Effect of look ahead software functions

[Hack]

I am currently driving my router with some steppers using TurboCNC and hear about how other software such as Mach 3 have look ahead functions. What I am wondering is how does that effect the steppers? Let me explain.

The way i see it is as software such as TurboCNC completes a move with an axis (G01 X4.0) comes to a stop, and then initiates the next line of code (say G01 Y10.0).

In the above moves what happens to the stepper motors during the moves. Obviously during the first move, the X axis is energized because it is moving, but what about the Y? Will it be "ready to move"? or will it only initiate only after the initial X move is complete? Also, when the x move is over, what happens to the X axis stepper, does it go to sleep or something until it is needed again?

How does this effect the speed of the moves. Or more to the point, the time between the moves? Will there be a delay between the x and y moves above with a controller that does not have the look ahead function?

Hope I clarified this enough.

Dan

[ger21]

Mach3 has constant velocity mode, which is what you mean I think. Constant velocity mode tries to always keep the tool moving at a constant velocity, and not stop between segments and corners. Say you're making a 90° corner. In TurboCNC you'd decelerate the current axis to a stop as you get to the corner, then the other axis would start to accelerate in the other direction. With mach3, when the first axis begins to decelerate, the other axis begins to accelerate so that the tool doesn't stop. The downside is that the corner gets rounded slightly, with the faster the accel the less rounding you get. When the corner is less than 90°, you'll of course get much less rounding.
Constant Velocity gives you faster runtimes, because you're not always stopping and starting, and a smoother running machine, for the same reason.

There are a couple ways to minimize or eliminate the corner rounding I mentioned above.
1) Mach3 has an angle setting so angles less than a specified angle will not get rounded. So you'll be in CV mode for larger angles, and exact stop for smaller angles.

2) If when you offset your toolpaths, you radius all the corners by the tool radius, You'll get toolpaths with rounded corners so the CV won't have to round them, and the part will still have square corners. You can also use Cutter Comp in Mach3, which will automatically do the offsets with radius corners for you.