Pennsylvania A3 Switcher (Kozo)

[Kim]

Thanks Chris, Dave, and Jeff! 

Kim

[Michael S.]

Very interesting progress! I congratulate on this result.

Michael   

[Roger B]

Looking good     

[Kim]

Thank you, Michael, and Roger! 

I'm finding this mini-project very rewarding!  It's quite different than anything I've done, and it seems like it's working out better than I'd feared!

Kim

[Kim]

I made the needle assembly from 0.020” brass wire and some 0.016” brass sheet.

The little brass sheet pieces are super small.  One is basically a washer with 0.046” diameter.   The other is slightly larger at 0.078” x 0.125”.  My plan was to drill the holes then do my best to ‘shape’ them.  Here I am drilling the holes in a little 1/64” thick piece of brass.  The holes are #75 (0.020” dia).


Drilling went well. As did cutting them into individual pieces, which I did with some little accurate side cutters (they are sold as sprue cutters for plastic models).


However, I could hardly hold on to those little pieces.  Even using my magnifying visor and tweezers, I’d be holding it in the tweezers and ‘bing’  off it would fly in some unknown direction.  Needless to say, I had a pretty poor track record of finding them once they went flying, though I did locate an escapee a few times. I ended up remaking the larger of the parts 3 times before I got smart and threaded some wire through the holes before I started working on it.  That helped to keep the parts under control immensely!


With those two dinky pieces finally made, I slipped them on the wire that would become the needle and soldered them into place.  The spacing of these parts is fairly critical.  I worked hard to get them spaced close to right.  The length on either side of the parts can be adjusted easily. But the location of them, once soldered, would be very difficult to adjust.  As before, these parts were soft soldered together using a soldering iron.


Then I carefully clipped and bent the wire. The wires are still too long in this photo, but I wanted to wait and trim them till I was sure what length they really needed to be.


I had to spend some time filing down my large solder blobs on the needle assembly in order to get things to fit in place properly.  However, once I accomplished that, I was able to assemble the needle to the stem/bourdon tube assembly with the bearing.


The next part will be the connecting link.  It will go between the pin at the end of the bourdon tube and connect to that little extra pin on the needle assembly, such that when the bourdon tube moves, the needle will move along with it.

Kim

[crueby]

Wow, thats some fine work, in both meanings of Fine!   

[cnr6400]

  Top notch Kim!

[Admiral_dk]

Impressive and Delicate - very interesting fabrication 

Per     

[bobh]

Electronic guys use something called desoldering braid to clean up joints exactly like that. Flux up a length, place it over the excess solder and place your soldering iron on the top. The excess solider wicks up the braid like magic. Good stuff to have around and cheap. Bob
https://www.mcmaster.com/products/desoldering-wicks/

[RReid]

Machinist, fabricator, boiler maker, steam fitter, instrument maker - you're pretty employable Kim!

[Kim]

Electronic guys use something called desoldering braid to clean up joints exactly like that. Flux up a length, place it over the excess solder and place your soldering iron on the top. The excess solider wicks up the braid like magic. Good stuff to have around and cheap. Bob
https://www.mcmaster.com/products/desoldering-wicks/

Good suggestion, Bob!  I actually do have some of that.  My concern was that heating up the part and even touching it could cause the little pieces to move, and I liked where they were.    So, going with the cold, abrasive round to remove excess solder seemed like the safest route to me at the time.

Thanks!
Kim

[Kim]

Thanks, everyone! 
Making this pressure gauge has been far more fun and rewarding than I'd imagined!  I'm so glad I chose to do it.

Kim

[Kim]

To make the link, you are supposed to set the needle to 30^o to the left of center then measure the distance between the needle pin and the pin on the end of the bourdon tube.  That’s not easy to do!  I gave it a good shot and came up with 0.180”...  and 0.220”... and 0.220”... and a few things in between.  So I just went with the length Kozo specified which was 0.200” between centers.

I made one of those and installed it to see where the resting position of the needle was (i.e. 0 psi).  The pencil marks behind the needle are marked at 30[usp]o[/sup] off of center, and the needle is just a little too far to the left.  Which meant I needed to make the link a little shorter.  So, I made one with 0.180” between centers.  You can see that one laying off to the left there.

Let me apologize for the lack of focus in several of the following pictures.  The camera was apparently having a hard time focusing in these shots and I couldn't tell that till I downloaded them to my PC and saw how poor the focus was.  I'm very sorry about that.

After swapping the 0.180” link into the gauge, the needle was then too far to the right.


So, I made one in the middle, at 0.190” between centers.  Here’s the three links.  The top one is 0.200”, the middle one 0.190”, and the bottom one is 0.180”.


With the 0.190” link installed, the needle looked to be in about the ideal position. Yay!  Success!  At some point along the way, I realized I probably could have just twisted the needle a few degrees and avoided making the additional links.  But hey, what I did worked, so I’m sticking with it.


The last part of installing the link was to make a permanent pin for the link/bourdon tube junction.  In the previous setups I’d just used a longish piece of wire.  Now I cut that wire to length and bent the top of it over like Kozo shows in his drawings.  This looked pretty good.


Now all I’ve got left to make is the case!  Oh yeah, and the dial face. Not really looking forward to that one.  But the case is next.

Starting with some 1” brass rod  I bored out the end of the rod to the size for the inside of the casing.


Then I turned the outside down to the appropriate diameter for the inner casing.


I’d made this deeper than it needed to be so that I could first slice off the spacer that separates the glass from the dial face.


Then I trimmed what was left to the correct depth for the case, drilled a short #0 hole in the bottom for the hold-down screw, and parted it off the parent stock.


And here’s our state of play for the pressure gauge.  I haven’t trimmed the needle indicator to length yet.  I’ll need to do that soon.  It clearly won’t fit inside the case when it’s this long!


Next up will be the outer casing and the glass face.

Thanks for looking in!
Kim

[cnr6400]

 

[crueby]

Impressive!