tool will give you a different reading on the indicator.

Before we go any further, let me explain what run-out actually does when machining a part with a tool that has it. If an end mill or a drill has excessive run-out, the side (or flute) that is bigger will do more cutting. If you’re milling out a hole with an end mill, it will cause the hole to go over-size if all of your program and offset numbers are right. A drill can also go oversize, as well as drill an oblong hole.

Now lets take a look at what causes a tool to have run-out. A brand new and unused tool can have run-out. Why? Not all tools are made the same, and if you buy cheap tooling, there’s a better chance that it was made with the same precision as a higher quality tool.

Not only can the tool be at fault, but a defective tool holder can cause run-out as well. On the other hand, you may check the tool while in the spindle and see that their is run-out, but certain tools (such as a reamer or drill) will allow you to slightly move it without removing it. This can often get rid of many run-out problems with longer tools.

Tool Deflection

Tool deflection should not be confused with run-out. It is a common term used when side milling with an end mill, and it causes a taper in the part feature that is being milled.

Take this as an example; you’re milling the outside profile of a part (2x2x2.25″) that has blueprint dimensions of 1.950″ wide, long, and 2.000″ tall. Using a 3/4″ end mill with greater than 2 inches of flute length, you mill around the part once. The top of the part is 1.951 all the way around, but the bottom is upwards of 1.954″. This is because the end mill is too long and was ‘deflecting’ because it couldn’t handle the pressure of removing all of that material.

That’s the most simplistic scenario of tool deflection. So, how do I combat this? Great question, and there’s quite a few ways to make sure your part is square, perpendicular, and/or parallel.

First of all, how deep of a cut are you taking? If you’re drilling a 1/4″ hole that’s .375″ thru, you don’t need a jobber drill with 4″ of flute length. When milling, a bigger diameter tool will be stronger and resist deflection better. If you’re milling a feature that is .400″ deep, using an end mill with 1/2″ flute length will achieve the best results. One last thing on tool length is that you should have the tool as short as possible in the holder. Do not clamp on the flutes, but if you choke up on the tool, this will also help prevent deflection.

Feeds and speeds. I’ve said it before, and I’ll continue to say it. Having the right RPM and feedrate for your tools is one of the major keys to success in the Machining industry. Even if the surface foot is close, having a high feedrate will naturally produce more tool pressure and in turn cause deflection.

Slowing down the feedrate can help, but in the end, you may have to take multiple passes to make a feature square, especially if you’re profiling out a part with an end mill.


2 vs. 3 Axis Machining – CNC Profiling

Traditional 2-axis milling on a CNC machine is still very common, you adding another axis to the equation greatly expands your possibilities. You can make parts that you might not have been able to before when just using 2-axis programming, and it can possibly reduce cycle times.

First, we must establish the difference between two and three axis machining. Most CNC mills these days should be able to accept and perform programs with 3-axis machining. Two and three axis machines both have an X, Y, and Z axis, but using that third axis for milling profiles can allow you to profile the surface of a part.

In 2-axis milling, you can move in the X and Y-axis at the same time if you’re milling the outside or inside profile of a part. If you’re using the third axis, you can make X and Z-axis moves while milling a profile, such as a waving contour. You can also move in the Y and Z-axis if you simply change the plane that you program in.2 vs. 3 Axis Machining - CNC Profiling

If you’re hand-writing the program, G17, G18, and G19 are the CNC commands for selecting which plane you want to machine on.

G17 is the XY plane.

G18 is the XZ plane.

G19 is the YZ plane.

Other than that, programming is virtually the same as any other G-code program. If you want to make a positive Z and negative Y move, an example would be:

G90 G20 G19 (To set the YZ plane and absolute)


G1 Y-.5 Z2.23

If you want to go back to the traditional XY plane, a line with G17 will be needed.

If you have rendering software or a program that simulates your program, I strongly recommend using it on a new program, especially if this full 3-axis machining is new to you. Good luck, and go experiment! The best is experience is with machine time and trying new things.

What Is Lean Manufacturing?

