Category Archives: Fanuc Turn

Modal and non modal G codes

Modal and non modal G codes

Modal and non modal G codes

Let Me explain

We all know that programming can be complicated. So let me explain to you how it all works. This article explains the real meaning of Modal and non modal G codes.

Modal means that once a command is issued it stays in the control.

How Can you Actually Use This?

If you issue a G0 or G00 command the machine is in rapid and you do not need to re-state it.

Rapid means all motors are flat out, like a teenager in a Ferrari.

Every move from then on will be a rapid move unless you tell it otherwise. The G code that changes it must be in the same group. For example G0 G1 G2 and G3 are all in the same group a bit like The Beatles used to be.

The other day I was talking to  a “young person” who hadn’t even heard of the Beatles. I mean fuckin hell, am I really really old or are they doomed to be forgotten?

By the way my definition of a young person seems to get older every day.

Imagine being called a “young person”. You hear politicians on the telly saying “oh yes I was talking to one of those young people the other day”.

God I hate the fuckin telly, well apart from Love Island, Naked Attraction, Embarrassing Bodies, Goggle-box, Coronation Street, Emmerdale Farm, East Enders, and Strictly Come Dancing.

To be really honest I watch everything but in my defence I never stop complaining and throwing Pot Noodles at the TV.

Here’s one I made before the program

My TV’s are covered in dents and scratched from various foreign bodies being thrown at them. Obviously I have a TV in every room and toilet. They all still work even when the noodles trickle inside.

I have five, toilets not TV’s. My mother said “you must use loads of water, not to mention lavatory paper”

I said “mummy darling don’t you understand that you can’t shit or a piss in five toilets at the same fuckin time”

Obviously I didn’t say toilet in front of my mother it’s always lavatory.

Oh Yea I Was Saying I Hate The Telly

I saw this thing on the Internet 8 huge Emmerdale Spoilers .

Now I know a lot of you CNC Programmers out there are big fans of the show but I got to say it.

Spoiler I mean how in the fuck can you spoil something that’s already a mind numbing piece of crap!!

When I hear the music to that show it gets me really enthusiastic about emptying the cat trays that are heaving with piss and shit. (I know you are not supposed to leave them for over a week but in my defence I am getting into a routine now)

“Come on Dave the swearing gets worse, the Americans won’t like it”

I admit this is a rant too far and I wouldn’t blame you for going to a different website.

This guy writes serious stuff about G Codes unfortunately for you, almost every post and video is full of mistakes and often blatantly wrong.

Anyway you deserve it for not sticking with me through  difficult times.

I shouldn’t say this but there are so many mistakes in these articles I don’t know how the fuck he gets away with it. Well that’s the Internet folks.

His new series of training videos is called “Learn The Five Quickest Ways to get Instantly Dismissed as a CNC Machinist”

Modal and non modal G codes

G0 Rapid.
G1 Feed.
G2 Clockwise arc.
G3 Counter-clockwise arc

It is pretty obvious that these would have to replace one another because if you had them on the same line they would contradict one another.

You can’t go around a clockwise circle and in a straight line at the same time.

Tigers Fighting About modal G Codes

G0 X0 Y0 (Rapid to X0 Y0)
(Control says “ok I get it, rapid again, no need to repeat yourself, I heard you the first time”)

Modal and non modal G codes. How do they actually Work?

There are not many non modal commands G53 and G4

Can’t think of anymore right now.

G4 is a dwell if this were modal it would cause many problems

G0 X50. Y50.     (Rapid move)
G4 X5.                  (Five second dwell)
X0                        (This would be a rapid command not another dwell because it remembers the G0)

It remembers the G0 but conveniently forgets the G4.

My third wife was a bit like that she said I slapped her in the face but conveniently forgot that this was only after she kicked me in the bollocks and chopped off my left ear with a potato peeler.

The machine will do the G4 dwell and then completely forget it. If you really want another dwell you’d have to repeat the G4. Otherwise it’s like being told it’s your turn to feed the dog, the command is ignored.

