G76 X The first defines the number of spring passes that the machine will take once the thread is cut to depth. This helps with surface finish and repeatability to help our threads remain in tolerance over many parts. The second value defines the angle of runout chamfer at the end of the thread while the third is the angle of the teeth of the thread i.
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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 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. So here we are. What Exactly is a 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. 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 attention.
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. G76 X 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. 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. Then at the push of a button your thread appears.
Haas and Some Fanucs G76 X P Q F2. First two being the number of spring passes. Second two are chamfer. More Details Third two are the tool angle. What on Earth are Spring Passes? 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. Just multiply the pitch by. The way you use this cycle makes a big difference to the way the tool performs. It is literally 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. Flank Cut????? 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.
A60 on a 60 degree thread form. A60 P2 if you have the option. 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. 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. A60 P2 F2. Providing you input the insert angle A60 on a 60 degree thread form then you will get flank cutting. 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. Bit of a mouthful. Enter the depth of thread K Value.
As in the example above. I know my depth of thread is 1. So you can use this formula to calculate the depth of every pass. 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. You only need run one pass like this. It may just scratch the first pass. It can be our secret Single Block, What about that? Come on think about it. These are both blocked by the cycle to stop you messing up your precious thread. A Few Rules.
Multiple repetitive cycles for CNC lathes have been an important part of control systems since the mid s. Still, to this day, they present the most innovative approach of material removal, particularly in the areas of turning, boring, and threading. Over the plus years of their existence, multiple repetitive cycles have gone through only two major changes. Earlier controls require these cycles to be programmed in a single block; later controls require two blocks of program input. At the beginning, lets look at the word convert.
Tapered Threading with Fanuc G76 Threading Cycle
The end position is perhaps a bit easier, particularly in Z, as you generally know exactly the length you want threaded and where that thread starts. Incidentally, our G-Wizard Thread Calculator software has a nice database of common threads that calls out this sort of thing. There are many different thread standards such as the Unified Thread Standard , so make sure you have the correct data for your thread. The Start Position is a little more interesting.
G76 Threading Cycle How Many Passes