Any company in the machining industry has to incorporate Lean Manufacturing in their business and process plan to survive these days. To put it in simple terms, lean manufacturing is the production practice of being efficient by eliminating any ‘waste’ in the process plan. Though they may not call it this, all companies strive to be lean because it makes their customers happy, and ultimately, more money.

Although there was seven original “Wastes” involved in lean manufacturing, we’ll look at eight of the most common ones in a machine shop. Most of them are simple, but it can take a lot of work and orchestrating to implement them all. There is no perfect company that has it all figured out. There is always room for improvement, which is why employers seek new ways to lean out their manufacturing process. The acronym for this practice is “DOWNTIME”. Now you could just look this term up on wikipedia, but it won’t give you a real perspective or example of what it means. Those are just general illustrations in the manufacturing industry, but working in a machine shop may produce different scenarios.

Defective Production:

If bad parts are made, it takes more time to either re-work it or make another one. More material, more machine time, more tooling wear, which can add up to almost double the cost of a part. The machine shop pays for this and not the customer, and that is why it is on the list of big “wastes” that companies try to eliminate. We are only human, so mistakes do happen occasionally, but the goal is to decrease the percent of defective parts.


I believe that this one can go either way, but if space is expensive, then overproduction is definitely considered a waste. If you make extra parts for a customer, it costs more time to make them, and the excess supply of parts costs more to store because it takes up more space in between machining and shipping, plus the time it will take for the customer to order more. If something happens to the customer and they discontinued that part or went to a different vendor, your extra inventory has now turned into a complete waste of money.


There’s two ways you can look at this; the parts that are waiting, or the machinist that is waiting. This happens whenever you have stock waiting to be cut or for operations on a machine. There is usually a waiting time in between finishing the parts and shipping. This takes up valuable time, as well as space. Although it may not seem like a big difference if parts are waiting an extra day or two to be worked on or shipped, the quicker you get the parts out your door, the quicker you can move on to another part/order.

Non-used Employee Talent:What Is Lean Manufacturing

This should be an easy, but too many employers miss it. If you have an employee that is skilled multi-axis machining and/or programming, putting them on a grinder or running simple mill parts is a waste of talent. Even if they need a little more training, it’s much more efficient to move that employee to the more complicated work instead of hiring another person, which you may have to train-in anyway.


Transportation is all of the unneeded movements of parts and materials. The shortest route from point A to point B is a straight line, anything else is wasting time. While it’s not always possible to do this in a machine shop, the shorter the distance parts and material have to travel the better.


This is similar to overproduction because having too big of an inventory takes up space and takes more machine time to run. If you’re making more parts than the order requires, it is considered wasteful inventory.


Much like wasteful transportation of parts, a machinist should reduce wasteful motion as much as possible to be efficient. If you’re setting up a job, all the tools should be set-up and ready to go or on the workbench next to the machine. This can be done during cycle time of the previous job to save time. When loading and unloading parts in the machine during production, as well as part deburring, having everything close by or within reaching distance will reduce motion and save time in the long run.

Excessive Processing:

Like mentioned before, time is the biggest money breaker or maker, and if you’re spending too much time trying to perfect parts or orders when it is not needed, then you’re wasting time. If you have wide open tolerances on some or most of the part features, spending extra set-up and/or cycle time to try and get it right at the nominal number is waste. As long as all of the parts are within tolerance of the blueprint, they’re good. If the part doesn’t go together during assembly or function properly, it’s that customer’s job to fix the print, not the machine shop’s job.

Now, how can YOU as a Machinist benefit from all of this? This can help boost your reputation at your current job, as well as your resume. The harder you work at being more efficient, the more your boss/foreman will notice. This may result in better raises, a promotion, or benefits in various ways.

Although not all of these factors directly relate to you, suggesting them to higher authority may give you better recognition in the long run.

Basic Programming Terms – CNC Structure In 4 Steps


The smallest unit in CNC programming is a character. It can be a letter, digit, or a symbol. They are combined to make ‘words’ in the CNC language. A letter is just what it sounds like; a letter from the alphabet. While 26 letters are usable for programming, read this article for a list of commonly used letter codes.

