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Old 8th May 2014, 05:12 PM   #1
MikeM
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Cool Going from AC3D to .stl

I'm a long time, but occasional user, of AC3D - mostly for rapid sketches of industrial kit and machinery - so no 'pretties'. I now want to try and make some pieces for a laboratory experimental rig using 3d printing, and rather than struggle to learn Solidworks, would love to do it in AC3D. However there seem to me to be a couple of issues I don't understand.

1 How do I make the dimensions 'real world' instead of grid units? If I want a 100mm disk - I can make it 100 units diameter, but how does the conversion to .stl know what this means?

2 What happens to surfaces that are hidden when you merge two pieces. Even if you weld the vertices there are internal surfaces, often hundreds if trying to make smooth curves to accurate dimensions

Thanks in advance for any comments
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Old 11th May 2014, 01:02 PM   #2
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Default Re: Going from AC3D to .stl

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Originally Posted by MikeM View Post
I'm a long time, but occasional user, of AC3D - mostly for rapid sketches of industrial kit and machinery - so no 'pretties'. I now want to try and make some pieces for a laboratory experimental rig using 3d printing, and rather than struggle to learn Solidworks, would love to do it in AC3D. However there seem to me to be a couple of issues I don't understand.

1 How do I make the dimensions 'real world' instead of grid units? If I want a 100mm disk - I can make it 100 units diameter, but how does the conversion to .stl know what this means?
STL coordinates must be positive numbers, there is no scale information, and the units are arbitrary. Say wikipedia When I import an STL file to Shapeways, it asks my for the units the grid is defined in.

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2 What happens to surfaces that are hidden when you merge two pieces. Even if you weld the vertices there are internal surfaces, often hundreds if trying to make smooth curves to accurate dimensions

Thanks in advance for any comments
I would suggest figuring out a work-flow where that is avoided, if possible.

You know about "snap together by distance...", right? Currently we don't have a tool to find intersecting surfaces (that I know about, anyway) but we do have a tool to find surfaces that aren't properly connected to each other (leaky surfaces).

Ron
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Old 9th August 2014, 11:46 PM   #3
Edymnion
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Default Re: Going from AC3D to .stl

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Originally Posted by MikeM View Post
I'm a long time, but occasional user, of AC3D - mostly for rapid sketches of industrial kit and machinery - so no 'pretties'. I now want to try and make some pieces for a laboratory experimental rig using 3d printing, and rather than struggle to learn Solidworks, would love to do it in AC3D. However there seem to me to be a couple of issues I don't understand.

1 How do I make the dimensions 'real world' instead of grid units? If I want a 100mm disk - I can make it 100 units diameter, but how does the conversion to .stl know what this means?

2 What happens to surfaces that are hidden when you merge two pieces. Even if you weld the vertices there are internal surfaces, often hundreds if trying to make smooth curves to accurate dimensions

Thanks in advance for any comments
You're in luck, I just happen to have gotten a 3D printer that runs off of ReplicatorG (which uses .stl as it's primary format).

The unit conversion is 100 micron = 1 small square in AC3D. Which makes one big square a millimeter.

However, working in that large of a scale is kind of impractical, the ReplicatorG software (the stuff that runs Makerbot) has a scale option built into it. I model mine at 1 small square = 1mm, 1 big square = 1 cm, and then when I import the stl into ReplicatorG I simply scale it all up by a factor of 10 to get a piece it likes.

One other thing to watch out for, stl format likes to lay things on their side. As in, any normal mesh you open with practically any program loads rightside up, the stl rotates it 90 degrees on the Z axis.

I've attached an image of a piece I'm printing out right now. The small one is the one I modelled in AC3D, the big one is the same one after I've rotated and scaled it properly in ReplicatorG for it to print the way I wanted.
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Old 9th November 2014, 11:10 PM   #4
bfeaver
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Default Re: Going from AC3D to .stl

I am using an Afinia 3D Printer. I have the AC3D major grid set to 1.0 m and the minor grid set to 0.001 m (1mm). I export my projects from AC3D as STL ASCII. To have my AC3D projects print actual size I must scale them up 39.368 times on the Afinia.

3D Printer projects from Make magazine and other sources print actual size without scaling.

Makes no sense to me. Any explanation?

Blue side up,
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Old 29th November 2014, 03:57 PM   #5
edi
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Default Re: Going from AC3D to .stl

Sorry for jumping on this thread, but ...

I also have a 3d printer and issues with stl conversion. Generally the scaling options of replicatorG is completely ignored for ac3dīs stl files, I always get the same size (ac3dīs original size). If I want to change the size I have to scale the bit in ac3d and reexport. But this might be a replicatorG issue and there is a workaround.

What affects me more is the fact that smoothing with +subdivision is completely ignored in the stl file. So if I draw a cylinder with 20 segments and press Subdiv+ several times, after my export to stl the printed object will still be a cylinder with 20 segments :-( What do I miss there?
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Old 29th November 2014, 06:54 PM   #6
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Default Re: Going from AC3D to .stl

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What affects me more is the fact that smoothing with +subdivision is completely ignored in the stl file. So if I draw a cylinder with 20 segments and press Subdiv+ several times, after my export to stl the printed object will still be a cylinder with 20 segments :-( What do I miss there?
There is a "Commit Subdivisions" button under "Object" in AC3d you can use to make the subdivisions permanent. Most formats don't have a concept of 'Subdivision' so you have to commit them before the export then undo that step.
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Old 29th November 2014, 07:31 PM   #7
edi
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Default Re: Going from AC3D to .stl

Thanks a lot, this has definitely changed things. But why do I have to undo the subdividing after the export? Why would I not want to make them permanent?
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Old 29th November 2014, 07:36 PM   #8
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Default Re: Going from AC3D to .stl

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Thanks a lot, this has definitely changed things. But why do I have to undo the subdividing after the export? Why would I not want to make them permanent?
I don't make them permanent because its much harder to work on a model that's been subdivision committed. Its more load on the gfx card, files sizes are huge, many more polygons... So I keep my masters uncommitted, and just commit for the print export copies.
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Old 30th November 2014, 12:22 AM   #9
bfeaver
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Default Re: Going from AC3D to .stl

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I don't make them permanent because its much harder to work on a model that's been subdivision committed. Its more load on the gfx card, files sizes are huge, many more polygons... So I keep my masters uncommitted, and just commit for the print export copies.
Thanks for this tip and follow up explanation.

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Old 30th November 2014, 12:36 AM   #10
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Default Re: Going from AC3D to .stl

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Originally Posted by bfeaver View Post
I am using an Afinia 3D Printer. I have the AC3D major grid set to 1.0 m and the minor grid set to 0.001 m (1mm). I export my projects from AC3D as STL ASCII. To have my AC3D projects print actual size I must scale them up 39.368 times on the Afinia.

3D Printer projects from Make magazine and other sources print actual size without scaling.

Makes no sense to me. Any explanation?

Blue side up,
Bob
Back to the original thread...

I know that number of cm per meter divided by number of cm per inch equals 39.37. (100 / 2.54 = 39.37). However, if ac3d units are in meters and Afinia printer units are also metric why should the use of any imperial units be required at all?

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