Replacement Atlas N Scale Motor Universal Connectors

Atlas make lots of railroad locomotives and rolling stock in a variety of scales, and I have several of them because of their quality and they enable me to use the chassis for other builds.  In particular, I use their C-628 and C-630 N Scale models as the donor chassis for my N Scale DT6-6-2000 and RT624 kits.  The chassis has been revised over the years to make improvements, but one version has an issue with the driveshaft coupling to the motor failing.  In this post I’ll share with you my fix.

Below are a pair of Monon C-628s; the rear one is actually a dummy using my 3D printed chassis kit.

The powered chassis is a standard design, used on many of Atlas’s N scale locos, with a central motor and flywheels.

The chassis is held together by the two screws near each end, and the fuel tank, which clips over both chassis halves.

Inside at each end is a driveshaft linking the flywheel and the worm gear, which drives the truck towers. These simply pull out.

The motor is clipped in a cradle which in turn is clipped into the chassis.

With the motor removed you can see inside the flywheel; there’s a plastic universal joint, and it’s cracked.

The universal joint is press-fitted over the axel and uses the friction to spin it with the flywheel.  Even when cracked it’ll spin so the loco will probably run okay on its own.  But as the load is increased, such as adding a train, the amount of force on the split universal is stronger than the friction, and the axel just spins.  So if your loco seems to run okay, but won’t pull very much, this is most likely why.

The universal joint is a plastic tube with two pegs which fit into the driveshaft.  The hole in the tube will be smaller than the axel to create the required tight fit but the constant pressure on this particular material causes it to crack.

Replacement universal joints are available from Atlas, but these have been known to fail as well.  So I’ve 3D modeled the part and printed it in Shapeways Smooth Fine Detail plastic because it’s both accurate and also hard-wearing

The new part is a direct replacement for the original.

If the old universal is cracked it should simply pull off leaving a clear axel inside the flywheel.

I fitted the new universal by placing it with a pair of tweezers but not pushing it on fully, just enough to hold it in place.  If it’s pushed at an angle it too may crack.

I then used a flat screwdriver, as to give even pressure, to push it on fully so the universal is all the way to the back of the flywheel.

And that’s it.  The loco is ready to be reassembled.

These are now available in packs of two and four using the links below:

2x Replacement Atlas N Scale Motor Universal Connectors

4x Replacement Atlas N Scale Motor Universal Connectors

This universal is used in many of Atlas’ diesel locomotives and will fit all.

I’m juggling an HO project as well as testing recent 3D printed replacement parts, but my focus is on returning to work on customer’s layouts where possible, so who knows what I’ll be sharing next week!

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.

New Gears For A Bachmann N Scale Doodlebug

The first post of this year showed you the problems with split axels on a Bachmann N Scale Doodlebug, which can be found here. In this post, I’ll show you the result of the 3D print.

The four 3D parts, as pictured below in the top of the image, are the two drive gear axels and two free axels.  The Doodlebug does have other gears between the motor and the wheels but it’s only these parts that break as they have metal axles forced into them, causing them to crack over time.

The two parts in the middle are an original cracked gear and axel, and at the bottom are an original gear and axel with the wheels fitted.

Before I fit the wheels to the new parts I pass a 1.5mm (0.058″) drill through each part. The drill is ever-so-slightly smaller than the hole in the part, so no actual material is removed, but it cleans out the 3D print residue and ensures a good fit.  If there’s residue the fit can be too tight and cause the new part to crack.

One thing to note; two of the wheels have traction tires and both fit onto one of the axels.  If, like me, you accidentally fit a regular wheel to this axel it can be very difficult to remove and there’s a good chance you’ll break a tooth on the new gear, which is what I did.  That’s why in the new set below I still have one original gear that wasn’t cracked.

The drive gear set clips into the truck tower, with the new gears meshing with the originals.

The plain axels for the trailing truck simply rest in the cutouts.  Both trucks have a plastic clip that holds everything in place.

With the trucks refitted, power pickups replaced, and truck sides attached, the chassis is ready for a test.

And it ran very well, smooth and free, so I refitted the shell.

At some point, I’ll fit a DCC decoder to the Doodlebug, but first I want to tone down the paint job.  Although it’s in the UP colors or Armour Yellow and Harbour Mist Gray, I do find it a bit bright.  But with some weathering, I think it’ll look just fine.

The 3D printed replacement axles for the Doodlebug are now available through my Shapeways shop and can be found here.

I’m slowly working my way through the older Bachmann locomotives which I’ve found tend to have split gears.  I’ve got the first two versions of the N Scale DD40AX and the N Scale PCC Interurban Streamlined Car next on the workbench and will be drawing designs for those for replacement 3D printed gears too.

An N Gauge Dapol Britannia Driveshaft

This week I have a new product to share with you.  The N Gauge Dapol 4-6-2 Britannia is a great model.  But in a similar way to the N Scale Roundhouse, now Athearn’s, 2-6-0 and 2-8-0 steam engines, and the Atlas N Scale 4-4-0, this particular model also needed a new driveshaft and yoke.

