G92threadingcycle

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”.

CNCthread cutting

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.

Where does this formula come from for using the square root to determine the depth of successive passes? Why not just divide it up into equal sections?

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.

G76threadingexample PDF

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

Cnc threadingmachine

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.

CNC threadingprogram examples

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

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.

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)

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

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.

But then in the next line you show the full gcode and the value for K is the thread depth 1.534 and then .4854 is used for D

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

Hi, Thanks for this post, everything works fine, however there is a factor which is not being controlled, The tool when going the rapid move out of the thread, it is touching the work piece, so it is making double thread ( main thread is getting messed up). Any suggestion how to solve this issue.

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.

An outstanding share! I have just forwarded this onto a coworker who was conducting a little homework on this. And he actually bought me lunch due too thhe fact that I found it for him… lol. So let me reword this…. Thank YOU for the meal!! Butt yeah, thanks for spending the time to talk anout this matter here on your blog. php patterns

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.

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.

G76threadingcycle formula

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

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.

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.

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.

Cnc threadingpdf

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.

G76CNC threadingprogram examples

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.

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.

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.

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

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.

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.

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.

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

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.

Step three of “Cut Depth” section appears incorrect. On one hand it says “1.534 / sqrt(10) = 0.4854 this is the value to enter for ‘K’ and the you show K.4854

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).