Miscellaneous attachment parts for pendulum springs - April 2016
This month Buchanan makes various parts that will connect the upper
and lower pendulum spring pairs to the pendulums as well as new set of
Buchanan now sets up
the computer equipment to make the attachment points for the balance spring
pendulum anchorage parts. The strips are made from Horolovar, the same
material used as the torsion springs in the one year duration anniversary
clocks. The metal is Invar a special steel alloy employed in pendulums that
render their lengths nearly impervious to temperature changes. These parts
are small and somewhat intricate in their geometry and there are eight
identical pieces needed, thus lending these parts nicely to the use of
CAD-CAM methods. The third photo shows a close up of the video monitor
revealing the individual steps the mill
cutting tool makes. There are 20 lines covering the part’s profile
representing the number of passes of the tool makes to complete the part’s
profile. Next the tool is seen
cutting the parts from a brass block.
After the cutting tool
has reached the appropriate depth, 20 passes, the block is flipped over and
a cutting tool is passed over the reverse side cutting through the thin
flash that holds the parts in place freeing all the parts from the
block. Of course CAD-CAM does not produce a finished part. Next the part has
to be drilled to accept the screws that will secure the spring adjuster
strips. Then hand filing and surface polishing are needed.
This set of photos show
the fabrication steps of the spring end clamps. CAD-CAM is again used here
for the multiple parts. These are made from another sector of the same brass
block used for the pendulum anchorage points. The milling and finishing is
similar to the anchorage parts. The last two photos show how small these
are, note the match stick. The smaller part is 3mm long x 2mm wide by 1.2mm thick.
The pendulum and spring
attachment pieces are completed with 48 parts total. There are two
pairs of springs one pair for the upper and one pair for the lower areas of
the pendulums. This leaves eight attachment points and there are eight
attachment strips. The four upper strips anchor one end of each spring to
the pendulum and the other four are wound around the pulleys within the
poising vernier adjusters with one end on the spring and the other attached
to the adjuster. The springs themselves are only test models. The final
springs are yet to be fabricated.
The spring attachments
are now installed. The two circled areas on the left hand side of the photo
show a pair of strips wound through the vernier poising scales with one end
attached to the sliding vernier and the other to the inner side of the
spring pair. These devices along with the sliding pendulum balance poising
weights, allow the operator to make the pendulums isochronous. The circled
area to the right attaches to the outer side of the spring and terminates at
the pendulum anchorage point just out of the photo on the right edge. All of
the attachment points, unlike those used on John Harrison’s original machine
are designed for easy installation and removal. Of course this machine will
not be going out to sea on a rolling 18th century ship!
We still have about hundred wheels and a multiple of that number of
components to still fit into the machine. I hope we find the space! The
orrery crowning the center is still a wooden mockup, the last piece from the original wooden model from 2006.
I have had a first trial heat treat of thicker spring wire. 32 thou, a
little thicker than the original set. When cool and released from the jig
you can see that I did not have a high enough temperature.
(because it did not hold the same diameter as the jig)
I heated to 300C, according to data on piano wire you can go to 375C before
you start to loose temper. I have them in again at 350C this time for two
hours so should have them out by lunch time. This as a stress reliving
process and actually increases the elasticity of the spring.
Here we have a successful fabrication of the next spring set. I like the
fact that Buchanan is using a bit thicker gauge as these will look better in
relation to the rest of the machine. the trial springs looked too thin for
Buchanan now mills decorative collars onto the pendulum ball mounts. These
match a similar design milled into the two vertical
pillar pairs that
support the time train
remontoire fly fans made in April of 2008.
Look at the attention to complex detail that is fabricated into these four
small and otherwise somewhat inconsequential parts.