A Baldwin RT-624 In HO – Part 1

At the end of 2020 I released my HO model of the Baldwin DT6-6-2000, you can find the post here. But that wasn’t the end of the journey because just as Baldwin updated the DT6-6-2000 to the RT-624, so am I.

The Baldwin RT-624 is the natural development of the Baldwin DT6-6-2000.  Built between 1951 and 1954 the locomotive is classed as a transfer unit, designed for moving strings of freight cars between local yards in big cities.  It was a heavy locomotive, giving it great traction, and it had, for its time, a lot of horsepower.  Baldwin had started changing their naming convention for locomotives by this stage; this locomotive was sometimes called a DT6-6-2400 but Baldwin’s correct name was RT-624.  RT stands for ‘Road Transfer’, 624 stands for 6 wheels per truck and 2400 horsepower.  To achieve the extra 400 horsepower upgrade from the predecessor’s 2000 horsepower, Baldwin replaced the pair of 606SC supercharged diesel engines with their newer 606A supercharged diesel engines.  These each produced 1200 horsepower and were more reliable.

The RT-624 is very similar to the DT6-6-2000 and at first glance, you could be mistaken in thinking they were the same locomotive. Apart from things which you can’t see, such as the larger engine size in the RT-624, there are many differences. Below is my original model in N Scale of the DT6-6-2000.

Next we have the RT-624, again in N Scale.

The first thing that stands out to me is the large section under the cab that covers the fuel tank; on the RT-624 this has been removed. I assume Baldwin did this for ease of maintenance rather than cosmetic looks. Next, at the ends of the locomotive, Baldwin introduced a fold-down walkway to allow crews to pass between locomotives that were coupled together working as MU (multiple units). This split the end handrail as well as adding pipework for the MU equipment.

The trucks on some of the RT-624 locomotives were also upgraded to Outside Equalized trucks from the original Commonwealth trucks. Out of the twenty-four RT-624s made, twenty-three went to the Pennsylvania Railroad, and only the last eight, built-in 1952 and numbered 8724-8731, had the new tucks.

Another difference from the DT6-6-2000 was the walkways on the side. The DT6-6-2000 was almost symmetrical but the RT-624 had one walkway that was a different shape from the rest. This one had a longer raised section allowing for more battery storage under the walkway, which you can see on the left in the image below.

Another visual change that only appeared on some of the Pennsylvania Railroad locomotives was the Trainphone antenna on the roof. I say some of the locomotives because in doing my research I’ve found images of the locomotives with and without the antenna.  The Trainphone system was started in 1945 and was phased out around 1967 so it may be that it’d been removed from some of the locomotives. Below is a good example, PRR 8730 (one of the last batch with the Outside Equalized trucks) is shown with no Trainphone antenna. This photo was taken by Michael Sirotta at Frankford Jct., North Phila. It’s a 35 mm slide photo and dates from 1965 or ’66. (The image came from www.railpictures.net/)

The main body also had many small changes such as different grill positionings, headlight configuration, number board locations, and horn types.

The good news, as with my N Scale version, the donor chassis for both HO DT6-6-2000 and RT-624 kits will be the same. All the differences will be on the 3D Printed or etched brass parts.

I’ll be making shells available for versions with and without the Trainphone antenna for the PPR. I hadn’t planned on making 3D printed replacement trucks as Bowser makes both the Outside Equalized and Commonwealth trucks, but if they become hard to get hold of please let me know.

Out of the twenty four RT-624s made only one didn’t go to the RRP; this went to the Minneapolis Northfield & Southern and was numbered Twenty Five. Researching this locomotive, I noted that a lot of the changes above had not been included. As far as I can see, the only changes between MN&S’s original 5 DT6-6-2000’s and their only RT-624 was a different position to the headlight and a raised grill on the nose side. The large plate under the cab covering the fuel tank was already omitted on their DT6-6-2000’s. So for that model alone, if anybody would like one, I can simply modify the Baldwin DT6-6-2000 HO Type 3 model I already sell, so please get in touch.

