carving a statue

[Dancy]

Imagine the statue of David. The z axis runs from head to toe and the work (feet) are mounted to a rotary axis of a multi axis machine. The statue is rendered in .stl format. It's pretty easy for me to imagine the tool path such that the area on the inside of David's thighs is cut as well as the area around his arms.

I need a strategy to approach this. I am just learning multi axis machining and normal path generation is leaving much of the sculpture uncut. Plus the fact that there are so many 3D and multi axis tool paths it's the needle in a haystack issue. Time is the other problem, if I get some setting not quite right MC spends hours generating a tool path only to crash.

Thank you!

here is a sample I have been using to test on. It's a bear skull. Nothing I have tried yet will cut out the eye/jaw pockets.



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[awerby]

You don't say what "normal" 4-axis routine you're using, but it sounds like you've got your Y axis stationary and your tool is progressing down X, then the A axis increments in degrees and it comes back the other way. This is not going to be able to reach the eye sockets of that skull, or between David's legs. You need to use a different strategy: indexed or "N-sided" cutting. This would treat the skull like a 3-axis part, with the Y being free to move as well as X and Z. When you've cut half-way down the eye sockets, you rotate the part 90 degrees (in this case, "N"=4) on the A axis and cut from the side, then another 90 to cut the bottom, and so on. I'm not sure if Mastercam has a pre-planned routine like that, but you should be able to make it work. Make sure that Y and Z are zeroed to the center of the rotary axis so nothing shifts when you rotate the part. If you can't get Mastercam to do it before it crashes, try DeskProto,

[Dancy]

Thank you Andrew;
Yes, I am a bit confused how to setup the various axis. It's because of how I hope to accomplish this. I am plan on cutting out a foam core and use it to make a mold. I have an industrial robot that can hold the work and move it against a stationary tool (a router). I have an interface program, RoboDK that can take tool paths from Mastercam and convert to motion commands for the robot.

It seems to me a five axis machine would be able to make all cuts and when transferred to the robot with six, I get ways to mitigate joint collisions. If the statue was smaller ....say 12" high. Something like the Okuma's 5-Axis Vertical Machining Center, MU-500VA should be able to do the job with the feet of the statue "standing" on the rotary table. That NC file "could" move the robot.

Keshka

[peteeng]

Hi Dancy - Its usual to have the robot hold the spindle and make the work stationary. This enables using the degrees of freedom of the robot. Why are you holding the work in the robot? Peter

[MARV]

In another life, I did this sort of thing using different construction planes in Rhino/RhinoCam posted out to IRBCAM, a piece of software that converts Gcode to proprietary robot code (Rapid for an ABB 6400 robot) with recognition of the constraints specific to 6 axis robots. IRBCAM can handle spindle mounted cutting tools, or mount the workpiece and cut with a stationary cutting tool as you are attempting to do. Once you understand the software, much easier to do than how it sounds.

In some cases, I programmed for tool paths as 3+1 indexed (in Rhino Cam) tied to a single construction plane (other than XY) and manually turned a rotary index table to address sequential operations. This approach will handle the work you're discussing, but the robot has to be fairly well "dialed in". Although IRBCAM is published in Norway, the support is very good (I have no connection to the firm that sells the software). Hope this helps.

[Dancy]

Peter;
the reason is the statue will be life size and cut from foam making it easy for the robot to manipulate it. If the robot holds the tool, it would require a rotary base for the statue and (grin), I don't have one of those!

in this example the robot is holding a vase and I had no issues as the vase has no "holes" in it. If it had a handle like a teapot....well, I would be stuck again.

[Dancy]

Thanks Marv;
I have not fooled around with Rhino for over 10 years but I think I follow your approach.
RoboDK does what IRBCAM does but for many types of robots. It's kinda the new kid on the block but doing very well.

[MARV]

Just took a look at RoboDK. Very interesting/capable and half the money. With all the idle robots out there sitting in warehouses, I'm tempted to run out and snag one and jump back in!

[Dancy]

I was really happy to find RoboDK Marv, I have had this bot for almost ten years and only the teach pendant to make it do squat. The pendant is fine if you have ONE job to do 100k times but for one off items it sucks.

Also check out Workspace LT. Doug Watson has come up with a unique idea. He no longer sells a one time license for boko bucks but rents it instead for less the $5 a month. Not as full dressed out as DK but it does work very well and no crashes.

[machinehop5]

...the box has many views.

where is my easy button

[3dcarver]

Hi Keshka,
Have you tried adding a zero thickness surface halfway down the holes so the CAM software can't see through the holes?
Just a thought...
Cheers,
John

[MARV]

Wow, the robot/cnc workspace has changed quite a bit since I was there. I never had to program using the teach pendent, but the translation software sometimes had an issue with singularities and would try to take a bite out of the workpiece. If you weren't sitting there with the pendent inland all the while, it was a big risk. Most of my stuff was one offs, so IRBCAM was a god send. Simulation not so much.

[Dancy]

John;
right now, since this is my first attempt at other than three axis. I don't know where to start so to speak. Mastercam has around 40 types of tool paths for 3D/multipath and each has a fist full of options. I don't know "flow" from "morph" and have no idea where to start or what would be best for this type project.

Keshka

[3dcarver]

Hi Keshka,
I don't have any experience with the software you are using to program your robot arm but if your solid vase shape worked then if you remove the holes in the skull shape, it should also work.
I use Rhino 3D for splitting and manipulating 3D models before sending them to our CAM system. In Rhino it would be relatively simple to add in a surface to block off the holes in the skull.
John

[awerby]

Even in foam, I'm doubting that this approach will work well for a life-sized figurative statue. Holding a six-foot chunk of foam out in the air and waving it around under a stationary router just doesn't seem like it will give you good cut quality, especially once you've removed a lot of material and it's just supported by its ankles. It seems more likely that the foam statue will simply break off than that it will end up looking like something carved by Michelangelo. But if you do get this to work, please post a video here, okay?