New Axles for a Second Generation Bachmann HO 4-8-4 Northern

Back in 2018 I shared with you my design for replacement axles and gears for a HO Bachmann 4-8-4 Northern.  You can find the post here. That turned out to be quite the adventure, as simply creating replacement parts didn’t work out so well!  Due to the thinness of the original components I had to engineer a much thicker gear which could handle the force applied from the motor.  This turned out to be a success.  But this gear and axle set only worked for the first generation of the Bachmann HO 4-8-4.   As it turns out, although Bachmann redesigned and improved the second generation, it too has problems with split axles and gears, and I’ve regularly been asked if I could produce a set for this locomotive.  Well, I finally have and in this post I’ll share the design with you.

To start, I want to explain the difference between the three generations that are commonly available.  I’m not going to go into any of the body or cosmetic differences, just the drive train so you can tell which generation you have.

The first generation, as I’ve already covered in other posts, has a pancake motor which drives the rear axle.  Below is an exploded schematic drawing, courtesy of John on the Tyco Depot Train Collectors & Model Railroading Forum. You can just about see the gear on the rear axle.

Looking at the underside of the locomotive there’s a bump over the rear axle to make way for the gear. 

This is the main clue that it’s a first generation.  This locomotive also has round wheel stubs and holes in the axles.  That’s what makes quartering the valve gear tricky on this locomotive.  ‘Quartering’ means setting the piston rods and side rods on each side of the locomotive at 90° to each other; as the wheel stubs are round it’s easy to get it in the wrong place meaning the loco won’t run smoothly.

The second generation had a lot of improvements such as a can motor and thicker gears and axles.  But most importantly the axles and wheel stubs also have square stubs and holes, making quartering far easier to do. You can just about make out the cracks in the axle and gear.

Below is an exploded schematic drawing, also courtesy of John.

The motor this time drives the third axle and there’s no bump in the base plate; this along with the lack of wires running to the tender tells you it’s a second generation.

The third generation, which I believe is the version currently available, had a total redesign.  It still has a can motor which drives the third axle, but everything else has changed.  Looking at the exploded schematic drawing below, again courtesy of John, you can see the axles are a different shape. 

To my knowledge, these don’t fail.  These are normally marked as DCC ready and will have wires connecting the tender to the locomotive; the DCC socket and speakers for sound are located in the tender.

Looking inside the second generation you can see the axles and drive gear on the third axle. The second axle is clearly split and once I removed the others I discovered they had split too. As the wheel stubs are square they don’t need to be such a tight fit as the round ones on the first generation.

Interestingly the axles are almost identical to the axles used on the UK Bachmann (former Mainline) designed locomotives that I have 3D printed replacements, for as shown below.  These were for a GWR Hall class and can be found here.

However, upon measuring the US 4-8-4 axles and gears I found them slightly different, so a new design was needed. These have been designed to be 3D printed in Shapeways Smooth Fine Detail Plastic.

The kit I’ll supply will contain three axles and a main drive gear. The idler gear between the worm and axle gear to my knowledge never breaks so I haven’t supplied that; if yours has, please let me know and I will add it to the kit.

These have now been sent off for a test print and I’ll see how well they work.  As with the first generation, and the UK Bachmann locos, I’m restricted by the size of the axle box and the size of the wheel stub.  This means the axle itself nearest the wheel is still not as thick as I would like it to be, and it’s possible to crack the new axles if not cleaned properly before use.  Once I’ve test fitted a few, if it appears too easy to crack the new ones I will include a few spares in each kit.

So now I’m waiting for the 3D printed parts to arrive, and I’ll share them with you when they do.

Updating Your Digitrax Products

As with most equipment, manufacturers often make improvements to their products after you’ve purchased them.  The nice thing with electrical equipment is these improvements are often related to the way it works rather than a physical change, so this can be updated.  In this post I’ll show you how you can check to see if your Digitrax equipment is up-to-date and if not, how to change it.

