This is a concrete table that also doubles as a USB hub, so that you can charge/sync multiple devices at once. I built this table to support another maker in the community, but this could serve in any office, dorm room, or even a living area. I'd never used concrete before I bought this bad, but it turned out to be a really easy material to work with so don't be intimidated by it.
1 - USB Hub
4 - USB extension cords
4 - Small plastic ramekins
1 - Bag of concrete - I used a basic bag of Quikrete from home depot
1 - Water source
2 - Small melamine shelves (you can use one larger piece this is what I had lying around)
1 - Tube of silicone sealer
1 - Set of legs - I used Harry's Hairpin legs
1 - Small box of screws (you will have left overs)
1 - Wooden board (Optional: More on this later)
Table Saw (Circular saw or Hand saw would work)
Mixing device - I used one of my daughter's shovels (shhh)
Step 1: Prepare Your Form and USB Hub
The first thing you need to do is build your form. I happened to have two melamine shelves in my scrap pile so I used those. Because they were the same size I knew that I could just evenly space out my cuts and they would be long enough.
I measured one board so that I could have four even strips. In this case they were 2.75" (~70mm). I used a speed square to ensure straight cuts.
Once you have them marked out make your cuts, and attach the sides of your form by pre-drilling holes and then screwing them in.
You will want to run a bead of silicone along the edges of your form to seal it.
I used a board to help reduce the weight and mount the legs onto. This is the step I mentioned was optional, If I was to redo this I would have not added the wood and attached the legs with masonry screws; while mounting the USB directly in the concrete.
You'll want to ensure the board fits inside your form, if not cut it to size.
Then measure out for leg and usb placement.
Cut small slits in the ramekins to thread in the USB cords.
Use a drill to make the hole for the ramekins and use silicone to seal them onto the board.
I used hot glue to mount the USB hub and cords to the board. I also applied a liberal amount of hot glue around all of the seal and connections to help protect them from the concrete.
Finally I screwed in a bunch of random screws into the board to give the concrete something to grab onto.
Step 2: Mix and Pour the Concrete
Easiest step of the project !
First part is optional, I chose to filter out some of the larger aggregate in an attempt to get a smoother finish.
Then you want to pour in a small amount of water (seriously it doesn't take much, so whatever you think you need half that and go from there)
The good news is if you add too much water you can add more concrete to even it out.
Mix the concrete throughly, I wanted to pudding like consistency so that it would mold around the board and USB. In a normal concrete project you are looking for a consistency closer to peanut butter.
Pour the concrete into your form and then press your board into the concrete.
I did not add enough concrete to go all the way up the sides of the board, so I made a thinner mixture (aka slurry) and pushed it down the sides.
I then added some weight so the board didn't float. You will want to let this dry for at least 24 hours.
Step 3: De-mold and Repair Defects.
Remove all of the screws and then slowly pry off sides of the mold. (If the sides are tight you can use a pry bar or screwdriver to gently pry them off; do this on the bottom so it's wood to wood and not putting pressure on the concrete.
My sides were damaged as shown in the picture. (I believe this is from the wood and that's why i'd avoid it, or make it smaller if I make another).
I mixed up another thin slurry mixture and let it fill the gaps. Tapping on the sides to ensure that it fills all of the voids and then smooth out the top.
After this dried, I lightly sanded to soften the corners and smooth out any high spots.
Step 4: Attach Legs and Test Out (Bonus Hub Playlist)
The last step is to attach the legs.
I used Hairpin legs which attached easily with 3 screws on each leg, because I added the board I could easily screw them in with normal wood screws.
Attaching the main plug to my computer I was able to test out the other ports and was able to charge my phone and access a hard drive at the same time. Mission successful. I also tested plugging the table into the wall to just act as a charger and that worked just find but you'll need to ensure you select a hub that won't burn out from too much electricity.
As I mentioned this was made out of support for another maker (Giaco Whatever) and here is a playlist that shows a bunch of makers making different kinds of USB hubs: goo.gl/h4eipE
If you make one of these I'd love to see it.
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