Cartierusm,
Simple question ......maybe be a long winded reply......the answer is not simple and threading is complex.
First just a few question's for my understanding:
-What version of 3.024.
is it .032 or .033?
-Using exact stop and not CV?
-How much of a change in your rpm?
-Using a VFD?
-Using a single index?
-Spindle speed averaging checked / being used?
- Describe what you mean by taper.
Is the taper cutting over the complete threading cycle or are we talking about when the spindle slowed down?
How much of a taper?
What end is smaller the beginning of the thread or the end?
It is difficult to watch what is really happening when threading at say 60 ipm. I will comment that one needs to
isolate each controller reaction to a slowed down rpm in the threading cycle. There is the overall threading "picture"
and the individual parts that make up the picture. So as i continue in my reply keep that in mind as there is a lot going on.
When the rpm's drop below what mach thinks is acceptable WHY does it start to cut a taper?
Apparently a taper ( carefull as to what you mean by taper) will be cut if say the rpm's drop, lets say 30%, and then rpm goes
back up during that cycle. As a result of the slow down, the machine must cut a varing thread pitch, not a taper over that time period.
The "relative" thread root for that cycle would ideally remain the same since the X axis location by code is the same / never changed
code wise or manipulated by Mach. Because the chip curl changed, that would create a tapered cut and you can add cutter / machine
deflection to that cut taper. Just one part of the picture.........
Mach monitors the rpm and changes the NEXT thread cycle based on how much the rpm changed. All the sampled rpm's over the cycle time
period will provide an adjusted rpm on which to base the next feedrate. That feedrate or other feedrates over all the
thread cycles should provide an a properly cut thread cut. The big picture.......
Hope this simplified reply is an appropriate answer to your question,
RICH