A New Gear for the New Year

Happy New Year!

This week I’m starting the New Year with some small 3D printed parts to repair a Bachmann N Scale Doodlebug.

The Doodlebug is the name given to a self-propelled railcar originally powered by a gasoline engine with a direct drive or connected to a generator to power traction motors.  They started to operate on small lines around 1907 as they were more economical to run than steam engines.  Typically they ran on their own but could pull another car if needed.  Below is a photo, from Wikipedia, of Santa Fe Doodlebug number M.119 at Isleta, New Mexico in 1943 with its extra car.

Backmann’s model is very similar to M.119 and is a mixed passenger and mail carrier.  It has a motor near the front which powers the front truck only.  The rear truck is free-running but also picks up current from the rails.

Both of the front axels have gears so they can be powered. The gear is molded into the plastic axel which electrically isolates the two wheels.  It’s impossible to see but the axel that’s been separated from the wheels has split.

This causes two problems; firstly, as the split is between two gear teeth causing a bigger gap, the meshing gear won’t line up correctly and this causes the doodlebug to click or lump as it runs down the track.  Eventually the gears will jam.  The second problem is the wheel will spin in the axel; this results in a loss of traction as the motor won’t drive the wheel.

The axels in the rear truck have also split as you can see below.  I’m unsure why these have split as they’re not under any load, but my theory is simply the pressure applied from the inserted wheel stub forced the axel apart.

The other gears in the truck tower all seem to be in good condition and I think this is because they don’t have anything like the wheel stubs pushed into them, forcing them apart.

To repair the Doodlebug I’ve drawn a replacement gear axel and plain axel which will be 3D printed in Shapeways Fine Detail Plastic material.  I use this material because it’s hard, smooth, and prints to a very high accuracy.  I’ve made the hole through the axels ever so slightly smaller than the axel so it will be a tight fit.  But hopefully not too tight so that it splits the new axel.

In order to keep the cost of the parts to a minimum, two gear axels and two plain axels have been joined on a loop of 3D printed material.  They don’t actually touch the loop so it can be cut off and used without any burs.  That’s a great advantage with 3D printing.

These gears have now been ordered for a test print and once they arrive I’ll fit them and show you how they perform.  If all works okay I’ll make the repair set available in my shop.

I know for a lot of us modelers there’s never enough time for the things we need or want to do, but I hope this year brings for you, as well as me, the opportunity to get some of those long thought out or dream projects done. Here’s to a productive 2020!

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.

A Dummy Knuckle Coupler for OO Gauge

It’s been a busy time over the last few weeks, which you may have noticed by my absence last week.  But I’ve not been idle and I have lots of new things on the way, but for now they are still on the drawing board or being tested.

One thing I can share with you is a new design for a fellow UK OO gauge modeller who is fitting Kadee couplers to his rolling-stock.  He wanted to have a non-functioning Kadee coupler to make sure that rolling-stock in fixed rakes would not come uncoupled but maintain the look of the Kadee coupler.  As most of the new OO gauge rolling stock now has NEM standard sockets it seemed that this would be fairly simple.

A working Kadee coupler with a NEM fitting, as shown below, rotates about a central pin and the knuckle opens and is held closed by the spring on the side.

I designed the dummy so that it’s fixed in the closed position.  I also omitted the rotating pin and made the whole coupling one piece.  Hopefully there’ll be enough play in the knuckle to allow for some rotation.  My first design looks like this.

This is now being test printed and as usual I will share the results with you once they arrive and I’ve had a chance to test them.

But for now it’s back to the drawing board.

Alco C-855 N Scale Replacement Lifters

Sometimes trains get damaged, I’m sure it’s happened to most of us at some time.  And there’s always that one point on a model which is more prone to getting damaged than the rest.  On my C-855 shells it’s the lifters at the rear of the model.

The C-855 has four lifting points to allow the whole body to be lifted off the trucks.  There are two in the nose and two at the rear. The nose lifters can be seen below; there’s a recess behind the hole to allow a lifting shackle to be attached.

The rear lifters are raised up on posts.  This is to keep all four lifting points at the same height.  On the real locomotive the posts would have been thick heavy metal but in N Scale acrylic they’re a little thin.  And it’s these that are likely to break if the shell is dropped.

If you can find the broken part it’ll fix right back on with a drop of superglue as this material usually breaks with a clean edge.  Injection moulded parts tend to distort when they break so fixing them back on can be harder.

But if you can’t find the part a replacement is needed so I’ve created a set of four lifting posts as the C-855B has four posts because it has no nose.

The set has two left and two right hand posts and they are all 3D printed on a ring which makes them a single part and therefore cheaper to print.  I’ve made them longer than normal so they can be shortened to the right length depending on where the break is.  As the material is hard these will not cut like injection model plastic but can easily be filed or sanded to get them to the right length.

The replacement C-855 lifters can be found here.

Bachmann N Scale 4-8-4 Replacement Gears – Part 1

Following on from last week’s post, this week is also about 3D printed replacement gears.  Although this week it’s for an N Scale Bachmann 4-8-4 Northern.

The Bachmann 4-8-4 Northern has been around since 1972 and there have been several versions over the years.  The first two, with the second released in 1975, are in my opinion rather lumpy runners but it’s the third version, released in 1982, that I’m working on and it wasn’t too bad.  However this release suffers from the same problem as the locos in my last two posts; split gears.  The loco in the image below is one of these (image from Spookshow.net) and you can see the rear driver is at a different rotation to the rest.