Digitrax equipment is very reliable and robust, but most of their equipment has had a small improvement made at some point.  Just like a computer or mobile phone, electrical equipment has a program that runs on the circuit boards. This program is called firmware, unlike software that runs on a computer, firmware is the program that tells the components what to do.

Below is an example of some common Digitrax equipment.  From left to right we have a DT602D radio throttle, a DT500 throttle, a DCS 240 command station, a DCS 51 command station and a PR3 USB to PC interface.  All of this equipment has firmware and all of it has an update available.

Some of the equipment, such as the newer DT602, tells you what version the firmware is when it starts up. Below you can see this throttle has SW Version 0000.1 and is dated July 15, 2021.

Other equipment such as the command stations and older equipment don’t have a such a clear display. But there are ways to find out what the firmware version is.  To do this Digitrax have a piece of software called DigiIPL and this can be downloaded from their website  This software can be installed on a PC, laptop or Windows-based tablet, but don’t start it up yet.

To connect the Digitrax equipment to the DigiIPL program you will need a USB cable, which should have been supplied with the command station.  If not, the same type of cable often used with printers will work. The cable needs a USB Type A fitting on one end and a USB Type B fitting on the other as shown below

The newer command stations, such as the DCS 240 have a USB port on the front of the unit but the older models such as the DCS 51 do not. I’ll show you how to connect those later.

With the USB cable plugged into your computer and the DCS (DCS stands for Digital Command Station) connected to its own power supply, the PC will assign a COM port to it. This is the address of the connection, depending on what else you have plugged in this will be different for each user, we will find out what it is in a minute.

With the DCS connected you can now start the DigiIPL program and it will look like this.

You’ll notice at the top left a Loconet Port has not been selected, this is where the COM port is entered. Luckily you can only select from Com ports that are active, mine had been assigned to Com 4. If there’s more than one, try the first and if that doesn’t work try the next. It’s also important to note the ‘Bit Rate’ should be set to 16457 although by default it always is.

At this stage I should point out that if you have lots of Digitrax equipment, particularly lots of the same item, it is a good idea not to have it all plugged in to the command station at the same time when doing this. Theoretically it should work but it’s recommended to do this individually.

Once you’re ready you can push the ‘Find Devices’ button and it will open another window listing the equipment, and below you can see the DCS 240 listed and is at SW version 0.3.

If I plug in the DT602D from earlier and push the ‘Find Devices’ button again you can see it listed showing the SW Version 0.1 as we saw before.

So now we know the current SW (Firmware) version but how do we know if it’s the latest? Heading back to the Digitrax website on their downloads page they have all the available updates listed. Below you can see the DCS 240 is at version 0.4 and the DT602 is at version 0.1 so only the DCS 240 needs to be updated. (I did the DT602 the other week).

To update the DCS 240, or any Digitrax equipment, download the relevant firmware to your computer. Then using the ‘Select File’ button, select the downloaded firmware file.

Pressing the ‘Start’ button will now update the equipment.

Once done you can check to see if the update was successful by pressing the ‘Find Devices’ button again to check the version.

When it comes to the older equipment, such as the DCS 51 that don’t have a USB port, an interface is needed. This is where the PR3 shown in the first photo comes in. Below you can see the USB cable connected to the PR3 and the PR3 connected to the DCS 51 via a Loconet cable.

With the new equipment connected the DigiIPL has to be restarted. This time it has connected on Com 5. Using the ‘Find Devices’ I can see the PR3 and DCS 51, but only the DCS 51 needs an update.

And thats it, all up to date. It’s always a good idea to update any firmware, Digitrax or otherwise. The chances are you will not see a difference in how your device works but there’s a good chance it will fix a problem you didn’t even know was there.

New Gears For A Bachmann N Scale Street Car & Brill Trolley

This is a project that I started at the beginning of 2020 so it’s about time I shared it with you. The Bachmann PCC Interurban Streamlined Car has been around since 1983 and was released in a large variety of paint schemes and liveries. However, all the models released up until about 2000, when Bachmann upgraded the chassis, suffer from the same problem; the white plastic gears on the axles crack. In this post I’ll share with you my 3D printed replacements to fix this.

