Numechron Digital Clock

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Introduction: Numechron Digital Clock

My Numechron Digital Clock design was inspired by the Pennwood Model 1364 digital clock. Clocks of this type originated in the 1930s, and were built for many years by the Pennwood and Lawson companies in many different wood, metal, and plastic case styles.

I really liked the Art Deco style of the Model 1364 case and chose to emulate it, although my clock is considerably larger than the prototype. While mimicking the original style, I employed considerable open space in the case design so that the clock's internals would be visible.

A Pennwood employee, F. Greenewalt, patented the mechanism for this type of clock in 1935. He developed an ingenious set of wheels, cams, and levers to flip the numerals and operate the clock. I consulted the original patent to design the mechanism for this clock.

Here is a video of the clock: Numechron digital clock

Here is a video describing design and build: Making Numechron

Tools

  • Carvewright CNC machine with carving bit and cutting bit
  • bench disc sander
  • drill press
  • clamps
  • screwdriver

Materials

  • 1/4" Baltic birch plywood
  • 1/4" aspen or poplar
  • 3/4" oak and pine
  • 1/8", 7/32" and 1/4" brass tubing
  • brass wood screws
  • small springs
  • super glue
  • wood glue
  • stain
  • polyurethane varnish

Step 1: Design

From the original patent we can see the parts of the clock that we will need to build and how they go together.

I used a Carvewright CNC to make all of the parts and the Carvewright Designer software to design the parts. I did cut some prototype parts and try them out on temporary jigs, then made design adjustments, to make sure that the mechanism would function and verify the design.

(Carvewright uses a proprietary file format, not standard STL or DXF formats, so the files cannot be used with other CNC machines. I do plan to make the files available in the Carvewright Pattern Depot in the future.)

You could also make these parts with a scroll saw (the digits would need to be painted on rather than carved). Some minor modification to the parts illustrated in my build would be required. Templates are provided for all of the major parts except for the case parts.

Step 2: Fabricate the Parts

Starting with the hours, tens of minutes, and minutes wheels pasts, make these using 1/4" Baltic birch. Baltic birch plywood is a quality material with many thin plies that are generally void free. All of my materials came from a local home center.

To make these parts without a Carvewright CNC, use the full-size templates attached below. Print the pdf file on 8.5" x 11" paper, and check to make sure that your printout scaled properly. Fasten the templates to the plywood and cut them out with a scroll saw. Sand.

I used 1/4" poplar for the hours and minutes numerals. The template contains a table of dimensions for these parts. Note that the top and bottom edges of each numeral must be mitered - cut at an angle - as specified by the chart. The seconds numerals can be cut on a band saw using the profile template provided.

Cut the frame parts and motor mount parts from 3/4" hardwood.

Step 3: Assemble the Digits Wheels

Once the parts for the wheels are all cut out, assemble the digits to the wheels one at a time. The digits pieces are trimmed as needed for a tight fit - I used a bench disc sander with the table set at the appropriate angle for the mitered edges of each digit. Glue and clamp.

Note that the tens of minutes, minutes ones, and seconds wheels all have a peg on the left side of the wheel. (Left while facing the front of the digits.) I used a small piece of 1/8" brass tubing, sourced from Ave Hardware, for this.

Step 4: Seconds Wheel

Because the seconds wheel moves continuously, unlike the other wheels which lock into place, the seconds wheel is best made as a cylinder. I made mine in six sections. You could use a bandsaw to make sections like this, or possibly turn a complete cylinder on a lathe.

Step 5: Frame

The numerals wheels are supported on a frame made up of several pieces screwed together. I used 3/4" oak for my frame pieces.

7/32" brass tubing is used for shafts and 1/4" brass tubing for bushings. The larger tube slides over the smaller tube allowing the wheels to turn with little friction. I got my tubing at the local Ace hardware.

The tens of minutes wheel fits in between the two arms. The minutes ones wheel rides on a shaft protruding from the right arm. The hours wheel rides on a shaft protruding from the left arm.

Step 6: Spring Arms

Spring-loaded arms ride on cams on each of the hours, tens of minutes, and minute wheels to hold the digits in place after they move. I machined the arms and brackets out of oak. The small springs came from my local Ace hardware store. The arms are adjustable for both tension and position. Too much tension causes strain on the motor; to little causes the digits to be misaligned when at rest. The position adjustment allows the wheels to be rotated slightly so that faces of the visible digits are aligned.

To set the time, you just reach into the back of the clock and manually rotate the wheels.

Step 7: Motor

The clock is driven by a 1 rpm synchronous motor. These can be sourced from time clock parts suppliers. A separate motor mount is used to hold the motor and seconds drum in place. Electrical wires run through the mount to the underside of the clock's base and are hidden. A cover hides the motor. These motors run quite hot, so ventilation slots are needed. These parts were all machined from 3/4" oak and glued and screwed together.

