Mach3 Lathe Threading Struggles

[battwell]

that was only tested on a few versions- it doesnt work in most as it wasnt succesful. only the spindle index pulse is used. (unless you get a motion controller)
the main reason for this is that the code is being processed in software- it has to see the pulses- calculate and pass the motion info on. this can take more than 1 slot of processing time- so it will always be done late. if it takes 2 processing slot time cycles because the pc is doing something- then its definately out of sync. - so it fails.
while these processing periods are very short time spans- the job is rotating fast- so it can make a big difference.
in hardware in a threading cycle- the interupt to the hardware processor is shut off- so all it does is the threading cycle- it can process the information in nanoseconds.

just today ive tested rigid peck tapping - which is the holy grail in the world of motion syncronisation. and it worked perfectly using the uc300 eth from cnc drive.com and using their uuccnc software . (which is my goto controller now for most things as it works so well!

[m_c]

What should happen with Mach3 threading, is the tool moves to the start point, it then waits for the spindle speed to stabilise, and then the threading move should synchronise with the spindle pulse.

However I did just remember, if Mach calculates that the axes can't respond quick enough to the spindle speed for the given move, then motion will just hang. It could be worth dropping the spindle speed down a good bit, and re-running the code.

[battwell]

multi slot indexing- does not work at all.
only single slot index. (and that index window has to be quite a wide slot- so it can be seen by the sensor in under 5ms.)

i widened the index slot on my boxford 125 to about 20mm long- and it would index every time. - but would still break tools etc.
i have to cut a new index wheel now- so i can run mine with uccnc. - next job once the triac is finished.

[m_c]

Just had a search, there is a quite a good threading guide here - http://www.machsupport.com/forum/ind...c,13017.0.html
However it doesn't cover that much of the setup, and even the main turn manual (http://www.machsupport.com/wp-conten...3Turn_1.84.pdf) is a bit sparse on details, other than saying the pulse has to be a minimum of 200 microseconds. Battwell is correct in that multi-slot doesn't work, so ignore that.

Battwell, the 5ms is likely to be the sensor response time, which is another often overlooked problem. I always used sensors from a reputable source with known response/trigger times. I've seen some sensors that have quite a long response time, and some from cheap sources give no figures, so are a bit hit or miss as to whether they work reliably. They also have to switch cleanly, which can be affected by non ideal sensors, and any optos in the signal chain (some BOBs use low speed optos, which may increase response times).

You just need to work through everything one step at a time.
Is the index pulse being fed back reliably?
You mention you have the RPM displayed, but is it accurate. Unless you're running closed loop, it should always be off from the requested RPM by at least a few RPM. From what I remember, Mach will show the commanded speed by default, not the actual speed.
Also, is the index LED going on and off on the diagnostic page when you move the spindle slot back and forth through whatever sensor you're using?

Are your axis tuned to accelerate/decelerate fast enough?
If they're set too slow, Mach will calculate they can't move fast enough, and just hang at any threads. Try running the spindle as slow as possible, and air cut a very small pitch thread. If it works, then check your motor tuning. Lathes will appear to run very well with low acceleration, it's only when you try threading that the poor acceleration will show.


If none of that shows a problem, then post on the machsupport forum. There are guys on there who know far better about potential problems than on here.

[mondrota]

[/QUOTE]

You just need to work through everything one step at a time.
Is the index pulse being fed back reliably?
You mention you have the RPM displayed, but is it accurate. Unless you're running closed loop, it should always be off from the requested RPM by at least a few RPM. From what I remember, Mach will show the commanded speed by default, not the actual speed.
Also, is the index LED going on and off on the diagnostic page when you move the spindle slot back and forth through whatever sensor you're using?

Are your axis tuned to accelerate/decelerate fast enough?
If they're set too slow, Mach will calculate they can't move fast enough, and just hang at any threads. Try running the spindle as slow as possible, and air cut a very small pitch thread. If it works, then check your motor tuning. Lathes will appear to run very well with low acceleration, it's only when you try threading that the poor acceleration will show.


If none of that shows a problem, then post on the machsupport forum. There are guys on there who know far better about potential problems than on here.[/QUOTE]

The STrue is always slightly out unless I run it in closed loop spindle control mode.
I tried running the threading program at 200 rpm but again it wouldn't actually start threading.
On the Diagnostics info screen the "missing index pulse detected" remains unchecked so I think there is no problem with that.
However I just noticed that the "rotation speed real-time" is about 180000rpm
Whilst the "application end rpm" is 598ish.
Would this be a problem?
I've attached a photo of this screen in my original post.

[mondrota]

Okay I think I found the problem (or a symptom) but I still need the cure :)
So I noticed that on the turn diagnostics screen the "Locked RPM" and "current RPM Variation" read 0 and "Highest Variation during thread" reads 1% when the Spindle Feedback is disabled. This is when the program will run the threading but with poor results.
However, when the Spindle feedback is enabled, all of the above fields on the diagnostic screen read " 1.#INF "
Please have a look at the attached picture.
For some reason I can't attach the other one with the fields reading the " 1.#INF "

I have a feeling that for some reason mach3 cant syncthe threading to the spindle speed.
I found a thread describing the same problem here:
http://www.machsupport.com/forum/ind...79.0/wap2.html
The person having this problem managed to sort it out just by fiddling with the sensor wiring. I've tried rerouting the wires but to no avail. Is there anything else that would cause the syncinc to fail?

Many thanks!

[m_c]

I'm not sure on the reliability of the threading diagnostics page.
If you open the diagnostics page with all the LEDs, does the one for the index go on/off as you manually move the spindle slot through the sensor?

It does sound like you've got a sensor problem. How big is the slot you're detecting?
Can you run the spindle any slower than 200rpm?

If it works at really slow speeds, it could be as simple as needing the slot enlarged.

[mondrota]

Yes, I can run it slower than 200 rpm. And yes, the index led flashes as I move the spindle by hand. I used to use a slotted disc with a proximity sensor, now I'm using a magnet on the shaft with a hall sensor. The pulse is nice and long, the rpm readout is stable even on max speed (about 1800 rpm).
Thanks

[mondrota]

Okay, it's been a while, and this project was put to a side but now I'm back at it. I bought a cheap USB motion controller from eBay
https://rover.ebay.com/rover/0/0/0?m...2F163110531211
I plugged it in to my laptop for testing, connected some relays and they work okay, however I don't get any rpm readout! The index light comes on in the diagnostic screen but no matter what I do, the sTrue stays at 0 🤔
Is the controller supposed to tell mach3 what the rpm is?
Did I go wrong by going cheap?
Help!

[battwell]

you need a controller that will support threading in the controller. this cannot be done in software.
the index signal must be interupt driven- so its very fast.
software will always lag so you will never get the same start point for threading.
you also require spindle encoder - which can be 2 sensors 60 degrees apart
threading- and cheap- are never going to work