There’s ten digits, 0 to 9, used to make numbers in programs. They are used in two different ways; with or without decimals. It depends on the mode, as well as the control. A number can also be used in place of a decimal-number if the controller allows it.

Symbols are the third type of character used in CNC programming. It depends on the control options, but the symbols used most often include: a decimal point, parenthesis, minus sign, as well as a percentage sign.


Words are the next step in the structure, and they are simply a combination of characters. A word consists of a capital letter, followed by a number, and sometimes a symbol, depending on the code. Words are used to specify speed, feedrate, position, commands, and other functions.


Basic Programming Terms - CNC Structure In 4 Steps

A Block, also known as a Sequence block, is multiple Words. A word is just one piece of information or instruction, while a block uses at least one word to make a complete command or cycle. Blocks are written on separate lines, and are separated by an “End-of-Block” code.


How do you get a CNC Program? You put a bunch of Blocks together that will machine a part. As simple as that sounds, you have to have all the right characters and words to get each command to work. A program will begin with a program number, and will be sequenced by blocks in order of operations, and end with a program stop or cancel code.

Character > Word > Block > Program

Letter Codes List For CNC Machine Programming

If you’ve already learned all of the Preparatory and Miscellaneous function codes, it’s time to move on to the Letter codes for CNC programming. Most of the letters of the alphabet are used on milling machines.

Just like the G and M codes, not every machine uses the same Letter codes. Also, there are several letters that are used in more than one function, but that depends on the input units.

Below is a list of the most commonly used letter codes when programming on a milling center. However, I recommend reading through your machine’s manual to confirm that they have the same function, or if your machine uses different letters/codes.

  • A – Rotary or indexing axis around the X-axis (unit in degrees)
  • B – Rotary or indexing axis around the Y-axis (unit in degrees)
  • D – Cutter radius compensation offset number
  • F – Feedrate function (may vary)
  • G – Preparatory command (G-code)
  • H – Tool length offset number
  • I – Arc center modifier for X-axis (radius)
  • J – Arc center modifier for Y-axis (radius)
  • K – Arc center modifier for Z-axis
  • L – Repetition count for subprogram/fixed cycle
  • M – Miscellaneous function (M-code)
  • N – Block or sequence number
  • O – Program number
  • P – Subprogram number call; Work offset number (used with G10); Dwell time in milliseconds; Block number in main program when used with M99
  • Q – Depth of peck in fixed cycles G73 & G83; Shift amount in fixed cycle G76 & G87
  • R – Retract point in fixed cycles
  • S – Spindle speed in Rotations per minute (RPM)
  • T – Tool function
  • X – X-axis coordinate value designation
  • Y – Y-axis coordinate value designation
  • Z – Z-axis coordinate value designation

Letter Codes List For CNC Machine ProgrammingMost of these letters you will be using over and over again in your programs. A and B are used if you have a four or five axis machine, otherwise you won’t need to use them.

Some letters have multiple uses that you may have to incorporate in your program. “P”, for example, can call out the time that you want to dwell (pause) with a tool, or it can call up a subprogram number.

It’s up to you to learn these if you want to know how to create and edit programs. A lot of the letters are easy to remember, so if you already memorized all of most of the G/M codes then this is a piece of cake.

M-Codes List For CNC Machine Programming

Miscellaneous Functions is another name for M-Codes. How are they different from the G-codes in my previous post? The G-code is a preparatory command for CNC programming, which presets, or prepares, the machine to use a certain cycle or mode. An M-code is an actual machine function.

A machine function is something that the actual machine does, whether it’s turning on the spindle or ending your program. Not every machine is the same because there are many different CNC machine manufacturers, as well as different controllers, so I recommend reading through your machine’s manual to see what M-codes you can use.