The PCC Interurban Streamlined Car, and similar Brill Trolley released the year before, share a similar chassis with the same trucks. The body is all plastic and clips over the metal chassis, which fills the body.

The underside is fairly basic and you can see all four axles are driven via gears. These are the gears that crack under the pressure of the metal axles press fitted into them.

With the body removed you can see the chassis, which is made of two halves and separated by Bachmann standard fastener and washer system. Should these brake I’ve made replacements available here.

With the two screws removed the chassis haves come apart and the trucks fall out, although the repair can be done without separating the chassis or removing the trucks if you wish.

The large drive gear in the centre of the truck doesn’t have any issues.

The wheels have a short axle which press fits into the gear, when fully inserted the two axles do not touch each other so the gear also forms the electrical isolation. The wheels should just pull out. If the gears are cracked they’ll come out very easily.

The original gears, as shown on the right of the photo below, are made from a material that’s prone to cracking and you can see the light change as it hits the crack in the gear. With the metal wheel inserted the crack opens up. This causes two issues; firstly the spacing between two of the teeth is larger than the rest and causes a bump as the gear turns or jams the other gear. The second issue is there is little friction between the gear and the axles so the gear may turn, but the wheel won’t.

3D printing a set of four to replace all the gears is the answer and given the small size of these gears, roughly 5mm (0.196″) diameter, the best material is Shapeways Smooth Fine Detail because of its accuracy and hard-wearing properties. All four have been printed on a sprue so they don’t get lost in the printer.

Unlike injection moulding the sprue doesn’t actually touch the gears, it just passes through the hole in the middle. This can easily be cut with side cutters and the gears are ready to use, although I would recommend cleaning out the hole in the axles of any 3D print residue before you use them.

Refitting the gears and wheels is fairly simple. Position the new axle gear inside the truck and lightly push the wheel axle through the hole in the truck and into the gear. With both wheels lightly fitted, press the wheels together to press fit them firmly into the gear, just don’t push them in too far. The inside distance between the back of the wheels, commonly known as the Back-To-Back dimension, should be 7.65mm (0.301″).

Even if only one of your gears is cracked I would recommend changing all four as it’s probable the others will crack once you start using it again.

And that’s it, the street car is ready to use. The set of four gear axles can be found here.

I have several new gears for different loco types and scales to share with you over the next few months, but if you have something that needs a gear, get in touch. Just like this project I started last year, I may have all ready done it!

Back To Work after the Summer Break

It’s been several weeks since I last posted but that’s not to say I’ve not been busy. Given the strange times we’ve all been experiencing over the last year and a half, including the necessary travel restrictions, I took the opportunity to do as much as I could away from the workshop this summer. And that’s included some model railway stuff which I hope to share with you when ready.

But for now I’m back in the workshop with my batteries re-charged ready get on with the existing projects which have been on hold, several locomotive repairs, new builds and new projects. And there are quite a few!

As each project gets worked on or finished I’ll be getting back into my regular weekly posts to share it all with you.

As for tonight I have just had a big clean up of my work benches and desk to make a start, let’s see what I can get done for next week!

A Baldwin RT-624 in HO – Now Available

This week, as promised, I’ve made the HO Baldwin RT-624 kits available to purchase. They’ve now passed all of my checks and had all the little improvements made.

There are two kits available, and both look very smilier but there are differences. Below is the first version.

This kit is for the early Pennsylvania Railroad RT-624 locomotives with the Trainphone. The kit has three parts; the main 3D printed shell, 3D printed detail parts, and etched brass Additions. The 3D printed detail parts and etched brass are the same for both versions.

The second version is for the later Pennsylvania Railroad RT-624 locomotives without the Trainphone. It also has some body differences such as a different headlight position.

The donor chassis used for this model is a Bowser C-628 or C-630, the kit does not come with this.

Please also note that these locomotives have the correct asymmetric trucks but they’re facing the wrong way round. It will work but in order to make it look right you will need to rotate the trucks. As with my DT-6-6-2000 kit I developed a 3D printed kit for rotating the bowser trucks and re-using their side frames. (Bowser sell the correct side frames as spare parts if your donor chassis has the wrong ones).

