Depthing and Troubleshooting

Residual internal friction is the bane of our wooden clock movements.  Friction can happen in a variety of places, and that’s why I always recommend Depthing as we build to help find and eliminate as much internal friction as possible before the assembly is completed. 

The Depthing process takes time, but it also saves time at the end in trying to find hidden friction points.  Once the Depthing of all the pieces is complete, it almost assures that the clock should run well once the pendulum is put into motion. 

Depthing is a simple process of testing one wheel with its pinion using the clock frame these two gears will be running in.  Depthing is testing ONE wheel and ONE pinion...not the whole train of gears at one time.

 In reality while building our clock, we don’t want to just test one wheel and one pinion.  We want to test those two gears on their completed assemblies, just as they will be running in our clock. 

 We want to first create a completed wheel arbor assembly (i.e.: wheel, connector and pinion on its arbor).  Then create a second complete wheel arbor assembly.  Then test these two completed arbor assemblies, with their spacers, in the reassembled clock frame. 

 I always recommend Depthing as the clock is being built, however, if the clock has already been assembled, to depth correctly the clock is taken completely apart.  All the arbors removed from the Frame, and then one wheel assembly and its matching pinion assembly are put back into the clock.  The clock frame is totally reassembled with just those two arbors, and then the wheel set (one pinion and one wheel is a wheel set) are tested by gently blowing on the large wheel.  This process will detect even the slightest bit of internal friction that could stop the clock. 

 Internal friction may be caused by the contact surfaces of the wheel and pinion, or possibly the teeth may be bottoming out in the dedendum (the valley between the teeth), or even a tight set of spacer tubes could be binding the arbor in the frame.  Any and all of these can be detected by proper Depthing.

 Because clocks never run backwards, only one side of the teeth is ever used.  That is called the Contact Side of the tooth. 

 If a space is too narrow between teeth we want to take the wood off of Non-Contact surface of the teeth.  Avoid sanding wood off of the contact surface of the tooth. 

Removing wood from the back of the toot allows the spacing of the front of the teeth to remain constant while at the same time opening up the space between the teeth enough for proper clearance. 

A clock wheel travels only in one direction, and with only one wheel and one pinion in the clock’s frame it gives us the opportunity to first visualize the direction that the wheel will be turning in the clock, and to decide which side of the teeth is the contact side. 

With one wheel and one pinion being tested inside the reassembled frame we are also simultaneously testing other parts, like the Frame’s arbor holes and the arbor’s spacers, and this allows us to make sure that these parts are not causing the increased internal friction. 

If the spacers are causing internal friction they can be filed or sanded slightly to allow freedom of motion of the two arbors.  There should be about 1/16” (1.5mm) of end play (front to back movement) in each arbor.

 Depthing also can let us know of another potential cause of internal friction - the arbor holes.  Possibly the arbor holes are binding because the holes in the front and back frame are not aligned, or because the drill holes are too small or because the fibers inside the drill hole are going in the wrong direction for that particular arbor.  

 Because our drill presses only turn the drill in one direction as we drill each of the arbor holes in the frame, that means that every other drill hole has wood fibers inside the hole that are facing in the opposite direction that the arbor will be constantly turning as the clock runs.  This is usually not a big problem, but if those opposing directional fibers should get damp and swell they can easily stop an arbor.  Burnishing the inside of the arbor hole can help in a couple of ways.  It can flatten the wood fibers and also add paraffin to decrease friction.  To burnish, simply chuck an arbor rod in a hand drill, add paraffin to the rod, and run it in and out of the hole.  Reverse the direction of the drill and burnish again.

 Then, after that first wheel set has been tested and the internal friction removed, the clock is then disassembled again and the first wheel arbor is removed.  The next arbor in the train is then to be tested the same way - one wheel and one pinion - with their spacers inside the reassembled frame - with a gentle puff of air on the large wheel.

 All of the wheel sets (one pinion and one wheel) throughout the entire clock are separately tested using this Depthing procedure.  Once the Depthing is complete you can be sure that the wheels, pinions and spacers are all going to work properly. 

 Once all the wheels and pinions are depthed correctly and the clock still occasionally stops, that may mean that the problem probably is NOT in the wheels or pinions but somewhere else, such as two parts rubbing causing increased internal friction.  This can happen as an arbor moves forward or back and begins to press its spacer into the clock's frame with enough force to stop the clock.  

