This design was picked out of a library book called “ADVANCED CLOCKS for the Scroll Saw”
The name “The Nashua” according to the text in the book says that Nashua was where the original clock was found.
The book included scale size patterns to cut the scrolled case for the clock. These patterns generally had to be enlarged by 155% to produce the full size clock. There is no mention of the movement so I’ll have to design my own.
Before I can start cutting the full size patterns have to be taped together for gluing on to the wood stock
The pattern lines are quite thick compared to gear drawing lines and it makes alignment a lot easier (forgiving)
The wood chosen for the case of the clock is Wenge
“‘Millettia Laurentii-Wenge’ is an African wood, a dark coffee brown in color, with a regular, closely spaced grain of dark brown to black.”
The glue up was quite easy even though the wood was very hard and working it produces a fine dust.
The pendulum rod was the first piece cut just to see how things would go. It cuts nicely and is strong enough not to breakout when the detailed cuts are close together.
The clock case is all made of 1/4” material and in the case of the sides and wings, two 1/4” pieces were contact cemented together so that the pieces would be identical.
The various pieces of the clock case were simultaneous being cut out and slowly a little pile of scrolled pieces grew on my bench
Removing the paper that has been glued on with contact cement is a whole lot easier if you microwave the piece for 15 to 30 seconds. If it is especially hard to remove I’ll put it back in the Microwave for another session.
The case is assembled with tabs that fit into slots cut into the mating piece. This shows the “works” base fitted into the back and the front.
Each piece has to have its tabs hand fitted so that the tabs fit snugly in their slots - but without binding.
The front capping piece is held to the case by four tabs extending out from the roof.
The assembled unit is mounted on the wall. The wings on the sides of the case have been installed and its ready for the clock works.
The Scrolled case allows a 5 inch wide space for the clockworks. The vertical measurement is not so critical as space can be created in this direction. The gear layout here matches my “Two Arbor” clock and so I know this arrangement is a possibility.
This layout is a little more conventional and allows for easier troubleshooting of the running works. It has a recoil excapement with everyting thing in-line.
The arrangement I finally decided on was based on a combination of the location of the center of the dial which is fixed by the case design and the rest of the space available. I should look something like this.
All things considered this is gearing arrangement which will accomodate the available space and match dial location. I am considering a 2” winding drum which will give a 40 hour movement.
The layout of the wheels doesn’t take up a lot of wood as the gear diameters are only 3 inches across.
This escape wheel has “flattened” points which helps a lot when cutting out the wheel. The flat surface of each tooth is the critical cut as it is the entry to the pallet. The curved surface does not contact the pallets and has greater tolerance.
The clock case calls for a 1/2 second pendulum (ie about 10” long) and the escape wheel has 30 teeth. This means 30 seconds per revolution of the escape wheel.
All three time train wheels have the same number of teeth, 60 and pinions of 6 leaves and the same module which allowed for all three to be glued together and then cut as a unit.
This side view shows all three 1/8” wheels temporarily glued together.
The plates are 1/4” Baltic Birch and this photo shows both front and back plates glued together. The four bolts will go through spacers to give a rigid framework.
The plates for the movement are from 1/4” baltic birch and all the arbors are bushed with brass. Since I want to make the clockworks really light I am using 1/16” arbors and 3/32” brass tubing to stabilize the wheels. In this way I hope to reduce wobble.
The spacers are 1/2” ply with 3/16” holes drilled for a bolt together frameworks.
The depthing tool is used to get the ideal spacing for the arbors and then the depthing tool is used to “center punch” the pivot locations. Next time I won’t do this as I had a lot of fine adjusting to do.
All the running train wheels are in place and running freely. Once I got a few teeth straightened out the works would spin on 2 ounces of weight.
The clockworks is mounted on a test bench to get some more of the bugs out of it. Although the works would spin on very little weight - the spin had a cadence to it which means there are some spots somewhere not as “free” as I would like.
Getting the works into beat.
I first used a brass pallets but they were too heavy for this scale of clock and I switched to 1/4” ply.
I found that the pallets were depthed too deep which meant that the works didn’t have enough power to keep it going. The clock would only run about 5 seconds and then stop but not because of binding
I reduced the depthing by sanding the pallet faces until I could get what seemed like a “robust” tick and then went to polishing the pallet faces and escape wheel teeth and finally - success.
I have a nicely scrolled Wenge pendulum rod but I’m not sure that I will be able to use it. I’m finding that with a small movement (5” by 7” total size) that the weight of some parts starts to really make a difference.
During the initial run in I use more weight than I want to end up with. I’ll work my way down as things break in. I hope to get down to 2 or 3 pounds for a 30 hour movement.
The movement is now running on 3 pounds of weight and is ready for mounting in the scrolled case.
The clock works compartment is only accessible after removing the facade, both roof halves and the front piece.
The clock works is not firmly attached to the housing - mostly because there is no place for the clockworks to go
The dial is paper on ply and theses hands will be replaced once I can decide on what would look best.
The time train called for (by me) some very tiny wheels and pinions. The ratios are very standard with a 6 leaf pinion driving an 18 tooth wheel and its 6 leaf pinion driving a 24 tooth wheel - to which the hour hand is attached.
The time train was adjusted on a construction block with the pivot spacing of 15.6 mm carefully drilled in the block. Arbors were placed in these pivots and the pinions and wheels were then adjusted (filed) to give a nice free movement in the correct direction
This little set will bind if you try and spin them backwards so all adjustments were done only with the final direction in mind
The construction block was used to locate the fixed pivot on the clock and the pivot hole drilled with the construction block placed firmly on the clock and a guide arbor temporarily in place on the center wheel pivot to ensure alignment
The Time train is place in front of the front plate of the clockworks and behind the face. I was unsure whether the time train would be compact enough to be hidden behind the face and a 1/8” space between the face and the clock housing was necessary.
The finished clock (oxymoron) runs on three pounds of weight. I was able to use the scrolled pendulum rod but the bob is extremely light in order to do so.
I got frustrated with running train because it was taking too much weight and was inconsistent.
I'm really at the point where only stubborness prevails!
I redesigned the works for a one second pendulum and a deadbeat escapement
Its a simpler design with only a Great Wheel, Second wheel and then the escapement.
With this arrangement the great wheel turns once per hour and so the time train had to be redone as well
If I went straight form the Great Wheel to the hands the clock would run backwards, so there is an intermediate gear to change rotation - but all three are the same size so there is no reduction.
The intermediate gear also runs the hour hand with a 12 to 1 reduction so that a 5 leaf pinion turns a 60 tooth gear. the Pinion is very small
This pinion is even smaller than the original and was cut on the CNC
This is the smallest gear I've ever cut. I used 1/4 inch material but only cut 1/8" and then chisled the gear off the ply
The re-assembled clock doesn’t look any different except for the longer pendulum and much improved reliability.