Step 8: Case

A case and faceplate finish off the clock. A wide variety of case styles may be used. I emulated a classic case, but built one with ribbed top and sides so that the clock's mechanism remains visible.

A wide variety of stains and finishes may also be used. I used Minwax wood stain and Minwax clear satin polyurethane.

Wood Contest

Fourth Prize in the
Wood Contest

Formlabs Contest

Finalist in the
Formlabs Contest

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68 Comments

I got a question on motor sources. Motors can be sourced from time clock repair suppliers like this one: http://www.compumatictime.com/partsandrepairs.html. I used the 1RPM CCW Acroprint motor.

thanks a lot

Holy ... ! That's gorgeous! I want one too. Have the CNC and laser cutting machines become a dime a dozen or something? Seems like everybody's using them anymore. Good luck in the wood contest.

I actually prefer your wood gear clock, but this is great too! I hope you win the grand prize as I know from 1st hand experience how much work there is in CNC.

user

As a electrical engineer and hobby wood worker/DIY enthusiast( I made 2 guitars and many other smaller projects out of wood - I just love working with wood) I like to see these kind of creations.

I have to say your Numechron is simple jaw dropping beautiful!


I am building myself a small CNC and I will definately try to make this!

The two arms seem to be too long. Had to scale them down .75%, Also The Spring Arms seem to be too short. Seems like all 5 arms should be almost the same length? I have the drawings completed, and starting the build with the frame and Tens Wheel.

2 replies

You're right about the two frame arms. I'm not sure about the spring arms yet - I will check. Converting the digital Carvewright files to graphic patterns involves some manual steps and I obviously made a mistake or two. I will try to get these corrected as soon as possible.

I corrected the scale of the frame arms in the Numechron templates pdf document, and also added a side view showing the wheels and frame arms respective to one another.

Very nice. Want to make this. Three questions. In the PDF, I don't see the Gear for the right side of the minutes wheel. What size are the carry over pins? I can't get the rule to scale, but adding 1/8 inch to the wheel sides, the sides appear to be to scale. I started to draw it up in SketchUp, before I saw the PDF. However I guessed the numbers were 1.5 high and 1" wide. Oh well, back to page 1. I have a plug in for SketchUp that will generate Gcode for a CNC Machine.

Thanks, and thanks for pointing out the missing part. I have added it to page 6.

On my computer, when printing pdf files I have options such as Fit, Shrink oversize pages, and Actual size. If I click on Actual size, it does print to the correct scale. I suppose if you're only off by 1/8", everything should scale the same, so if you use the templates as is everything should work. Just make the numerals a bit smaller too.

Great work congratulations :)

i like it but for me is a fake handcraft. i you were make it whitout cnc machine. i would be proud of your hands and brain. i hope one day do stuff by your self out cnc machinery. like the original ones they really was people behind the tools using they real skills. not the computer skills. thats not fair for those proyects that really use handtools. and even more cuz prices are for smart people not smart laptops. i hope you understand and use your hands.

4 replies

Thank you for your opinion.

I have been a woodworker since I was a kid in my dad's shop. Like many, I started out with a few simple hand tools, and added to my skills and suite of tools over time - power drill, table saw, power sander. I got my CNC machine about 5 years ago, and it has allowed me to work projects that I could not otherwise do, much like the table saw and drill press facilitated projects otherwise not possible. It is another woodworking tool. There are woodworkers who continue to make dovetail joints by hand, but I suspect today many more use a router and jig. Some of us have added CNC machines to our woodworking tool suite. I think that, for those who have not used one, the perception is that you just push a button and everything is done for you. That is not the case. You do need to learn and master new and different skills to design and build well with a CNC, but these skills supplement the traditional woodworking skills and tools, they don't replace them.

My shop tagline is "Digital AND traditional design and woodworking".

Nicely said...CNC it's not just pressing a button and there is no problem with using it.
I understand the opinion of "Rgonzalez52"... there is the magic in handcrafted items, but this is not the case. This was hand made as well !!! The CNC was just a tool as any other.

Well done. The clock looks really great !!!

An excellent answer, and a gorgeous piece of work. Thank you for sharing it!

From my experience, you're not going to pull off something like this unless you have great basic woodworking skills, the mill is just another tool to be mastered and not a 'cheat'.

So, hats off to the author, a beautiful piece of work.

I added a pdf file of templates which can be used to build parts for this clock using conventional tools such as a scroll saw. Some of the parts will need to be fabricated a bit differently from the way I did using my CNC, so naturally some parts will not look identical to the ones in the photos, but they will be quite similar and be functionally equivalent.

i bet you to do it whitout electricity. whos the best carver? if you win. now you gonna feel proud of your skills.
or put a challenge. i coud compete to you on anything about real woodworking. im 24 years old and i have a nice cnc machine hands whitout electricity. i give you a real challenge for your kind of shoes you are wearing.

1 reply

Great! You should enter the contest!