Cut3D estimated times are way off from the actual cut times.

[betacrash]

When I am setting up a cut file that is 20" x 4 x 1.5" . The estimated time for the finish cut with a .25 ball nose with a .0275 stepover and 6ipm is around 11 minutes which I thought was really fast but it ends up taking about an hour. Any ideas why the time would be so drastically different?

[billp]

Shawn,
I'm going to guess that you're cutting a "3D"piece.If not, disregard all that follows;
One of the major reasons the numbers would be off are the "Z" moves which most programs will not/ can not predict reliably. Even though you set the machine to run at "6ipm"(is that really ipS?) you will rarely, if ever, get up to those speeds in a 3D cut unless you have large, flat areas where the machine can ramp up to it's intended speed. With a ".0275"step over you will have a gazillion Z moves, each one taking time (one thing you can do is to set your Z speed higher by the way...).
Another possibility would be to check and see if you are looking at a preview with an "end mill" instead of a "ball nose"which will also throw your projected times off tremendously.
The usual "workaround"in situations such as this is to keep a record of your 3D cutting files, and compare the projected, versus real results. if you then have a similar style job to cut you can project some sort of "ratio" ( 3X longer, 6X longer, etc.)based on your cut file log.You might also check the projected time in both your design program, AND in the "preview mode"of the Shopbot software and see which one gives you the more reliable number.I would agree though that there is a large difference between 11 minutes, and one hour...
Another option is to be sure to do a roughing pass. That should knock off a lot of material, so your finishing pass will run faster, and smoother.

[betacrash]

hey bill, thanks for the reply. it was 6ips not ipm. I did do a roughing pass and that seemed to take two or three times longer as well. Is there a set of values that I can use to optimize my PRT Alpha? Also, once it is roughed out what would be a suitable speed to run the bit both Z direction and X,Y? And I double checked and I was doing the preview with a ball nose. this project is to carve out two ukulele necks done in halves.


3756

[billp]

Shawn,
Actually an hour to cut these parts seems reasonable to me, and 11 minutes doesn't! I'll assume that you are cutting them in the "long" axis rather than "across" the necks, and with an almost 10% step over it IS going to take some time.
What did the Shopbot software tell you in terms of projected cutting times?