I’ve already started working on the HO model and will have some progress images ready to share with you soon as well as a rendering of the model I’ll be sending for a test print.

Bachmann Mainline Replacement Wheel Centers – Part 3

A few weeks ago I received my first test print for my Bachmann Mainline replacement wheel centers, you can read the post here.  Although the first test prints looked good, one of the dimensions was incorrect, and consequently they didn’t fit.

This week I’ve received the second test print.  Again these have been printed in Shapeways Smooth Fine Detail Plastic.

Compared to the originals you can see there are four wheel centers with small counterweights and two with large ones.

This time the wheel centers fitted perfectly.  There was a little 3D print residue inside the crank peg hole which I cleaned out before test fitting.  The wheel centers are a snug fit and it’s worth bearing that in mind when painting; if the paint’s too thick it’ll prevent them from fitting correctly.

These can now be prepped for painting.  I do this by soaking the parts in Goo Gone for 24 hours, rinsing under a warm tap, and then leaving to dry for a few days.  Any 3D print residue left behind will turn to powder and can be brushed off.  I’ll then spray them black and re-assemble the locomotive.

As the wheel centers are a snug fit it’s unlikely they’ll fall out but as a precaution, I’ll put a few drops of superglue on the center of the wheel.  I wouldn’t recommend putting any around the outer rim or under the spokes as it’ll certainly spill out.

These are now ready to be ordered and can be found using the link below.

Bachmann Mainline Replacement Wheel Centers

These will fit the Bachman (Mainline) Split Chassis Standard 4MT, as well as any other locomotive that has a wheel diameter of 24.5mm (flange to flange) and an inside diameter of 20.6mm.

If you need a wheel center for a different locomotive, please let me know and I can make that available as well.

Bachmann Mainline Replacement Wheel Centers – Part 2

In December last year, I shared with you my designs for a set of Bachmann Mainline Replacement wheel centers, you can find the post here.  This week I received the first test prints, so I want to show you how they came out.

I printed them in Shapeways Smooth Fine Detail Plastic as this material is very accurate and cost-effective.  They were printed on a sprue, and as they are transparent, you can see the circles on the far side where the sprue was cut off.

Initially, I was very happy with them, although they still need to be cleaned ready for painting, they looked perfectly round, and all the detail, such as the raised counterweight edge and rounded spokes, have come out well.  But I’d made a mistake; the offset hole which fits over the connecting rod fixing peg didn’t fit.  Looking at the wheel below you can see this fixing peg has two diameters.  The wheel center fits over the larger section and I measured the smaller.

Consequently, as you can see below, the hole in the 3D printed wheel center was too small.

But I still needed to see if the wheel center fitted in the actual wheel, so I used a drill in a pin vice to open out the hole.

This didn’t go so well.    The Smooth Fine Detail Plastic, unlike the original flexible injection-molded plastic, is hard and therefore brittle so the wheel center cracked as the drill went through.  To be fair the material was very thin at this point and was never designed to be drilled out.  But this did allow me to test fit it in the wheel, and it fitted perfectly.

I also wanted to test the wheel center with the smaller counterweight, although it should be the same size.  This time, to make the hole for the side rod peg larger I used a round needle file.

I just about managed to keep the wheel center in one piece; I had to file it down so it was only 0.3mm thick.  Again the wheel fitted, so once the hole is increased these will work.

I’ve now modified the 3D computer model to allow for the larger pin.  I also added a small radius to the rear edge to ensure any discrepancy in the wheel inside corner would not affect the wheel center.

I’ll do another test print to ensure these modifications work. This material, although it doesn’t always respond well to being drilled or filed, is perfect when the design is right. That’s the beauty of test prints, it allows me to perfect the design so the material is never compromised.  I can then spray them a flat black and permanently fit them into the wheels, ready for reassembly of the locomotive.

Bachmann Mainline Replacement Wheel Centers

Over the last few years, I’ve been making replacement parts for the Backmann Mainline split chassis locomotives.  These consisted of replacement axles and the fastenings that hold the chassis halves together.  However some of the locomotives also suffer from another problem, although not as common, and in this post, I’ll share with you my fix.

