A Baldwin DT6-6-2000 in HO – Trucks Part 2

In last week’s post, I shared with you the first steps in the HO Baldwin DT6-6-2000 project and I ended with the image below showing my 3D model of the truck centers which hold the gears in place. You can find the post here. The reason for modeling the truck centers was to allow me to work out how to reposition the gears to allow the axels to be positioned differently.  The trucks are asymmetric and I need them the other way around.

In this week’s post, I’ll share with you my solution to solve the issue.

Inside the truck centers, in the original configuration, are 5 gears, as shown below.  The green gear at the top connects to the worm gear at the end of the drive shaft.  This drives the large blue gear which turns the center and right axels, shown in black.  The center axel then transfers the rotation through the three red smaller gears to the left axel.

Because I need to move the center axel to the left, the gearing will need to be rearranged and ideally, reusing the same gears would make sense, but that wasn’t possible as you can see below.  By swapping the red and blue gears over, all the axels are connected but there’s a big gap between the green gear and the red, so another gear needs to be added in.  The purple gear is the same size as the red.  But this configuration has another issue in that the blue gear is too big for space.  Looking at the outline of the truck center you can see the shape was tapered above the blue gear’s original position and that would not be possible in the new location.  The part would either become too thin and weak or project up and hit the chassis.

So, as an extra gear was unavoidable, I decided to make four extra gears, as shown below, and remove the blue gear completely.  The four new purple gears are all the same as the red ones.  To allow space for the new configuration of the red gears, the top of the truck center will also need to be extended, but that’s okay as there’s room between the truck center and the chassis.

Both sides of the truck chassis can now be properly drawn with the new gear holes set out.

The four new gears have been modeled inside a cage to make them one printed part, even though they don’t actually touch the cage.  This reduces the cost of the 3D print.  These parts will be test printed in Shapeways Smooth Fine Detail Plastic material for accuracy.

As well as the trucks I also had to model the Bowser chassis to see if it needed to be modified in any way to fit inside the shell.  The green section is the existing circuit board, with an 8 pin DCC socket.  The black section is the motor with its two brass flywheels.  Everything else is metal.

The shell, taken directly from my N Scale version looks like this.  I’ll be refining some of the details as they don’t need to be so big for HO, and replacing some with brass parts, such as the grab irons.  I’ll also be making the grills at the bottom of each nose section from a fine brass mesh.

 With the shell split in half you can see the chassis inside and it’s a good fit, with nothing requiring modification on the chassis.  As the DT6-6-2000 is longer than the original body shell for this chassis I can update the new shell to utilize the original shell and fixing points.

Next week I’ll have some progress on the shell to update you with and once the test truck arrives I’ll share that as well.

A Baldwin DT6-6-2000 in HO – Trucks Part 1

Ever since I released my N scale kit for the DT6-6-2000 in 2014 I’ve been planning to release it in HO scale. The project has had a few challenges getting started but finally, it’s underway.  And the first place to start is the chassis.

As with the N Scale version, I’ll be using a ready-to-run chassis to make things easier, and more reliable.  I’ve chosen the Bowser Alco C628/C630.  It comes with a big central motor, two flywheels and lots of weight, which will be ideal for a model of a DT6-6-2000.  It also has a circuit board with a DCC socket which I also intend to use.

This particular chassis came from a Canadian Pacific C630M and has different trucks to the Commonwealth trucks used on DT6-6-2000, but when I purchased the locomotive I assumed the wheel arrangement was in the same asymmetric positions with different side frames.  However, despite appearances, the wheels are evenly spaced.

But the good news is I was able to order a set of Commonwealth trucks from Bowser with the correct asymmetric wheel arrangement.

They’re a direct replacement in the chassis and now I’m at the right starting point.

The main difference between the Alco C-628/C-630 and Baldwin DT6-6-2000 chassis is the asymmetric trucks are facing the other way.  With the N Scale Atlas chassis, the truck gear tower is in the middle so they can simply be fitted facing the other way.  But with the Bowser trucks, the gear tower is at one end.  Luckily the front and rear wheel sets are already in the right position.  The DT6-6-2000 has an overall wheelbase of 54’9″, as you can see in this original blueprint below.  (Clicking on the image will make it bigger).

Converting that to Metric and HO scale works out at 191.8mm which is exactly the wheelbase the new chassis has, so it’s all good apart from the fact that the center wheel is in the wrong place.

The good news is the truck side frames are separate from the truck centers which hold the gears in place.

My plan is to 3D print some new truck centers with different gear spacing allowing the side frames to be refitted around the other way.  I’ve already drawn the truck centers with the original gear spacings.

My next step is to work out the new gear spacings which I’ll share with you once complete.  Then I can turn my attention to the 3D printed body shell.

