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Author Topic: Problem with an STL file  (Read 1120 times)
GreatDane
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« on: December 03, 2011, 17:27:20 pm »

CAMBAM seems to be ignoring the shape of the attached STL file. All that will happen is a flat toolpath with a few interspersed 'bumps'. The appearance is that there is no depth to the STL image. My version of CAMBAM is the latest - L.

I have tried Blender and Meshlab. I have cleaned the file in Meshlab and saved with a different name - no change. I have saved as a 3DS file from Blender - no change. The ideas I have to fix this are tapped. Can you please take a look? I want to create a 'bas-relief' this image. Another STL file, a simple oval, works fine. Thanks.

* smo Egyptian Figure.stl (3354.67 KB - downloaded 62 times.)
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lloydsp
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« Reply #1 on: December 03, 2011, 20:30:39 pm »

I don't do a lot of surfaces, but it sounds like you've got the mesh up above the material's Z=0 point, and only a few spots are penetrating beneath zero.

I did a few of those for experiments, and had to fiddle with Z

LLoyd
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Imagining
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« Reply #2 on: December 03, 2011, 22:20:41 pm »

Some of the face normals are facing to the inside of the object rather than all face normals facing to the outside of the object.  [Read below for an excruciatingly detailed explanation of face normal.]


You can see incorrectly facing face normals after the object is Edit>Aligned to 0,0,0. After this operation, most areas of the object are not red [which they should be when highlighted] but are a dark green on my monitor [they could be black on yours].

If the object is rotated so the underside is visible, most of the underside is red and other portions are dark.  Again, the faces being red means that is the face normal, which indicates that face normal is facing the opposite way of how it should be so a toolpath can be generated.

You need to get all the face normals facing out so Cam Bam can see them.  As they are Cam Bam thinks that surface does not exist when seen from the orientation you need to generate toolpaths on what is termed "the top".  And Cam Bam is doing is job correctly, the STL has just given Cam Bam the wrong information for it to function as you expected.  Probably those digital demons fussing on your computer ....

There should be a operation in the Edit function on the tool bar of your CAD software to make the normals all face one way.

ALSO SEE:  http://www.cambam.co.uk/forum/index.php?topic=1989.msg11641#msg11641


This is from CNC Zone:

The orientation of the surface normals of the object are opposite of what they should be, which is why Cam Bam is machining the back; its doing exactly what it is suppose to. I know this VERY well as it was one of the processes in CAD that can really drive you mad in CAM.

Read this to get a good grasp on "normals": http://csanet.org/newsletter/winter01/nlw0107.html

REMEMBER THIS: When an object is Selected in Cam Bam, it turns red.

So do the following to solve your dilemma:

1. In your CAD program, reorient the normals to the top of the object [the convex surface].

2. In Cam Bam, Edit> Align Objects and enter these settings: X to Left with a zero value [0 in the white box at the bottom of each axes column]; Y to Bottom, with a zero value; Z to Upper with a zero value. This will align the object along the X and Y axes, and will make the surface of the object the Stock Surface.

Also:

1. Use the Advanced settings in the Object Property Window [the one on the bottom on the left] to enter the parameters of the Tool Path.

See User Interface in the Help screen.

2. Set Boundary Method to Shape Outline [the default]

3. Set Boundry Margin to -0.15. That will keep the cutter on the surface and so it does not try to cut the edges.

Read this for a full explanation by Andy, the inventor of Cam Bam. Inefficient and unexpected moves during machining 3D profile  http://www.cambam.co.uk/forum/index.php?topic=2013.0

And finally, I am not a genius, I made everyone of these mistakes, and more than once too!!

One last suggestion: Go to the Cam Bam Forum and search STL and 3D. That is how I began solving my problems when I switched from 2D/2.5D to 3D.

Give this a go and if you still have problems, post again.
« Last Edit: December 03, 2011, 23:02:16 pm by Imagining » Logged
oregondane
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« Reply #3 on: December 04, 2011, 15:59:34 pm »

To net out the response: I used the command to reverse faces in my artwork software and the problem was solved.

I did see Andy's comment regarding the reverse face early in the problem-solving process but didn't make the connection to my problem. I had created a simple oval that was handled as expected by CamBam. Comparing this to the problem artwork, I noticed the oval was red when selected and the problem artwork was black, as stated by Imagining. Then, I made the mental link to Andy's comment. When I reversed faces in the problem artwork, the problem went away.

Is there a way for CamBam to detect this and warn the user?

Thanks for the Forum and the great support.

Regards,

Jay
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Imagining
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« Reply #4 on: December 04, 2011, 17:32:14 pm »

If you have not changed any of the default settings in Cam Bam, when a object is highlighted it will be all red. [This assumes only one layer.]

If the object is not completely red, then Cam Bam is alerting you of the face normal not facing the correct way.

Also, if there is any uncertainty about all the face normals facing in the appropriate direction, rotate the object to inspect the bottom of the object.

If there is any red on the bottom of the object that you are only milling one side of [no back side milling], then the original drawing needs to be reconfigured so all the face normals are facing to the top [TOP= side of the object chosen for machining in a one-side machining operation] of the object.


A problem solving suggestion:  When designing an object with complex curvilinear shapes in three dimensions, and when there has been a lot of editing and adjustment of a curvilinear shape, then in the CAD program the last operation before converting to a STL or 3ds file should be to to make all face normals face to the side of the object that is to be machined.

When making the transition from 2./2.5D to 3D the work flow operations need to be thought through.  In some respects 2/2.5D is similar to 3D, however, the addition of another dimension of machining in 3D is different and does take a different mind set.  

Keeping track of face normals and their relationship to the actions of the bit seems to me to be the stepping stone to problem solving in 3D making.
« Last Edit: December 04, 2011, 17:52:00 pm by Imagining » Logged
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