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

------------------------------------------------------

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

------------------------------------------------------

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 (http://webpages.charter.net/davidgardner/Elk%20Carving.jpg)

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


7734

I will post the rest of the photos under the woodworking section at www.beckwithdecor.com/forum (http://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?


7735

[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

[david_gardner]

It's not in the file guys, it has to be mechanical. I'm going to pull the z motor tomorrow and check the pinion. Movements is nice and smooth with no binding so it either has to be the pinion gear or the gutless stepper itself.

[david_gardner]

Material was held down with two Bessey K bodies, it didn't move.

[jhicks]

Only 3 comments you may wish to consider.
1) I find that there is little value in roughing passes even with some fairly deep relief files.
I've done up to 2" thick material by using the following technique.
The logic goes like this.
A) I cut 99% with an offset strategy from inside out. The relief is "generally" highest in the middle of the art and I Zero on the top with an .015 offset below Z Zero. Therefore the depth of cut in the middle is quite shallow. Given that the step over is usually 8% to 10%, once you start in the middle with an offset strategy, the change of depth going around and down each step over is quite tiny. By the time you get to the outside final max depth, you've done so with shallow changes in step down and are basically shaving material so not any problem with bit capability.
This completely avoids any roughing pass at all.
B) I get the point about raster strategy but with an raster cut you are basically making such radical depth changes it runs slower for me and has a lot more opportunity for bit deflection and rapid plunge /Z changes. It becomes obvious to me whan I watch a raster run like a sewing machine and an offset run like a river.
2) On the area clear aspect I agree. Do that with another bit and TP around the major area clear area as a primary cut before the 3D. That way the final outside ball nose cutting will have only a minimal amount of deep cuts around the design vectors and not much to cut through except in the crevices your 1/4" end mill cant reach into.
3) Finally IF you are using Gary's 1/8" BN and want a crisp edge after the area clear. Simply run an outside profile to depth to outline it with an 1/8" end mill or your ball nose to clean corners at base of area clear and outside profile edges but usually this is unnecessary.
Hope this makes sense.
It may be true that you will need to tweak Z plunge rate or feed rate in some materials but by eliminating a roughing pass, you end up saving time overall.
Good luck with your experimentation. In the end its all about tweaking until you find what works best for you.

[Brady Watson]

David,
From the looks of your part, it appears that you have a little bit of backlash in your Z axis. It is good to inspect and/or replace the Z pinion and adjust the backlash via the V-roller beraings on the Z towers. Take care not to overtighten because you can spread the Z towers.

You also want to make sure that you have 2 large coil springs counterweighting the 5HP spindle. You can call SB to make sure that you have the right ones. The ones on my machine are about 1" in diameter. Lighter spindles use lighter springs. From the looks of your relief, it appears to be a backlash issue & I see no indications of positional loss by the steppers. A little fine tuning, care and patience in adjusting the Z & you should be tip top.

-B

[magic]

Has anyone ever made a counter balance system for their router/spindle? If you run 2 pulleys over the tower and used counter weights instead of springs the router/spindle would be balanced all the time.

THANKS....I have a new project to do.

[Brady Watson]

It's much easier to adapt a gas strut type counterweight than monkeying with pullies. I don't think that counterweight is David's issue, as the machine is not showing signs of lost position or indications that it went into Alpha mode.

-B

[david_gardner]

Thanks to all of you who took the time to read this and offer suggestions. Here is the same file cut with an offset strategy. While some aspects of it are better, I think that overall it really isn't an improvement over the first picture.

Specs:

Relief Dimensions

Width: 13.00000 inches Height: 5.80000 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: 00:43:37
OptiFeed Time: 00:43:37

------------------------------------------------------

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: 30.000 inch/min
Safe Z: 1.000 inches
Spindle Speed: 13500 r.p.m
Stepover: 0.010 inches
Tolerance: 0.001 inches
Allowance: 0.000 inches
Home Position: X:0.000 Y:0.000 Z:1.000
Comments: Machine Relief

Feed Rate Length: 3487.3 inches
Plunge Rate Length: 0 inches
Rapid Rate Length: 4 inches
Machining Time: 00:43:37
OptiFeed Time: 00:43:37

Elk Offset Strategy (http://webpages.charter.net/davidgardner/Elk%20Carving%20Offset.jpg)

Maybe the picture will ring a bell with somebody. Frank at shopbot is thinking it's a weak z axis motor and I'm inclined to agree because I can push the z axis by hand pretty easily (~25 lbs. of force) with the motor engaged while the other motors I can't push at all. I'm going to try swapping it with one of the x motors tomorrow if I can figure out how to easily remove the z motor.

[rcnewcomb]

It looks like the smaller stepover did help.

I think Frank is right about the weak Z. Look at the area around large Z transits and notice the "dots" as the Z is bobbing -- around the antlers, near the body, etc.

The other thing I would look at is if the Z is plumb. It almost looks as if it is slightly out of square.

Search on the forum for some quick cheap ways to check the Z alignment.

[jhicks]

Boy, even the background area clear has way too many machining marks. I tend to agree with the others. Looks like there is some backlash or general looseness in your Z stability and/or not perpendicular as well.
Do you get a smooth/flat table when you surface it or lots of machine marks between passes?
Background should be same as your table with surface cut.
I know you said the part is firmly held down otherwise I would be suspicious of movement as well. In fact I'm still suspicious it may be lifting and/or moving.

[magic]

"It's much easier to adapt a gas strut type counterweight than monkeying with pullies.

Brady, I never considered a strut because I'm not that bright. If that's the case, how would you select the correct one?

I think, when i get time that I'll make the pulley system. It should take a few hours then I'll have something else to watch as the machine works it's magic.

Pictures to follow

[khalid]

here is my counter weight version on my 1st machine...


7736


7737

[dray]

Cool setup Khalid how is the resolution on that machine?

[Brady Watson]

Search McMaster.com for "Gas Springs". Find something with a stroke longer than your Z axis travel and a pull equal to the weight of your router + t-rail. You'll have to come up with your own brackets & mounting scheme, but it shouldn't be difficult.

-B

[khalid]

Thanks Danny.. I was getting 0.06mm Resolution on that setup (Ball screw)at 150IPM... After installation of 48Voltage power supply and new home made SLA-7062 based controllers , i just removed the counter weight...

Currently this machine is not working due to faulty ball nuts...

[bcammack]

The only thing that comes to mind about using a counterweight system vs. a spring is that a counterweight system is going to add mass and, subsequently, inertia to the equation.

Your steppers are going to be starting/stopping the movement of more mass and, therefore, working harder to accelerate/decelerate it.

I suspect that is why, beside it's inherent simplicity to implement, ShopBot uses matched springs to counterbalance the weight of the Z-axis assembly.

[khalid]

Totally agreed to Brett