The Bachmann Mainline 4MT, with the split chassis, as shown below, is a great loco and a reliable runner, even by modern standards. But apart from the axle and chassis fastening issues, it sometimes also has issues with the actual wheels.

The wheels are cast metal so as to pick up power, but have a plastic insert for the detail.

The issue with these is the plastic sometimes starts to deform and spring out of the wheel.  Looking at the main drive axle below you can see the plastic wheel center on the left is sticking out a lot.  It’s supposed to be flush with the face of the wheel.  This causes a problem because the connecting rods fit over the spigot, which you can see, and will hit the deformed plastic as the wheel rotates. This then jams up the connecting rods and valve gear which will cause the axles to crack; that’s probably what happened to this locomotive.

The plastic center will pop out.  Because it fits into the wheel and is located by the spigot passing through it, they are not usually glued in place.  I think they’re press-fitted, and eventually the force of the metal wheel combined with expansion and compression due to heat changes, causes the plastic to deform.

The counterweight, which balances the wheel against the offset connecting rods, is also molded on the plastic center but not on the wheel.  I originally thought this was done so the same wheel could be used everywhere but actually, the center wheelset has a longer spigot to receive the connecting rods, main rod, and eccentric rod, which are held on with a pin, whereas the other wheels have a smaller spigot just for the connecting rod, which is held on with a screw.

The plastic inserts are also different as the counterweight is different.  A center wheel, as shown on the left, has a larger counterweight as the main rod connects here as well as the connecting rods.

What surprised me is the counterweight is not centered under the spigot.  The spigot is between two spokes but the counterweight spans an odd number of spokes meaning it’s not directly opposite the spigot.  I did wonder if this was a mistake in the injection mold?

If you look at the image below of GWR Saint Class 2935 ‘Caynham Court’ the counterweights, big and small, span an even number of spokes and are centered under the spigot.

But an actual photo of a 4-6-0 Standard 4Mt, number 75078, shows the counterweights spanning odd numbers of spokes and offset, just like the model.  Looks like Bachmann Mainline knew what they were doing.

As to why the counterweight is located like this I did a bit of research and found a document titled ‘Steam Locomotive Rail Wheel Dynamics Part 2: Mechanical Balancing of Steam Locomotives‘.  It’s based on US locomotives but the principles are the same, I believe it’s to do with cross counterbalancing.  Page six in the document says:

“Due to the fact that the rotating parts of the locomotive are not in the same vertical plane as the driving wheels, where the counterweights were located an additional imbalance was introduced by the counterbalancing material. Also known as “dynamic balancing” in the US, cross counterbalancing was developed to mitigate these forces. This required an additional small counterbalance weight to be placed in the opposite wheel to balance the near wheel on each wheelset. In practice, it usually meant additional weights were placed on the wheel roughly halfway between the crank pin and the counterweight, a location that is ultimately determined by calculation. In some engines, the cross counterbalance weight was combined with the main counterbalance weight, the total weight and location being determined by calculation.”

So that means the plastic wheel centers will be the same on both sides of the locomotive, not mirrored and for the 4-6-0 I would need two with large counterweights and four with small.

The rear of the plastic insert needs to be flat, but as you can see by the way the original curls on a flat surface it is now deformed even when free of the wheel.

Getting measurements from the metal wheel and original plastic part I was able to draw the new insert.   

The two different counterweights were added.

And a set of six made ready for printing.  The face of the wheels will be printed facing upwards to get the best possible finish as this will be the only side visible.

These will be 3D printed in Shapeways Smooth Fine Detail Plastic and when they arrive I’ll share them with you.  There are several Bachmann Mainline locomotives that have this type of wheel insert and there are all sorts of sizes.  Once I know this replacement part for the 4-6-0 4MT works I can make sets for other locomotives.  If you have one with this issue, let me know via the contacts page and I will try and do that loco first.

