3D carving bit stepover

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hmatyas
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3D carving bit stepover

Post by hmatyas »

Hi

I am planning on carving out the bald eagle that is included in the clipart. My plan is
to enlarge it first at 18 inches by 6.XX. The preview time for cutting it out with a 1/4 inch end mill
and a 1/8 inch tapered ball nose with a 12 % stepover is 3 hours and 48 minutes. If I increase stepover
to 24%, the time drops to 2 hours and 28 minutes. I can't see in the preview any big difference between the
two. If I go to 36 inches by 12 or 13 inches the time increases to 18 hours with the 12% stepover.

Any opinions on what I could do to decrease the cut time? The smaller eagle is to show everyone what
the bigger eagle should look like. Also, the larger eagle will not fit on my machine without tiling. So if I find a bigger
machine to cut it, time on the machine maybe a factor.

Also, my modeling resolution is at very high (7x). if I lower that vs stepover what are the advantages and disadvantages?
I know that I could cut samples out to check, but sometimes asking questions, you get solutions that you didn't even think of.
Thank you for any ideas or links that explains the differences in different stepover settings and modeling resolution.

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Rcnewcomb
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Re: 3D carving bit stepover

Post by Rcnewcomb »

Try previewing with a larger bit for the finishing toolpath such as a 1/4" ballnose with a 10% stepover. For 3D work the stepover is usually 10% or below. YMMV.
- Randall Newcomb
10 fingers in, 10 fingers out, another good day in the shop

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adze_cnc
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Re: 3D carving bit stepover

Post by adze_cnc »

Without knowing the exact model used, material thickness, feed rates, pass depths, and what roughing strategy was used it's difficult to suggest things. Having said that I created file and set the feed rate for the 1/4" roughing router bit and a 1/8" diameter ball end bit to 60 inches per minute and got a machining time of 18 hr 32 min.

So here's my attempts at reducing that time for my chosen model and tool setup. The eagle head is around 11.5 inches by 11.5 inches. The material and model thickness are 1 inch.
 
1a-slow.png
 
Notice that the roughing toolpath is 17 of those 18.5 hours? Let's work on reducing that. I didn't know what roughing strategy you used but I figured like most people it would be 3D raster. This is the result:
 
1b-3D raster preview.jpg
 
How about changing that to z-level roughing?
 
2a-z-level.png
 
2b-better-time.png
 
From 17 hr down to 8 hr 24 min. And the preview:
 
2c-z-level-preview.jpg
 
The pass depth for the 1/4" router bit was set at 1/16". If my spindle can handle deeper cuts (and it can) I could try 1/8" pass depth:
 
3a-z-level-deeper.png
 
3b-z-level-preview.jpg
 
Another 3.5 hours trimmed off. Let's view the 3D finishing path:
 
3c-roughing-and-finishing.png
 
I used a step over of 0.015" (12%). For many woods that may be overly small. Douglas Fir for example might be OK with 0.045". But I'll try 1/32nd of an inch 0.3125". Beech seems to like that and so does walnut.
 
4a-finishing-32nd.png
 
4b-32nd-preview.jpg
 
I've dropped the finishing time from a little of 1.5 hrs to 46 mins. Total machining time down from 18.5 hrs to 4 hrs.

I'd probably want to excerpt a small but detailed area of the model to see if I can get by with the 1/32" stepover. Perhaps 0.025" might work as well.

I've also set feed rates to 60 inches/minute. Perhaps I can pop the 1/4" cutter up to 90 in/min? Or the ball end up to 75 in/min?
 
5a-warp-speed-mr-scott.png
 
Etc. Just a little study on possible ways to reduce time.

You'll note that I use absolute values for step overs rather than percentage values. If you are going from 12% to 16% step over on a 1/8" bit it seems like a reasonably big step (an extra 1/3 !) but it's going from 0.015" to 0.020" or a touch more than the thickness of a yellow sticky note.

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martin54
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Re: 3D carving bit stepover

Post by martin54 »

From what I remember being told some time ago the vectric models are all made for use with a 1/8" ball nose at their imported size which I believe is somewhere around about 6 inches. Using a smaller bit will not give you any more detail. If you increase the size of the model then you may be able to use a larger bit with no loss of detail as Randall has suggested. The toolpath preview should show you if using a larger bit will give the level of detail you require.
Always use the largest bit you can for any 3D work, it can save you a lot of time. Don't automatically think a smaller bit will give you more detail :lol: :lol: :lol:

hmatyas
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Re: 3D carving bit stepover

Post by hmatyas »

Thank you for all of your answers. You can watch all the video you want, but answers to specific questions to me are the second best
way to learn (The best way to learn is by experience which includes mistakes!).

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Re: 3D carving bit stepover

Post by Bob Reda »

Also consider what the speed of the z axis is. I always put the z axis speed way high knowing it will never go that fast but will decrease the time immeasurably if you have it set too low

Bob

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Adrian
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Re: 3D carving bit stepover

Post by Adrian »

That is an important thing to remember with 3D toolpaths. There is a lot of 3 axis movement and when there is 2 axis movement it's often very short. The machine needs to worry about accelerating and decelerating whereas the simulation doesn't. There is no guarantee the machine will ever reach the programmed speeds.

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adze_cnc
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Re: 3D carving bit stepover

Post by adze_cnc »

Something I should have mentioned above is that is all in VCarve 9.5. A supplemental for VCarve 11 (trial in my case) is that the 3D Roughing toolpath strategy "3D Raster" can be speed up by using the "Avoid machined areas" option.

Doing that can reduce the above initial 17 hr roughing time for 3D Raster down to 7 hr 26 min.
 
avoid.png
 
3D roughing.png

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