The next step on the bourdon tube is to flatten it. I did this in the bench vise. As you flatten it, it eventually gets wide enough to slip a 0.020” spacer into. This spacer keeps you from closing the tube completely.
Then I filed a semicircular notch in one end of the bourdon tube. This will be the end that connects to the pressure input.
For the other end, I needed to make a little pin connection. I did this by taking a thin strip of the 0.005” phosphor bronze sheet (the smaller one I cut yesterday), wrapping it around a 0.020” diameter mandrel (24 gauge brass wire), and clamping that in the vise to give me a nice tube to accept the pin. I did the same procedure to solder it together, then I removed the head and tail of the solder-holding screw.
To finish up the pin connection, I made a 0.020” slit in the middle of this piece. Kozo specifies 0.016” width for this slit, but the link that will connect in here is specified to be 0.013” thick. I’m using 0.016” thick material (1/64”) which was easier to source. So I made my slit a little wider to accommodate. I used a very slow speed on the slitting saw, which worked well. After I completed this step I noticed that Kozo shows to use some sacrificial packing pieces on either side of this part while cutting the slit. That would have been a good idea! I didn’t do that, but It came out OK anyway.
Here’s the end piece with all operations complete.
Next, I cut the end piece down to a very short length (about 5/32” long), slid that inside the other end of the bourdon tube, and used a soldering iron and soft solder to solder it in place. It’s not the greatest solder job, but it seems to be airtight, as best as I could tell. Kozo has you use soft solder here so that you don’t anneal the part. You want the completed bourdon tube to be work-hardened so that it has some springiness to it and will retain its shape.
Before shaping the bourdon tube further, Kozo has you create several skinny shims. I used the same 0.005” material I’m using for the bourdon tube. I cut four of them, which when stacked, should fit in the 0.020” thickness of the tube.
These were then threaded down the end of the bourdon tube. As you can see, I couldn’t get the last one all the way in. But I got it most of the way there. It was not easy getting them in this far and I didn’t want to cram too much harder because I was worried about getting them back out after forming.
And here’s the forming step. Of course, the shims keep the tube from collapsing during this fairly brutal forming step.
Kozo has you form it around a 5/8” mandrel. That worked for the initial shaping, but I couldn’t get the curve tight enough, so I switched to using a 1/2" diameter mandrel.
Now for the real test – could I pull the shims out without messing up the nicely formed bourdon tube? Yes! I could! It wasn’t even that hard. Of course, I used pliers to pull the shims out, but they actually slid out much easier than they went in. I was pleased!
Next, I moved on to a piece Kozo calls the bearing. This will support one end of the needle pivot. I marked the shape on a piece of 1/64” brass sheet (again, Kozo specifies 0.013” thickness, but I’m using 0.016”). The spacing of the holes is the most important thing here, so I did that first. The tiny hole is a #75 hole. That’s 0.021”! I can safely say that this is the smallest hole I’ve ever drilled. I cranked my mill up to the highest RPM I could get (about 2200RPM) and it worked. Of course, I only had 0.016” of brass to drill through which probably helped
After drilling the two holes I cut off that piece and used a combination of nibblers and files to shape the piece. It isn’t perfectly shaped, but the important part – the distance between the holes - is precise. So I’m happy with how it came out.
That’s the state of progress today. Thanks for looking in,
Kim
