Concrete Bookstand | Making in Mixed Reality

This project is twofold:

1. a casting project, using CNC machinery to realise a furniture piece in concrete.

2. a software project (highly experimental!) building my own mixed reality CAD platform to design and fabricate digital parts using only your hands, a webcam and off-the-shelf projector.

That's a lot for one build, so I'll keep the how-to section mainly about the casting itself, but I've detailed the bigger picture project below in case you're interested. Hope you enjoy!

Bigger Picture

Building a bookstand was really a case study for computer-aided fabrication workflows: I wanted to know whether I could build a software tool that allows me to intuitively sketch parts on a digital canvas using just my hands, and then lay them out on a CNC bed using an assistive, projected overlay, so virtual shapes can be transformed into physical outcomes - in this case the layers of a mould.

This experiment brings me one step closer to an accessible tool that anyone can use to prototype their ideas intuitively. If you want to find out more, check out what I'm up to on my Instagram or Youtube, @paveworkshop.

Bedside Bookstand

Setting myself a real design brief - I needed an appealing bookstand by my bedside to hold the books I'm reading at the moment. And I'm desperate to try more casting! An industrial aesthetic was a must for me, so that it would suit a rustic, modern or minimalist setting. With this in mind, I designed a form with free-flowing curves to be extruded and cast in concrete. I experimented using a layered mould to give the part a texture that is reminiscent of clay 3d printed parts.

I also considered a guilty design observation - I'm good at starting books but not finishing them. How do I limit the number of books I can pick up and read on the go? I decided to play with the idea of hostile architecture by creating a slightly disfunctional bookstand that only lets you store a few books at a time.

Concrete

It should be noted that this cast is actually made from reinforced mortar not concrete, although I use 'concrete' for its ubiquity. Mortar is just a cement-sand mix with no aggregate added. This makes the part weaker, so I inserted galvanised steel mesh into the slurry whilst it was wet in order to reinforce it under its own weight.

Disclaimer: concrete furniture is not eco-friendly, and we can do better. This project was a way for me to use up a couple leftover bags I had, and set my sights on more green casting options in the future. Cement production alone accounts for 8% of our global carbon emissions.

Mixed Reality CAD toolkit

I've been working on this mixed reality CAD toolkit for a while now! There's been a lot of progress in the way of demos but now I want to start putting together the pipeline and using it in my craft.

In the first video above, Phygital Fabrication, you see me sketching curves on an augmented reality canvas. Pinching your hands extends the curve by depositing new points, whilst dragging allows you to adjust the position of control points, and therefore the shape of the spline curve. After using my networked framework to transfer this design to a CNC machine, you can layout these parts on the bed, or draw more primitives, and then command the machine to cut them out. This reveals a slight discontinuity in the video, because this section is taken from an earlier demo with plywood. I would have liked to show me lasercutting foamboard with this gestural technique but I don't have access to a lasercutter that would support a GRBL API as I have built.

Although a few stages of process were manually assisted, this stuff really works. It has involved hundreds of thousands of lines of code to allow the user to do a very simple task intuively. Working on this project taught me a lot about spacial maths, computer vision, interaction design, network protocols and more.

What is Phygital Fabrication?

'Phygital' is the best word to describe processes that stitch the digital and physical worlds, in this case fabricating parts using blended digital-physical workflow. This is something I achievw with mixed reality techniques like projection mapping.

In recent years, there's been a strong pull towards the use of digital CAD and CAM tools for prototyping; designing parts virtually, and it makes for an incredibly powerful workflow. However, physical craft and experimentation remains equally satisfying and often far more informative when considering the user, or real world limitations. I want to reintroduce that feeling of physically manipulating parts when using digital workflows - whether it is sketching, tracing or laying out parts - building in one's hands with touch and gesture should be encouraged wherever possible.

Mortar - premade mix of sand and cement. You can use concrete, but you might want to pick out the larger bits of aggregate. I had leftovers, maybe you can find a more eco-friendly alternative.

Galvanised steel fencing mesh - to reinforce the mortar mix. Steel wire mesh might corrode inside the wet, alkaline cement environment so galvanised steel is better (ideally cut with tin snips, or using an angle-grinder in a ventilated area. Grinding and welding galvanised material releases zinc fumes which can make you feel ill.)

