057-058 - Making a Wooden Clockworks 2.pdf - drewniane zegary - wojtuspan

Making a Wooden Clockworks

Part two: Getting things ticking

by Wayne Westphale

is the time to make one. There are a variety of ways to cut

gear teeth, methods that cover a broad range of accuracy,

speed and expense. The method you choose will depend on

your goal, your shop equipment, and your budget.

As an example of how low-tech clockmaking can be, for my

first clock I turned the arbors on a lathe setup that consisted of

an electric drill (as a headstock) clamped to a 2x4 (the lathe

bed). A piece of angle iron, drilled and tapped to carry a pointed

bolt, became a tailstock. A chisel served as a lathe tool and a

piece of scrap as a tool rest. My first tooth cutters were reground

spade bits, as shown in the bottom right photo on the facing

page. Needless to say, this was doing it the hard way.

I've always tried to surpass each clock I've built with a better

one, and along the way I've invested in some pretty sophisticat-

ed equipment—machines more often found in a metalworking

shop. These are not essential to building a good clock, but they

allow me, as a matter of routine, to achieve repeatable accuracy

with little fuss. Expect this clock to tax your ingenuity in getting

the necessary precision from your own machines and tools.

There are ways around every problem as long as you understand

the features in a clock that are critical to its operation.

Horologists don't speak of gears, but of wheels and pinions.

Wheels, the large gears, have teeth; pinions, the small gears,

have leaves. I cut teeth and leaves on two different machines, but

the process is basically the same—I use a set of reground router

bits to cut the gullets between the teeth.

The preparatory step, laminating plywood gear blanks, was de-

scribed in part 1. The photos on the facing page show some of

the actual cutting, including my jig for bandsawing circles. To

cut the wheel teeth, I mount a stack of gear blanks on a mandrel

and mount the mandrel on an old metal lathe, which I also use

to turn clock arbors. The tool-bit holder on the lathe's cross-slide

and compound has been adapted to carry a router, with the rout-

er bit perpendicular to the lathe centerline. By cranking one of

the lathe's control wheels, the router bit can be positioned clos-

er to or farther from the work, then locked in position to give a

cut at a set depth. By means of another control wheel the router

can be moved precisely along the length of the work.

The first step in cutting the teeth is to turn the lathe on at slow

speed, then use an end mill or hinge-mortising bit in the router

to trim the blanks to true round, sizing them to the correct diam-

eter at the same time. This ensures that the arbor hole will be

exactly centered.

The lathe is then turned off, and the blanks are indexed by a

pin and a shopmade plate. The router roughs out the gullets one

by one by traversing horizontally along the stack. I crank the

router from the tailstock end up to the headstock end to cut a

tooth gullet. Then I crank the router back to the tailstock end,

turn the stack of wheel blanks to the next index location and

repeat the process. (The escape wheel is a special case. It has

three very critical surfaces on each tooth, and I make these as

shown in figure 3, on p. 62.)

To minimize chipping—and maximize cutter life—I make sev-

eral passes, each with a different cutter. The first cutter, as shown

in figure 1, has straight faces, is easy to sharpen, and has an in-

cluded angle of about 32°. It is a wasting cutter. I set it to about

80% of full depth. The next cutter profiles the tooth face and cuts

to final depth. The last cutter eases over the tooth tip. The relief

angle of this cutter is only 2° to 3°—the desired effect is to round

over and burnish the tooth tip in one pass. Next, I lightly sand

with 400 grit paper over a soft block to remove the burr left at

the tips of the teeth.

This produces a stack of identical chip-free wheels. The meth-

od suits itself both to small scale production or, if you are mak-

ing just one clock, to making any identical wheels that may be in

it (there are two identical pairs in my grandfather clock). Pinions

are cut in a similar way on a milling machine, as shown in center

photo. The same operation could be accomplished with a drill

press fitted with a compound table (available from Sears for un-

der $80 and from time to time in various bulk-mail catalogs for

even less) and a properly contoured cutter.

I profiled my cutters in a series of steps, as shown in figure 1. I

began with a full-size drawing of each of the gear-tooth profiles.

Figure 2, on p. 61, shows the exact profiles of the teeth and

leaves in my grandfather clock. To achieve the necessary variety

with the fewest number of cutters, I taper my cutters slightly at

the tip, so that the tooth size, the width at the pitch circle, can be

controlled by depthing the cutter as required. Pitch circle and

other technical terms are explained in part 1.

