3D carving results and survey.

[david_gardner]

As a few of you know I'm a new ShopBotter with the purchase of a 2004 PRTAlpha a few weeks ago. I've had great fun and success doing 2D and 2.5D projects and am very pleased with the machine and excited by the opportunities it opens up for me in the future. Some of those opportunities involve 3D carving and I am slowly learning about 3D and how very different it is than doing 2D & 2.5D.

Gary Beckwith has been a tremendous hep to me in this process and has been very patient with my beginner questions. He is a great asset to this board and the Bot community. This board and the searchable archives have been a great resource as well and as my wife will testify I have spent countless hours searching, reading and absorbing information.

Now to the meat of my post. After many attempts and learning experiences I believe I have produced a carving that is as good as my machine will produce. I would like some opinions about whether this is true or not.

Here are the details:

Machine:

2004 PRTAlpha 60x144.
Vexta 1:1 steppers on all three axis, the original alpha motors.
5hp Colombo Spindle.

Material:

3/4" Hard Maple.

File:

Vector Art 3D, original size, no modifications whatsoever.

Relief Dimensions

Width: 5.81250 inches Height: 13.00000 inches
Min X: 0.00000 inches Min Y: 0.00000 inches
Min Z: 0.39568 inches Max Z: 0.75000 inches

Material Thickness = 0.7500 inches

Z Zero = Bottom of material

Machining Time: 00:39:18
OptiFeed Time: 00:39:18

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Z Roughing - End Mill 1/4 Inch

Tool: [1] 0.250 inches dia. slot drill
Feed Rate: 200.000 inch/min
OptiFeed Min: 200.000 inch/min
OptiFeed Max: 200.000 inch/min
Plunge Rate: 30.000 inch/min
Safe Z: 1.000 inches
Spindle Speed: 15000 r.p.m
Stepover: 0.100 inches
Tolerance: 0.003 inches
Allowance: 0.040 inches
Home Position: X:0.000 Y:0.000 Z:1.000
Comments: Z Roughing

Feed Rate Length: 217.5 inches
Plunge Rate Length: 4 inches
Rapid Rate Length: 31 inches
Machining Time: 00:01:54
OptiFeed Time: 00:01:54

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Machine Relief - Ball Nose 1/8 Inch

Tool: [1] 0.125 inches dia. ball nose
Feed Rate: 120.000 inch/min
OptiFeed Min: 120.000 inch/min
OptiFeed Max: 120.000 inch/min
Plunge Rate: 50.000 inch/min
Safe Z: 1.000 inches
Spindle Speed: 15000 r.p.m
Stepover: 0.012 inches
Tolerance: 0.003 inches
Allowance: 0.000 inches
Home Position: X:0.000 Y:0.000 Z:1.000
Comments: Machine Relief

Feed Rate Length: 2988.9 inches
Plunge Rate Length: 1 inches
Rapid Rate Length: 10 inches
Machining Time: 00:37:24
OptiFeed Time: 00:37:24

The results can be viewed here:

Dialup beware, large file

I'd love to hear any and all feedback on the process and results. I'm still learning and trying to get man and machine performing at a top efficiency and quality level.

[rcnewcomb]

Based on the lines that I am seeing I'd try it with an 8% stepover (0.010). I would also raster with the grain rather than cross-grain.

It also looks like there is a bit of slop in the Z-axis. Note the area above the antlers. Make sure that your Z-axis is solid.

Are you using one of Gary's 1/8" ballnose or a different brand? I highly recommend Gary;s bits for 3D work.

[david_gardner]

That is Gary's 1/8" ballnose.

Thanks for your suggestions.

[ljdm]

I am by no means an expert on this, but ......
Definitely raster with the grain when possible.
8 or 9% stepover to reduce lines.
Looks like your Z is going deeper in some passes than others. you bought a used machine - is everything tight, pinions, v-rollers, etc?
Looks like in some areas of the carving it is deeper than it should be?

[david_gardner]

Yes, the Z appears to be going deeper, and even bouncing at some points. The pinions appear to be tight. I'm wondering if the 1:1 motor is having a hard time maintaining position with that big 5hp spindle on it. Could the springs be getting weak?

Here's the big question. Would upgrading to the new big dog geared motors take this from where it currently is to perfection?

[garyb]

David,
Lou and Randall have made some good observations, about the only time I cut across the gain is if its in an offset strategy.
I created the same file and cut tonight for you to compare.
The relief is 9x9x0.5624
Cut time was 29:28 min for the profile in a rastor with my .125 tapered ballnose. 10% S.O.
The area clear time was 13:08 min using my .125 tapered endmill.40% S.O.

Here's the piece as it finished cutting still on table with no clean up. You will notice a couple of areas that need cleaning from grain kick up.
takes about 30 seconds with a 220grit star sander


39696.jpg

I will post the rest of the photos under the woodworking section at www.beckwithdecor.com/forum tomorrow

[david_gardner]

Thanks Gary.

You are cutting only the relief with the ballnose and the flat with a standard endmill? I cut the entire file including the flat with the ballnose, maybe thats why I'm getting the streaking and "bounce". I'll try it your way tomorrow.

[david_gardner]

Is this what you mean by a star sander?


39700.jpg

[garyb]

Yes thats a star sander, some people call them a flap sander as well.
The streak and bounce that you are seeing looks more mechanical to me but check you sbp code to be sure

[ljdm]

David - what are you using to hold down the material? Always hard to diagnose from pictures, but it looks like either the material has some movement, or your Z is erratic. Just for the heck of it, double check Z pinion, doesn't take much to produce line like that, and what looks like little holes where they dont belong. A few thousandths play in the pinion will show up in flat areas if the Z does some passes lower than the surrounding passes. Also, if the Z pinion is good, check for any binding in the Z. A little tight spot in an area of the Z that might not have been used as much by the previous owner could cause those lines. If you think you are getting a "bounce" with the Z, pinion slop would be the likely cause, not using the ballnose. I had similar lines in my carvings, it was due to a combination of pinion adjustment and binding of the Z. You never know - might also be the same situation with you? 2 cents worth.
Lou