How to Convert 3D Models into STL Files
RHINO
Printing from RHINO:
Open Rhino. First type ‘Options’ into the Command Line. Hit enter.

In the options dialog navigate to Rhino Options –> Appearance –> Advanced Settings –> Shaded
Open the pulldown menu next to Backface Settings, select ‘Single Color for All Backfaces.’

Then Select a Bright color other than Yellow (Yellow is Rhino’s selection color – this can cause confusion) and Click ‘OK’. I like to use green.

Changing Backfaces to green will make all ‘Inverted Normals’ appear green, so you know something is wrong. All normal faces will be the correct object color.
An object with an inverted normal will now look like this:

To fix this first explode the object (type ‘explode’ into the command line) or ungroup (type ‘ungroup’ ) until you are able to select individual faces. Select the inverted face and type ‘flip’ into the command line. The face is no longer green.

Select all faces in the object. Type ‘join’ into the command line. You now have a single object with all the normals facing the correct direction.
Now on to the 3D Print.
Type ‘Import’ into the dialog box. Navigate to your OBJ file and select open.

Zoom Selected to Center your model into the Viewports. [ ‘Z’ enter, ‘S’ enter]

Note : If your model looks like it did in Maya (doesn’t look like this) skip ahead to scaling the object.
If your model appears slightly different from the model in Maya, as mine does above, select your model and type in Explode.

WHOA!! Everything is green!! But, now the model looks like it did in Maya.
The fact that everything is green is good. This means all our faces are facing the same direction, but they are facing the wrong direction.
To fix this Select the entire object and type ‘flip.’ as shown above.
Select the entire object again and type ‘join,’ again as shown above.
Your model should now look as it did in Maya. Orbit around make sure there are no other Normal issues. In this case we are good to go!

Scaling the Object for Printing
If you are printing to a specific scale you must first take your object by the appropriate scale factor. 1/96 for 1/8″=1′-0″, or 1/48 for 1/4″=1′-0″ for example.
Since we are dealing with an abstract object we do not need a precise scale. We do need to scale the object to a size appropriate for the 3D printer.
The Printer Bed is 8″*10″*10″
Create a Box with these dimensions.

Now scale down your model (type ‘scale’ into the Command Line) until it fits inside the box.

Great! We have solved our Normal issues and scaled the object to the print size we want.
Only one more step. We have to make sure the object is water tight.
For this we will use the ‘OffsetMesh’ command.
Delete the box, we don’t need it anymore. Select your model and type ‘offsetMesh’ into the Command Line.

Now In order to be structurally sound a 3D print needs to be at least 1/8″ thick. Since our model from Maya already has thickness however, so in this case we only need to add a nominal thickness to make sure all the surface intersections are closed.

First, make sure the offset is in the right direction. Our goal is to add thickness, after all. If the new mesh (White) is inside the object click ‘Flip/All’ to make the offset go outward.
Check the box ‘Delete Input Mesh’ use a thickness of .02 and select ‘OK.’ Make sure the offset did not create any Normals. Ours did not.
We are now ready to export to Z Print.
Select your model, type ‘export’ into the Command Line.

Select Stereolithography (.stl) as your file type. Name your file and save it. We are now ready to open the file in ZPrint.
Printing from 3DS MAX:
Open 3DS Max
As with Rhino I will again first explain how to solve Normal Issues. Max is prepared to show flipped Normals without any extra set up by us. Thank you 3DS Max!

Objects without inverted Normals show as the object color. Inverted Normals appear black, instead of object color.
To fix this open the Modify panel, select edit ‘polygon.’ ‘Polygon’ is 3DS Max’s word for ‘FACE’. Now select the inverted (black) polygon. Then on the Modify Panel click ‘Flip.’

Now, onto our Model. Click on the Max Logo –> Import –> Import

Select the OBJ file we exported from Maya. Click ‘OK.’

The default settings are fine. Make sure your geometry is selected and click ‘Import.

Whoa!! All of our geometry is black!
(Note: If your model shows up with the object color, and not black with a colored wireframe, skip ahead to scaling the object.)
As in the Rhino example all of our Normals are inverted. Open the Modify Panel, as above. Select ‘Polygon’ Select the entire model. Click ‘Flip.’