A Brief Pause

I’m going to hold off posting tonight and prepare a proper post for a few day’s time. The news concerning the new restrictions to keep us all safe and well were not unexpected but I am spending the evening relaxing with my family. We will regroup and proceed as normally as we can tomorrow!

Stay safe, and let’s pick up steam again soon.

Adding DCC To Older Locomotives With Smoke Units

Hello all, my apologies for the silence over last month.  It’s been a very busy time and I’ve been doing a lot of work away from home making it hard to work on trains, draw and generally model railroad.  But I’m back and to start with I have a ‘How To’ to share with you regarding adding DCC to an older steam locomotive with a smoke unit.

A perfect example of this is the Hornby Schools Class 4-4-0 as shown below.  This is not to be confused with the new Hornby Schools DCC-ready locomotives which are a very different model.

These earlier models were only designed for analog or DC operation only.  They are tender driven with the tender wheels picking up power from one rail and the locomotive the other.  Adding a DCC decoder is fairly easy but what makes it complicated is the smoke unit.

With the loco shell removed and you can see the smoke unit which has been pulled out of the boiler.  Normally this locomotive only picks up power from one rail, as previously mentioned, but when Hornby added the smoke unit they added a pickup to both rails but this extra pickup only feeds the smoke unit.  This is because, as standard, there’s only one electrical connection to the tender via the drawbar.

In the image above I’ve run four wires through the loco cab into the tender where the DCC decoder and motor are.  Two are from the power pickups bypassing the electrical connection in the drawbar to utilize the extra pickups for the decoder.  The other two are connected to the common DCC wire (blue) and the auxiliary wire (green) and go straight to the smoke unit.

The smoke unit itself is an oil reservoir with a heating element in it.  It runs on 12v DC and sends out smoke when it gets hot.

Normally on DC or analog operation the smoke unit works very well, getting hotter as the locomotive goes faster because of the voltage increases.  But it also draws much more current than a headlight or other features.  So when connected directly to the DCC decoder, as shown above, the amount of smoke is restricted by the current capacity of the decoder.  The particular decoder fitted in this locomotive has a maximum current output of 250mA for its functions, which is not enough to make the smoke unit work.

To solve this some electronics can be added which will allow the smoke unit to draw power directly from the track, but still be turned on and off from the DCC decoder.  To do this I use a bridge rectifier and a relay.

The bridge rectifier, on the left, converts AC power to DC.  The DCC power in the track is basically AC with the DCC signal embedded. This device, which is a set of four diodes, will convert the power to a clean DC power supply that will drive the smoke unit as if it was on full power.  The relay is an electronic switch that can be operated by the DCC decoder and only draws a very small amount of power.  But the switch inside can be used to connect things that draw lots of power, such as the smoke unit.  This particular relay is a Double Pole Double Through (DPDT) switch, which means it can switch two separate wires between two contacts at the same time, but I will simply use it as an on-off switch.  I like it because it’s very small.

The two input connections on the bridge rectifier connect directly to the power pickups in the loco.  The outputs go to the smoke unit with one wire passing through the relay. The symbols on the bridge rectifier are shown below.  The two wavey lines are the AC connections and the positive and negative symbols are the DC.

The relay has 8 pins.  Pins zero and one are the two wires, common(blue) and auxiliary (green) from the decoder which turn the relay on and off. I used pins two and four for the smoke unit.  With the relay off they’re not connected, but when it’s on they are.

I soldered the wires to the components and used heat shrink to cover the bare wires as they could cause an issue if they touched the metal chassis.

Because the parts are small they can both be tucked into the boiler behind the smoke unit, so they’re out of the way when the locomotive shell is refitted.

This fitted DCC decoder has been set up so F1 turns auxiliary on and off.  When the locomotive is sat on a live DCC track pressing F1 will cause the loco to smoke even though it’s stood still.  This could never have been done on DC as the smoke unit needs to heat up and the train would already be moving before that happened.

These parts are readily available from places like Radio Shack, RS components or even some model shops and are an easy way to overcome the issue.   This can also be used when fitting an aftermarket smoke unit such as Seuthe.  I’ve fitted a pair of Seuthe smoke units to a double chimney locomotive using this method with great results.

Next week I plan to have some news on one of my upcoming 3D printed locomotive projects to share with you.

Replacement Bachmann OO Chassis Fasteners & Washers

This week I have another new replacement part to share with you. A locomotive was brought in to get DCC sound fitted and I know from experience there’s a good chance certain parts will break when the locomotive is taken apart, and in this instance I was not mistaken.  The Locomotive in question is a Gresly V2  made by Bachmann under their Branch Line range.

These locomotives are very good, although now an older model, and are normally very reliable.  The primary problem these, and other locos in the range, suffer from is split axels and I’ve already 3D printed parts to repair them, which you can read about here.

