Lathe threading

[craig]

Been using parallel ports on lathes with mach3 for many years. Pretty good threading but not perfect and consistent. I tried adding a uc400eth and 360ppr encoder and it wouldn't thread. I believe because my breakout board isn't fast enough for the encoder input. The manufacturer (machmotion) wouldn't give me a frequency limit for inputs. IN fact they were surprised it would even thread with a single pulse per rev. index signal. So my question is, can i connect the encoder directly to the uc400eth board on the correct pins? Would the threads be more accurate? Or would this be a waste of time?

[eabrust]

Hi Craig,

I have two lathes setup on UCCNC, one on UC100, one on AXBB. No reason to think your UC400 won't work. I'm quite happy with the threads, also having come from using Mach3 w/ the 1/rev index forever...

When you say it won't thread, what does it do, go to the start point to thread and wait without proceeding?

I've found that will happen also if you have the encoder inputs reversed or if the index signal isn't getting picked up. Try swapping the A and B inputs, and verify you see the A, B, and index inputs all light up as you rotate the spindle by hand.

regards
Eric

[ger21]

Been using parallel ports on lathes with mach3 for many years. Pretty good threading but not perfect and consistent. I tried adding a uc400eth and 360ppr encoder and it wouldn't thread.

If you do a deep dive on lathe threading on the old Mach3 Yahoo group, I think you'll find that Mach3 threading is riddled with issues, which vary based on Mach3 version. There may not be a version that's 100% accurate.

[craig]

So am i to understand mach 3 threading is no better using a uc400eth? Changing to uccnc software is what really improves things. I hesitate to do that because there is no feed per rev or constant surface speed.

[ger21]

I've never used Mach3 lathe, but my understanding is that there are underlying bugs in Mach3 that affect the threading, and a motion controller cannot overcome these bugs.
I think it's something to do with how Mach3 uses 1 pulse per rev for threading. ANY variation in spindle speed while threading will lead to errors.

[craig]

I set it aside and went back to regular parallel port and single index threading. I may revisit this when time permits. But i feel like I'm going to have to connect the encoder directly to the UC400eth as the breakout board optos are just too slow and i'm not willing to change the breakout board.

[craig]

Finally getting back to this. Using an axbb-e on a small lathe with servo spindle. Does threading still use the 1 pulse per rev for threading or does it now use the a/b encoder signals. I slowed and sped up the spindle while threading and it does not compensate. So it seems like it is still using the 1 pulse/rev. The information on mach3 threading with UCCNC products is non existent. I wish there was more documented info on this.

[cncdrive]

It uses the encoder A/B and Index channels for threading or Index.
The problem with Mach3 is that our plugin can't compensate the feed after initial syncronisation to the spindle.
So, if your spindle speed varies too much will create errorous thread pitch.
So, my advice is to startup your spindle to the target speed and do the threading and not change the spindle speed.
Ofcourse you can change the spindle speed between passes.

In the UCCNC this problem does not exist.
This issue only exists with Mach3 due to several bugs in the Mach3 plugin interface.