Yes folks you can use X or P for a dwell command. I use X cos I love the feeling when the operator comes back to me n says “Dave you got this wrong”.

First of all I ignore him because my name is David and I don’t answer to Dave.

When he finally gets through to me, I love that feeling of power and superiority when I explain to him it works with P and X.

G53 is a machine position command.

If you use a non modal command you have to repeat it for every line you want to use it on.

G53 Z0;
G53 X0 Y0;

“Wake Up State” Modal and non modal G codes.

What’s This all About?

These are the G codes that are active when you turn on the control. Wake Up State, not to be confused with getting out of bed with a steaming hangover after a night on the piss.

Modal and none modal G codes
Wake up state

This wake up state cannot be guaranteed as you can change this state by parameters.

There is also a parameter which controls what happens when you press the reset button. So for example pressing reset may cancel a canned cycle. (Or not).

Modal and non modal G codes
Worn out reset button
Your modal G codes will change when……
  1. You press reset.

  2. When you first turn on your machine (Wake Up State)

  3. You read an M30 at the end of a program.

M Codes

These are not actually called modal but the same applies once you start the spindle (M3) you do not need to write it again until you want to stop or reverse it. M4 will start the spindle in reverse CCW. M5 will stop spindle.

No need to programme M05 just M5 will do try reading this.


Speeds are modal but your machine may wake up with a speed of zero.
So in MDI if a speed is active and you program M3 the spindle will start at the active speed (so be careful). 

If you program just a speed S2000

If the spindle is running it will change. If the spindle is not running it will change but not start. When you later start the spindle it will be at the new RPM.

When you program just a speed the machine becomes a smart arse. It laughs at you saying “Fuck off sucker, I’m not starting the spindle cos you didn’t ask me”

Wasted Code

When I first started programming CNC machines in 1905 each program had loads of information at the beginning. None of us knew what the fuck it meant and no-one dared to alter it or take any of it out.

It could only be altered after a religious ceremony and the ritual slaughter of a Gerbil when there was a full moon.



Did someone say Gerbil

You could be fired on the spot for even talking about these G Codes.

If only we had known about Modal and non modal G codes life would have been so much better.
So now I am all grown up, I say “do everything for a reason”. Consider your Modal and non modal G codes.

The program on the right has wasted code.


Oh and in the early day’s we often used to turn the machine off and back on again which usually sorted most problems.

No one knew why the fuck we did this but because it seemed to work we always did it.

Women often say why do men keep putting their hands down their pants. The answer is we don’t know but we do it anyway. Well I don’t know maybe you do know why.

Coming back to turning the machine off and on again. Imagine if you didn’t have a G50 in your CNC lathe program and it was set to a very low speed in another program that you had just been running.

You could wonder why you machine was running so slow. Obviously if you turn the machine off this would reset. Everything would work fine again.

So let’s see how this works.

You may want to include this line at the beginning of your program as a standard thing.

G40 G80 G90 G21

G40 Cancel tool radius compensation.
G80 Cancel canned cycle.
G90 If you state this at the beginning of each tool then you don’t need this at the start of the program.
G21 Metric, if you never change to inches you don’t need this at program start.

Here is an article on well set out CNC Code.

Anyway if you must write a load of bollocks at the beginning of your program please learn what each G Code means and why it’s there. Oh and don’t blame me when your fingers wear out.

It’s just not good enough to say “the bloke on nights always puts that in”

And That’s Not All with Modal and non modal G codes

If you are running short on memory these are things to look at. Some CAD systems will output loads of unnecessary shit but you need to sort your post processor to stop this. It’s quite easy to fix. Loads of leading and trailing zeros to get rid of.

X0.000 same as:
X050.000 same as:

Feed-rates are modal too so you only need to state them once and then again when you wish to change them. 

It is best to state all of the modal information you require at the start of each section of code. Just after the tool change is the best place.

Try to program each tool as a section, as if it were a program on it’s own.

Each tool should have all the necessary information to run on its own. Nothing should be assumed at the start of each tool. Oh and always take into account Modal and non modal G codes.

