3D carving large pieces - quickly and efficiently

[tonty]

I make large 3D sculptures and have CNC with lots of Z to allow me to rough out. I'm pretty new to all this so still finding my way.

A typical piece for me would be 60' x 18' x 24".

I have been experimenting with a large bit that can shift a serious amount of wood (1/4" at a time at 200 IPM), this is great for roughing, but when I come to smoothing, the large bit has left large parts that cause issues with the smoothing path. They are too big.

So, I was thinking there might be some sort of intermediate path that would know what was left by the roughing but that doesn't exist in VCarve (it does in RhinoCAM, but that's 20k). I did try running the roughing again with a smaller bit, but that doesn't take into account the fact that the piece has already been roughed and so I have to run the whole thing again.

Just wondering if anyone else has found and solutions for this.

[Rcnewcomb]

Use multiple bits for the finish toolpath. The software is smart enough to have the smaller bits only machine detail areas that were too small for the larger finishing bit. Try running a simulation with the finish toolpath using three bits: 1/2", 1/4", and 1/16" ballnose bits. Run different combinations of two or three bits to see what provides the results and machine time that is optimum.

Depending on the project, starting with a large diameter finishing bit may eliminate the need for a roughing toolpath.

[adze_cnc]

I have been experimenting with a large bit that can shift a serious amount of wood (1/4" at a time at 200 IPM), this is great for roughing, but when I come to smoothing, the large bit has left large parts that cause issues with the smoothing path. They are too big.

And what would the size of cutter for finishing be?

For that matter what would the size of the cutter for roughing be? Shifting a 1/4" at a time could be done with a 1/4" bit so that doesn't help much.

And what would be the roughing toolpath strategy be? Z-level or #D raster?

[TReischl]

.....

I have been experimenting with a large bit that can shift a serious amount of wood (1/4" at a time at 200 IPM), this is great for roughing, but when I come to smoothing, the large bit has left large parts that cause issues with the smoothing path. They are too big.
.....

You are babying your machine. A 1/4" at 200 iPM is not a serious amount of wood removal. See this:

https://youtu.be/Pt8n43_YRjI

That is my homebuilt running at 800 IPM in the cut with a 1/2 inch endmill. The video is not sped up at all. Enjoy.

[AboveCreations]

"A typical piece for me would be 60' x 18' x 24".

Is that a typo? Sixty Feet is purty huge! I'll assume you meant inches... lol.

[tonty]

Thanks all,

Yes, a typo, 60" X 18" x 24",

My roughing cutter is 2-1/2" the smoothing is a 3/8" ballnose.

Strategy was 3D raster.

The 2-1/2 cutter left lots of corners (understandably as it just wasn't able to get in there) and when I ran the smoothing path it was trying to cut far too much.