yes a ran the turn diagnostic, dont see anything wrong there.

now to thread with G32, do i have to write manualy the code or is there another whizard to do it? if i have to do it manualy, how do i tell the program to wait for the index pulse to start the cut?

If you open the M1076 macro (in your C:\Mach3 folder you cant change the line where it says Test =false  to Test=True an the wizard will write G32 code.
Hood

the final chapter

i think i get it working for good now. from wath i can see the problem was a timing problem. i dont know how mach3 manage the threading sequence but from wath i can see, if the spindle slows down a little bit while threading because of a change in load, probably mach3 expected an index pulse that is comming a little too late, it then assume that it missed it and realign the z speed accordingly. so i end up with a z axis that is one turn of the spindle too late and eat the thread on the shaft.

i had to cut this thread the same day i upgraded from a previous version of mach3 and assume the upgrade was the problem. so if cutting acme thread use the low gear on the lathe and light cuts because it takes more power then the v thread of the same pitch.

thank you for your help

and by the way, where did you get the info about that g32 thing? is there a secret mach3 bible!

Not sure how Mach through the parallel port reacts to a slowing spindle, I was under the impression that it would slow the axis to compensate but as I use the SmoothStepper I cant test. Actually I couldnt really test anyway as the spindle on my lathe would t' get affected by even taking a full DOC in a threading op.
  I can confirm however that the SS does react to spindle speed, this was proved to me when a key inside the headstock had sheared and I didnt know, I started a thread and heard the spindle slowing and was about to hit the e-stop but noticed that I heard a change in axis motor speed so let it continue. It did all 10 passes and I did a feedhold and inspected the thread and it was perfect. During the threading the spindle was at 1000rpm at the start of each pass but by the end of each pass it was down to 200 or so rpm and to say the least I was very impressed with the way the SS handled things.
Hood

Hi there,

I've just had exactly this problem cutting a M14 x 2 thread. As soon as the cut reach sufficient force to slow the spindle by more than 20rpm (from 400) then the next cut would advance the X axis into the work giving a taper to the thread, and the next cut would do the same if I left it. I'd then stop it, rewind the code and run again. It would then do loads more cuts until again the depth was sufficient to slow by more than 20rpm and then the X axis would start advancing in again, making the spindle slow more...

My lathe is small so I ended up with 0.04mm deep cuts and about 40 passes! But got there in the end. However, it shouldn't really do this so I wonder where am I going wrong?

Parallel port operation
No missed steps that I've ever noticed
Mach3 R3.042.020
Single index pulse with very clean signal - never seen any glitches

No problems at all air cutting 40 passes, the macro seems fine
No problem with very very light cuts
Just X axis moving (in the DRO and in practice) in G76 threading when the cut slows the spindle more than 20rpm

So, why would the X axis move if the spindle slows >5%? Its doesn't make sense?

Also, the pitch is perfect. The Z axis copes fine with the change in speed as Hood mentioned. Just that X axis move - I don't get it.

Thanks if you can point me in the right direction, otherwise, threads take soooo many passes!

I'll try the "turn diag" and version ..43.0 when I get the chance.

I also found feed-hold during threading a little hit and miss. Is there guidance when you can and can't use this - obviously not during the cut!

Thanks for your help!

Woody.

Woody,
I'll fool with threading hopefully today and use V3.042.20. I want to test out the "PUNNY" lathe here anyway.
Can use the PP port or the SS, slow the spindle down, and with new steppers installed and backlash down to
.001 on the Z can now try threading at a variety of spindle speeds probably out to 1300 rpm.

I don't have an answer for you, but, just quickly dry running a few times, motor running and steppers disengaged i was able to see the DRO's change at rpm decreases of less than 5% and really go bonkers if you varied the
rpm at certain times of the thread cycle. I wouldn't put much credibility to the above as it wasn't done in a disciplined way. One thing I did notice though, was, that during the "threading" part of the cycle, if the spindle slowed down,...... the x axis didn't change / stayed at it's position.

Later,
RICH
 

Are you sure you dont have a taper set for the thread, thats really the only way the X should move while in the threading pass. Can you attach your xml and I will see if I can find anything amiss therel
Hood

Hi Hood,

Thanks for looking - well, I checked carefully, and taper was set to 0, and its cuts perfectly on very light cuts but anything that slows the spindle more than 5% on a cut then on the next cut, the X-axis moves in slowly over the cut - its totally repeatable for me. I think this is coming from mach3 because when it does this strange behaviour with the X axis, it does not miss any steps at all. It comes right back on the next cut to the right place, then repeats exactly the same behaviour. I'll see if I can make a video of it.

I wonder if its linked to the index pulse timing signal, but the rpm info is perfectly smooth as far as I can see.

I'll dig out my xml and Gcode when it stops raining and I can reach the workshop!

Thanks Rich -grateful for your experiment (how did you do that!??). Yes, it only seems to do it with real cutting on the lathe under load. Its OK air-cutting too.

tubular2000 - what version did you use that worked OK for you in the end and do you think it was just the light cuts that fixed it?

Thanks, really appreciate it.

Woody.

Do you have the "Use Spindle Feedback in Sync mode" checked on Ports and Pins, Spindle Setup page?
Hood

WOODY,
I just have a Sherline lathe that is CNC, so with finger pressure or usng the manual spindle rpm adjustment
you can play with slowing the spindle down and see what happens. Don't even think about something like that
with some other lathe. Even a punny lathe can hurt you!

The X axis shouldn't move at all when once the threading starts. I think i am correct in that all variations
in cutting, when spindle slows down, are taken care of in the following Z axis feeds.  It will be a few days before i can experiment in an intelligent way.

RICH