Modal and none modal G codes

But There is a Catch

Be careful when using MDI with Modal and non modal G codes as you do not know what G codes are active. All controls will have a screen displaying active G codes.

There are loads of them on this screen, don’t worry if you don’t know what they all are (even Fanuc don’t really know, they just make them up).

How Can you Actually Use This?

If for example in a section of program you have only one feed rate then that is all you will need to alter. If it’s repeated in several places (which your pesky CAD  system may do). Then you will need to remember to change each one.

I very much doubt that you enjoyed reading this article but their are loads more

Loads of articles on CNC Programming, enjoy yourself:

Checking CNC Programmes

Using a Decimal Point

CNC Programming

Zeros Not required on Haas Control


G0 Cancels Canned Cycle

Modal and non Modal

G28 Verses G53

An introduction to Macro Programming

Just an Address will do…

Turning Basics G50

Letter O number Zero

Running Order

Leading and Trailing Zeros

Jumping Sections of Program

Well Set Out Code

Thanks for reading my article.

Please contact me if you require:

  • CNC programming training.
  • Want to learn CNC programming.
  • Fanuc control training.
  • Yasnac programming training.
  • Any type of CNC course.
  • CNC lathe training
  • CNC Vertical Machining Centre training
  • If you have won the lottery and you want to give some money away.

Services offered at CNC Training Centre

Classroom programmer training.

Onsite CNC Machine Training.

CNC Programming and Training on all controls and machines.

Mazak Training Fanuc Training

Don’t forget we offer training on all types of Mazak Machines and all Fanuc Controls 6m to 31i Oi old to young.

Jumping Sections of Programme Using M99 and Block Skip


Click for M99

Please contact me if you require:

  • CNC programming training.
  • Want to learn CNC programming.
  • Fanuc control training.
  • Yasnac programming training.
  • Any type of CNC course.
  • Fanuc training courses
  • CNC lathe training
  • CNC Vertical Machining Centre training

Contact: 07834 858 407

Services offered at CNC Training Centre

Edgecam training.

Classroom programmer training.

Onsite CNC Machine Training.

CNC Training on all controls and machines.

Mazak Training Fanuc Training

Don’t forget we offer training on all types of Mazak Machines and all Fanuc Controls 6m to 31i Oi old to young.

Jump Around Using M99 Plus Block Skip

Using M99 Plus Block Skip

Call David 07834 858 407

M99 Plus Block Skip, M99 on a Fanuc, Haas or Mazatrol ISO control can be used to jump sections of code.

Learn to use this in conjunction with the block skip command to switch it off and on.

Now I know you are all thinking “Dave you’re wrong it’s the end of a sub-program”. (Please in the name of holy shit do not call me Dave.)

Well you are right and you are wrong.

Yes it means continue and is used at the end of a sub program.

But it also has another nifty use.

Imagine you want to skip a complete section of program in the case below it’s the Spot Drill.

Let’s See Some Crap Ways Of Doing This

(If you want to do this on a Toshiba Tosnuc 888 or similar control go to the end of the article)

In this example it’s a spot drill we want to miss out.

M99 Plus Block Skip
Standard Code

You could delete it and make two programmes (sounds like hard work and loads of errors). Not to metion wear on your finger tips. Truth is it’s just a shit way to do it.

M99 CNC Code
Block Skip

The programme above  contains BLOCK SKIPS sometimes called BLOCK DELETES.

When you switch on your BLOCK DELETE/BLOCK SKIP switch, each time a forward slash (/) is seen that block will not be processed and the control will move on to the next block.

M99 Plus Block Skip

On most Fanuc controls it’s B.D.T not to be confused with CBT (Cock and balls torture) please do not google this in company time.

It works ok but it is very time consuming. If you want to skip a big section of code you will have to write in loads of block skips.

Call me a lazy bastard but I definitely couldn’t be arsed with that.

Some controls even have two three and four block skips so you can switch on any combination of these switches, mmmm complicated. Good luck with that one.

Do You Have Adequate Life Insurance?

