While you're winding a weight-driven clock, you deprive the movement of power; essentially, you are turning the gear train backwards. So, to prevent escapement damage when the clock is wound, this clock has maintaining power. This is a clever mechanism which applies a forward force on the gear train during winding. Usually, the maintainer is located on the main wheel arbor, but for simplicity and variety I decided to put the maintainer on the second arbor -- I've successfully done this before.

The maintainer for this clock consists of a specially designed pinion. The pinion has an outsize flange whose outer rim is notched to form a ratchet. The flange contains a recess which houses a small brass spring, which will provide a forward force on the gear train during winding.

The spring is horseshoe-shaped, with loops on it ends. These two loops are looped around two pins; one pin is fastened to the pinion-ratchet wheel and the other pin is fastened to a cover. The only part directly attached to the second arbor is the cover, which is set-screwed to the arbor. The pinion-ratchet wheel turns freely on the second arbor.

The pinion is driven by the main wheel. It transfers force through the maintaining spring to the cover, which drives the arbor. When power is removed from the main wheel, the ratchet wheel turns backward a bit, until it engages a pawl mounted between the clock plates, thus allowing the maintain spring to apply power to the gear train.

The pins which hold the ends of the maintaining spring fit through elongated semi-circular notches in both the pinion-ratchet and the cover. This permits the cover and the pinion-ratchet to move vis-a-vis one another in spring-loaded fashion.

I constructed the pinion-ratchet from a single piece of 1" brass. The pinion is a lantern pinion (which I use in all my clocks) in the form of a spool. I cut the waist of the spool with a cut-off tool in the old South Bend lathe. At the same time, I drilled and reamed the center hole of the ratchet-pinion to 1/8". Then I used the cut-off tool to part off the ratchet-pinion, leaving the flange about 1/8" thick.

Next, I cut the teeth on the ratchet wheel. These I cut by mounting the ratchet-pinion on a stub mandrel in the Sherline chuck mounted on the the Sherline rotary table. I used the vertical axis of the Taig mill to do this job, turning the spindle to horizontal. The teeth were cut with a ratchet flycutter, similar to the one used to make the winding ratchet. You're working the flycutter close to the chuck, so it's wise to make some limit marks on the mill column to prevent a nasty collision. The direction which the teeth on the ratchet are facing is also tricky, and care must be taken when cutting them; one must have a complete grasp of the operation of the maintainer before cutting the teeth.

Next I drilled the 20 holes which will hold the pinion trundles. I mounted the ratchet-pinion on a 1/8" stub mandrel in the Sherline chuck and screwed the chuck to the Sherline rotary table on the bed of the little Taig mill, which are really nice tools. Before drilling, I centered the mill spindle over the center of the ratchet-pinion and the rotary table by clamping a piece of 1/8" brass rod in the 1/8" collet held in the mill spindle. By moving the X and Y axes, you can get it so the 1/8" brass in the chuck just fits in the 1/8" hole in the end of the ratchet-pinion as the spindle is lowered. Thus the mill spindle is exactly centered.

Then, I used a dial indicator which indicated the longitudinal mill axis, and offset the mill bed by the amount of the radius of the pinion. (One could also use the graduations on the mill handles to do this job.)

This radius I calculated by first measuring the pitch diameter of the wheel which will drive it -- the main wheel, multiplying the result by PI to get the pitch circumference, then devided that by 120, or the number of teeth in the main wheel. This gives the tooth pitch. Then the tooth pitch is multiplied by the number of pins in the pinion (20 here) and then re-divided by PI to get the pitch diameter of the pinion.

I first make a pass around the pinion with a center-drill with the smallest-size tip to ensure accurate drilling, indexing the rotary table by 18 degrees. Then I drilled only the upper flange of the pinion with a .022" drill mounted in a 1/8" brass "haft" as described in an earlier chapter. I did not drill the lower flange of the pinion because I've found that if you extend these tiny twist drills the length of the waist of the pinion, they can flex enough to make inaccurate holes in the bottom flange.

So I made a special center-drill to center through the holes just drilled to make center marks in the lower flange. The special center drill is made from a .023" needle, the same material I'll use to make the pinion's trundles. I ground a sharp pyramid on the business end. I did this job by hand, with the needle chucked in a pin vice, using the lines on the pin vice as a visual index. Using magnification, of course. Then I hafted the needle as I had the twist drill.

Once the special center is made, I made another pass around the pinion in the rotary table, this time center marking the lower flange with 20 divots. Then I made still another pass, using the little twist drill to make the holes. I put a mark on the twist drill to mark it's limit so the holes will be of uniform depth. They are blind holes.

Next, I cut the recess in the back side of the ratchet-pinion. I did this by chucking the flanges of the pinion in the Sherline chuck in the Taig lathe, using a boring tool to make a recess that's about 1/32" wide. A flange is left at the hub and at the outer circumference of the recess. The wheel is also thinned to about 1/16" past the flange up to the ratchet teeth.

The cover is made from .020" steel shim stock. I sawed out the blank with a jewelers saw, drilled a center hole and mounted it on a stub arbor to true the outer rim and to polish it. I made a collet for the cover which has a 1/8" hole for the second arbor and holes drilled and tapped for a 2-56 set screw. The collet is riveted onto the steel cover. When it's all finished, I'll heat blue it.

I cut the semi-circular notches in the ratchet-pinion and its cover with a 1/16" end mill. I chucked the flanges of the ratchet-pinion in the Sherline chuck and put it on the Sherline rotary table to mill the notch. Without changing the setting of the mill axis, I unchucked the ratchet-pinion and chucked its cover by its collet, then milled a similar notch in the cover. This means that the notches in the ratchet-pinion and its cover are congruent. I turned the rotary table 25 degrees to make the notches.

The pins which will secure the ends of the maintaining spring are made from 1/16" steel, with a tang made on one end so that they can be riveted into holes in the cover plate and ratchet-pinion. I also thinned the pins a bit with a graver in the old watchmakers lathe so there's clearance between them and the semi-circular holes they fit through. They must not rub the notches, as smooth operation is important in proper maintainer functioning.

I marked the locations for the pin mounting holes with a 1/16" transfer punch, transferring through the semi-circular holes in the ratchet-pinion and cover. Placing these holes is a tricky business, and one must firmly grasp the operation of the maintainer to do it properly.

The maintaining spring is made from #30 hard brass wire. One advantage of this design is that the strength of the spring can be changed, if necessary, when testing the clock, without having to dismantle it.

The pawl which engages the ratchet will be made at a later time.

Today's links:

Cutting pinion waist
Milling ratchet teeth
Vertical axis limit marks
Centering mill over pinion
Setting offset
Twist and centering drills
Drill and center points
Drilling pinion 1
Drilling pinion 2
Pinion drilled
Ratchet recess
Milling notch in cover
Xfer punch for pins holes
ratchet-pinion and cover notched
Maintaining spring
Spring in recess
Ratchet-pinion and cover
Pretty maintainer