Tuesday, March 17, 2009

8 Day Weight Driven Clock Movement

I've been working on a brass clock movement for about a month. This is an 8 day movement with a one second pendulum. The plans are from a book by John Wilding called "How to make a weight driven 8 day wall clock".

So far I have the front and rear plates made. The pillars are cut to size and the ends are turned to dimension. I have just started into the barrel and great wheel. Shown are the blanks for these pieces.
This is my first venture into making an actual movement. There are many lessons learned along the way.

One lesson is that Metal working is all about using your tools to make tools to make your parts. The other lesson is it takes me longer to produce results in metal compared to wood. Must be the experience. Go figure.

Not shown here is the effort in getting to this stage. The front and rear plates which measure 6.5 by 4.5 inches were rough cut on my (old) table saw. Cutting brass this way is very loud - make sure you have hearing protection!

The rough sized plates were pinned together with small split-pins. The combined plates where then milled to dimension on my milling machine. I used a fly cutter to make a clean edge. The plates were separated after this.

The corner holes where drilled on the plates on the milling machine. A jig was used to hold the corners in position while I drilled a 7/32 hole. The plates where pinned back together and then the holes where reamed to 1/4 inch. I later enlarged the back plate holes slightly as I tapped them for 5/16-24.

The pillars where done on the lathe and took a new tool to complete. The pillars are made of 1/2 inch brass round. One end is turned to 1/4 inch to fit the front plate holes. The other end is turned to 5/16 and threaded 5/16-24 to fit the back plate. The 1/4 inch ends are to be tapped to accept a screw. The screws need to be made as well. The plans call-out threads in English BA sizes so I have been converting to my closest Imperial or Metric size on hand.
In order to thread accurately with a die I built a tail-stock die holder. Yes this was an excuse to make another tool, but it gave me a chance to mill a hex hole to fit the dies, knurl an edge for better grip and make a huge amount of aluminum swarf as I turned some stock to size.
The tool is a modification of a design by Ralph Patterson. Look here for this and many other mini-lathe mods. http://www.toolsandmods.com/ralph-patterson.html
I use a Jacob chuck in the lathe tail-stock to hold the 1/2 inch drill rod. The die holder is reamed to 1/2 inch on center so that it floats on the drill rod. A piece of 3/8 drill rod is threaded into the die holder to stop it from rotating while you thread.
The die is held in the holder via a set screw. The setup holds the die co-centric with whatever is in the lathe chuck. The threading work is done with the lathe OFF and rotated by hand. I start threading with the die's "start" side presented to the stock. Then I turn the die around in the holder to get threads closer to the shoulder on the pillar.
This has become a fun project and an exercise in working to precision. The book is 64 pages long and I have barely made it to page 15. At this rate I am looking at a completion some time in the fall of 2009.