optimizing blue foam / cut3d project

[meeotch]

I've got a project which is basically a huge face (see pic). It's pretty flat - about 4-5', chin to forehead, and 1-2' thick at the nose. I'm going to be cutting it out of blue foam on a ShopBot using Cut3d to generate toolpaths at my school sculpture shop. The final will be sanded, and then I'm going to make a mold & cast it.

Our foam is about 2.125" thick, giving 8 slices. As you can guess from the pic, the first few slices are pretty much just big oblong discs with a few holes. However, I'm getting roughing + finishing times of about an hour out of Cut3d for each slice. (30min each)

The shop manager said their experiments with cutting foam indicated that the roughing path was necessary, because it removes material from the top-down, rather than diving to the bottom right away as the finishing pass does. Basically, trying to carve too much depth at one time causes tear-outs on the foam.

The problem is that they charge $1.50 a minute - so the whole project comes out to about $500 just for the cutting, which is beyond my meager budget. Anyone have suggestions for optimizations?

Parameters we're using:
0.25" End Mill 3" bit
slice thickness = 2.125"
roughing pass depth - 0.6" (the max we could get experimentally)
stepover - 50%
spindle speed 12000rpm
feed rate 2.5"/sec (experimental max)
plunge rate 1.5"/sec (experimental max)

[rcnewcomb]

Try at 1" ballnose with a 20% stepover rather than the end mill. At least when I tested it the ballnose had a faster machine time with a better surface and no need for a roughing pass. My quick and dirty estimate with an offset strategy showed a machine time under 2 hours.

Also, have you set up bounding vectors to limit and control the area that is cut?

[meeotch]

Randall - thanks for the response. I tried plugging in a 1" ball nose, 20% stepover into my current Cut3d setup, and got the following times for rough/finish on each slice:

1 = 19 + 14 = 35
2 = 22 + 16 = 38
3 = 29 + 19 = 48
4 = 34 + 22 = 56
5 = 34 + 18 = 52
6 = 11 + 6 = 17
7 = 5 + 2 = 7
8 = 2 + 1 = 3
TOTAL = 256min ~= 4.5 hours

Better than my original total, but still more than twice what you were getting... Perhaps there's something funny about my setup? I'll post workflow below for reference.

Re bounding vectors - I'm not sure I know how to do that in Cut3d. However, when I bring in each individual slice, the "Use Model Silhouette" option seems to be forced to "on", and the cutting paths do seem to be constrained to the area that needs cutting, plus some amount of offset from the profile. The distance box next to "Symmetrical" seems to have no effect on this offset, however.

FYI - here's my workflow:
1) load stl for full model (size is 48.0 * 27.2 * 15.1 inches).
2) hit Apply & Next.
3) Slice Model, with thickness set to 2.125", and Minimize Slice Areas "on".
4) load first slice.
5) increase material size slightly, to avoid paths running off the edge.
6) select tool with parameters given above.
7) calculate rough & finish passes.
8) go to #4, repeat.

[rcnewcomb]

I'm using Brady Watson's 3D ramp settings with feed rates of 5ips XY and 3ips Z.

[meeotch]

Ah - that could be the difference. I'm using feed of 2.5"/sec and plunge of 1.5"/sec. These were the numbers given to me by the shop manager. Apparently, our 'Bot tops out at 3"/sec, and these numbers were what he worked out as the max workable for cutting foam.

I really wish there were some way I could ditch the rough pass, and do it all in one. But as mentioned, the shop manager has found that results in trying to cut too much foam at once, with tearouts being the consequence.

[myxpykalix]

mitch,
the stl i d/l'ed seemed very blocky (low polygon count) compared to the picture you posted. You need to make sure your model is smooth or you will be very disappointed in the results.

[meeotch]

Yes - that stl is just a rough first version. The final will be smoothed. But the dimensions are accurate, so I'm using it for estimating cutting time.

[rcnewcomb]

Mitch,

You might try contacting Glen Kadelbach at Innovative Foam
http://www.innovativefoam.com (http://www.innovativefoam.com)

He does a lot of large foam work and may have some suggestions.