The motor, and DCC decoder, is packed into the tender and a drive shaft runs through the cab to power the main driving wheels.  The motor axle has a yoke fitted to the end, as does the spindle in the cab.  A driveshaft connects the two yokes and allows the tender and locomotive to twist without breaking the transmission of power, just like a drive shaft does on a car without being affected by the car’s suspension or steering.

I modeled the three parts after taking measurements from the originals.  I made the driveshaft slightly longer as I’ve often had originals come apart when handling the locomotive. The set on the left are loose, but in order to avoid an individual part print charge, I’ve combined them into the set on the right.  None of the parts actually touch the sprew which can simply be cut away.

The parts were printed in Shapeways Smooth Fine Detail Plastic, as it’s the most accurate for small parts, and they came out very well.

On the model, it was the yoke on the motor axle which was missing.  This is normally due to the original splitting.  If the valve gear on the locomotive jams and the motor carries on trying to spin, the force can cause this to happen.

The new yoke, with a little bit of pressure, fitted onto the axle.  I’ve designed the hole in the yoke to be very slightly smaller than the axle so the pressure fit will prevent it from spinning on the axle.  Whenever fitting anything like this it’s important to make sure the inside of the yoke is clean and free from any 3D print residue, as this may cause an even tighter fit and could lead to the new yoke cracking as well.

As the old yoke on the locomotive spindle was intact I didn’t change it, but as you can see the new driveshaft fits well.

With the locomotive reassembled I also tried it with the original driveshaft; you can just make out the black spokes in the new tender yoke.

But I did find, as with the original setup, the driveshaft came out too easily.  The new 3D printed one is almost 0.8mm longer than the original and this helped keep it in place as you can see below.  Another alternative would be to slide the tender yoke slightly closer to the locomotive.

The last step was to test the new driveshaft and as you can see below I’ve lifted the locomotive driving wheels off the track for the first test.  I wanted to run the loco at speed for a while, and as the rear set of drivers have traction tires which are susceptible to coming off, I didn’t want to give them the chance.

The next test was to do several successful trips around the layout with twelve coaches behind, which it did with ease.

The Dapol N Britannia Driveshaft Repair Kit is available here.

This coming weekend is the NMRA(BR) Benson winter meet and I’ll be there with my fellow club members and parts of our ‘Solent Summit’ layout.  As this is only a one-day event we won’t be putting on a 5 Mile show like we did at Warley!

The event is at the Benson Village Hall, Sunnyside, Benson, Oxfordshire OX10 6LZ from 10am till 4pm. I hope to see you there if you can make it, if not I hope to get some photos to share with you next week.

A Dummy Knuckle Coupler for OO Gauge – Part 3

Back in July, I shared with the second part in my design of a dummy knuckle coupler for OO gauge rolling stock.  You can find the post here.  Since then the first prints have been through several tests and they performed very well.  In this post I’ll show you the small changes I made to the design and share with you how to get some.

The original design, as shown below, was printed in both Shapeways clear Fine Detail Plastic and the Black Versatile Plastic.  The Black Versatile Plastic turned out to be so good I’ve carried on with only this material.  Not only is it strong, but as it’s already the right color, they’re ready to use.

The original design was for a dummy knuckle coupling which would work with Kadee couplings as well as each other.

The first issue I had with them, albeit a small one, was with the knuckle section.  As the actual knuckle, unlike the Kadee, doesn’t swing, and it tended to grip on tight curves.  I opened the jaws slightly to allow a bit more movement.  This solved the issue.

The second issue was due to height.  As I’ve said in other posts about couplings, despite there being the NEM standard regarding couplings and height, different manufacturers have positioned their coupling pockets at different heights. Some seem to be high and some low, which leads to the situation of an uncoupling, especially on gradients as the rolling stock crosses the transition from flat to inclined.  My first answer was to offer three different types, as shown below; high, standard and low.

However given there may be a few different lengths, this makes for a large number of different couplings to manage.

A much simpler idea was to make the knuckle 2mm bigger.   By moving the top up by 1mm and the bottom down by 1mm all versions are covered.  The wings either side of the knuckle were also removed as they performed no real purpose.

This new design was 3D printed on sprew in the Black Versatile Plastic.  The sprew helps reduce the cost of the parts.

The Bachmann OO Class 66 has, what I consider, to be a correctly positioned NEM socket, that is, it’s in the middle of all the rolling stock I’ve tested.  The new coupling fits perfectly and doesn’t look too out of place.

Compared to a standard Kadee in another Class 66, the new coupling looks okay, even if it’s a bit deeper.

The two coupled perfectly and as you can see the new coupling sticks up and down by 1mm, ideal if the coupled item of rolling stock has its NEM socket out of place.

This coupling length is based on a Kadee No. 19. which works well for most items, although I found Hornby coaches ended up with a larger gap between them than I liked, so a shorter version will be designed soon.

For now, these are available in packs of 10, 25, 50, and 150 and you can find them using the links below.

OO NEM Dummy Knuckle Coupling (Large) x10

OO NEM Dummy Knuckle Coupling (Large) x25

OO NEM Dummy Knuckle Coupling (Large) x50

OO NEM Dummy Knuckle Coupling (Large) x150

Once the length of a shorter coupling has been finalized, to reduce the gap between Hornby coaches etc, I will share this with you too.  But now it’s back to the drawing board as I have several projects to wrap up which I’ll also share with you in due course.