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Benefits of 3D modelling and top-down design - Acrylic box

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Benefits of 3D modelling and top-down design - Acrylic box

3D modelling has a lot to offer when developing a design including customisation and design for manufacture. To illustrate this I will describe a common project in secondary schools, a small, laser cut acrylic box.

Currently students might hand sketch on paper their idea with key dimensions.  They then use a non-parametric 2D draughting program to re-draw the outlines. Checking whether everything will slot together properly requires considerable 3D spatial awareness.  Some schools might use DXF fomat files imported into a 3D modeller like Creo to assemble for checking prior to laser cutting.  Without the 3D model there is every chance something will have been missed with parts needing to be modified and re-cut.  I skipped over the difficulties of importing a non parametric DXF into a parametric environment and editing it to become valid for 3D feature creation.. It's no surprise the majority of schools use this method, 2D draughting has been around much longer than 3D modelling and teachers have probably never had cause to consider if there is a better way.


How about this strategy?  The freehand paper sketches are scanned and imported into PTC Creo Parametric and scaled as a template for creating extruded parts. These can be assembled quickly and anlaysed for interference. Cross sections scanned through the 3D parametric model check for gaps and kinematic motion proves the movement of the lid. Motion paths might also check clearances. The student will now have significant confidence the box will go together and work as planned so needs files for cutting. An assembly of the parts laid flat is used to create a drawing that can be saved as a DXF for laser/CNC cutting.

The best thing about this workflow is when you want to change something. All steps in the process up to DXF output are associative so any changes to individual parts or assemblies can be rechecked and then immediately output to DXF as the changes ripple through automatically. Contrast that with trying to edit the non parametric 2D sketches re-import as a DXF, re-edit the sketch to make it parametric, etc...!

Design iteration was never easier or, is there an even better way?

Probably the most elegant solution, particularly where a design needs to be customised, is a top-down parametric 3D model.  Typically, a skeleton part has all the critical geometry with parts and assemblies referencing the skeleton.  Examples might be a gearbox casing that resizes automatically to accommodate different ratios or a water wheel that rebuilds itself to match the flow and height of the water supply in a specific location.

The attached zip file contains three models of a small acrylic box. The first is bottom-up, the other two are top-down with one being controlled using parameters and relations and the other using a skeleton part. There is a document that explains things. I hope you find it useful.