As you know - CV is a compromise. With Exact Stop you get the exact path you programmed but with a stop at "segment" junctions. With CV you get Mach's
attempt at a constant feedrate (never sure why it's called CV as technically a constant velocity can only ever be a straight line - any whatever - I digress
). If you're happy with the "out of the box" CV for any particular job - then cool - it works very well. However there are times when you might want to tweak the way CV behaves.
So, when Mach needs to do (say) a corner, with CV it will cut (round) that corner as much as IT likes to keep
as close to the commanded feedrate as it can. BUT - suppose you want to tighten that "rounding" a bit. There are a couple of ways you can do it and ONE is to set the CV Feedrate button ON. Then it effectively says to Mach - don't worry too much about keeping the feedrate up - I'm prepared to let you drop it to -
whatever's in the CV Feedrate DRO. If you go with the default value in the DRO i.e. 1 you're saying to Mach - you can drop the feedrate to 1unit/min if you like. Which is about the same as turning OFF CV - i.e. just about exact stop.
So, instead of turning CV Feedrate OFF - which says "go as fast as you can round corners etc." you could set (say) 75% of your commanded feedrate in there. Now Mach will allow the blended feedrate to drop to 75% of the commanded feedrate if it needs to. It'll tighten your corners a tad but at the expense of dropping the feedrate a bit more than it would have done.
Hope that makes sense.
BTW - not sure why it's turning itself ON when you set it off - but it doesn't do that here. Checkout the <CVFeedOn> tag value in your XML after you've turned it off and closed Mach. It should be 0. If it is and when you restart Mach it's back on again then something's turning it on again - a macro maybe? guessing...
Ian
PS - I'm going to move this to general - FAQ's is not really the place for this.