Union Pacific Big Boy in 3/4 Inch Scale

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RET
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by RET » Sun Jun 05, 2016 10:18 am

Hi,

Here is the initial small collection of pieces. The tabbed rings will be silver soldered onto the ends of the copper tube and the springs with spacers go inside the tube. In full size, to get the force needed, there are smaller springs inside the bigger ones with the coils wound the other way so they wont "nest" together. Lots more bits & pieces to make and assemble.

Richard Trounce.
Attachments
Initial parts.jpg
Just the first few bits.

RET
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by RET » Wed Jun 15, 2016 8:42 pm

Hi,

Here are the next two progress pictures. The first picture shows the pieces that go together to make the center assembly with the springs inside. As you can see, the tabbed rings mentioned in the previous post have been silver soldered onto the ends of the copper spring tube and the holes in them tapped for #2-56 thread. The hex bolts I already had. The support pieces that hold the spring tube in place on the smokebox saddle still have to be made and attached to the tube. The four springs and spring spacers all go in the center tube to make a soft spring with fairly constant restoring force.

The second picture shows all the parts put together. The end sleeves are drilled with a 5/16" center drill one inch deep so that the centering bars will be guided as they move away from center when the locomotive goes into a curve. The centering bar on the opposite side pushes the end sleeve into the center tube against the internal spring pressure which supplies the restoring force.

When properly assembled, the bars just contact the bottom of the center drill holes when the locomotive is on straight track. A simple concept; I just have to make the pieces and modify the assembly slightly so it will fit into the space available.

Progress is slow, but I'm getting there.

Richard Trounce.
Attachments
Centering device parts (reduced).jpg
bits & pieces required for center section
Centering device partial ass'y (reduced).jpg
This is what the initial assembly looks like

RET
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by RET » Thu Jul 21, 2016 11:22 am

Hi,

As you can see, I now have the center section of the centering device finished, painted and mounted on the smokebox saddle. Its a bit slow making and silver soldering all the bits together and finding the space to fit everything in place.

I still have to make the outside pieces that push on the inside of the end tubes. As you can see in the pictures, I put a teflon "shoe" on the bottom of the saddle to make it slide easier.

One step at a time, but we're slowly getting there.

Richard Trounce.
Attachments
Center section in place.jpg
As you can see, it has to fit in the middle of all the other stuff.
End view.jpg
This is the end view. You can see the teflon "shoe" in this picture.
Center section in place.jpg
A general view.
Showing one end in position.jpg
Not quite in focus, but it still shows how it fits in place

RET
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by RET » Thu Oct 20, 2016 7:31 pm

Hi,

A little more progress. As part of the installation, I had to move the brake line that supplies the front cylinder on the front engine. I did this by cutting a groove in the plate for the 3/16" line and bending the copper tubing to fit the groove.

Its amazing how fast the copper work hardens after you anneal it. I had to anneal the tubing 4 times to get the bends I needed and I only had to reshape some of it.

Originally, the line ran on top of the plate near the end but it would have obstructed the travel of the support shoe of the centering device as well as interfering with the mounting of the end centering bar support on the end of the plate. I'll post some more pictures when I get the end bits made and installed.

The pictures should give you a better idea.

Richard Trounce.
Front view of brake line routing.JPG
As you can see, now the tube runs in the groove in the plate.
Side view of centering device in position.JPG
This is a better view of the assembly in place.
Rear view of brake line & centering device.JPG
Rear view of the same assembly.

RET
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by RET » Sat Dec 30, 2017 8:28 pm

Hi,

I'm like Don, I tend to work on different projects or even different parts of the same project. In the last several months, I started to put the Big Boy boiler together permanently. I installed the throttle/superheater assembly permanently and the 3 longitudinal stays. I also installed the hollow stay for the blower. As it turned out, I made a mistake at that point by using NeverSeez on the threads of the stays (because I thought it might be nice to be able to take things apart some day). I used clear silicone seal to seal the stays.

When I applied air pressure, I found there were multiple leaks in the boiler, many of them quite serious, including a number inside the combustion chamber. I used the stethoscope part of an automotive stethoscope to try and locate the leaks. I have a small 3/4 hp. single stage air compressor and when that was connected to the boiler, I couldn't get the pressure over 25 psi. because of the leaks. After a little thought, I decided to use Loctite 290 (the wicking grade) to plug the leaks. I found that it works VERY well. It wicks into the cracks and seals them and once sealed, those particular leaks never reoccur. According to the internet, it is activated by contact with metal (it won't work on aluminum) and I've found by experience that within a few hours the Loctite sets up glass hard even if it is out in the open.

Gradually, I was able to get the air pressure up to 30 psi. and as the pressure got higher over the days I found that it became easier and easier to hear and locate the source of the leaks. There were several serious ones inside the combustion chamber. I got those sealed in stages by laying the boiler on one side and squirting the locktite into the chamber, then rocking the boiler back and forth a bit to spread the loctite. Obviously, application of the loctite is not done under pressure. Capilliary action works surprisingly well. I did one side of the combustion chamber, then the opposite side and finally the middle. Since I could hardly even see where the leaks were, the fact that this worked was a real bonus.

