Estimated machining time, and how to get it right

[Sentinel]

At this point, my machining time takes almost 3 times the estimated machining time in VCarve.

Now, if you could help me understand few things, it'd be great

From what I can understand, estimated machining time is based on feed rates. However, VCarve can not account for machine movements when it's not cutting (for example). So, am I correct in understanding that my machining times are way off because "rapid machine movements" (or whatever is it called) are slow comparing to what VCarve would expect?

So, if I am carving with V-Bit letters ABC, time needed to actually carve letters will be ok (that is based on feed rate specified by VCarve), but time needed to move spindle around is what is causing the 'delays'.

Now, if I got that right, I have another question.

Do these movements (non-cutting) depend on movement speeds I have defined in Mach3? And only cutting speeds (feed rates) are defined in VCarve g-code output?

Reason I ask this is because I am pretty sure I've defined very 'conservative' speeds in Mach3, so could I expect faster machining times if I increase those values in Mach3?

Hope it makes sense

Thanks.

[BrianM]

The inaccuracies generally come from the acceleration / deceleration of the machine. We do take account of the rapid moves and you can enter the rapid rate for your machine on the form.

However if we tell a machine to move at 200 inches / min along a 200 inch straight line the machine will probably take pretty close to a minute.

If instead of a straight line we ask the machine to cut say a gear wheel with a total circumference of 200 inches, the machine is likely to take considerably longer. This is because the machine will have to slow down to go around the tight curves of gear tooth profiles and will probably never reach its programmed speed before having to slow down again for the next change in direction.

The scale factor in the programs let you approximate this slowdown for your machine, but it will vary depending on the type of work you are doing. Many people will use one scale factor for simple 2d work and another for 3d or VCarving. The best way to calculate it is just to take a note of estimated and actual machining times of a period of time.

For machines where the controler provides an estimated machining time, these should be more accurate as the controller can determine where the machine is accelerating / decellerating and take account of this.

Brian

[Thkoutsidthebox]

I timed a couple of jobs I did on my machine. I then went into V-Carve and adjusted the scale factor until those cuts were bang on the time. I averaged out this and I then used this scale factor ( 1.28 ) in future and am usually within a few minutes which allows me to give a relatively accurate machining time to quote for on paying jobs.

I haven't done much 3D work yet, but am working up to it. Using two scale factors depending upon 2D or 3D work is a good idea. Thanks Brian!