M99 CNC Code (Now let’s use it)

The next example is the easiest way.

You probably normally see an M99 at the end of a sub programme.

In the case below it tells the control to jump to N100 (M99 P100).

The P part is the N number you want to jump to.

M99 P600 (Jump to N600)
M99 P6666 (Jumps to N6666)


M99 Plus Block Skip

If you put the BLOCK SKIP/BLOCK DELETE on it will not jump the spot drill.

You would have a choice. If you temporarily want to skip a section of code.

Be careful what N Numbers you choose so as not to mix them up.

Maybe you broke all the taps and you don’t have anymore so you want to skip the tapping. In this case I’d just jump with M99 and then take it out before saving the program.

However, see the next Example.

For this last example you might have to think a bit. Call me finicky but I like the BLOCK SKIP/BLOCK DELETE as a default to be off.

Most machines now don’t have a mechanical switch for BLOCK DELETE/BLOCK SKIP so when you turn on the machine block skip will always be off.

That means the default would be to jump the code.

My way of looking at it, is that you would want the default to be running the whole program as normal.

So We Are Agreed

The default should really be the way the programme was originally done.

In the example below if the block skip is off, which it will be when you start up your machine.

The first thing it will do is jump over the bit that tells it to jump the code.

Meaning it runs as normal not jumping any tools.

The Clever Shit (M99 Plus Block Skip)

M99 Plus Block Skip
What’s This?

Now I know this is a bit confusing and maybe I didn’t explain it too well. Trust me it works.

What’s the matter with you lot just take some time to fuckin read it.

Sorry I’m losing my temper a bit here, the dog’s just pissed on the TV remote again. Just read through it a few times and the penny will drop.

CNC Training Centre Classroom Training

Where the teacher is never angry.


Yes you can do this with GOTO

This is my pet Cockroach his name is Boris

GOTO 100
Same as M99 P100

To do this you must have the Macro Option if you don’t then this is where M99 comes in handy.

Best way to see if you have macro is to try using it in MDI.

In MDI Type in #1=6 if you have macro it will work if you don’t you’ll get an alarm and your machine will self destruct in 15 minutes.

Jumping Sections of Code on a Toshiba Tosnuc 888 or Similar

This is how you do it on a Toshiba (the blue bit).

Don’t forget it’s GO (that’s G and letter O) not G0 which is G and number zero (Rapid Command).

Don’t get your letter O’s and your number zeros mixed up.

/M99 P50                                   /[GO,50]               (JUMP TO N50)
M99 P100                                    [GO,100]            (JUMP TO N100)
N50                                              N50                      (ARRIVE HERE
N100                                            N100                      (ARRIVE HERE)

Without Fancy Shit  (Just jump some code)

M99 P100                                    [GO,100]            (JUMP TO N100)
N100                                            N100                      (ARRIVE HERE)

If you have macro you can do a similar thing on Mazak, Haas or Fanuc.

Services offered at CNC Training Centre

Edgecam training.

Classroom programmer training.

Onsite CNC Machine Training.

CNC Training on all controls and machines.

Mazak Training Fanuc Training

Don’t forget we offer training on all types of Mazak Machines and all Fanuc Controls 6m to 31i Oi old to young.

Call 07834 858 407

G96, G97 and How To Calculate Surface Speeds

Basic Turning

Basic Turning
G96 Hamsters Large wheel Small wheel
Call us for CNC Training and hamsters

Basic Turning, in the early days of CNC Turning G96 was one of the things that really made a massive difference.

It meant that instead of having to turn a part at a fixed speed and feed, the part could be programmed in G96 which was a constant surface speed.

Where diameters changed, particularly when facing, it made a massive improvement to tool life and surface finish as well as speeding up the whole process.

G97 Speed In RPM

In Basic Turning when you program G97 your machine will start the chuck up at a speed in RPM. So if you program.
G97 S1500 M3
Your chuck will start revolving clockwise at 1500 rpm.

G97 for Drilling Tapping and Screwcutting

When drilling  a hole you are on the centreline of the machine so you just want plain old simple RPM.