It’s possible that the wheel on the other side of the locomotive is in the correct position but it’s more than probable that it too is misaligned.

The chassis, as shown below, is in one piece with the motor above.  The gears sit off-center within the chassis. Each axle is powered by gears so the side rods are cosmetic but if they get out of quarter, as with the loco above, everything jams up.  The most common axles to split are the rear two as these are the first to be driven by the motor and therefore under the most stress but it’s not uncommon for all of them to split.

The original axles are asymmetric, that is to say the gear is not in the center of the axle. You can see below the splits on the axles.  This releases the friction grip on the wheels, which are simply pressed into the axles, and allows them to spin in the axles.

To start with I 3D printed a set of axles in Shapeways Fine Detail Plastic, formally known as FUD.

Compared to the original they are the same, but the inside diameter of the axle was too big, so there was no grip on the wheels at all.

So I 3D printed another set with a smaller inside diameter. I also 3D printed the other gears as it makes sense to supply a full set of replacement gears.  This includes the two idler gears and the twin transfer gear that fits under the motor worm.

All the original gears look like this.

Below are the new gears compared with the old.

Test fitting the second set of gears on the axles I found they did fit with a push and I thought that the friction would be enough to prevent them from spinning on the wheels.

To fit the axles properly the chassis plate needs to be fitted between the axles and the wheels.  The chassis plate positions the wheels and transfers electric from the metal wheel to the motor; there’s one on each side.

This is the tricky part.  When the chassis plate, axles and wheels are fitted to the chassis the wheels must all be at the same position.  The position of the axle on the wheel can also affect this as the teeth on the gear need to mesh with the idler gear teeth; if it’s off it will force the wheel to rotate slightly as the teeth mesh.  I reckon they had a jig for doing this in the factory.

The wheel sets on the other side must also be fixed so all four are at the same rotation but quartered compared to the other side.  To find out what quartering means and why it’s done see the post from two week’s ago here.

On test running, the motor drove all the gears and everything rotated etc but it was lumpy.  On inspection one of the wheels was not as well aligned as it should have been and as I attempted to rotated it the wheel spun in the axle. The new axle has not split but it means the diameter of the hole in the axles is still too big and needs to be smaller giving a tighter grip on the wheels.  I was reluctant to draw the hole too small to start with because if it’s too small and the wheel is forced in it will probably split the new axle.

Next I’ll make the necessary adjustments to reduce the size of the hole in the computer model and test print another set.  Although it fitted okay I’m also going to make a small adjustment to the twin transfer gear as it was also a little too loose.  When they arrive I’ll share the outcome with you.

EMD DD35 With Body Mount Couplers – Part 1

This week I have a modified shell to share with you for my N Scale EMD DD35 project.  The new shell option incorporates body mounted couplers rather than truck mounted.

My DD35 3D printed shell is designed to fit onto a modified Bachmann DDA40X chassis which has truck mounted couplings.  Only the shell and fuel tanks are 3D printed, the trucks and pilots come with the chassis.  You can find the kit here.

The real DD35, and the DDA40X, has body mounted couplings, or rather chassis mounted, which allow the trucks to rotate freely under the chassis.  I originally decided to leave the truck mounted couplings on the model, simply because of the length of the locomotive.  As it’s so long, body mounted couplers will cause a problem with tight curves.  As the locomotive navigates the tight curve the coupling moves too far away from the center of the tracks and can pull the connected rolling stock off the rails or derail the locomotive. That’s also why Bachmann built the DDA40X model the way they did.

But some layouts have larger radius curves than others and I was asked if I could produce an extra part to allow body mounted couplers to be fitted.  So I did and they looked like this.

These came in the form of a pilot section with a cutout for a body mount coupling which, with a bit of modification, could be fixed to the underside of the shell.  You can read my post about them here and they can be found here.

But the ideal situation is to have the pilots 3D printed as part of the shell and that’s what I’ve done as you can see in the renderings below.

The new pilot section has the pocket and screw hole for Micro-Trains body mounted coupling.  The problem comes with fitting the new one piece 3D printed body section onto the chassis which is now too long.  As the pilot sections tuck under the chassis this makes it impossible to simply drop the body down onto it.

The original modified chassis, as shown below, has the pilots attached to the trucks and the chassis stops roughly where the pilots start.

To make the new shell fit, the first thing to do is remove the existing pilots.  These are held on with two screws which release the coupling and pilot.

The pilot mount is plastic and projects from the truck frame.

This needs to be cut off and that can be done with pair of side snips.

The chassis also had to be shortened by filing the ends.  From point to point the chassis needs to be 150mm (5.906″) long in order to fit inbetween the new pilots on the 3D printed shell.

With the chassis reassembled it now looks like this.  I also filed a chamfer on the four corners to ensure the shell was a good fit.

One other modification I made was to file off the four locating bumps on the sides of the chassis.  These normally located the DDA40X shell which has matching holes on the shell.  As the DD35 shell doesn’t have these holes and is held in place by the length of the chassis they are not required.  They will also cause the shell to spread if left in place.

The new shell, which is 3D printed in Shapeways Fine Detail Plastic, fitted onto the chassis and clipped into place, as did the fuel tank.

Once the shell has been painted I will fit the body mount couplers and get some videos of the DD35 traversing curves with its body mounted couplings. I’ll share that with you in another post.