stl. files

[thegroover]

I'm trying to create stl. files for rapid prototyping , and get the warning that the part is in negative space. How do I alter that? I've moved it so all the integers describing maximum and minimum of the xyz axes are positive in the stl. menu , but still get the warning.
Also , regarding the other factors in the stl.menu , is there somewhere that tells me what different values of Angle and Distance might mean in practice?
Thanks for any assistance.

[Mike Swartz]

This message is only a warning. Some STL machines cannot deal with negative numbers. (most can)
To resolve this issue, you first need to determine where the part is in regards to World 0,0,0. You can do this by selecting Measure-->Point 3D, and selecting a point on your part. Notice the data in the Output Window. One or more of these dimensions will probably show a negative number.
You then need to move the part. (Part and Assembly-->Modify Position-->Two Points)
Select the point on the part that you think is in the most negative location, (this is your starting location) and move the entire part to a positive location. You can enter in the coordinates of any point in the command line. For instance, if you want to move the part to X 1.0,Y 1.0 1,Z 1.0 you would enter in 1,1,1

As far as the distance and angle settings. These are relative numbers that are used to refine the facets that are used in the display of your parts.
You can test this, by building a cube. Check the part properties and look at facet refinement. There will be no options, because there are no curves to generate. Add a hole to your cube, and check again.

An STL file is generated from what you see on the screen (facets) not the actual geometry of the model. These numbers will vary depending on the geometry you have created. If you look at a feature of your part, such as a hole, you will see that it does not display as a circle, but actually, a number of small straight lines. The distance and angle numbers represent these lines.

The more you refine these facets, the better looking your model is on the screen. The STL file has a direct relationship to these facets. The more you refine the facets, the more triangles you calculate in your STL model. Do not go too far, as the file size can get huge, and your STL machine usually has a limit in how thin a layer of material it can build. Usually this is the limitation when it comes to building a smooth looking prototype part.

I have had best results when I ignore the numbers, and refine the facets by a factor of two. Then I look at it on the screen, and if the curves look good, I generate the STL file. If it does not look good enough, I refine it again. When it comes to STL files, what you see is what you get.

[thegroover]

Thanks for your reply Mike , could you just explain what "refining by a factor of two" involves ? Is it changing Angle and Distance figures to half their number or twice ? Or just one of them? Do I just ignore the "unexpected data" warnings that come up?
Thanks again
Oli

[John Scheffel]

You can refine the facets from the Part Properties. The exact menu picks depend on which version you are running, but in 2008 you open the part properties, select Facets in the left frame, then choose a "Refine by:" factor from the drop down list.

[thegroover]

Thanks John , that's the bit I didn't know how to find , I was looking in the wrong place , at the save point.
Much obliged
Oli