Biretrograde Clock - Lasercut

I love unusual clocks, and a retrograde clock is definitely unusual.

A retrograde clock has a hand that moves along an arc before rapidly snapping back to its starting point, unlike a conventional hand that moves in a full circle. Biretrograde means that there is more than 1 hand that does the retrograde movement. In my clock, the biretrograde movement is used to display hours and minutes, with the hand resetting at the end of its designated path.

This is a work in progress. See notes below for more info.

Tools needed:

Access to a Laser cutter that can cut 1/8" and 1/4" Baltic Birch plywood stock

Hammer

Pliers

Needle File

Sandpaper

Q-tip or Toothpick

Small Spring Clamps or Binder Clips

Wood Glue

Super Glue (Ethyl cyanoacrylate )

Materials Needed:

1/8" thickness sheet of Baltic Birch Plywood (Qty 1) - must be at least 9" x 6" ~$8

1/4" thickness sheet of Baltic Birch Plywood (Qty 1) - must be at least 9" x 7" ~ $8

Fluted 1/4" Dowel pins (Qty 2 ) ~ $3.28

(Home Depot: https://www.homedepot.com/p/General-Tools-1-13-in-x-1-4-in-Fluted-Dowel-Pins-840014/202252099)

Qty 4 1/4 Inch x 1/2 Inch x 3/16 Inch Precision Bearings ~ $7.79

( Amazon: https://www.amazon.com/uxcell-R188ZZ-Groove-Bearings-Shielded/dp/B082PQ9FSY)

Qty 1 High Torque Clock Movement with a 7/8" Shaft from the Clock Shoppe Part #863845 ~ $4.49

(Hobby Lobby: https://www.hobbylobby.com/crafts-hobbies/wood-crafts-blank-surfaces/clock-making/high-torque-clock-movement/p/110777 )

SVG Files for Retrograde Clock

In this step you will cut out all the parts on a laser cutter.

I am making the assumption that you have some experience with (or are working with someone that does) using a laser cutting machine. I will not be covering what settings to use on the laser cutter, as each machine has different settings for cutting the material. Your laser must be able to cut 1/8" and 1/4" wood. When you bring in the file to whatever software you are using on the laser, you must ensure that the scale is set so that the size is exactly what the Yellow Bounding Box is specified below in each file.

Please cut / engrave/ score as per each file description below.

BiRetrograde_1_8 inch.svg

This is the file for cutting the 1/8" parts of the clock. I have called for 1/8" Baltic Birch plywood, but any laser compatible 1/8" thickness plywood would work for this project.

The svg file is drawn with 4 colors:

Black - These are the Cut lines

Burgundy - These are the Score lines

Orange - These are the Engrave Lines

Yellow - This is a 9" x 7" Bounding Box

BiRetrograde_1_8 inch.svg

This is the file for cutting the 1/8" parts of the clock. I have called for 1/4" Baltic Birch plywood, but any laser compatible 1/4" thickness wood would work for these parts.

The svg file is drawn with 4 colors:

Black - These are the Cut lines

Green - These are the Engrave Lines

Blue - This is descriptive text of the parts - Do Not Cut, Engrave, or Score

Yellow - This is a 9" x 6" Bounding Box

There are 2 clock wheels, one for the Hours and one for the Minutes.

In this step you will assemble the hour wheel.

The Hours wheel has 2 pieces that need to be assembled, a top and bottom piece.

The top piece is the wheel with the smaller hole, the bottom piece has the larger hole.

You will need to glue these 2 pieces together, using the wood glue, q-tip or toothpick, and the spring clamps.

Add the glue to the bottom side of the top piece, then assemble with the bottom piece. See the photos for the correct orientation. (The pictures show the glue applied to the top of the lower piece, but this was a mistake)

Make sure the two pieces are aligned together, then clamp together. The outside edges need to line up together. When the glue is dry (~1 hour) you can remove the clamps. Feel the outside edge, it should be smooth, if not then use the sandpaper to even it out.

In this step you will assemble the minute wheel.

The Minute wheel has 2 pieces that need to be assembled, a top and bottom piece.

The top piece is the wheel with the larger hole, the bottom piece has the round hole with the flat sides.

You will need to glue these 2 pieces together, same as the directions for the hour wheel above.

Once this is dry it will slip onto the top shaft of the clock mechanism.

Looking at the photos, the top shaft is the silver metal with the flattened shaft. It will pull out of the clock mechanism if you pull it up and away from the mechanism body. Do not twist it as you pull up.

Once you remove it, slip the bottom portion thru the hole in the wheel and press it in. It should be very tight, and you should be able to press it tight against the round collar that separates the threaded portion from the smooth portion of the shaft. When pressed in it should look like the photos although the photos don't show the two piece glued together. You may need to use the needle file to open up the hole slightly if it won't slip on, but again, it should be tight.

In this step you will insert the bearings into the two arms. The method is identical for each arm.

Take a bearing and press gently. See if the bearing starts to drop into the hole. If not (likely) you may need to sand the inside of the hole slightly. The top of the arm is when you can read the letters correctly.