As time went on, I finally got to the stage in Loctiting the leaks where the little compressor would slowly pump up to 78 psi. and then shut itself off.

I have never heard of anyone using Loctite before to seal leaks in a boiler, but I must admit that it seems to work very well. When I checked with Dave Powell, he seemed to think there was nothing wrong with the idea. End of the first installment (there's lots more).

Richard Trounce.

RET
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by RET » Sat Dec 30, 2017 8:44 pm

Hi,

As I progressed, I found it harder to determine where the leaks were. Here are a few pictures to give you an idea of the different stages I went through.
air leak bubbles at back of fireboxa.jpg
air leak bubbles at front of fireboxa.jpg
small leak in firebox staysa.jpg
The first two pictures show the compressed air bubbles when I poured water in the front or back of the firebox, while the third shows the foaming from minor leaks in a couple of the firebox stays. As you might expect, as the pressure increased, more and more leaks popped up.

Richard Trounce.

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Fender
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by Fender » Sat Dec 30, 2017 8:49 pm

Presumably the joints are sufficiently sound to withstand a hydro test. Another sealing method would be to put a solution of sodium silicate and water in the boiler, apply air pressure to force the solution into the joints, then drain out the solution. Carbon dioxide in the air causes it to harden. This is how block/radiator sealer works. The silicate is non-organic and won’t soften with higher temperatures.
Dan Watson

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Bill Shields
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by Bill Shields » Sun Dec 31, 2017 9:20 am

I worked with a British fellow 35+ years ago who did his entire boiler stay sealing with Loctite.

Stays were threaded into the inner and outer wrapper with high temp Loctite as the primary sealant and it worked a charm.

I have no idea how well it held up since I lost my connection with him 4 years later.

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JohnHudak
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by JohnHudak » Sun Dec 31, 2017 9:34 am

Wow, why didn't I hear about using locktite to seal small leaks before this?
It would have saved me many hours and headaches...!

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NP317
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by NP317 » Sun Dec 31, 2017 10:42 am

How will the Loctite survive the high temperatures of the fire and steam?
Inquiring minds are curious...
~RN

RET
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by RET » Sun Dec 31, 2017 10:56 am

Hi,

As I got closer to the 78 psi. mark, I kept on with the cycle of using the stethoscope to find the leaks then marking them with a felt marker and using the Loctite to seal them. Its a slow process because you have to wait hours to be sure the Loctite has set before going to the next cycle. The only good thing is that as the pressure goes up, the air leak gets louder. Eventually, and it seems like forever, you run out of leaks at that pressure.

I also started getting leaks at the safety valves, so I started making special bronze recessed washers to hold "O" rings that seal the safety valve where they screw into the boiler. The safety valves that Gerhardt chose are very well made, are settable and "pop" very nicely when they go off. As you can see in the pressure test pictures (to come), I had to make bronze plugs that thread into the boiler and use "O" rings to make the seal for the hydraulic pressure test phase. All of this takes time.

Before I started, I looked at the way this boiler was constructed and I felt there was very little if any chance of a catastrophic failure. If it failed at all, I expected that one of the firebox stays might let go because of a poor silver solder joint, but even that seemed unlikely because the stays are at 1" spacing, so the force on each stay is only the applied boiler pressure in psi. and even a poor silver solder joint should be able to handle that.

At this point, I changed to water for the next stage in the pressure testing (just to be on the safe side).
Hydraulic pressure test setup (front)a.jpg
This shows the primitive, but practical setup I used in the laundry tubs. Using this setup, I was able to raise the pressure to about 130 psi. when the hollow stay started to leak severely through the threads.

Richard Trounce.

RET
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by RET » Sun Dec 31, 2017 11:22 am

Hi,

To answer your question NP317, the operating temperature at 90 psi. is still within the Loctite operating parameters, but the only way to find out for sure is to try it. According to Bill Shields, his friend used it successfully. My experience with the Boston & Albany seems to be that small leaks will seal themselves over time. To help with this process, I added a tablespoon of ginger to the water (Dave Powell's suggestion).

At this point I called on Don for help for two reasons. First, I needed a witness for what I was doing, and second, I needed a second pair of hands because to fix the leak I couldn't be at both ends of the boiler at the same time. The hollow stay is copper with an ME (model engineer) thread and as I mentioned above, I'd put NeverSeez on the threads when I put it together. Of course, at high pressure, the water tunnels through the NeverSeez and won't seal. We had to take the fittings off both ends of the stay and clean the threads completely. Since when in place, the stay is the same length as the inside of the boiler (just inside the front tube plate and the backhead), working on it is a real ball because it is very easy to lose it inside the boiler.
hollow stay (back)a.jpg
hollow stay (closeup)a.jpg
To prevent this, we used a long rod inside the stay so we could guide the end of the tube back through the holes when we needed to. Eventually we were able to clean everything off and on reassembly I used the clear silicone seal on both the threads and the fittings to make the seal. After allowing a full day to make sure the silicone was fully cured, we went back at it and found our repair was successful.

Richard Trounce.

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