A Different Material for Gears – A Second Attempt

For several years I’ve been producing replacement gears in Shapeways’ Smooth Fine Detail, formally know as Frosted Ultra Detail (FUD).  But what about other materials?

Back in June of 2019 I tested a different material, Multi Jet Fusion Plastic or PA12.  You can find the post here.  This test was not successful, as you can see below, because the definition simply wasn’t there.

To be fair these gears were small, measuring only 4.38mm (0.172″) in diameter.

But this material is a lot stronger than the Smooth Fine Detail.  The Smooth Fine Detail is an acrylic and although it’s very hard, it’s brittle and impacts can cause cracking.  That’s why my replacement Bachmann HO 4-8-4 gears needed to be much thicker than the original.  The PA12 is a nylon plastic and some of its listed key properties are high strength and durability, as well as good impact resistance.

To give it a good test I needed to try a larger part and the ideal opportunity came along when a  customer wanted some replacement gears for an O Scale 3 Rail brass AC6 Cab Forward.  These 4-8-8-2 are huge and a lot of power is transferred to the driving wheels to be able to pull prototypical trains.  This particular model has an idler gear that runs between a metal worm gear and a metal axle gear. An idler gear is a gear that spins freely on an axle without turning that axle between two other gears, the purpose is either to change the direction of the second gear or to simply space the gears out. (Image take from https://www.notesandsketches.co.uk)

The original idler gear was plastic, and due to the constant wear from the two metal gears, had become damaged.

The reason for this gear being plastic rather than brass was it had a left-hand twist, as you can see below.  This is not impossible in brass but it’s very expensive compared to regular gears with straight-cut teeth.

But this sort of complex 3D geometry is ideal for 3D printing.  This gear has a diameter of 9mm (0.3543″) so is twice the size of the previous gear and has much larger teeth.  In order to allow for spares, several were test printed at once on my typical sprue.

The PA12 material has a coarser finish than the Smooth Fine Detail but given the scale of the components, this is not an issue.  As you can see below the new idler gear fits well into the AC6’s transmission.

After assembly, the locomotive had several hours of use with no problems at all, so in this case the PA12 material is a success. At the time of writing the cost of the set of five PA12 gears is the same as a set of Smooth Fine Detail gears.  When the PA12 was first introduced it was more expensive.  The base color for the PA12 is gray but the black, as used here, can be chosen for a little extra cost.

With this successful test, I now have another material available for larger gears that don’t rely on tiny smooth parts.  The point where Smooth Fine Detail will need to be used over PA12 will be different from model to model and will depend on things like teeth size, but I’ll endeavor to use this where possible.

I still have several new gears to try for projects I’m working on, but if you have a need for a gear that’s proving difficult to source please get in touch and hopefully I can produce it for you.

Solving Common Bad Running Issues With Kato Diesels

Kato makes some fantastic N scale locomotives and they run very well, that is until they don’t.  In this post, I’ll share with you the three most common issues I find as to why these reliable locomotives stop working.

There are of course typical things such as dirty wheels and track, but the three issues I’m sharing with you take a little bit more to fix.  They’re also common on other brands of locomotives that have similar parts.

The first issue has become apparent on this Kato SD40-2, as shown below. This model was custom painted by Paul Begg.  This is a 6-axle locomotive that picks up the power on all 12 wheels.  The power is transferred to the chassis halves via copper strips and then into the circuit board.

With the shell removed you can see the circuit board. This particular locomotive is DCC fitted with a Digitrax DCC drop-in decoder, but I’ve had the same issue with DC versions.

The circuit board or decoder drops into the chassis and pushes forward which clamps it in place and at the same time makes electrical contact with the chassis halves and motor contacts.  Below, you can see the decoder has slid back exposing the electrical contacts at the front.

Close up you can see the electrical contacts, and the slots in the chassis halves they slide into.  Ideally, this should be a tight fit requiring a little force to push the decoder forward.  The friction then prevents the decoder from moving and ensures good electrical contact.  But sometimes the decoder is a loose fit; this may because the DCC decoder is ever-so-slightly thinner than the original circuit board or maybe the chassis has been affected by the pressure of clamping the decoder.  The consequence is the decoder slides in and out easily, and the electrical contact is very poor.

The electrical contacts or pads on the decoder are copper, which is ideal to solder too, so to fix this issue I flash over the pads with a soldering iron to put a thin layer of solder on top.

The layer of solder can’t be too thick, otherwise, it’ll prevent the decoder from fitting at all. To get a thin layer I first use the iron to put some solder on, then I clean the iron tip on a wet sponge and quickly run it over the pad again. Excess solder will be removed on the iron, leaving a thin flat surface.  This may take one or two passes with a clean tip each time.

The decoder can then be pressed in.  It will take a good press as the pads are now thicker, but if it feels like you need to press too hard, rather than risk breaking the decoder, pass a clean iron over the pads again to remove a little more solder.

Once fitted the decoder should not move and you’ll have a solid connection, because the solder is softer than the copper and the chassis will dig into it.

The second issue I see a lot is to do with the actual pickups in the trucks.  The AC4400CWs below, again custom painted by Paul Begg, suffered from this.  The first fix above has already been done. This is one of the older chassis where the chassis screws need to be loosened slightly to release the truck.

With the truck bottom, and side frames unclipped the pickups will fall out.  Each wheelset has a plastic axle and metal wheels with a spike on the outside of the wheel.  The spike fits into the cone of the brass pickup.

The issue is dirt and crud that builds up inside the cup.  Below you can see two pickups from the same truck. I’ve cleaned the cups on the lower one.

To clean these cups I use tiny cotton swabs dipped in Isopropyl alcohol. These fit perfectly into the cups to clean them out.  Another alternative is a small Philips/positive drive screwdriver of a similar size.  One note about using Isopropyl alcohol to clean contacts: if they’re from a 3D printed truck, clean the Isopropyl alcohol off fully before refitting the pickup because 3D printed materials and Isopropyl alcohol don’t mix very well.

As well as cleaning the cups the wheel spike should also be cleaned and for this, I use a regular cotton bud dipped in Isopropyl alcohol.

The last issue is also to do with trucks and is something I’ve come across several times.  Below is another SD40-2.  The decoder is not loose in the chassis and the pickup cups are clean, and as you can see below it’s receiving power as the light is on.

However, if the front truck is lifted off the track the power stops.

Lifting only the rear truck shows the power returns so one or both sides of the rear truck is not working correctly.

This is one of the newer Kato chassis and the trucks simply pull out and clip back in.  When removing the trucks the drive shaft will also fall out, so be extra careful not to lose the bearing on the end of the worm gear as they will also fall off.  Should it fall off note that there is a tiny plastic washer between the bearing and the worm gear.

With the truck removed the problem becomes apparent; you can just about see it in the image above but it’s clearer below. The righthand pickup, with the cups in, has a post that stands up to make contact with the chassis copper strips and it’s bent.

Compared to the one on the other side you can see it’s pointing towards the truck rather than up.  This will prevent making contact with the copper strip and reducing the locomotives pickup by half on that side.  The solution is to bend it back into the right place and this can be done with a pair of tweezers or small needle nose pliers.

Now with the truck reinserted in the chassis, the locomotive should work with either truck on the track.  And with both trucks picking up power, clean pickup cups and a good connection to the decoder, the locomotive should run as well as new.

Clean wheels are also important, and a little lubricant on the gears is also a good idea while you have the trucks out.  If you’re wondering what oils or lubricants to use on the gears I’ve written a post about that which can be found here.

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.

https://www.shapeways.com/shops/JamesTrainParts

Happy shopping!