Adjusting Clock Hammers
By Steve Callihan FBHI
The following article was published on the Clocks mailing list and Steve has given permission for it to be published on this web site. Steve can be contacted on SCallihan@AOL.COM
INTRODUCTION
Wear and dirt are not the only problems found in mechanical clocks. The finer points of hammer adjustment deserve attention. Clocks that were repaired properly in every other respect, have been stopped cold by overlooked hammer adjustments.
Basic Adjustments
There are three adjustments that can be made to improve hammer function. They are; Rebound Damping, Hammer Lift, and Hammer Clearance. These adjustments are interrelated. The work sequence can be as important as proper execution. A few clocks have adjusting screws for each of these. In most clocks these adjustments will involve a little judicious bending of the hammer assemblies.
Recognising the problem is the place to start. In most clocks the hammers are the least likely source of problems. First, look for the things that routinely stop a clock. Dirt and wear are the primary causes of stoppages. Damaged parts and improper set-up are secondary causes. Previous repairers efforts can also be a source of concern. A clock in good condition that stops striking for no other apparent reason, may need hammer adjustments.
The Best Case Scenario (See Figure 1)
The hammer stroke begins with the hammer lift. The strike pin engages the hammer tail raising the hammer. As the tail clears the pin, the hammer falls. The rebound damper strikes the hammer stop and begins to slow its descent. By the time the head reaches the rest position, the damper has stopped the tail. The hammer's inertia drives it through the clearance space. The hammer rod flexes and the head strikes the chime rod once, then rebounds to the rest position. The rod or gong vibrates to produce one musical tone. Sounds simple enough.
Situation Normal
Things don't always go this well. For example, the gap between the head and the gong might be so small, the rod buzzes against the head producing a less than musical tone. The lift could be so high that the hammer binds against the movement or case. The hammer could bind on its arbor and not even hit the rod.
Checking it out
First, carefully observe the hammer action. It must be free to function properly. Check this by lifting the head and dropping it. If it drops without binding or sticking, then look elsewhere for faults. However, if the hammer is reluctant or is so sloppy that it could miss the rod, correct these faults so their presence won't mask other problems.
Note the speed of the train as it runs under normal load. Raise the hammer(s) manually while the train runs and note the difference. (i.e. with no load). It is normal for the train to run a little faster without load. Each clock is different. However, the train should not slow by more than 30% in most clocks when raising the hammer(s) on its own. Observe two sequential hammer pins. If the lift duration is too long, the first pin will not release its hammer before the second begins its lift. The train must then raise both hammers simultaneously. Recognising this problem requires running the chime train slowly enough to observe each individual lift. No hammer should rise before its predecessor has dropped. Many times, the clock will oblige by simply stalling out while this test is being conducted. In the absence of excessively tight bushings or lack of end shake, its reasonable to conclude there is a hammer adjustment fault.
There are a few clocks that will not tolerate any of these adjustments. Either because the materials are brittle with age or, because the designers never considered the necessity for these adjustments.
Hammer Lift (see Figure 2)
Improper Lift is often ignored as a cause of strike and chime woes. The lift is the height the hammer is raised before dropping to produce a tone. A short lift produces very little volume. Too much lift is a problem if it requires additional power or if the hammer hits anything on its way up. Chime trains work with small power reserves. Requiring them to carry any extra load makes no sense. Correctly setting the hammer tail is the key to efficient, reliable chiming.
Lift height is a direct result of the lift pin moving the hammer tail. The further the hammer tail is pushed, the higher the lift. Figure 1 shows a properly adjusted hammer tail. Note that the lift pin makes contact after it passes the line of centres and NOT before. This is the most efficient way to transfer power for the lift. Lift occurring before this line must come at the expense of power lost to engaging friction. Early contact also causes accelerated wear at the tail contact point that, in turn, reduces the lift available.
These losses are important in chime trains because many hammers are lifted in a sequence with equal duration for each lift. Unless ample power has been provided, properly designed and adjusted chime systems do not allow overlapping lifts. The cost-cutting efforts of some manufacturers have led to smaller diameter chime rolls. The smaller the diameter, the worse the overlapping lift problem becomes. Chime trains will stall if they lift too many hammers at once. There are many clocks that do not play by these rules. Even so, minimising engaging friction at the hammer tails will allow them to perform their best.
Rebound Damping (see Figure 3)
Damping is the controlled slowing of the hammer just prior to impact with the chime rod. Proper damping controls hammer bounce. The hammer can be made to slow down abruptly or gradually by adjusting the angle between the damper and the stop post. The action will vary with each clock. However, if the hammer bounces more than one and a half time (when dropped from full lift), the damping action is too weak. Other adjustments being equal, aggressive damping will give a quieter strike.