A Baldwin DT6-6-2000 in HO – Etched Box Windows Part 14

Now the first three body types for the HO Baldwin DT6-6-2000 have been made available, (see the page here) I need to share with you how some of the details work.  In this post I’ll discuss the etched brass box windows that appear on the Minneapolis, Northfield, and Southern Railway no 21. (Picture from Illinois Railway Museum http://www.railroadmichigan.com/illinoisrailwaymuseum.html)

The 3D printed shell for this particular locomotive is my Baldwin DT6-6-2000 HO Type 3 and can be ordered from Shapeways using the link below.


Several posts ago I shared the design for the box window and you can see the parts which need to made from brass in the image below.

I even designed them so they could be modeled in the open position if required.

To make this design work the shell has a different window configuration, with slots to receive the etched brass on all sides and nothing in the middle.

Because the test print had the standard windows, and I didn’t want to print an entire shell to test the box windows, I simply 3D printed a cropped out section of the window.

You can see the slots around the window opening.

The etched brass sheet has two sets of box window parts at the bottom of the fret.

On the left is the roof, base, and sides, and on the right are the sliding windows.

After I cut out the parts they looked like this.  I confess I rushed this a little and have bent a few parts.  Time should also be taken to file off any burs to ensure a good fit.  But for this test, a quick install is all I needed to do.

The base has two prongs that fit into the slots below the window.  There is a bar on the base that should be facing up.

The roof fits in a similar way with the bar facing down. The roof will fit at an angle because the slots for it are tilted to run at the correct angle.

The sides, when not bent, fit between the roof and base with the two prongs locating in the 3D printed slots.


Both sides are the same so it doesn’t matter which one is used for either side.

The square windows are the parts that slide and fit behind the fixed sections.  They’re designed to rest against the two bars on the roof and base.

Once the square window is positioned the C-shaped window can be fixed resting on top of the square window. Any glazing would ideally be fitted before they are fixed in place.  This can either be cut to fit inside the window frame or fixed to the rear.

With both windows fitted, the assembly is complete.  The left window is closed and the right is slid half-open.  With the parts carefully cut out and any burs removed the box window will be a nice snug fit.

Of course, fitting the glazing before spraying the body may cause an issue, so some careful planning will need to be done.

The windows could be glazed then masked for spaying.  Or the glazing could be fitted last.  Or the body could be sprayed before the brass is fitted and glazed.  I guess it all depends on the modeler’s preference.

A full set of instructions for the whole locomotive will be made available soon for all the parts needed and over the next few weeks’s the other shells will be made available for the different DT6-6-2000 locomotives and RT-624s.

A Baldwin DT6-6-2000 in HO – Project Update

It’s been several weeks since I last posted about the Baldwin DT6-6-2000 HO project but today I had some good news which means we are just about ready for release.

The bulk of the design and 3D printing has been done, as you can see from the photo of the successful test print below, but what was missing was the etched brass parts.

But today I had confirmation that they’ve been shipped from the etchers and I’m expecting them to arrive by tomorrow or Wednesday at the latest.  This means I can do all the test fitting this week, and assuming everything fits okay, I can release the full kit for sale in next Monday’s post.

The Baldwin RT-624 and some of the DT6-6-2000 varients are still being modified, but I should be able to release shells for Baldwin’s demonstrator, number 2000. ()

Elgin, Joliet, and Eastern Railway early DT6-6-2000s. (Uncredited image – If you know where this image originates from please drop me a message).

Santa Fe’s early models. (Picture from http://www.snowcrest.net/photobob/sfl2.html),

The Trona Railway locomotives. (Photo from Vernon Ryder, Jr.- collection of Mark Laundry – http://baldwindiesels.railfan.net/trona/index.html).

The Minneapolis, Northfield, and Southern Railway no 21. (Picture from Illinois Railway Museum http://www.railroadmichigan.com/illinoisrailwaymuseum.html)

And Peabody Coal Railroad’s locomotives. (Picture from Railrpictures.net)

There’ll be more as the variants get done, but if you have a specific DT6-6-2000 which you would like to model, please get in touch via the contacts page and hopefully I can make that shell available too.

I’m really looking forward to seeing the locomotive with all the brass fittings, I’ve just got to decide what color to paint the test print now!