Spindle speed variation ssv for chatter control

You should be able to use the siggen component to apply a sine wave offset to your spindle speeds.

Yes. Siggen set up to output a sine wave with low frequency. Maybe the amplitude and frequency adjustable with a pyvcp panel. Use sum2 to add it to your spindle speed command.

Sounds simple to me...Not...

if someones got the time, I'd like an idiots guide to this please

A _very_ minimal example:

loadrt siggen
addf siggen.0.update servo thread

setp siggen.0.frequency 1 # 1 Hz
setp siggen.0.amplitude 50 # +-50 RPM

net spindle-speed => siggen.0.offset
net mod_spindle_speed <= siggen.0.sine
net mod_spindle_speed => your-spindle-hardware-speed-pin

I started to look at this but PCW has done it already. If you read the docs
linuxcnc.org/docs/devel/html/man/man9/siggen.9.html
and review what each pin does will clarify what is happening.