Hi Kirk,
Every big windstorm we have has me wondering which tree will fall across our
powerline or house. But I like the trees too much to remove them.
The problem I find when looking for " START_SPEED_FEED_SYNCH " is they are all
either printf functions or null as in they don't appear to do anything:
void START_SPEED_FEED_SYNCH(int spindle, double feed_per_revolution, bool
velocity_mode) {}
After that function (wherever it is and whatever it does) returns the actual
threading pass to the target_z position is done:
STRAIGHT_FEED(block->line_number, boring? safe_x + depth: safe_x -
depth,
start_y, target_z - zoff, AABBCC); //over
The carriage is brought to the correct Z + offset location where the offset is
the tan of the X distance and angle to follow the slope of the thread angle.
Like setting the compound to 29.5 degrees.
Then we wait for some sort of sync. It appears the Z may well be stopped at
this point and the tool is at the depth for cutting the next pass. I guess it
depends on how slow the spindle is moving.
But that parameter "feed_per_revolution" probably is probably used along with
the Z axis "MAX_ACCELERATION" in the INI and HAL files to count out a specific
index position so the START_SPEED_FEED_SYNCH function returns not at the index
position but where it would be given Z axis acceleration at the current angular
velocity of the spindle.
Have I got that right? And if so where is the real code for
START_SPEED_FEED_SYNCH?
John Dammeyer
> -----Original Message-----
> From: Kirk Wallace [mailto:[email protected]]
> Sent: January-20-21 8:07 AM
> To: [email protected]
> Subject: Re: [Emc-users] Spindle speed changes with threading.
>
> (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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