All the parts are available from the links below;

Early PRR HO RT-624 Body Shell

Late PRR HO RT-624 Body Shell

3D Printed Detail Parts (For both versions)

Etched Brass Additions (For both versions)

3D Printed Truck Rotation Kit (DT-6-6-2000 Kit also for all RT-624 versions)

Commonwealth truck side frames are available from Bowser with their kit 96-603; it can also be used to upgrade an older Stewart Chassis to better pick up if that’s the one you have.  It can be found at the bottom right of the Bowser page using the link below. (If these become hard to get let me know, I can make a 3D printed set of side frames available.)

The couplings for this locomotive has been designed as Kadee #148 HO Scale 140-Series Whisker® Metal Couplers with Gearboxes – Universal – Medium (9/32″) Centerset Shank.

These locomotives have also been designed to receive powered Kadee couplings using Precimodels motors. To make the couplings powered you’ll need the Precimodels kit.

The last shell in the HO RT-624 range will be the single Minneapolis Northfield & Southern locomotive numbered Twenty-Five which I’ll soon have finished.

If you have any issue ordering or any questions please let me know. Ready-To-Run versions can be made on request if you prefer, please contact me via the contact page for a quote.

Now the kits are finished I’m going to paint up the two test prints. I have an ATSF DT6-6-2000 and an early PRR RT-624 which I think will look great, and I’ll share them with you once done.

A Baldwin RT-624 in HO – Part 6

This week I have the final stages of testing to share for the HO Baldwin RT-624 before it’s released next week.

The big news is the etched brass has arrived. Thanks to all of you who pre ordered, your etch will be in the post this week.

The etch fret contains handrails, sun visors, grab irons, windscreen wipers, train phone antennas and MU hoses.

All the parts for the HO RT-624 kit look like this.

You may also need the truck conversions to rotate the Bowser trucks in the donor chassis as shown below. These are the same as for the HO DT6-6-2000 model and when I release the RT-624 next week I’ll include a link for these.

Lots of the details on the RT-624 etch are the same as the DT6-6-2000 but I still wanted to test fit as much as I could. Please note that in the photos the shell and 3D printed parts haven’t been fully cleaned yet and the brass is not glued in, just resting in place.

The end handrails are half etch and half 3D print. For strength the etch parts pass through the 3D print.

The sun visors fit nicely into the angled slots in the shell.

HO RT-624 - Brass Test Fit 06

The side handrails all have holes or locating lugs to fit into and it fits well, but as you can see its a little bent. This is simply because I got a little over enthusiastic cutting it out. As the etch is thick, 0.5mm, it takes some force to cut. I cut mine out on a cutting mat with a large craft knife (Box Cutter) and the force bent the handrails. The trick is to put something hard and flat on top of the etch to prevent the part you are cutting out from bending up.

HO RT-624 - Brass Test Fit 07
HO RT-624 - Brass Test Fit 08

The grab irons are basically the same as the DT6-6-2000 but I’ve made a slight change to the holes which made them a perfect fit. I fitted them without bending. Once pushed all the way in they easily bent down. Each grab iron has a small lug preventing them from being pushed in too far. When fitted with glue these will be secure and strong.

HO RT-624 - Brass Test Fit 09

All four on the side are the same.

HO RT-624 - Brass Test Fit 10

The top grab iron doesn’t bend.

HO RT-624 - Brass Test Fit 11

The last check I wanted to make from the etch was for the MU hoses. Each end has eight and they push into the square holes in the 3D printed section of the end handrail.

HO RT-624 - Brass Test Fit 12

It looks a little out of line as nothing is glued in place but once it’s all painted and securely fitted I think they’ll look very good.

HO RT-624 - Brass Test Fit 13

I now have a few small details I want to tidy up on the 3D printed shell but it’s almost finished. Next Monday I’ll release the model in two versions. The PPR early version with the Trainphone and the later without. There will also be one extra RT-624 for the single Minneapolis Northfield & Southern locomotive numbered Twenty Five.