CNC Turn threading problem

Hi,

I´m currently threading 1 7/8¨- 8 UN nuts with a CNC turning machine (2 axis Victor V-turn 26), the material I´m working with is 4140 steel (28-30 HRc)

The problem I have is when I use the G76 code for threading, I only manage to thread like 30 nuts (with one side of an insert), but if I use G92 instead, I can do more than 60 pcs. I think the problem is because G92 I can control the amount of passes manually, so I do 16-17 passes for the thread, and with G76 it does only 12 passes.

My question is: Is there any way to adjust the total amount of passes with G76? I can only manage to adjust the first passes and the last ones, but nothing in between. I´ve already tried changing the first Q parameter and putting it below 100, and didn´t do anything.

Did anybody have the same problem, or know if I could do anything?

Thanks.
José

Quote:

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Originally Posted by José L.

Hi,

I´m currently threading 1 7/8¨- 8 UN nuts with a CNC turning machine (2 axis Victor V-turn 26), the material I´m working with is 4140 steel (28-30 HRc)

The problem I have is when I use the G76 code for threading, I only manage to thread like 30 nuts (with one side of an insert), but if I use G92 instead, I can do more than 60 pcs. I think the problem is because G92 I can control the amount of passes manually, so I do 16-17 passes for the thread, and with G76 it does only 12 passes.

My question is: Is there any way to adjust the total amount of passes with G76? I can only manage to adjust the first passes and the last ones, but nothing in between. I´ve already tried changing the first Q parameter and putting it below 100, and didn´t do anything.

Did anybody have the same problem, or know if I could do anything?

Thanks.
José

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Hello Jose',
Yes, but its a work around; a bit of a trick. When programming an internal thread with G76, you specify the Major Diameter and the Height of the Thread Form. With these two arguments, the control is able to calculate the minor diameter of the Thread. A third argument used is the Depth Of Cut for the first pass of the Threading Cycle. Each successive Thread Pass will be an ever decreasing depth relative to the First Pass Depth. Accordingly, if the First Pass is 0.25mm. all other passes will be a decreasing values of 0.25. For the most efficient Threading Operation, this First Pass should be as great as the Threading Tool and the Workpiece holding will tolerate. In this way, each progressive Threading Pass will be as great as it can be.

When the correct Thread Height is specified, and say a 0.5mm First Pass is programmed, the First Pass with be at a Diameter 1.0mm greater than the Minor Diameter calculated by the control using the Major Diameter and the Thread Height included in the G76 cycle, and all successive passes will be based on the First Pass Depth of Cut of 0.5mm. If a Thread Height that is 0.5 greater than it actually is, a First Pass can be program to be 0.5 greater (1.0) and still only take a 0.5mm actual Depth Of Cut on the Workpiece. However, all successive Depth Of Cuts will be based on the First Pass argument of 1.0mm and therefore fewer cuts will result in the complete Threading Cycle. You may need to do some fiddling to get the optimum Thread Height/First Thread Pass combination, but its not all that difficult.

Regards,

Bill

Attachment 258610

Try this. (it will work)

G76 P...... Q100 R..
G76 X.. Z.. P? Q100 F..

( Q100 = 0.1mm)

Put the same amount in both Q (the insert will last longer). The first is the amount of cut until reach final X and the second is the first pass.
and specify P it the K in the image. Is the depth of the thread in micro. For 1mm you put 1000. ( is radial not in diameter against the X depth that is diameter)

So... I ' ll give an example that I am using to cut (sry , will be in metric)

M10 external thread.

T0101
G54 G40
G97 G99
M3 S500
G0 X11 Z2 M8
G76 P010060 Q100 R0.05
G76 X8.1 Z-20 P920 Q100 F1.5
G0 X11 Z2 M9
GO X150 Z150
M30

This will cut 0.2mm in every pass of thread. It will make 10 - 8.2 = 1.8 / 2 = 9 passes and one more finishing ( P01 - R0.05 )

If I want to double the amount of passes then I put Q50 so it will cut 0.1mm every time and so on..

hope this will help.