Deselect your model and it will appear with all the faces as the object color.
Scaling the Model for Printing
Again we will scale our geometry to fit with a 8″x10″x10″ box, the size of the printer bed.
First a note about scale factors in Max. You cannot simply type in the scale factor as you can in Rhino. It is slightly more complicated.
To scale to a scale factor you must first determine that scale factor as a percentage. Max does not use fractions.
To scale to 1/8″=1′-0″ for example, we must first find out scale factor. We know it is 1/96 or .010416666666667. As a percentage this is 1.0416666666667
Now, Select the object you wish to scale.
First click and hold on the Scale Tool and select ‘Uniform Scale.’
Then click and hold on the Selection Model and select ‘Use Selection Center.’

To scale to 1/8″=1′-0″ Right click on the ‘Uniform Scale’ tool.

Type in your scale percentage and hit Enter.
For abstract scaling create a box that is 8″x10″x10″
Open the Create Panel, Select ‘Box,’ Draw your box on the screen. Enter the size parameters on the create panel.

You will now have a box next to your model.

Right click on the box and select Object Properties. In the dialog box check the box next to ‘See-Through Object’

Now the Box is Clear. Select your Model. Make sure the Scale tool is set on ‘Uniform Scale’ and the selection mode is ‘Use Selection Center’ as described above.
Scale your model down until it fits inside the box.

Now we must make sure the model is water tight for printing.
Delete the box. We don’t need it anymore.
Even though we visually scaled down the model, 3D Max still retains its original site. If you right click on the model and open the Object Properties you will see that its dimensions are still greater than 8″x10″x10″.
To fix this select your Object. Open the Utilities panel (The Hammer Icon). Click ‘Reset X-Form’ then click ‘Reset Selected.’

This tells Max that we really want our model to have the new dimension that fit inside the Printer Bed.
Now right click on your Object, and select Convert to –> Editable Poly. This deletes the object history.

Now we are ready to apply a thickness to make the model water tight.In Max this is called ‘Shell.’
Select the geometry, open the modify panel. Click on the Modifier pulldown and select ‘Shell.’

Now in the modifier panel, in the shell settings we have to add a very small shell. The default 1″ is already WAY too thick!
Since we did the reset x-form however, we can work at fractions and add a shell of the appropriate size. As this model already had a certain thickness from Maya, we only need to at a nominal shell to print correctly. Instead of 1/8″ we can use 1/16″ for this particular model.
Type 1/16″ into the outer shell window.

Now once again check for Normals. We are ok, so right click and convert to Editable Poly one more time, and we are ready to export.
Select the Object first, then navigate to the Max Logo –> Export –> Export.
DO NOT USE THE EXPORT SELECTED OPTION IT WILL NOT WORK FOR 3D PRINTING!!!

In the export selected dialog select Stereolithography (.stl) as your file type, and name your file.

Click ‘OK.’

An new dialog will come up.Be sure to check the box ‘Export Selected Only.’
Click ‘OK.’
Congratulations! You have successfully exported your STL file.
Z PRINT
Now for the last step.
Open Z Print.
When prompted open your .stl file.

Make sure inches is selected and click ‘Next.’
You should see something like this:

Excellent. Now we check for Normals. Go to Edit –> Normals –> Invert All Normals

Now you should see something like this:

Just like in Rhino and Max we have turned all of the faces inside out and now they are black. This is good. If you look closely at the above image you will see a handful of small white dots. These are improperly aligned Normals.
However, if all you see are tiny dots like this your Model has been successful. If you see larger white areas then you will have print problems and it will be necessary to repeat the export process until there are no large areas of white.
But, this model is ready to go. Go back to Edit –> Normals –> Invert All Normals to make the model right side out again.
The last thing we do is go to View –> Calculate Part Statistics

This brings up the Part Statistics Dialog Box which tells us how big our 3D Print will be.

But be sure not to make it too small.
Guess what?! You’re Done. If you have successfully created a .stl file with no Normal issues its time to truck on over to the 3D print lab and make this dream a reality!
Credit – https://tutorialhbaal.wordpress.com/2010/10/17/creating-a-3d-print-from-maya/