However, the axels on this locomotive are fine; the issue is with the split chassis fasteners.  A lot, if not all, of the Bachmann locomotives of this generation, have a split chassis.  This means the chassis is in two halves with each side conducting power from the wheels to the motor, eliminating the need for wires.  For DC operation this is perfect.  But for DCC I need to separate the chassis halves to electrically isolate the motor.  The chassis halves need to be screwed together but electrically separated.  This is achieved by using a plastic chassis fastener, plastic washer and metal screw.  The fastener has a square head that fits into a square recess in the left chassis half to stop it rotating.  The washer fits between the chassis halves, over the fastener to separate them, and the screw pulls the parts together as it bites into the fastener.

The problem comes, as with this V2, when the locomotive has never been taken apart and the plastic fastener has either deteriorated or maybe shrunk.  I’m not sure what actually happens.  But the screws are very tight and the force needed to get it to move is often more than the fastener can take and the tube section twists off the square head; as you can see below.

Or the tube section simply breaks at the end of the screw, which also happened on this locomotive.

It is possible, if you’re both careful and lucky, to glue the parts back together, but more times than not it doesn’t work and I often come across these locos with several missing fasteners.

So my solution, as is my way, is to 3D print replacement parts.  I designed the fastener to be a direct replacement and included a washer as sometimes the originals can get lost.  They are 3D printed in Shapeways Fine Detail Plastic as it’s the most accurate.

Before these can be used it’s very important to clean out the tube section.  This is because it will be full of 3D print residue which, if left inside, will add pressure to the tube wall as the screw is driven in, cracking the tube.  To clean out the tube I use a 1.26mm (0.049″) drill in a pin vice.  This won’t actually remove any of the tube material, just ream out the hole, as you can see below.

There’s usually a lot of residue in the hole because it’s small and Shapeways post-cleaning processes can’t get in there.

With the fasteners ready the chassis can be reassembled.  The V2 uses five, as you can see below by the holes in the right side chassis half.

With both sides fitted you can see the square heads in the left side chassis half.  It was only when I put this photo up I realized I had the front one in the wrong way round.  Fortunately with that one it works from either side.

The square recess in the left chassis half has a bit of tolerance so the head will rotate a little.

These replacement fasteners and washers can be used on a large variety of Bachmann split chassis locomotives and I’ve made them available in a set of 6 here and a set of 12 here.

This particular V2 is now back up and running and has an ESU sound DCC decoder, working lamps, and a realistic firebox flicker whenever the fireman opens the firebox door, which reflects nicely around the cab.

If you have another part, such as this fastener, which has broken and you can’t find a replacement I’d be happy to see if I can draw it up for 3D printing.  You can get in touch via the contact page.

Replacement Bell Cranks for an MRC/Rowa N Scale 2-8-4 and 2-8-8-2

Back in May of 2015 I needed a replacement eccentric rod for an N Scale Rowa/MRC 2-8-4 Berkshire to replace a missing one on a second-hand locomotive, and designed and 3D printed the part.  The post can be found here.

Since then I’ve had a request to provide a replacement bell crank for the Rowa/MRC 2-8-8-2 Y6B.  This mighty steam locomotive was one of the original N scale greats dating back to 1969 when MRC first released it.

It went through a few changes and was re-released in 1977 by Con-Cor/Rivarossi.

One of the main differences in the two versions is the side rods and valve gear.  The original MRC, and later Rowa version had plastic parts, whereas the later Concor/Rivarossi ones had metal.  The part I’m replacing is on the earlier MRC/Rowa version, which coincidently is exactly the same on their 2-8-4 Berkshire.

The original Berkshire bell crank and eccentric rod are shown below.  They simply clip together and the bell crank rotates about the round lug, which is at the other end from the C section.

The new 3D printed bell cranks are printed on a sprue, simply because they’re so small.

Up close you can see the new 3D printed part is slightly chunkier than the original injection molded part to give some extra strength to it.  Once fitted it’s very hard to see the difference.

On the Berkshire, with the bell crank removed, you can see the circular hole at the back of the bell housing to receive the round lug.

The new part clipped right in and rocked back and forward with ease.  The part will ideally be painted silver before the final install.

The original eccentric rod clips into the new bell crank and the main drive wheel, fixing with ease, and that’s it.  This particular Berkshire has no motor in it so I can’t show it running, but it ran freely along the track by hand with no issues from the new bell crank.

The Y6B, as I said before, has the exact same bell cranks, just more of them.

The only difference is the eccentric rod is shorter, which is caused by the altered geometry of smaller driving wheels compared to the Berkshire.

A pack of 6 bell cranks for MRC/Rowa 2-8-4s and 2-8-8-2s are available here.

I’ve had some time to get around to finishing some other long overdue 3D printing projects and over the next few weeks, I look forward to sharing these with you and making them available to buy.