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1,477 Posts
Discussion Starter · #23 ·
I finished most of the rear engine today and made most of the front engine parts so it should go together fairly quickly.
I want to show the construction of the expansion link which is the heart of the Walschaerts valve gear.

In the photo below from left to right are the link, backer link, backer pivot bar and ball bearing set.

The pivot bar is 1/8" stainless turned down to 1/16" at the shoulder. It is a snug fit which keeps it perpendicular to the link back
It is then silver soldered to the link. You can see the snippet of solder and the flux ready for the heat

Since the backer link is low carbon steel, I only pickle it in citric acid for 20 minutes as not to corrode the steel. It comes out slightly pink.

The wire wheel cleans things up

2-56 socket head screws hold the two pieces together and .070" spacers are used to provide a slot for the 1/16" wide radius rod

Another tricky part of the Walschaerts gear is the combination lever which advances the timing at top dead center by moving the valve to the just open position.
The holes are drilled in an exact proportion of two times the lap plus the lead to the cylinder stroke. This ratio is usually around 10 to 1.
To stay in scale with the Samson, I need to have a very short combination lever which makes the two upper holes less that .100" apart. That means that the valve rod and radius rod need to be ground and filed to clear each other.
Here is the valve rod

And the radius rod attached.

So here is a side view of the chassis

And a top perspective


251 Posts
Wow Bill, making the expansion link from scratch is a marvel but the close fit on the expansion link pivots is a work of patience and precision, well done this job is coming along nicely. I can't wait to see it finished and running.

30 Posts
Thank you very much for the detailed sharing, it will come in very handy in a couple of years when i will building my own.
I read all of your posts with a lot of interested.

With best regards Igor

30 Posts
Thank you very much for you detailed posting and pictures.
But your wheels are in a "smaller corner" then mine?
I think that i do something terrible wrong( i like prototypical but it seems not to work!!!(Bigger loco's btw) it is not working
My wheels have a to large angle(3 degrees off), and yours "seems to be 90 degrees"
I hope you are willing to share for me a drawing with the proper cutting angles and what ever comes with it.
I think for the bigger locomotives "on scale" it must be almost an exact 90 degree angle and what i was doing so far is wrong...
This screenshot is prototypical but it will not work and thus wrong for scaling down...


yes i 3d printed them for try and error before i am going to cast them in aluminium.
But what about your thoughts?
It seems we have two different wheels "running surface???"
What would be your advice or recommendation or thoughts, because what i did, it does not work( yes i am losing the prototypical idea)

Thanks in advance with best regards Igor

1,477 Posts
Discussion Starter · #27 ·
three degrees is correct
This is what I use for wheel sizes and profiles. I think it is from G1MRA

968 Posts
Your angle as measured on the screen is close to 12degrees. So something is wrong with your 3D model. We have been using 3 degrees for many years and they work well. Also you should have a radius between the flange and the running surface of the wheel (R in Bill's drawing).

1,477 Posts
Discussion Starter · #29 ·
I was able to get both engines tested on air and they both run great. In the photo below, you can see the two bolted together with the strap which allows them to negotiate curves. The front deck is now complete and painted with the working headlight, hand rails and the sand box between the two decks.

You can see the strap connecting the two chassis in the next photo. This has to be closely coordinated with the boiler mountings to prevent binding on turns. I first make it as short as possible without interference between the two chassis on y 7' radius track and then measure the distance between boiler mounts which I will use on boiler mounts. I also use a cushioned pivot on the strap which will give a little when going over dips in then track.
The piping is what I use on all on my compound locos. It is a bypass valve that lets only a small amount of superheated steam into the LP cylinder at startup which prevents LP cylinder lockup. As the amount of steam which bypasses the HP cylinder id so small, once the loco is underway, it is working on full compound

The next photo shows the completed valve gear with the reverse arms and cross bar. The wires are for the headlight and haven't been routed yet.

Here is the boiler shell which was cut out from a piece of type L 2" copper pipe.

The end plate and tubes were drawn out on CAD. I used to just do it with a compass and straight edge but this is a little more accurate. I then cut it out and glue it to the plate cutout, The cutout is then clamped to the piece that will be the throat sheet and holes are drilled through both pieced so that the tubes will be perfectly aligned.

A step drill is used to drill out the tube holes

The throat sheet is then cut out to fit in the boiler shell. Both pieces are now done,

1,477 Posts
Discussion Starter · #30 ·
As you can see from the last posting, the boiler is very long and narrow. Here I am setting the tubes up prior to soldering. As they are bunched together tightly, I make rings from 1/32" silver solder which will surround each tube.


The solder rings melt and fill the gap between the times and the holes in the throat sheet

The other side has full access so the standard brazing technique works here

The assembly is cleaned up in citric acid and two pegs made from copper ground wire are set in place for support of the crown sheet during the soldering process

Here a piece of copper is set in place to show how the pegs will support the crown sheet
The irregular shape on the top is for alignment on the sides and the center raised portion is to keep the steam pipe that goer from the dome to the throttle from dropping down. The valleys are for water flow

Three pegs are set in the front to support thr tube sheet while it is soldered

The saw cut in the boiler is 3/32" wide and the throat sheet is the same thickness so it makes for a nice soldering joint

The throat sheet and front tube sheet are soldered in the same setting

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