Graderworks 2.3 Release

by: Anthony Garland
Follow @AnthonyPGarland

UPDATE: Changed from experimental to production on 8/9/2016. No known bugs exist.

Graderworks 2.3 is now available. This version may contain a few minor bugs.

New features include 

1. Similarity scores can now be computed using just .stl files. This function lets you compare 1000s of .stl files against a target reference .stl file. For example, if you use another CAD application, then you could export models as .stl files and compare the models against a target 'correct' file. Or, you could download 1000s of files from Thingiverse and compare how similar they are to your particular .stl design. 
2. Scaling of files for similarity checking. Often files are alike but at a different scale. For example, a student might draw a metric part in inches. Therefore, we expect all the dimensions to be exactly 1:0.0254 smaller than the correct shape. In the past, the similarity score would have been zero, since the algorithm requires the two parts be on the same scale. Now, Graderworks will try automatically scaling the part, and then comparing the parts at the new scale. For each reference file, 3 columns will be generated. 
   1. The similarity score without scaling. This score is the standard score that was used before. 
   2. The scale between current file and target reference. Graderworks will attempt to scale the current model to be the same size as the target reference. It will export the scaling factor in this column. 
   3. The similarity score of the scaled file. After scaling the current file, the similarity score will be computed again. 
3. Reference file properties analyzed. When specifying one or more reference files for the geometric similarity comparison check, the mass properties and meta-data will be exported in the first few lines of the output.CSV file. This information is helpful since often it is used for grading. 

Example

As an example of the similarity score comparison of .stl files compared to .stl files, I will give a short example analyzing 'wheel' files from Thingiverse. I downloaded several wheels from Thingiverse, put them into a single folder, copied the absolute file path of this folder to the root folder textbox in Graderworks, selected '.Stl files' as the assignment type, and entered 'Volant.stl' as the reference to compare against, and checked the "Compare Part to References Specified Below" and "Autoscale and Recompare" checkboxes. 

Files

Download the files here.

• Mini Monster Truck With Suspension Left Wheel
• PLA Spring Motor, Rolling Chassis Wheel Front and Wheel Rear
• OpenRC 1:10 RC Truggy Rims OpenRC_Truggy_Rim.a.1
• Parametric airless tire spiral wheel
• Formula E Race Car formulaRwheel_repaired
• Tractor Volant

Run

After running Graderworks (Analysis->Start), the output.Csv file showed the raw similarity, scaling factors, and scaled similarities after scaling. 

After manual scaling the parts according to column E, this is the size they look on the build platform. 

Conclusion

The similarity score at first seems suspiring since we think of all wheels the same. Indeed, we think in terms of schemas of what constitutes a wheel. We have a mental model of what 'wheelness' means. While examining the results, the key geometric features that raise the similarity score are 1. The width of the wheel and 2. having spokes of some sort. 

To test this hypothesis, I drew a simple wheel in SOLIDWORKS and then reran the comparison. As expected, my wheel with a simple rim and spokes had a high similarity score when compared to the reference model, 'volant'. I put the test wheel on Thingiverse. 

Try it!

Give Graderworks a try even if you don't have SOLIDWORKS on you computer. Graderworks only takes about 2 minutes to download and install! Try analyzing some .stl files and let me know what you think!

Download it here.

.stl files with errors do not work well with Graderworks. So be sure your file is a manifold.