Foamboard, 5mm and 10mm - to create a stepped mould from layered cut-outs. Foamboard doesn't stick well to concrete along its edge which is ideal, and when lasercut (do this at your own risk, noxious gases may be released), a groove is created as the inner layer vapourises, which helps give the part a ridged texture.

PVA glue - to laminate the foamboard layers.

Melamine hardboard - to serve as the base of the mould, a waterproof surface concrete won't stick to.

Plastic sheeting - to seal the moisture in the mould whilst the concrete cures, and prevent leaks. I recycled mine from the offcuts of a mattress cover.

First I had to come up with a simple yet striking form. This profile curve would determine the bookstand's shape and storage capacity, so I measured the 'shelf' gaps against several real books to ensure they'd fit. This is the advantage of being able to sketch in mixed reality; you can conduct physical and digital checks.

I took to paper (and eventually my augmented reality canvas) to start drawing out various iterations. I went with an organic, slightly anthropomorphic style. They looked a bit alien, and reminded me of the pave logo, so I was happy.

Remember concrete is heavy, so you want to keep these limb-like extensions relatively short, and add more support material where they join one another. Download my sketch below for a headstart!

The mould is made up of a stack of identical foamboard cutouts laminated together. The lasercutting process adds a desirable concave to the cut edges, which becomes a convex ridge in the concrete cast.

After I transferred my design to the laser cutter, I cut the profile out of 5mm and 10mm foamboard many times over. The foam core burns up easily, and may create noxious fumes. Proceed at your own risk!

I had some warped sheets lying around that weren't usable for small prototypes but could be held flat as a large sheet. So I used wooden planks to weigh them down on the laser bed, being extra careful to ensure these weights also cleared the gantry. In theory you could break the mould into sections that nest more nicely, but this wasn't an option for me because of the warping, and the rectangular outline helped the mould maintain its alignment and integrity under the weight of the concrete slurry.

I alternated 5mm and 10mm layers to create the ridge pattern you see on the final part. I would laminate 3 x 5mm layers followed by a single 10mm layer, and then repeat this sandwich 7 times for a total thickness of around ~180mm.

Weak PVA glue actually works good here - I would stick to something cheap because there's a lot of surface area! I didn't let the glue fully dry before pouring, which was strategic to make demoulding far easier. I recommend you let the glue dry for a couple hours only. After pouring, as the slurry solidifies, water from the concrete will seep into the paper layers and 'undo' the adhesive slowly, keep the glue wet, and allowing you to pry the foamboard layers apart again afterwards.

I roughly estimated the volume of mortar I'd need to completely fill the mould, which came out to about a bag and a half. I followed the mixing instructions, using a mixing attachment for my power drill. I poured the concrete in batches, working quickly, shaking the mould between pours, and tamping the full depth of the mix with a wooden stick to ensure there were no voids or bubbles.

I had precut some metal mesh just shorter than the height of the mould, and bent it to fit the curved profile. I now inserted these strips into the wet slurry, making sure they didn't touch the edge like a game of Operation.

Leave the cast for at least 48 hours to cure. Counterintuitively, you want to keep the concrete from drying out too quickly, so it doesn't crack. You can cover it with plastic or damp cardboard if it's curing in a particularly hot or dry environment. In hindsight, leaving the mould for another day would've been a good idea - when I began demoulding, the concrete was still slightly wet and crumbly.

I carefully pulled away the foamboard, layer by layer, using a boxcutter to break the mould into smaller sections I could more safely rip out. The ridge idea was untested, but I was pleased to see that the foamboard had imprinted the texture on the concrete successfully. I lost a little detail because of crumbling material, but I think this is probably inevitable with a foamboard mould. The paper edges seem to bind slightly despite the foam releasing easily. Thick foam is the go-to option if you have access to a hot wire cutter.

Now the part is exposed to the air, you can let it stabilise and dry further before handling it or weighing it down with books.

Success! The bookstand has a good quality finish and no visible cracks. It withstood being carried and the weight of the books being stacked, and this is probably down to the mesh reinforcement I added. I like how one side is rough (from the top of the pour), and the other (from the bottom of the mould) is smooth. I can't decide which I like better.

Casting with concrete was fun, and mouldmaking was made easier because of my phygital workflow. I am however determined to find a more environmentally friendly casting medium for next time, let me know if you have any ideas.

Stay tuned!