When tapping or spot drilling it’s the same.

Screw Threading (G76) can only be done in G97


G96 however means meters per minute. This is a surface speed.
G96 S200 M3
Your machine would start up at a surface speed of 200 meters a minute. Now your RPM would depend on where on the diameter the tool was positioned.

Basic Turning

If the tool was positioned  at a 100mm diameter it would be as if the tool were able to run around this diameter at  a speed 200 meters a minute.
It’s a bit like being on a running machine if you ran at 200 meters a minute and placed various diameters under your feet the large ones would turn at slow rpm and the small ones would turn at high rpm. (Just like the hamsters above)

Basic Turning

 That’s why on a manual lathe it is hard to face a large diameter without changing speed half way.


You know when you face a part on a CNC Lathe and you hear that change in pitch? It’s the spindle increasing in RPM as it gets closer to the center of the part.

When it gets to the center your spindle is flat out so the G50 becomes crucial.

The G50 restricts the speed of the machine.

G50 S2000 machine will go no higher than 2000 rpm.


G96 G97 hamster on a Wheel

Did you have a pet hamster as a child?

I know it’s a random question but bear with me there is a point to this.

Well maybe you still have a Hamster and that’s not a problem. Time you fuckin grew up but it’s not for me to judge.

Anyway I did and his name was Harold Wilson (British Prime Minister at the time).

Well I bought my hamster loads of different wheels to play on just like the one above.

My hamster suffered with depression on account of being stuck in a cage all day and not having a girlfriend oh and he had a lot of credit card debts too.

These wheels varied in diameter from about 6 inches to a massive 2 foot one. They kept him happy all night. He was so tired he slept all day.

Harold could only run so fast but I noticed when he was on the small 6 inch wheel it absolutely whizzed around. Now on the big two foot diameter one it took him ages just to get it to spin around once.

Basic Turning
G96 G97 all about hamsters

Harold Had G96

A CNC machine in G96 will give a lovely finish because the surface speed always remains the same.

So even though Harold ran at 200 metres a minute (this is fuckin lightening speed for a hamster)

The wheels ran at different RPM depending on what diameter they were.

Harold Was a Clever Bastard

Oh by the way Harold had a tail (unlike other hamsters) and a maths qualification.

He knew that if he multiplied the diameter of the wheel by .00312 it would give him the circumference of whatever wheel he was running on in meters.

200 mm wheel (.00312 x 200 = .6864)

All he now needed to do was divide this answer into the speed he was running at and he would know how many RPM his wheel was revolving at.

If he was running at 200 meters a minute not only would he be fuckin knackered but the wheel would be running at 291 rpm

200 / .6864 = 291

Basic Turning Manual Machining

Using a manual machine you have to compromise. At the outside your speed is too fast and when you get to the centre you are too slow.

Manual Lathe

On a CNC lathe we would normally program in mm per revolution as well because the speed is changing all the time so we need our feed to be locked into the speed.
With a machining centre our cutter is always revolving at the same speed so the feed can be constant in mm per minute.

Someone out there will be thinking “what happens in G96 when you get to the centre of the part”. Well the spindle will be flat out!

Could be a problem. That’s where your G50 comes in to restrict the speed. Very important! CNC Basics G50

cnc turning basics
G50 Warning

Watch the video

See how surface speeds are translated to speeds in RPM. There are many converters online that you can use for this and I do recommend their use. It will also mean you don’t have to watch my tedious video.
When I train people at the CNC Training Centre my emphasis is on understanding not memorising. I usually start by saying “please don’t remember all the things I am telling you”.

 In the early days training students in Basic Turning I remember them saying to me the next day that they had G codes floating around in their head from the lessons the day before.

Basic Turning
G96 and G97

What I really mean is that the most important thing is to understand what the machine can do and the concepts of programming and Basic Turning.
You could say “I know there is a G code that makes the machine run in RPM” so all you need is a list of G codes.

If you can be bothered to work through the simple maths above. It will help you to fully understand how G96 is works.

Here is a list of Basic Turning G Codes.

