Nyone get the wrong cutting time in v carve or photocarve?

[knight_toolworks]

Made up the lithophane files in photo vcarve not positve but I think it was the same time v carve gave me after I imported them and rearanged the placement in v carve. but I was told 4:10 minutes cut and it turned out 5:40 minutes to cut getting me home very late.

[Brian Moran]

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

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.

However, 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 over a period of time and use these to calculate a suitable scale factor for your machine and type of work.

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

Brian

[jamesgilliam]

Steve, Don't feel bad about it being off that much. I started a file Monday evening at 6 that should have run in six hours, Instead it ran for nine hours. Now I won't start anything big after noon.

[knight_toolworks]

atleast I know now so I can plan better. this is the first large thing I ahve done so I need to plan better.
if you hit spacebar in the middle will the spindle turn off after a bit? I know when you start again (right away) you get the start spindle prompt.
that way I could start it hit pause have the machine idle go to lunch come back warm the spindle and get going again.