[kvom]

The locomotive needs a "petticoat" in the smokebox. This part is an extension of the smokestack and held direct the exhaust up the stack. Starting with some round rod, machine the end to match the inside diameter of the smokebox.

Attachment 196320

Then lathe work to bore plus taper the lower edge.

Attachment 196322

Not seen are two tapped holes in the upper side for which screws attach both the pettitcoat and the stack base to the smokebox.

The saddle is the piece that supports the smokebox, and with it the front of the boiler. On many locomotives this is a casting to which the cylinders mount, but here it's a separate assembly. The first task is to fabricate the top, which is the piece that attaches to the smokebox directly.

Attachment 196324

Attachment 196326

Attachment 196328

Attachment 196330

Next. machine two pieces that form the front and back of the saddle.

Attachment 196332

Attachment 196334

Test fit with the smokebox and boiler:

Attachment 196336

To fabricate the rounded sides, I started with a length of DOM tube.

Attachment 196338

Attachment 196340

Attachment 196342

The assembly was then welded.

[MRM RCModels]

WOW! This is a lot of work. Looking good.

[SCzEngrgGroup]

My mind boggles at the scale of this project! That is one BIG honkin' loco!

Regards,
Ray L.

[LeeWay]

Is that T shaped iron it is running on? I don't think I have ever seen that before if it is. It kinda looks like it in the pictures. Very nice stuff you have going on here.

[kvom]

My mind boggles at the scale of this project! That is one BIG honkin' loco!

Regards,
Ray L.

For 7.5" gauge locos, this is about the smallest possible. Only 4 wheels, 6" boiler, 250 lbs dry weight. Most of those at my club are much larger. One loco weighs 1800 lbs. The subtitle of Kozo's book is "The first project for the beginner."

[kvom]

Is that T shaped iron it is running on? I don't think I have ever seen that before if it is. It kinda looks like it in the pictures. Very nice stuff you have going on here.

That is a temporary stand I cobbled together from 2x4s and the t-shaped stock. I used it to transport the chassis to the track a couple of times during construction to check that it ran smoothly, pulling it behind the club loco. Now I have a transport board (4x8' plywood sheet with 1/2" square HRS rails screwed on). I also built a rolling stand where the loco and tender live when in the shop.

[MRM RCModels]

For 7.5" gauge locos, this is about the smallest possible. Only 4 wheels, 6" boiler, 250 lbs dry weight. Most of those at my club are much larger. One loco weighs 1800 lbs. The subtitle of Kozo's book is "The first project for the beginner."

250 lbs! You're not moving that around too much?

Great work. Got to make one myself.

[kvom]

A locomotive's pulling capacity, or "tractive effort" depends on how much weight is on the drivers. The heavier the weight, the more it can pull without spinning the drivers on the track. Therefore I wanted to use very little aluminum in the construction. Some builders have used lead sheet as lagging on the boiler to increase the weight.

To transport the loco and tender my rolling stand height is just above the level of the tailgate on my pickup, and I have a steel " bridge" to mate the stand to the carry board in the bed of the truck. Once on the truck the front is coupled to a bar at the far end using the coupler pocket, and then fastened down with ratchet straps. At the club tracl we have a hydraulic rolling lift to move the train from the truck to the track and back again.

[kvom]

To make the handles for the throttle and reversing levers, I used the NM200 as a lathe. Material is 3/8" diameter brass rod.

Attachment 196616

Here's a setup for machining the sides of the cab. The fixture plate is a piece of Corian from a sample for a kitchen counter. It's flat enough for sheet metal work and cuts with a jigsaw. CNC was nice for drilling all of those holes, which will be filled with drive screws to simulate rivets.

Attachment 196618

Similar for the front of the cab.

