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Dr. Mike

Maintaining and adjusting scale in blender

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Hello Embodi3d,

 

I was recently asked a question about maintaining and changing scale of objects in blender, and I thought I would share the answer with you. Here was the question:

 

"I just ran through your tutorial regarding slicer, blender, and mesh mixer. I noticed that you mentioned how blender translates 1mm scale into different units.

Is there a simple way to ensure a continuity of scale from CT scan to final print?

In other words, is it possible to create a scale model of the structure taken form the CT/DICOM file?"

 

Blender uses a fictitious unit of measurement called a "blender unit." When you import an STL generated from a CT or MRI scan, the default unit of measurements is mm. So, 1 mm on the scan is translated to 1 blender unit in blender. The default scene in blender starts with a cube that is 2 blender units large, or 2mm. That is why when you import a STL into blender it appears HUGE. You don't need to change the scale however. When you export the model from blender to an STL file, the blender units are again converted back to mm, and your model will have the correct scale when sent to the printer.

 

If, however, you wish to change the scale of your model. You can do so by selecting the object in blender and hitting the "s" key (for scale). You can then freehand adjust the scale. If you wish to do so precisely, you can just type the number after the "s". For example, if you type "s" and then "0.5" the object selected will scale to 50%.  Export to STL and your object should be at 50% size.

 

Hope this helps.

 

Dr. Mike

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