PLA and Concrete Hexagonal Wall Clock

A little bit of concrete can go a long way in creating a feeling of heft and quality in a 3D printed piece like this.

I've been experimenting with concrete and 3D printing for a few years now and have created many molds for casting concrete items, but this is the first I've ever combined a 3D printed frame WITH concrete.

The clock was designed to be mounted on a wall but also has a wide enough base to stand upright on a flat surface.

Further assembly instructions and parts needed below.

Print Settings

Printer:

Prusa i3 MK2.5S

Rafts:

No

Supports:

Yes

Resolution:

0.2mm

Infill:

30

Filament: Inland PLA Notes:

Print in PLA, PETG, or ABS. My outer walls came out sort of rough so a lot of sanding was involved, in retrospect I'd have preferred to print in something more sandable than PLA.

Print frame back-down on the bed with supports to support the bridging under the insert area for the clock mechanism, you don't want any drooping here if you want the mechanism to lay flush with the back of the frame once assembled.

The Frame V2 Joined Hands.STL is a version that prints the frame and hour dials in one piece if you don't want different colors for these from the frame.

The STL titled Plug is best printed in TPU, or in my case, 3D Solutech's Flexible Filament, which is easier to print than TPU but still bendy enough for it's purpose. This part will be used to create the hole in the concrete when pouring later on.

The hour indicators and Hour, Minute, and Second hand should be printed flat on the bed, since the holes in the hands are very tight I printed the first layer extra slow (10mm/s) so I could lay them down perfectly... I use the smooth PEI bed to make the top side of these parts look finished, you could always do some sanding though.

Post-Printing

Assembling

First, insert and glue the hour indicators (hours 1-12) to their corresponding platforms with CA glue. (disregard if you printed the all-in-one stl for the frame, Frame V2 Joined Hands.STL)

Second, plug the frame's clock shaft hole with the TPU Plug you printed, push it in firmly so it isn't wiggling and make sure it is perpendicular to the frame base.

Third, mix up a small batch of concrete (around 500 grams), it's best if you get it as flowable as possible if you want a smooth finish. I use Rapid Set Cement All from Home Depot, but a portland-based cement would also suffice. You can get creative here with cement dyes if you like, I chose to stick with a natural tone.

Forth, pour the cement mixture into the frame while shaking the model back and forth (it may help to have an extra pair of hands here), keep slowly pouring and shaking until the concrete is level with and reaches the hour indicators, continue to vibrate the frame to release all air bubbles, or don't, bubble can look cool.

Fifth, once the concrete is cured, carefully rock the TPU plug back and fourth until it releases, leaving a hole that lines up with the frame's hole. At this point, if you wish, you could spray the whole piece with a clear coat for protection.

Sixth, the Second Hand needs to be assembled. The clock kit will come with it's own second hand, we are going to scavenge a part off this, get a pair of flush cutters and snip the hand off the center piece that plugs into the clock shaft (this is the endcap, the piece we need), clean up the snipped endcap with the cutters until you cannot see any bit of original clock hand. Place a drop of CA glue on the backside of the scavenged metal endcap, then press the printed Second Hand firmly onto the tiny shaft and maintain pressure so the glue can cure the PLA to the back of the endcap.

Seventh, assemble the clock mechanism by placing the rubber gasket pad over the shaft, placing the mechanism into the frame, turning over the frame and placing the washer on the shaft over the concerete followed by the hex nut. Tighten this hex nut down but be careful not to over-tighten as you could crack the concrete. Push the Hour hand down firmly onto it's shaft, then the Minute hand, then the second hand. Follow steps in your clock kit if confused.

Your assembly is now complete, manually nudge all hands to the midnight position then pop in a battery and set your time with the mechanism's dial and enjoy!

Materials

Around 500g of cement, including water... you probably won't use all of this. I prefer Rapid Set Cement-All, it cures in 15 minutes and sets harder than regular cement, it also takes dyes really well.

PLA/PETG/ABS, and a little bit of TPU or flexible filament.

Youngtown 12888 Clock Mechanism, 59/64 Inch Total Shaft Length. https://www.amazon.com/gp/product/B078S2JFBX/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 The Shaft Lenth is all that matters, you can go with other brands, but the super cheap ones seem to have terrible reviews. This was $9 on amazon, but I saw a wall clock at Walmart that uses the same mechanism, if it has the same shaft length I may end up buying those for $4 instead.

One Carbon Zinc AA battery, it's important to NOT USE ALKALINE in these clocks, from what I've read they can damage the clock as they deliver too much power to the delicate mechanism. The batteries are also meant to be used in remote controls and other low-power items, and one should last a year or more. (My wall clock as work has been running on the same battery for over two years)

How I Designed This

All parts were sketched out in a notebook then designed in Fusion 360.