  • M00 – Compulsory program stop
  • M01 – Optional stop
  • M02 – End of program (no rewind, usually with reset)
  • M03 – Spindle on (rotate CW for R/H tools)
  • M04 – Spindle on reverse (CCW for R/H tools)
  • M05 – Spindle stop
  • M06 – Automatic tool change (ATC)
  • M07 – Coolant mist ON (optional)
  • M08 – Coolant ON
  • M09 – Coolant OFF
  • M19 – Spindle orientation
  • M30 – Program end (always resets & rewinds)
  • M48 – Feedrate override cancel OFF (deactivated)
  • M49 – Feedrate override cancel ON (activated)
  • M60 – Automatic pallet change (APC)
  • M78 – B axis clamp (nonstandard)
  • M79 – B axis unclamp (nonstandard)
  • M98 – Subprogram call
  • M99 – Subprogram end

M-Codes List For CNC Machine ProgrammingUnlike a G-code, you can only use one M-code per line/block of code. Using an M03 and M04 is not possible because they do two opposite functions.

The more M-codes you try out, the more efficient you can become. M98 can significantly decrease programming and possibly cycle time because it calls up a sub-program that can be repeated over and over any given number of times.

There are more Miscellaneous functions than listed above, which are referred to as ‘machine specific codes’. You will have to learn the codes used by your individual machine and controller to get the most out of your CNC machine, whether it’s a milling or turning center.

Basic Machining Tools – Terminology

There are a lot of tools used in machining today, so it’s often hard to keep up with the names of all of them, especially if you’re new to this career. Every tool has a specific job, and while a variety of tools may be able to get the job done, some are better than others.

Just so I don’t overload you, I’ll go through a list of the most common tools used in Machine shops, as well as Machine Tech schools. Each tool has a specific purpose, and there are many different kinds of the same tool. The more tools you use, the more knowledge you will get and know what works better for a certain material or operation. However, you must get an understanding of the of machining tools before just using any specific one without knowing what it’s meant to do.

End Mill

The almighty ‘End Mill’ is one tool that you will use almost every day if you run milling machines. If you need to cut both ends of a part to get it to a certain length, and end mill will side-mill the ends to make a clean and parallel surface. It can cut out pockets, and make square or round features in a part. There is so much that you can do with an end mill on a CNC milling center.

3-Flute End Mill
3-Flute End Mill

Whether you need to rough out a large solid piece of steel, or you’re just making some finish passes on aluminum, there’s an end mill for each job and every one in between. There are many different kinds of end mills. Here are the main variables you will have to decide when ordering tools: size (diamter), length (flute length), material/coating, roughing/finishing, number of flutes, and more.


Need to drill a hole? How about a few hundred holes? While there may not be quite the selection for drills as end mills due to the fact that you can only do so much with them, there are definitely right and wrong drills for any given job. 118 degree HSS or coated drills are the most common since they work well with most basic materials. However, you may need a drill for a hard stainless job, or perhaps a copper part that requires a deep hole with a close tolerance.



There’s not much else you can do with a tap other than tapping holes. Are you doing a blind or a thru-hole? Is it a metric or a U.S. standard thread? If you’re on a mill, the most popular taps are: cut tap, roll form, spiral point/flute, as well as a thread mill.

Cut taps produce chips because they literally cut a thread into the existing hole. You must use a drill that meets the minimum diameter tolerance for the specific thread you want. They are used on thru-holes because the chips won’t get in the way of the tap.

A roll form tap does not make chips because it forms and pushes the threads into place. It’s great for blind holes because the tap won’t break from chips collecting at the bottom.


A ream is used after a drill or a bore to meet a close tolerance call-out on the blueprint. Cheap drills are far from perfect and can easily make a hole over-sized, which will be rejected if it’s not within print. However, if you drill the hole .010″-.015″ under-size, you can then use the correct size ream to get a much more accurate and consider hole.


However, you should know that a ream will not ‘fix’ a hole. A ream just follows a hole, so if it’s crooked or out of round, the tool will follow that path. This is one reason why you may need to drill the hole then use a boring bar to make it perfectly round and straight before you ream it to size.

That’s it for the basic tools on this article from CNC Machinist Training. Stay tuned for another article that explains more advanced tooling that makes it much easier to do a job…