On Mon, 18 Jan 2021, Gene Heskett wrote:
Date: Mon, 18 Jan 2021 23:36:37 -0500
From: Gene Heskett <ghesk...@shentel.net>
Reply-To: "Enhanced Machine Controller (EMC)"
<emc-users@lists.sourceforge.net>
To: emc-users@lists.sourceforge.net
Subject: Re: [Emc-users] Spindle speed changes with threading.
On Monday 18 January 2021 22:21:00 Peter C. Wallace wrote:
On Mon, 18 Jan 2021, Gene Heskett wrote:
But because once locked, its not a big deal if the cutting load
slows the spindle 25%, its still locked at that phase angle and it
will stay that way until the end of THAT cut stroke. But if YOU
change the spindle speed, then YOU have changed the synch delay at
the start of the next stroke and that changes the cutter position as
it tracks the next stroke, cutting a wider groove with that next
stroke. If you speed it up, the extra cut is the back edge of the
tool because it synched later in the spindles rotation.
I dont think thats true, the initial delays do not affect the thread
past any initial issues when the thread starts.
This is because once synchronized, the Z is effectively in a
_position_ locked loop with spindle rotation relative to the
accumulated angle past the index. Changing the speed may change the
start of the threads due to the lock-in time but not that main
threading pass. You can verify this by turning the spindle by hand and
doing multiple threading passses.
This is true of both G76 and G33.1, with G33.1 maintaining sync until the
tap has been totally withdrawn, while G76 releases the synch during the
Z retrace, so it can move at G0 speed, then both checks spindle-at-speed
and if true, starts the next pass on the index if you've written a peck
loop, exactly the same as for a single pass if your spindle has the
hueavos to do it in one pass.
Hidden in this is the fact that either resyncs the spindle to z phaseing
at the starting/resting place for either a G76 or a g33.1 for every
stroke it makes. And a change in spindle speed will change that phasing,
screwing up the thread.
I dont think so, both G33 and G76 are _position_ locked so the initial
start of thread may vary but the thread phasing is independent of spindle
speed.
Peter Wallace
Mesa Electronics
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