Instructables

I'm doing quite a few things here I've never done before: kerf bending plywood, waterjet cutting, making a large-scale moving structure... In order to work out as many kinks as possible early on, I 3D printed a scale model. This was particularly useful in figuring out big picture things like range of motion, overall stability, etc.

With this full-scale mockup, I was able to test the details I've been thinking about, figure out the fabrication process, and try to encounter as many surprises as possible before making the finished product.

 
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Step 1: Modeling the Mockup

With this project, I'm FINALLY making myself really learn Autodesk Inventor (this series of tutorials has been super helpful). I've been trying to force myself to transition from nurbs modeling to solids modeling for years, so I finally bit the bullet and did it with this mockup. This software is essential for this project for a number of reasons I won't get into here, but assemblies and parametric geometry are two of the major factors in streamlining this process that Inventor offers.

Most of my larger scale CNC work has been done with a Shopbot or comparable CNC router setup. What I've always found is that you need some wiggle room to get finger joints to go together, so naturally I modeled this in Inventor. This turned out to be totally unnecessary, but we'll get to that later.

This thing needs to be portable, but I'm making it out of 3/4" plywood with weighs about 2LB/SF. I did a rough estimate, and if I made it all out of solid panels it would weigh almost 1000 LBs- not exactly portable. My solution is simple- cut out most of the plywood. Yes, I know it's more waste but it's a prototype and I've only got a couple of weeks!

I subdivided the panels with solid lines along the edges and the main lines of the structure (basically X's through the panels) and left at least 1 1/2" of material as a rule of thumb.

The separate panels fit together using finger joints.

Super excited to see this come together! note that kerf on the metabeam may be 0.004", but the waterjet kerf is around 0.040". note that the waterjet software takes this into account though...

JON-A-TRON (author)  sheetmetalalchemist4 months ago

Thanks for the tip! I assume you mean that the software knows the difference between inside and outside cuts? What if you have both in a single file- should you run separate files for inside and outside?