Problem with threading

[avangard]

Hi
Sorry for my English
I have a problem with threading. 5 days I try to set up the machine but nothing works.

Machine parameters
Samsung AC Servo System CSDJ Plus Servo Drive on X and Z. Servo motor with 2048 encoder.
Z axis 4mm per revolution with reduction 25/3
X axis 2mm per revolution with reduction 25/3
Spindle motor with VFD 1.5Kwt Encoder 1:1 Atek type ARC S50 4096 HPL 6 3M ABC Y100

https://youtu.be/8oQq6XrW5Bo

I read almost everything on the forum about the causes of improper threading. I tried changing the parameters 240 and 242. Something is changing but still the thread is wrong.
I checked the encoder and it gives 16386 pulses per spindle revolution.
I checked the encoder readings with a manual tachometer. Indications are the same.
I double-checked the accuracy of movement along the Z axis. When moving 200mm, accuracy is 0.002mm.

I guess I missed some little thing and I can’t figure it out myself.
I really hope for help.
Thanks.

[Chaz]

That threading is very fast. Slow it down to something like 240 RPM and try it.

Are you 100% sure that your Z and X are set correctly?

You say 0.002 micron, this cannot be. I assume that's mm?

[avangard]

I send a command to the machine to move 200mm along the Z axis and as a result I get 200.002 - 200.001 mm

[avangard]

That threading is very fast. Slow it down to something like 240 RPM and try it.

And what will it give me? The machine allows me to cut threads at 1000 rpm and must do it correctly both at 1000 rpm and at 240 rpm.
The machine does not cut the correct thread at any speed.

[tblough]

Does your spindle index pulse repeat at the same spindle orientation once and only once every revolution? Your encoder should be giving 16,384 pulses per revolution - I assume the 16,386 was a typographical error? On the PID screen are there any errors listed for the spindle axis in the DQOA column?

[avangard]

No errors on PID screen. Encoder gives 16384. I checked the encoder readings with a manual tachometer. Indications are nearly the same.
I changed the spindle speed from 320 to 1000 revolutions. I changed the parameter 240 to 8. The beginning of the thread is more similar, in the end just a groove is made. If 240 is set to 0.5, the thread becomes exactly two times smaller, such that it is possible to freely tighten the nut.

[avangard]

Does your spindle index pulse repeat at the same spindle orientation once and only once every revolution?

I do not fully understand your question. I rotate the spindle one revolution and see in PID 16,384 pulses. Is that right?

[cncsnw]

If you make just one pass, rather than cutting the thread all the way to depth, do you get a clean cut with the correct lead?

It looks to me like the starts are not synchronized. That would indicate a problem reading the index pulse (Z channel) from the spindle encoder.

The index pulse should come around just once per revolution, at the same place every time. The data sheet for your encoder indicates that it is gated with A and B high, so the index pulse is only one count wide. On the PID Configuration screen, when the index pulse comes around, you will see an asterisk ('*') flash next to the label 'N' in the left-most column, for the 5th axis (spindle encoder).

Check this first while turning the spindle by hand. Does it come around once per turn, in the same place every time?

If you have an oscilloscope, use it to watch the Z and /Z wires of your spindle encoder, first while turning the spindle by hand, then while running it with power from the spindle drive.

I am guessing that you will see nice clean index pulses once per turn when you turn the spindle by hand, and that you will see a lot of noise (which the controller may read as index pulses in the wrong places) when the spindle drive is running.

[avangard]

Thanks. I will check with the oscilloscope and manually. Maybe you're right. It’s just very expensive to buy an encoder from Centroid in my country. With shipping, its price is about $ 650 ...
Therefore, you have to choose from what you can really buy here.

[Chaz]

That threading is very fast. Slow it down to something like 240 RPM and try it.

And what will it give me? The machine allows me to cut threads at 1000 rpm and must do it correctly both at 1000 rpm and at 240 rpm.
The machine does not cut the correct thread at any speed.

Because doing it slower might give you the opportunity to see why its not doing it correctly.

Of course the machine should work (within reason) at all speeds.

At slower speeds you are removing the need for high acceleration. Its good that you are using servos, that generally rules out missed steps but clearly something is not right. Just trying to help.