Expert: Martin Meyer - 12/11/2008

Question
QUESTION: The hour hand is one minute off. Can I adjust it myself

ANSWER: Hi Pete,

I'm wondering if you mean the MINUTE hand? The hour hand moves from one hour number to another each hour (e.g., from the "1" to the "2"), so one minute off would be a movement of 1/60th of the space between the "1" and the "2", and I don't know how you could be able to see such a small difference.

Your clock has a minute hand with a bushing for this adjustment. At the center of the hand is a circular or hexagonal piece with the square hole which fits on the hand shaft. This piece is riveted onto the minute hand, but can be turned to adjust the hand to point exactly to the :12, :15, :30 and :45 points when the clock chimes.

To perform this adjustment, insert a square-sided awl or small screwdriver in the square center hole. Hold the minute hand tightly near its base, and turn the screwdriver or awl, so that the bushing turns, thus changing the orientation of its square center hole. Be careful not to bend or break the minute hand as you do this. The bushing will usually be quite tight, but will turn with enough effort. If the bushing is not tight, and turns very easily, you should set the hand on an anvil and give the bushing a couple light taps with a small hammer to tighten it up. After adjusting, put the hand on its shaft and turn it to see if it correctly lines up with the chime point. This is a very precise setting, so it will almost certainly take several adjustments to get the hand perfectly in synch with the chime.  

If the problem is, in fact, the hour hand, the correction is simple. The hour hand is a simple friction fit. It can be moved to any position without affecting the clock mechanism or moving the minute hand. Just move the hour hand to point to the correct position. This is most accurately done at 12:00, when the minute and hour hands are aligned identically and vertically toward the "12".  http://www.clockmasteronline.com


---------- FOLLOW-UP ----------

QUESTION: Thank you very much, you answered my question. Indeed it is the hour hand that is off. I don't how it got that way unless I inadvertently bumped it.  Pete

Answer
Hi Pete,

It is very common for the hour hand to get slightly moved when the clock is being set by turning the minute hand.

As a footnote, both the hour hand and the minute hand have a certain amount of tolerance, or "slack". The tolerance resides in the gears to which the hands' shafts connect, and is essential because otherwise the gears would bind and lock, and the movement could not run. Clocks are not made with very fine tolerances relative to other machines. I cannot quantify the amount of tolerance in the hour hand of a clock, but it is almost certainly more than 1 minute, even on the mechanically tightest of clocks. 60 minutes per hour X 12 hours = 720 minutes in one revolution of the hour hand around the dial. This equals .5 degree of the dial's  circle.

This tolerance, or looseness, is, of course, affected by gravity. So, when the hour hand is at 3:00, gravity pulls the looseness of the hand downward, in effect making the hour hand read fast in the amount of the tolerance. At 9:00 the reverse is true, and the hour hand will read slow in the amount of the tolerance. At 12:00 the looseness is essentially in a swing-back-or-forth condition, and the tolerance error can read either way. If your clock's dial is perfectly aligned relative to level, i.e., so a plumb line would pass precisely through both the 12:00 mark and the 6:00 mark (most clocks are not set up this perfectly), then 6:00 would be the one time in the 12-hour cycle at which the hour hand would read neutrally relative to the tolerance, i.e., half the tolerance on each side of the position of the hour hand.  http://www.clockmasteronline.com