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.

A New Year and Look Back

Happy New Year to All!

2021 is here, and despite wanting to look forward rather than back at 2020, for the first post of the year I wanted to reflect on some of the positive things from last year, mainly the new parts and kits released.

The year started out well with the Bachmann N Scale Doodlebug getting a new set of gears and axles to replace the cracked ones.  You can read about these here.

The esteemed N scale MRC/Rowa Y6b 2-8-8-2 also had some new parts in the form of a replacement bell crank. These also fit the 2-8-4 Berkshire and you can read about them here.

Stepping up the scale to OO, the Bachmann and former Mainline brand locomotives received replacement chassis fasteners.  Given that these are a common part to fail with split chassis locomotives they have proven to be a great aid in repairing lots of them.  The parts can be found here.

Returning to N Scale, the UK Britannia 4-6-2 locomotives made by Dapol received a replacement driveshaft.  These tender-driven loco powered models suffered from the same cracked plastic problem as other models I’ve fixed such as the Atlas 4-4-0.  You can read about the Britannia here.

Speaking of Atlas models, the N Gauge diesels also suffer from cracked drive parts.  The universal connecter inside the flywheel often cracks, leaving the locos underpowered.  But new 3D printed parts are now available and you can read about them here.

In a similar way to my Bachmann/Mainline OO replacement axles, the locomotives of the Replica Railways OO range also received a new set of gears and axles.  These are smaller than the Mainline ones, but again come in a set of three.  You can read about these here.

As well as axles and gears I also released a set of dummy knuckle couplings that work with Kadee couplings.  These have NEM fittings designed to fit into European trains forming a permanent coupling that can be easily separated.  You can read about them here.

After the earlier releases of the OO Gauge Bachmann/Mainline fasteners & washers, I was asked to do the same thing for the Bachmann N scale range, so I did.  You can find them here.

One of the older British locomotive models is the iconic Class 14xx made by Airfix.  However, given the huge amount of miles some of these have now clocked up the main drive gears are wearing out. But a new one can be found here.

The final release for 2020, and literally the largest, was the HO Baldwin DT6-6-2000.  This behemoth of a locomotive has been on the drawing table for a long time and I know many of you have been following its progress throughout the year.  You can read about its release here.

So what next, what will 2021 bring?  There are lots of projects in the pipeline and several to finish off.  The HO Baldwin RT-624 will be next as it’s almost ready, and then I want to finish my N Scale 900081 Rotary Snow Plow project.

And I’m sure there will be lots of gears, parts, and other interesting bits along the way which I’ll share with you as we go.

Thank you for your continued support throughout 2020. I hope 2021 is a good year for all and I look forward to sharing my 3D printing projects and modeling adventures with you.

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.

Shapeways Sale – Cyber Monday

With the holiday season well underway Shapeways have announced their Cyber Monday sale.  They’re offering 10% off everything from 12:01am EST all day on November 30, 2020.

To enjoy the savings all you need to do is enter the code CYBER2020 at the checkout.

All of my 3D printed models, including the new HO DT6-6-2000, are in the sale and can be found either by using the dropdown Shop menu above or going direct to my Shapeways site using the link below.

Happy shopping!

Cutting Out Etched Brass

Etched brass features in several of my model kits and has been used as a way to model tiny detailed parts for many years.  But how do you cut the parts out?

A sheet of etched parts, or fret, normally consists of a sheet of metal with all the parts attached by a half-etched tag.  This means the area around the part has been fully etched away except for a small tag which is only half as thick as the rest of the sheet.  Below is the etched brass ‘Additions’ sheet for my N scale Alco C-855B locomotive.  As well as the larger handrail section there are also several other parts, such as ladders and grab irons, which are much smaller and more delicate.

The half-etched tag serves two purposes; it marks where the part finishes and needs to be cut off, and it makes the actual cutting of it easier, as the material is only half as thick.

With thinner sheets and softer metal such as brass, the tags can be cut with a sharp knife.  I use what is commonly called a Stanley Knife as the blade is strong but sharp.

However, there’s a risk of damaging or bending the parts as the pressure needed to cut the metal is more than the force needed to bend the parts, particularly with tiny parts. Stainless steel etches are harder to cut than brass etches, because the material is harder. This is more noticeable especially on a metal or hard surface, and you may struggle to cut the etch at all. If you cut either material etch on a cutting mat the blade will drag the part down as you exert the force needed to cut through, resulting in bending the part.  The stainless etch below has some very small parts, the squares on the cutting mat are 0.5″ (12.5mm).

This stainless steel etch is from a kit by Keystone Details and zooming in you can see some of the tiny details.  Under the ladder is an electrical box that needs to be cut out and folded to make the box.

If I attempted to cut any of these parts out with a knife they would certainly get damaged.  So I use a special pair of scissors designed for doing this job.  Mine are made by Tamiya specifically for photo-etched parts.

The tips are small and curved which allows them to easily fit in the gap between the part and the fret so you can cut the tab releasing the part.

It’s not always possible to cut the tab off exactly where the part starts, so this little burr will need to be filed off.  Be sure to hold the part firmly between flat surfaces otherwise the filing action could also bend it.

Sometimes the fret is made from fairly thick metal.  The HO DT6-6-2000 etched brass Additions are made from 0.5mm thick brass compared to the N scale ones at only 0.25mm.  This was done to give the desired size of the handrail on the HO model, but it does mean the tabs are much harder to cut.

I use a much larger pair of scissors here with a strengthened set of blades for thicker metal.  These are ideal for removing sections of the fret to enable better access to the parts.

So I use a mixture of the Stanley Knife and scissors, depending on the part I’m removing.  It’s best to test cut a section of the fret that you don’t need, to gauge which tool is best.

This isn’t the only method for cutting parts from etched frets, there are also other tools for cutting photo-etch, however, I haven’t tried them yet because what I have works well for me. As modelers, we’re inventive in our use of tools and materials, but it’s helpful when we find a tool designed to get the job done, ie cut out parts that aren’t bent or burred.

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

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.