NOTES FROM THE BENCH
Clock Repair Archive - - Repivoting hints:
Repivoting skills are a must. The only way to become proficient at this is
practice; lots of practice. Accuracy to within +- .0005in. is absolutely necessary if
repivoting jobs in clock repair are to be done properly. With the piece in the lathe,
perfectly centered, bring the point of the graver SLOWLY to the center of the work as
it is spinning. The graver must be sharp. Razor sharp. In the instant before the end
of the graver contacts the end of the spinning stock, holding your breath is a good
way to steady your touch because you must be absolutely steady or the first cut will
be off. Of course, using the steady rest as a solid anchor for the graver is a must.
In order to make the stock end true center visable; square off the end with a file as
it is spinning in the lathe again makeing sure it is running absolutley true before
you do this. The resulting circular pattern will appear to come to a point like a
bullseye; the point is the true center of the spinning stock. If the true center is
struck, there will be a cone shaped indentation in the end of the stock. If there
is a tiny protruding dimple in the middle of the cone, then center has not been
properly struck. Do not attempt to "drill away" this imperfection, that will not work.
You will have to start over with a flat surface again. You must either have exceptional
vision, or learn to use a magnifier. Drilling the center of a shaft that is .040 of
an inch in diameter is routine. This must be second nature for you. A sharp graver is
needed. Continue to practice striking center and avoid the small dimple in the middle.
When you drill the stock go slowly and use a pivot drill whenever possible, and use oil.
Do be sure, however to get ALL of the oil out before you drive the new pivot in. The
hole that is drilled should be about .001in. smaller than the stock you intend to use.
Be certain you know how the drill bits you are using react. Most high speed drill bits
drill a hole slightly larger than the size stamped on them. This is true for most
repivoting work in clocks on straight shafts larger than .020in. . Use the lathe and
wire chucks to install (drive in) the new pivot. It should not be necessary to strike
the pivot end very hard to get the pivot to seat properly. If possible the hole for
the pivot should be twice as deep as the pivot is long. This is not always possible,
however. If you are drilling into a shaft that has a gear over where the pivot is located ;
be very careful not to drill into the gear so as to weaken it. Check this out in advance.
In order to drill hard steel properly , you will have to draw the temper on it do the
work, and then re-temper the piece when you are done (before you install the new pivot.
This is the correct way to fix a bad pivot in almost all cases. Repivoting may seem
impossible when you first start; but it will get easier with practice. There will
indeed be times when it may not be practical to repivot. For example : a french clock
with the pinion gear as an integral part of the shaft with a bad pivot in the opposite
ind: the shaft will be very hard steel , and it will be very difficult to strike center.
Sometimes repivoting is not the correct solution. For, example, repivoting a mainspring
arbor is not a good idea usually. By the time you get the arbor drilled for the new
pivot, you most likely will have taken off too much metal and the arbor would likely
break when the full power of the mainspring is applied. Knowing when and when not to do
this comes with experience. This is part of that section in the essay where I describe
how a person must know the meaning of differences in power like what is 10 times, and
what is 100 times, and so forth. You must know by the feel of the power of the mainspring
if a repivoting will hold up. All the more reason to practice your repivoting skills.
Know what will break and what will not break with a given force.
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Copyright (c) 2002 David Tarsi.
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