(bottom posted this one)
On 1/19/21 9:42 PM, John Dammeyer wrote:
I dont think, the z position is "geared" to the counts beyond
index so locked unambiguously to spindle angle beyond index,
after initial sync is acheived.
Peter Wallace
Mesa Electronics
So far that makes sense. From "LinuxCNC User manual"
"The tool will pause briefly for synchronization before each threading pass, so a
relief groove will be required at the entry unless the beginning of the thread is past
the end of the material or an entry taper is used."
Following that is:
"Unless using an exit taper, the exit move is not synchronized to the spindle speed
and will be a rapid move. With a slow spindle,the exit move might take only a small
fraction of a revolution. If the spindle speed is increased after several passes are
complete, subsequent exit moves will require a larger portion of a revolution, resulting
in a very heavy cut during the exit move. This can be avoided by providing a relief
groove at the exit, or by not changing the spindle speed while threading."
So there are side effects to changing the spindle speed but nothing that infers
it can't or shouldn't be done.
The implication is that at the start of the G76 based on spindle speed and Z
axis acceleration along with target Z axis speed a specific spindle encoder
value is used after that to determine when the axis is synchronized.
Or N encoder counts before the index is used as the starting point for the Z to
begin so it's up to speed, ready to engage, at the spindle index mark.
Synchronizing it to the index mark for up to speed condition if you want to
create multi-start threads makes sense. Move the start point by half the
pitch to the right. Since the position of tool entry at speed is the index
pulse regardless of spindle speed the thread should start 180 degrees from the
first.
So where is this calculated? In the Trajectory Planner? I'd like to look at
the code but no idea where to even start looking.
John Dammeyer
snip ...
I left the trail here:
https://github.com/LinuxCNC/linuxcnc/blob/master/src/emc/rs274ngc/interp_convert.cc#L4881-L5028
I think this is my next stop:
https://github.com/LinuxCNC/linuxcnc/tree/master/src/emc/motion
(but after a day of 50 mph winds, there are a few chores to attend to)
Kirk Wallace
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