Back Up Next

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 springs.



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.


 Buchanan comments: 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 my taste. 


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. 


Back Up Next