Attachment 196620

Mockup:

Attachment 196622

After almost exactly one year of building, I got to the milestone of "chassis on air. For the first run I had no gaskets, so lots of air leaks:

Kozo A3 1.5 scale locomotive - first chassis run on air - YouTube

The second run had the valve timing a bit better

Kozo A3 in 1.5" scale - second run on air - YouTube

[CROSSHATCH]

So cool

[kvom]

The control mechanism for the throttle starts with the "steam dome". This is a sealed container above the boiler and open to it. Steam rises into the dome, enters the throttle valve, and passes back through a closed dry pipe to the smokebox. The throttle itself is a globe valve controlled from the cabin by a reach rod. The reach rod is enclosed in a throttle tube, also pressurised that connects the steam dome to the turret. The turret is the area where steam is directed by valves to all of the auxiliary functions.

The steam dome body I fabricated from a 3" diameter steel rod. After truing in the lathe, I used the NM200 to bore out the center.

Attachment 196840

Attachment 196842

Attachment 196844

Afterwards, holes were drilled and tapped for 8 10-32 screws used to attach the lid. Then a hole was milled in the side to accommodate the throttle tube and reach rod. To attach the throttle tube, which must be removable, I made a flange from 316 stainless that would be welded to the steam dome.

Attachment 196846

Attachment 196848

Here are the parts before welding. The throttle tube is copper and the flanges on either end are brass, silver-soldered.

Attachment 196850

The boiler with steam dome welded:

Attachment 196854

[kvom]

Getting towards the last CNC parts made for the loco. The next is the blower. This is needed to provide draft when the loco is not moving. In order to keep the fire going and to suck the smoke through the flues there needs to be air flow up the stack. When steaming up, we insert an exhaust fan on top of the stack. Once the loc is in motion, the exhausted steam is directed up the stack, but when stopped there is no exhaust. Therefore some steam is fed into the smokebox and directed up the stack; this steam is controlled by a valve in the cab. Here's my design for the blower:

Attachment 196950

Attachment 196952

The blower sits over the exhaust nozzle and the high pressure steam blows vertically through the small holes. Here's the test fit:

Attachment 196954

And a view with the smokebox in place, showing the exhaust nozzle, blower, and the petticoat above.

Attachment 196956

[kvom]

Here's a photo of the parts of the throttle bar laid out. The CNC parts were the piece with the gear teeth and the hand lever.

Attachment 197110

and the test assembly:

Attachment 197112

Installed:

Attachment 197114

The most recent CNC parts are brackets to attach the steam whistle to the running board. The first op:

Attachment 197116

Attachment 197118

Then after separation with a slitting saw:

Attachment 197120

The whistle mounted and plumbed to the turret:

Attachment 197122

In the above photo, the whistle valve is mounted upside down, a fact I discovered the first time out when steam pressure opened the valve.

[skray775]

Awesome work!

To date I have only made a tunnel portal for my model railroad in HO scale but what you have done is
fantastic!

[kvom]

Looking back through the pictures I took during the build, I noticed these I hadn't mentioned. The pieces form the latch lever that holds and releases the ash pan. The ash pan is located beneath the firebox and catches the burnt coal and ash that falls through the grate.

Attachment 197512

[kvom]

Here's the last CNC part made for the loco, the steam dome base. And it's the first 3D CNC machining I've attempted. The 3D surface is cylindrical to mate to the boiler jacket. First job was to size the aluminum blank. For reducing the diameter to 5.25", I turned it between centers on my manual lathe, using a 1/4" screw as a dog:

Attachment 206196

Now for the NM200 to mill soft aluminum jaws to hold it:

Attachment 206198

Attachment 206200

Next, mill a through pocket to allow the base to fit over the dome itself:

Attachment 206202

Then the 3D roughing pass using a 5/8" 2-flute HSS endmill

Attachment 206204

And the finish pass with a 1/2" 2-flut HSS ball mill

Attachment 206206

Off of the mill for a test fit. Seems it will need some "fettling" to get to it's final form. I need to face about 1/2" off the flat side for clearance.

Attachment 206208

[kvom]

Test fit to the boiler.