Arbors and bearings —I turn arbors in the metal lathe—it is fast

and sure and will maintain 0.001-in. tolerances (exact sizes are

shown in figure 2). I strive for a snug fit of wheel to arbor. A

metal lathe is not absolutely necessary, though I would not rec-

ommend using dowels straight from the hardware store either.

You'll find that commercial dowels are only approximately sized

and only approximately round.

I recommend a piece of tool steel or -in. drill rod be pressed

into the arbor to serve as a pivot. Wood-on-wood is too ineffi-

cient at this point from the standpoint of friction as well as dura-

bility. The pivot must be accurately centered. If your lathe has a

I n part 1 we discussed the theory of how a clock works. Now

At left, large gears are cut by a

router mounted on the cross-slide

and compound of a South Bend

metal lathe, which the author

bought used for $4,000. The

blanks are indexed by the pin op-

posite the router bit. Above, West-

phale cranks the router along a

stack of six wheel blanks, backed

up at each end by a hardboard

blank to prevent tearout.

Left, a milling machine is the met-

alworker's precision version of a

drill press, equipped with a table

that can be moved horizontally

on X and Y axes by hand cranks.

The stack of pinion blanks is in-

dexed by a dividing head, which

calculates angles by means of per-

forated plates and a gearbox. It

takes forty turns of the crank han-

dle to rotate the output shaft one

full turn. Far left, an efficient cir-

cle-cutting jig: The board has a

runner on the bottom that rides

in the bandsaw's miter-gauge slot,

and a number of axle holes to suit

the various gear sizes.

Cutters are reshaped as shown in

the drawing at left. Tooling need

not be high-tech. Westphale shows

two of his early gear cutters, re-

ground spade bits, alongside the

highly evolved ones he uses today.

Fig. 2: Wheels, pinions and arbors

Fig. 3: Escapement data

Westphale makes the teeth on his escape

wheels with a series of straight cuts, as shown

above, then routs out the curved shape of the

gullets using a template and guide bushing (far

right). The escape-wheel blank (or a stack of

blanks) is mounted on a mandrel through the

arbor hole, and the mandrel is fixed to a divid-

ing head. The dividing head rotates and locks

the wheel blank a fixed amount for each cut,

ensuring even tooth spacing. Cutters are held

in the chuck of a milling machine, the metal-

working equivalent of a drill press. The milling

machine adjusts precisely in three planes to lo-

cate the cutter relative to the work. The divid-

ing head is attatched to a sliding table, worked

by hand cranks, that moves the work horizon-

tally past the cutter and back again for the next

cut. When routing the gullets, the work is in-

dexed under the template by the dividing head.

Spokes are routed the same way (photo, facing

page) then rounded over on a router table.

hollow headstock you can drill the pivot holes as I do, with a bit

in the tailstock. If not, I'd suggest clamping a piece of scrap to

your drill-press table and drilling a hole the diameter of your

arbor through the scrap just off the edge of the table. Maintain

the setup but change the drill to a size a few thousandths smaller

than your pivot material; I find that a #53 drill bit works well.

Insert the arbor from the bottom and drill carefully into the end.

As the arbors are different diameters on each end, at least two

different setups will be required.

Bearings, which I make from nylon rod, can be drilled with a

similar setup. In this case, just drill part way through the scrap.

For instance, if you use in.-dia. bearing stock, drill a -in. hole

in. deep with a Forstner bit into the clamped scrap. Then drill

a -in. hole all the way through. Cut your bearing stock into in.-

thick wafers. Insert the wafer, drill the appropriate size pivot

hole, then push out the completed bearing from below.

Engagement testing —Test wheel-and-pinion engagement pat-

terns at various center distances. In a scrap of plywood, drill a

hole for a pin that will represent the wheel arbor. Around it,

draw a series of pinion-arbor holes, one at the nominal distance

from center, the others at -in. increments from the ideal.

Mount the pinion on a pin in various holes, revolve the gears,

and note how the teeth mesh. Part 1 explains what to look for.

Choose the distance that gives the smoothest action. There is

some latitude, but many times, while working out the tooth pro-

files of the grandfather clock, I had to refine the contour of one

cutter or the other, and sometimes both. You don't have to go

with the exact tooth profiles and distances I've worked out, but

they work well and I recommend that you try to match them.

Once the teeth have been cut, the wheels can be lightened

with any number of spoke configurations. Spoke shapes are

limited only by what is practical and aesthetically pleasing. My

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