Sand a little, then test the fit again until it seems like the bearing is starting to fit into the hole. You want a tight fit - the bearing gets tapped into the hole with the hammer, but you don't want the hole so tight that the wood breaks.

When you tap it in, make sure the arm is on a flat surface that you can hammer on safely. You want to end up with the bearing flush with the bottom edge of the arm. It should fit evenly flat on the bottom. The top edge of the bearing will sit up ~1/16" from the top of the arm. See the pictures for examples.

In this step you will insert the bearings into the two cams.

The method is the same as the one used for the arms. The top of the cam is the side whold it ith the two engraved dots and the engraved hand outline.

As with the arms, you may need sand the inside of the hole slightly. Again, You want a tight fit. When you tap it in, make sure the cam is on a flat surface that you can hammer on safely. You want to end up with the bearing flush with the bottom edge of the cam. It should fit evenly flat on the bottom.

After you have tapped the bearing in you will glue the hour and minute hands onto the cams. Use the super glue for this step. Add the glue to the bottom of the minute/hour hand on the circular area. The cutout circle goes over the bearing, centered, and the hand portion aligns with the engraved markings on the cam (see drawing). Use the spring clamp to hold the clock hand against the cam until dry (~ 1 minute). Follow these steps for both hour and minute hands.

In this step you will insert the dowel pins into the clock face, then attach the clock mechanism to the clock face.

Put the clock face, engraving side up, on a flat surface that you can hammer on safely.

Take a dowel pin and tap it into one of the two outside holes. You want the bottom of the dowel pin flush with the back of the clock face, and the pin should be straight.

Repeat this step in the other outside hole with the second dowel pin.

Take the clock mechanism and place the rubber washer over the shaft.

Push the shaft of the mechanism through the middle hole.

Looking at the back of the clock mechanism, the battery compartment should line up with the bottom of the clock face.

Take the nut, and thread onto the shaft and tighten with a pliers until tight.

In this step we will add the hour and minute clock wheels to the clock mechanism.

Start with the hour wheel.

The hour wheel will slip over the white part of the clock mechanism shaft. Once you have it centered on the shaft, holding the back of the clock mechanism, press down firmly and evenly on the hour wheel until seated . It should be sitting just above and parallel with the clock face.

Next seat the minute wheel.

Slip the metal shaft with the Minute hand over the shaft, making sure it goes over the second hand pin that sticks up. Making sure the metal shaft is aligned with the shaft in the mechanism and that the hour wheel and minute wheel are parallel and aligned to each other, press down until the metal shaft is reseated in the mechanism shaft.

In this step we will assemble the Arms and Cam/Hand Assemblies onto the clock face.

Start with the hour arm.

The arms slip onto the right hand dowel pin. Slip the Bearing on the arm over the dowel pin and press it down until it is almost but not quite touching the Clock face. Make sure the An easy way to do this is to take one or two thick business cards (used as spacer shims) and lay them next to the dowel pin before pushing the arm down.

You want to make sure that the arm pointer hits the hour clock wheel, and isn't hitting below the wheel.

Next is the hour cam/hand. This is the longer of the two hands.

The cams slip onto the left hand dowel pin. Slip the Bearing on the arm over the dowel pin and press it down until it is almost but not quite touching the Clock face. If you have the heights right, the cam gear an arm gear should line up, and both the cam and arm should rotate freely and parallel to the clock face.

Place two spacers (A Spacer) over the right hand dowel pin, and one spacer over the left hand dowel pin.

Push on the minute arm just like you did with the hour arm, and again leave a small space between the spacer and the minute arm bearing.

Push on the minute cam just like you did with the hour cam, and again leave a small space between the spacer and the minute cam bearing. Just like the hour assembly, the cam and arm should rotate freely and parallel to the clock face. If there is interference, you may need to adjust the position of the arm or cam on the dowel pin until they move freely.

In this step we will line up the arm with the cam.

You will notice both the cam and the arm have small engraved circles on the ends of the gearways. These should line up with each other on the arm and cam. See the photos for alignment. The bottom circle on each cam should line up with the bottom circle on the corresponding arm

In this step we will add the feet to the clock face.

Take each of the feet and match the slots together, with the longer part of the foot to the back of the clock face, as shown in the picture.

In this final step we will set the time and get the clock running.

Insert a AA battery into the Clock mechanism.

Rotate the time adjustment dial until the hour and minute dials line up with the correct time on the clock face.

Hopefully, if you have adjusted the arms and cam/hands so they move freely.

You should now be able to watch the retrograde movement when the minutes hand reach 60 minutes and when the hours hand reaches 12 o'clock.

While making this clock (3 iterations with fixes so far) I have found a few things that will need to be improved on.

1. It is difficult to get the minute and hour hands to drop at the correct time - (when the hours are at 11, going to 12 and the minutes are at 59, going to 60) depending on how you insert the minute clock wheel, the minute hand might drop first, and a minute or so later, the hour hand drops, or inversely, the hour hand will drop before the minute hand hits 12. I think this is a matter of positioning the minute wheel correctly, and might take some trial and error.
2. It takes some tweaking of the arms and cog to get the arms to drop easily. I think additional weight on the arm would help with a consistent drop.