Rubble Desk Clock

I had bought this clock hardware on amazon a couple months ago to make a clock for my desk, however, I couldn't decide on a design, a type of wood, the shape, etc. When I saw the concrete contest it gave me the idea to have a go at working with concrete.

Materials:

• Rapidset Cementall
• Water
• 3/4" Plywood (See cut list on next step for amount)
• 1/4" Hardwood (I used Jatoba) (See cut list on next page for amount)
• Small Clock kit (I purchased clock hardware from amazon for $13 CAD)
• Wood Screws
• Sheathing Tape
• Hot Glue
• 5 minute epoxy
• Wood Finish (I used a mineral oil and bees wax mix, any finish will do)

Tools:

• Hand Saw
• Hand Plane
• Shooting Board
• Drill & bits
• Impact Driver & Bits
• Bucket
• Trowel (or something else to mix with)
• 90 degree clamps
• Other assorted clamps (not imperative)
• Hot glue gun
• Flat Surface (I used a scrap piece of ply, needs to be at least 6" x 6")
• Wood burning tool

3/4" Thick Ply:

PART A: Two 3 1/2" x 3"

Part B: Two 5" x 3"

Part C: Two 2 1/2" squares

1/4" Thick Dressed Hardwood

Part D: One piece that is larger than a 3/8" diameter circle but no larger than 1" square

Part E: One 3" square

Use your hand saw to cut out each of the above pieces, than, use your hand plane and shooting board to square up the pieces if necessary.

Parts A, B, C, and D from the cut list are used in the form assembly. First, use parts A and B to create a box that forms an interior square that is 3 1/2: x 3 1/2". I used two corner clamps to hold the pieces together, then drilled pilot holes and screwed them together. (See photos 1-7). This forms the outer part of the form.

Then, using parts C and D create the interior. This consists of sandwiching part D between the two part Cs as seen in photo 11. Drill a hole through the center of each part C and Part D, then use a screw to hold them together.

Effectively, part C will create a sunken face for the clock and the other part C will create a sunken spot for the clock movement to be hidden. Part D will create some space between the part Cs for concrete to flow into but won't allow it to flow into the middle so that the clock stem can pass through, leaving a face for the clock movement and the wooden face plate to be mounted.

Then, using a flat surface (I used some scrap plywood) draw out your form. This consists of tracing around the component your created using parts C and D. Place it on the surface and trace an outline, this should leave a 2 1/2" square. Then, draw a line from one corner of the square to the other, extending the line 3/4" past each corner. Do this in both diagonals. Then, connect the ends of the lines you just drew to create a larger square, this should be the interior dimensions of the component you made using parts A and B. (See photos 14-16).

Stick sheathing tape over the drawing, and tape all surfaces of your components so that concrete cannot stick to anything ( it may be easier to tape up parts c and d before putting them together, they can always be unscrewed, taped, and reassembled. (See photos 17-19) Lastly, use hot glue to stick your two components onto your drawing,ensure there is no hot glue squeeze out inside the form. (See photos 19-22)

Use your bucket and trowel to mix up a bit of concrete (you won't need much). Add water and the mix until it is a little less viscous than honey, this will ensure it can be poured without being too weak. Once mixed, pour the mixture into your mold until you are level with the interior form component, you do not want to pour over this component as you will then be unable to get it out. (Photos 1 and 2)

Allow to cure for about an hour before removing the form. (Photo 3)

Once it has cured for a few more hours, you can take your cast concrete and try to break it in half, then try to break each half in half (should result in 4 corners) (see photos 4 and 5). I was able to do this with my hands, however, this could be done by hitting it against your workbench, on your basement concrete floor, on the driveway. Ensure you use gloves and safety glasses when doing so.

Part E will be the face plate. Take your 1/4" x 3" x 3" piece of hardwood and draw lines that connect the corners, where these lines intersect will be the center of the piece. Then, drill a 3/8" hole through the center (the clock spindle will pass through this). Sand your lines off of the piece. (See photos 1-3)

Than, along each edge, make a mark 1 1/2" from each corner, this will mark your 3, 6, 9, and 12 on the clock. (See photos 4 & 5)

Lastly, use your wood burning tool to burn over your pencil marks approximately 1/4" from the edge towards the center. (See photo 6) If desired, you can apply a wood finish to the face of the clock (do not apply to the sides or the back so that it can still be glued to the concrete).

Mix up some 5 minute epoxy and apply to two of the concrete pieces where the face plate will be mounted. Then stick the face plate to these pieces. Clamp the face plate to the pieces. Leave to cure for an hour. (See photos 1-3)

Then, mix up some more epoxy and do the same two the other two pieces of concrete, then stick them to the face plate and leave to dry (clamp if you can, I did not have clamps capable of doing so, though the epoxy was enough to make it stick and stay in place). Leave all pieces to cure for another couple hours. (See photo 4)

Lastly, take the clock hands that came with your clock hardware kit and trim them with scissors if necessary (then need to be short enough to turn within the concrete sides). Then mount the movement (mine was mounted with a nut) and install the hands.

Then you're done! Enjoy and pretend that you didn't accidentally crack your concrete when removing the form which is why you made it a "rubble clock" instead!