The ones you use every day you will remember whether you want to or not.

G96 Whoopee It’s amazing

So use G96 for everything.

Except for:

  • Drilling.
  • Tapping
  • Threading (Screw cutting)
  • Cutting the Lawn

If you feel you have been affected by any of the issues mentioned in this post please Contact me

If you liked this video, please don’t forget to subscribe to my YouTube channel by going to: CNC Training Centre

Please contact me if you require:

  • CNC programming training.
  • Want to learn CNC programming.
  • Fanuc control training.
  • Yasnac programming training.
  • Any type of CNC course.
  • Fanuc training courses
  • CNC lathe training
  • CNC Vertical Machining Centre training

Services offered at CNC Training Centre

Edgecam Training.

Classroom programmer training.

Onsite CNC Machine Training.

CNC Training on all controls and machines.

Mazak Training Fanuc Training

Don’t forget we offer training on all types of Mazak Machines and all Fanuc Controls 6m to 31i Oi old to young.

G76 Threading Cycle How Many Passes

G76 Threading Cycle you must agree that it’s not easy to use.

Read this article, no more sleepless nights worrying about G76 Threading Cycle. Myth busting information that simplifies and demystified. Applies to Haas, Fanuc and Mazak ISO

G76 Threading Cycle

Be sure to read the end of this article to see a simple way to calculate the number of passes needed.

I noticed quite a few people posting problems on Machining forums etc and as usual loads of misinformation. I decided to do a search on this and frankly there is “Bugger All”. So here we are.

 What Exactly is a G76 Threading Cycle?

G76 Threading Cycle

To cut a thread with a long hand G code program would take ages. Just one thread could need 30 lines of code. So to me that means loads of opportunities to screw up and it’s complicated.

Oh and It Gets Worse.

If you want to change something it is a nightmare. You will have to reprogram it just to change the depth of cut.

And not to mention all that boring maths that you will have to do. You remember that teacher with the beard that kept banging on about ratios and differentiation? Well, maybe you should have paid more attention.

Just One or Two Lines and It’s Done.

Read on, it’s simple and it’s complicated.

Sounds daft I know but you can miss out a lot of the complicated stuff in the cycle as a lot of the values have defaults (meaning you can miss them out).

Some of them are just boring and only used by clever fuckers, not normal people like you and me.

G76 X16.93 Z-25. K1.534 D.485 F2.5 (Simple as this)

Multi Repetitive Cycles do you know what they are?

Really, you don’t need to know, it’s just me trying to impress. Most of the cycles on a CNC Lathe are wrongly call Canned Cycles. The correct name for a cycle like G76 Threading Cycle and G71 Roughing Cycle is a Multi Repetitive Cycle. No that’s not an illness it’s the correct name. So don’t start ringing the “no win no” fee lawyers.

Canned cycles repeat each time a position is given. Multi Repetitive Cycles do what the title suggests, they repeat moves within a process. In threading, the cycle creates all the repeated moves needed for the thread to be produced.

That’s another piece of useeless information.

G76 Threading Cycle. So How Does It Work?

On a Fanuc control this is either a one line cycle or a two line cycle depending on age of control and parameter setting. Haas is a one line cycle.

You tell the cycle the depth, pitch, core diameter, length and maybe a few more “bits n bobs”. Then at the push of a button your thread appears.

Haas and Some Fanucs

G76 X16.93 Z-25. K1.534 D.485 A60 Q0 P2 F2.5

X = Core diameter of thread
Z = Thread end point
K = Depth of thread (as a radius)
D = Depth of first cut
A = Insert angle (Assumed A0 if not entered)
Q = The thread start angle this is used for multi start threads and can be omitted.
P = Cutting method (see later explanation, can be omitted)
F = Pitch of thread

Note on the Fanuc control you would have to enter the D value with no decimal point (D485)

So G76 Threading Cycle in it’s simplest form

You could write:
G76 X16.93 Z-25. K1.534 D.485 F2.5


G76 P010060 Q20 R.02
G76 X16.93 Z-25. P1534 Q485 F2.5

G76 Threading Cycle First Line
P01   One spring pass       00   Chamfer        60   Thread angle
Q       Minimum depth of cut
R       Finishing allowance

G76 Threading Cycle Second line

X         Core diameter of thread
Z         Thread end point
P         Depth of thread (as a radius no decimal point)
Q        Depth of first cut no decimal point.
F         Pitch of thread

On the Fanuc control it uses a two line display the P010060 is split into three sets of two digits.

