Exoskeleton Frame Sourcing

I agonized over the exoskeleton framing material. I was open to any method I am reasonably familiar with: wood, steel tubing, and aluminum extrusions.

• Wood - Plentiful cheap tools, strong dowel rods, easily reinforced where necessary - about $70 from Home Depot
• Steel Tubing - Welds stronger than screws, but squareness would be difficult - about $70 from Home Depot
• Aluminum Extrusions - Flexible, but expensive - about $130 with shipping

I ultimately went with the aluminum extrusions for their flexibility and forgiveness. If the z-axis isn't aligned, I can loosen a bracket and slide the offending framing. Wood or steel require more time to fix mistakes, though the monetary cost is not prohibitive. Also, if I decide to change projectors for more resolution later, the frame can easily be modified to adjust for throw distance.

Model made in AutoCAD 2015

The front of the frame (toward the right, parallel to the x-z plane) will hold the projector and its mount inside the frame. The back of the frame, with lower support bars running parallel to the x-axis, will hold the z-axis leadscrew. The vertical extrusions (z-direction) rest on the extrusions that run parallel with the y-axis so that I can move the projector and z-axis leadscrew to a proper distance apart. The extra extrusions in the middle running parallel to the y-axis can support a wiper system if needed. Most of the corners will have brackets for support. Each bracket requires 2 screws and 2 nuts.

At first, I was shopping on Amazon for 25mm x 25mm aluminum extrusions from 80/20 Inc. These extrusions were significantly more expensive for the frame I was going with ($200 for the simple box). Luckily, I continued searching in my agony and found a website for sourcing a MendelMax that used Misumi 20mm x 20mm extrusions. These extrusions were a little thinner, but much cheaper, and much cheaper than 80/20's 20mm x 20mm. However, if I compared Misumi and 80/20 for 25mm x 25mm, the cost comparison would have been much closer.

Misumi can be tricky to order from. Use the Misumi extrusion search tool to get an idea of what extrusions and related brackets are available. Then price each part using the paper catalog, which you can request for free, or with some effort online. Misumi will cut the extrusions for free, and group the order for reduced shipping.