Pennsylvania A3 Switcher (Kozo)

[Kim]

Thanks Chris and Jeff! 
Kim

[Kim]

The outside of the case was also made from 1” brass rod.  Very similar process to the inside of the case, however, this part had a smaller diameter for the last bit of the bore. It’s hard to pick out in this picture, but it’s there.  I forgot to leave that at first and turned the whole length to the larger diameter, but that would have meant there was no bezel to hold the glass in place!  So I bored out a little more at the bottom with the smaller diameter then shaved off the excess length on the front end.  It worked out, just cost me an extra 1/8” of material 


After parting it off, I flipped it around in a 63/64” collet, and boy, am I glad I went ahead and got all the 1/64” collet sizes!  I may not need them a lot, but when an application like this arises, they sure come in handy!  And I had no worries of distorting the thin walls of the case because the collet held it nice and evenly all around.

Anyway, I was able to make a chamfer on the inside of the bezel in this way, which looks very nice. It would have been difficult to do that by hand and difficult to hold in a 3 or 4-jaw chuck without deforming the part.


Holding the case in a square collet block I milled out a 7/32” wide section for the neck of the gauge stem.  (That’s a 3/16” end mill, BTW.)


Then to finish up the outside casing, I drilled and countersunk a hole for a 0-80 screw that will hold the case parts together.


Then I made a similar cut out for the stem in the inner case.  I had to come up with a different way to hold the part since the cut had to go all the way to the base of the part.  It wouldn't leave anything for the collet to hold onto.  So this is what I did, which worked fine.


Here are all the parts of the case, minus the glass. That’ll have to wait for another day.


Here’s pic of the test assembly of the gauge.  You can see that I finally trimmed the gauge indicator needle to a length so it will fit inside the case.


The glass and the dial face are the last parts to make for the pressure gauge.

Kim

[crueby]

More wow-ness.  I'll  take a dozen!

[RReid]

Really great work, Kim. It's fun watching the process for something a little different. I don't know if I'll ever want to make a pressure gauge, but now I know what's involved!

[cnr6400]

 

[Kim]

Thanks, Chris, Ron, and Jeff! 

Appreciate the comments and encouragment!

Kim

[fumopuc]

WOW
Kim that is an extraordinary little project.
I would never have had the idea to make such a gauge by myself.
The description in Kozo´s book seems to very extensive.

[Roger B]

Excellent watchmakers work     

When can we place orders? 

[gunna]

Extraordinary work Kim, but....
I might be wrong but if the bourdon tube expands, ie opens out, under pressure, won't that move the pointer to the left? Or have I missed something?

Ian.

[Kim]

Thank you Achim, Roger, and Ian! 

I might be wrong but if the bourdon tube expands, ie opens out, under pressure, won't that move the pointer to the left? Or have I missed something?

Interesting question, Ian!

The end of the bourdon tube moves upward and to the right, under pressure.  And as it moves up and to the right, it pulls the link which is connected above the pivot point of the needle.  And the needle moves to the right.

Here you can see that the link connection on the needle is above the pivot point:


And here's a close-up of the link connecting the end of the bourdon tube to the needle.


When pressure is added inside the bourdon tube, it increases the diameter of its curve.  Since the left end is solidly attached to the stem, it doesn't move. But that increase in diameter makes the other end (the end on the right of the stem) move outward and upward just a little bit.  The entire movement isn't much over 1/8".  But it's enough to move the needle quite a bit.  I don't know what the full scale is yet as I haven't tried it with the gauge fully assembled. That may come later today.  We'll see 

Here's a video of the bourdon tube expanding under pressure. Hopefully, you can see what I mean about moving up and to the right a little?
<a href="https://www.youtube.com/watch?v=4zMHMeTXg2M" target="_blank">http://www.youtube.com/watch?v=4zMHMeTXg2M</a>

This has been a very rewarding little project, that's for sure!
Kim

[Kim]

Today I cut and ground the glass for the face of the dial.  It took me a couple of tries but that’s par for the course for me when working with glass.  I used the same process as I did for the headlight glass (Look here for more details).

My ‘finished’ product is on the left.  It’s pretty rough around the edges, but the bezel hides that nicely.


Then, I cut out a temporary dial face from a piece of paper and put the pressure gauge together, leaving out the glass.  That way I could mark on the paper where the various graduations should be.

I started by marking the zero point, then added the center 25 psi weight and marked that.  Then I added the second 25 psi weight and marked that:


I proceeded to mark each 25 lb/in^2 increment.  Here’s the 100 lb/in^2 mark.


And finally, the 150 lb/in^2 mark.


It seems quite repeatable.  I stacked the weights on and off several times and the gauge indicated the same each time.  It does seem to take the system a few seconds to move back down in pressure. The oil oil system seemed to take a few seconds to equalize to a lower pressure.  But does get there.

Here’s a short video showing the settings up to the full 150 lb/in^2 that this gauge is calibrated for.  I’m highly pleased!
<a href="https://www.youtube.com/watch?v=lXu7U0o0xp4" target="_blank">http://www.youtube.com/watch?v=lXu7U0o0xp4</a>

Now I just have to translate that temporary dial face to a nicely printed one and I should be about done!

Kim

[cnr6400]

 

[crueby]

Awesome!!

[Admiral_dk]

Another major Milestone reached 

Per       

[Kim]

Thanks Jeff, Chris, and Per! 

I'm getting very close!
Kim