First two being the number of spring passes.
Second two are chamfer. (More Details)
Third two are the tool angle.

So G76 Threading Cycle (Two Line) in it’s simplest form

Sorry there ain’t one, it’s complicated!

What on Earth are Spring Passes?

G76 Threading Cycle

When you cut a thread you get push off on the last cut so you can go over this a few times to get the correct size. These extra cuts are called spring passes. It depends on the material as to how many you will need.

Fuck The Zeus Book

Oh and by the way don’t go looking up the thread depth in some Zeus Book or some such thing. Just multiply the pitch by .614

Lets Cut an M20 x 2.5  Thread Using The G76 Threading Cycle

Thread Depth =.614 x Pitch

.614 x 2.5 = 1.535

X Minor Diameter to cut = 20 – (1.535 x 2)

X Minor Diameter to cut = 16.93


G76 Threading Cycle

G76 X16.93 Z-25. K1.535 D.485 F2.5

Have You Been Doing it Wrong for Years?

As I said above when I started googling G76, it’s not a pretty sight. For one there’s not that much information and not least of all some of it is wrong.

There are some absolute pricks out there claiming to know all about CNC Programming who actually know Jack Shit.

The way you use this cycle makes a big difference to the way the tool performs. The default above for the Haas G76 Threading Cycle would give you what is known as a “plunge cut”.
G76 Threading Cycle

It is where the tool plunges into the thread and the cut gets wider and therefore is more prone to chatter as it deepens. It is going straight down the centre of the thread vee.

If you put in A60 then the cycle will flank cut.

Flank Cut?????

See below:

Don’t know what flank cutting is? Don’t worry it just means you are stupid. I won’t tell anyone, your secret is safe with me.

Help is At Hand

Ways to cut a thread

(1) Plunge: cut straight down the middle of the thread programme. A0 or simply miss it out.


G76 Threading Cycle

(2) Flank cut: Cuts down the flank of the thread. A60 on a 60 degree thread form.

G76 Threading Cycle

(3) Alternate flank Cut: Switched from side to side cutting down the flank of the thread. A60 P2 if you have the option.

G76 Threading Cycle

So Which One Is Best.

The last one number (3) is the best and number (1) is worst.

Sorry to you geeks but I am going to over simplify it.


With method three you get a nice even cut with less chatter and less tool wear. It’s also kinder to your insert and better for the environment.

G76 Threading Cycle

If you don’t believe me then talk to your tooling guy. He knows more than me anyway.

G76 has a P value of 1 to 4 (P1 P2 etc). This determines the four different methods you can use. My advice is just ignore them all and use P2. This means the tool cuts by alternating between the two sides of the thread as above. You will also need to input A60 for the angle of the tread.

G76 D.485 K1.534 X16.93 Z-25. A60 P2 F2.5

Yes and as Always There’s a Catch

You will only have alternate flank cutting on a newer machine if you have an old banger then you’re stuffed.

Not to worry just use method (2) flank cutting it’s fine.

G76 Threading Cycle

Providing you input the insert angle A60 on a 60 degree thread form then you will get flank cutting.

 Cut Depth (The Elephant in The Room)

How do you work out the number of cuts?

G76 Threading Cycle

Be honest I know what you do, you guess. Well you are not alone actually I think loads of people do this. They guess a depth for the first cut then they just run the cycle and see how many passes they get.

Is this you?

Come on now this is not good.

For years I had seen that formula in the big yellow Fanuc Manual.

To be honest it just looked way too complicated. Then one day when my counselling sessions had finished I gingerly opened the big yellow book and decided once and for all to conquer it.