Adjusting Rebound Damping (See Figure 3)
The damping action is decreased by opening the angle. Opening the angle increases bounce and striking force. Closing the angle reduces bounce and striking force. It is critical to make the bend in the proper location along the damping wire to achieve consistent results. This can be a tricky adjustment. Be certain there is a problem before bending anything. Changes in damping affect the hammer lift. The much maligned Seth Thomas model 124 often suffers from collapsed dampers. The brass wire is too soft and, after a few thousand cycles, as the damper radius diminishes the hammer tail position gradually passes forward of the line-of-centres. The resulting engaging friction makes the 124 appear to be under-powered. It is not. It is merely misunderstood and maladjusted. French pendule de Paris {round movement} clocks are not as power sensitive as the Seth Thomas 124. Their strike function can be improved nevertheless. On these the hammer stop or rest is located between the plates. Typically the stop is a simple taper pin driven in from the front of the front plate. This pin should be positioned so that the tail is on the line of centre drawn from the centre of the hammer wheel to the hammer arbor. This is done by bending the rest. Damping is done by a similar pin which protrudes out the back plate and impinges on a special flat on the hammer bushing. In practice the stop pin only functions to prevent the arbor from getting out of position when the hammer is removed. The damper flat does double duty as stop and damper.
Positioning the Hammer Tail
The position of the hammer tail relative to the line-of-centres establishes the total lift available and the timing of the lift. It is set by bending the damper as close to the hammer arbor as practical. In Figure 2, bending the wire down will reposition the hammer tail in front of the Line-of-centres (LOC) The tail can be moved behind the LOC by bending the wire up. Make sure the hammer head isn't laying on the chime rod before and after this adjustment. Make certain the changes made in the tail position have not adversely affected the damping action.
Hammer Clearance (see Figure 4)
This is the space between the hammer face and the chime rod when both are at rest. This is the easiest of the adjustments to make and the least understood. The clearance space prevents buzzing by allowing room for the vibration of the rod after impact. It is not the primary method for controlling volume. Hammer Clearance is usually obtained by bending the hammer wire at the location. Some clocks have an adjustment screw specifically for this purpose. The clearance should be between 1/16 and 1/4 inch. There are times when larger clearances are necessary. The rule is, "Whatever it takes to keep the vibrating rod from buzzing against the hammer.
Lubrication
It makes good sense to lubricate the hammer tails and damper contact areas lightly. Grease works best as it stays where its applied. The reduced friction and corrosion prevention are worthwhile reasons. Also, a little lubrication prevents these parts from producing squeaking noises that customers object to.
Customer Satisfaction
There are several issues that are likely to arise when a clock is returned to it's owner. These can range from the ridiculous to the merely impossible. Some can be remedied by the adjustments described. Others will require diplomacy. Some examples of each later on.
Volume, Tone Quality, Buzzing, and Tempo
Volume can be the biggest headache in this group of adjustments. It's either too loud or too soft. This problem is compounded by the fact that the acoustic environment of your shop is always different from the clock's home environment.
Adjusting the Lift is the most effective way to control volume. Do not try to get more lift by positioning the hammer tail ahead of the line of centres. This may cause lift overlapping and stall the train. If the tail is already on this line, and a louder strike is needed, try reducing damping or clearance. Recheck the hammer tail position after making any damping adjustments.Tiny chime rolls or tight cases may require short lifts. A smaller hammer clearance and/or weaker damping may be necessary to provide adequate volume. Some hammers have return springs to produce consistent hammer action. Do not adjust these springs unless there is some indication of previous tampering and all the other adjustments are correct.
HINT: Shop acoustic conditions almost always make the customer think the clock is too loud because there are usually fewer sound absorbing materials in a shop. The best thing to do is ask the customer to take the clock home and try it for a few days. If the adjustments followed the suggested guidelines, chances are, the clock will stay home. Call to check on the situation within one week. Then, if there is a problem, you are able to solve it instead of losing the customer to your competitors.
Tone Quality
Tone quality refers to the fidelity of the musical notes produced by the chime rods. In this connection, it is worth noting that most manufacturer's warranties specifically exclude tone quality from coverage. Make sure the chime block is securely attached to the clock case. If it is, the only recommended adjustment is changing hammer inserts. Soft leather, hard leather, wood, brass, and plastic all produce slightly different tones. Do not try to tune chime rods unless you are musically inclined. Even then, customer relations might be better served by following a former first lady's advice and "Just say no."
Buzzing
This unpleasant noise often accompanies the chime. There are two common sources for buzzing. The most likely cause is insufficient clearance between the vibrating chime rod and the hammer. However, the case itself can produce a similar sound. Often the door glass rattles in its frame. Case parts sometimes vibrate against each other.
Tempo
The speed or pace of the chime often concerns customers. With spring-wound clocks the pace will vary from fully wound to unwound. Explain this to your customers. If the clock has just been serviced and still plods through its chime, it is likely that there is still a problem.
Conclusions
It is in everyone's interest for each clock to perform its very best. Improper hammer adjustment is the kind of fault that can slip by unnoticed until the customer gets it home. This can produce a costly comeback. Returned work costs you at least three times. The first time you do it, the second time, and the new work not done while repairing the comeback. There are the hidden costs of lost referrals and repeat business. Take care of these little problems before they get to be big ones.