 You can visually check.  When a clock has been running well and then spontaneously stops for no apparent reason, check to see if the arbor has moved forward or back and is rubbing on the frame or some other part.  In a clock that is not properly depthed, this movement of the arbor, combined with the improper Depthing might create enough internal friction to cause the clock to stop....not from just one problem, but from the combination of two or more residual problems.

 The most common place for the arbor shifting to happen is at the Center Wheel arbor and its Cap (but any arbor can shift increasing internal friction).  On the Center Wheel arbor it is usually not the arbor itself shifting that is causing the friction, but the minute and hour tubes that have slid forward into the Cap.  

 A common cause of shifting arbors is mounting the clock to a wall that is not plumb.  If your arbors are shifting, check the plumb of the wall.  An easy fix for this is to shim the clock’s frame so that the clock sits level on the wall. 

 Also, once the clock is mounted level, another fix that can help minimize shifting arbor friction is to cut a couple of nylon or Teflon washers to fit between the tubes and the Cap.  These washers will allow the tubes to turn at the Cap, but not rub on the Cap.

 To cut your own washers, you can use something like a plastic coffee can lid.  Drill the plastic with a brad point bit that is just slightly over-sized for the arbor.  I use brad point bits for these center holes because they give a cleaner cut and don't leave a ragged plastic edge around the hole.  Once the center hole is drilled, the washer can be cut to size from the lid with scissors or even a larger brad point bit.

 Sometimes internal friction as slight as the tubes rubbing on caps is enough to stop a clock, especially if it happens in concert with another source of internal friction.

 To minimize internal friction even more paraffin can be used on the contact surfaces of the teeth, on the arbor rods, and in the arbor holes in the frame.  I prefer using a color coordinated Crayon because the paraffin of a Crayon is softer than candle wax and the sharp tip allows us to get the paraffin in between the teeth easily.  But not too much!  Too much paraffin can pack into the dedendums (the valleys between the teeth) and cause the teeth to bottom out into the wad of wax.  This bottoming out will stop the clock.

 Another source of internal friction that has nothing at all to do with the clock’s gear train could be the groove in the pendulum pivot rod.  Too deep a groove can cause the clock to stop.  The groove in the pendulum pivot rod should be 1/32” (0.75mm) or less in depth.  We want only enough depth to hold the sharp, knife-edge point of the pendulum pivot from slipping side to side.

 The Pendulum/Pallet/Crutch assembly can be tested for friction by simply removing the Escape Wheel.  With the Escape Wheel removed, move the Pendulum’s Bob to the side about two or three inches and let it go.  The Pendulum/Pallet/Crutch assembly should continue to rock freely for at least 60 seconds, and 90 seconds is even better.

 If the Pendulum/Pallet/Crutch assembly does not rock freely for at least 60 seconds, check all contact points for friction.  Maybe the arbor holes in the frame are not aligned, or the arbor holes are drilled too small.  Or possibly the Crutch Pin slot in the Pendulum is too tight.  The Crutch Pin should move freely in the Pendulum’s slot, but not with too much slop.  Too narrow a slot will cause binding friction with the Crutch Pin.  Too wide a slot will not allow the Crutch Pin to deliver the impulse to the Pendulum.  With loss of this impulse from the Crutch Pin the clock will stop.

 So to summarize, one tests the pinion on the escape assembly with the third wheel assembly without the center wheel assembly (a with b) and then the pinion on the third wheel assembly with the center wheel assembly without the escape assembly (b with c).

 With all this done, then all three (a + b + c) should run freely in the assembled clock.  

 Also, the cannon is tested with the intermediate wheel and then the intermediate wheel is tested with the hour wheel.

 And the pallets are tested with the escape wheel (see FAQ's for more information on manually testing the pallets and escape wheel).

 And the pendulum is tested with the crutch assembly of the pallets.

 The more Depthing and testing that is done during assembly the better chance that the clock will continue to tick with the first gentle push of the pendulum.

 Remember also that changes in humidity can affect these wooden clocks.  With high humidity the wood can swell and stop the clock.  In very humid conditions I simply do nothing.  It is best to do nothing because as the atmospheric conditions change the clock will begin running well again.  The Woodworker’s Hygrometer is an excellent kinetic sculpture for detecting these changes in humidity.