Wooppee It’s Easy

It’s just the depth of the thread divided by the square root of the number of passes. Bit of a mouthful.

So on your calculator:

(1) Press keys for depth of the thread eg 1.534

G76 Threading Cycle

(2) Press divide key (÷)

then press the √ key

G76 Threading Cycle

(3)Enter the number then press 10 then press =


G76 Threading Cycle

1.534 ÷ √10 = 0.4854

This is the value to enter for D


So Easy You Can Do it Backwards

So your cycle reads

G76 D.485 K1.534 X16.93 Z-25. A60 P2 F2.5

So how many passes will I get from this?

  1. Enter the depth of thread (K Value).
  2. Press ÷
  3. Enter depth of first cut (D value)
  4. Press =
  5. Press the squared key (²)

The answer is:

10.01689871 that’s 10 to you.

G76 Threading Cycle

So next time you cut a thread don’t guess the number of passes uses this formula it’s dead easy. You can also loose weight if you do this as part of a calorie controlled diet.

As I Said You Can Do it Backwards

Depth of thread divided by the depth of first pass squared.

As in the example above.

I know my depth of thread is 1.534 and I have

(1.534 / .4854)²

1.534/.4854 = 3.1602

3.1602 x 3.1602 = 9.98737 (10 to you)

Read on To See How to Get Every pass.

So you can use this formula to calculate the depth of every pass.

1.534 ÷√1   = 1.534      Cut = .000
1.534 ÷√2  = 1.084     Cut = .450
1.534 ÷√3  = 0.885     Cut = .199
1.534 ÷√4  = 0.767     Cut = .118
1.534 ÷√5  = 0.686     Cut = .081
1.534 ÷√6  = 0.626     Cut = .060
1.534 ÷√7  = 0.579      Cut = .047
1.534 ÷√8  = 0.542     Cut = .037
1.534 ÷√9  = 0.511      Cut = .031
1.534 ÷√10 = 0.485     Cut = .026

Notice how as the thread gets deeper the cuts become smaller. This is because the width of the cut gets bigger.

So making the depth less levels out the load on the tool.

Some friendly Advice

Keep it simple on your first attempt. That means missing out as much as possible. Cut your thread in fresh air (no component in the chuck). Then you can play around with all the little adjustments and watch what they do. This engineering business is so much fun. Oh and slow the speed down when you are testing it so you can see exactly what is happening. You can get ready with the E Stop.

Oh Yea Here Is Another Tip

Run your spindle really slow (like 100 rpm) that way you can stop the machine with the E Stop if it looks like it’s going to collide with a shoulder.

You only need run one pass like this. It may just scratch the first pass. Put your speed back up and you won’t see it. (It can be our secret)

Single Block, What about that?

When using G76 you can’t use feedhold. On some controls the tool will retract but please check the small print first or try it in fresh air.

Why? ……. Come on think about it.

You also can’t use spindle override. These are both blocked by the cycle to stop you messing up your precious thread.

In “Single Block” each press of the cycle start will give you one complete pass.

A Few Rules

Rules rules always stupid dumb ass rules.

  1. Always use G97 speed in RPM you can’t use G96.
  2. Don’t move the Z start position unless it’s by a multiple of the pitch.
  3. Don’t change the speed.
  4. Machine has to accelerate into the thread so start at Z5. depending on the speed and pitch this may need to be more.
  5. Watch out for that Z end point. That’s the one that will make it hit the chuck if you get it wrong.
  6. Come and train with us.

Some more useful information from Vardex.

Thanks For Reading

Don’t forget there’s loads more folks.

And a YouTube channel

Contact Us

Services offered at CNC Training Centre

Siemens Sinumerik Training

Edgecam training.

Classroom programmer training.

Onsite CNC Machine Training.

CNC Training on all controls and machines.


Mazak Training Fanuc Training

Don’t forget we offer training on all types of Mazak Machines and all Fanuc Controls 6m to 31i Oi old to young.

WP to LinkedIn Auto Publish Powered By :