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.

N Gauge Peppercorn A1 Replacement Bell Crank Covers

This week I have another new replacement part to share with you for an N Gauge Bachmann (Graham Farish) Peppercorn A1.

These locomotives, as pictured below (Bachmann stock photo), are fairly new and therefore not a lot goes wrong with them.  They are fantastic runners.

But from time to time parts can come off and get lost, and that’s what happened to this one.  Where the eccentric rod connected to the bell crank Beckman have secured the rod with a plastic molded part with two pegs as shown below.  These parts are opp-handed so they are different for each side.

Drawing the part is fairly simple, as I had one to copy, and I’ve joined both parts together to make them cheaper to print and keep them in pairs.

The new parts, which being transparent are very hard to photograph, came out very well and are almost identical to the original.

On the locomotive below you can see the eccentric rod hanging down.  The two holes under the running board receive the pegs on the bell crank cover.  The hole nearest the front of the loco pins the eccentric rod.  At the end of the rod is a plate with three holes; the middle hole is oversized to allow the plate to rotate in on the pin.

With the original cover fitted, as shown below, you can see how it all fits together.

On the other side the new 3D printed part fits in the same way.

This 3D printed part has one of the pegs ever so slightly, and I mean 0.3mm, too low on the cover.  This causes it to appear to be at an angle.  I’ve corrected this in the model file.

Once painted with a matte acrylic black, the new cover fits right in with the locomotive.

For symmetry I changed the other side for a 3D printed part as well and again it fits right in.

Upon test running, the locomotive is as smooth as when it was new.  A pair of replacement N Gauge Bachmann (Graham Farish) Peppercorn A1 bell crank covers can be found here.

Next week I’ll have another new replacement part to share with you and then it’s back to the projects in hand.

Union Pacific Rotary Snow Plow 900081 – Part 4

To start this week I’d like to apologize for the lack of a post last week.  It had been a busy weekend at work and I simply ran out of time.

But the good news is I’ve made some, albeit small, progress on my UP Rotary Snow Plow project.  If you are new to this project you can start reading about it here.

Most of the body section is now drawn, although there is plenty of detail to add.  The one big space left to do was the rear of the unit.  And as most of the attention is drawn by the large fan at the front, the rear is often overlooked by photographers. This causes a problem for me to get information, and there’s a lot going on back there.  However thanks to Flickr and the photos of Dustin Holmes I have some great resource material to draw from, as you can see below.

Apart from the door, which is not centered on the body, and all of the grab irons and pipes, there are two lifting points which frame the door and the large fan at the top behind the grill.  This 48″ fan is a Dynavane blower, which delivers clean air to the motor, and traction motors which drive the cutting fan on the front.  This is necessary when the snow is falling hard and the air supply gets congested!

In order to model this and make sure the fan could be seen I’ve decided to make the mesh from etched brass. Below you can see the mesh closing off the rear of the body.

Behind the mesh will simply be the fan and a recessed area.  The sides of the body extend into the void as I need to alow space for the grab irons to run into and to give structural integrity to the body.

The actual fan will be printed as part of the body and therefore unable to rotate, but I don’t mind that, after all this is N Scale.

I will look at making the actual mesh as fine as possible so the light can get in and show the fan but from the render below you get the idea.

I’ve also added a coupling pocket for a Micro-Trains 1015 Body Mount coupler.  There will be a screw hole printed into the body to hold it in place.

I’ve also finished the directional cover which forces the snow either to the left or right.  This again will be made from etched brass as I want to be able to move it from side to side.  If I made this as a 3D printed part it would be too bulky and not look very realistic.  There will be a pair of holes on the cover which will clip over two pegs 3D printed onto the side of the exit chute.

Now I really need to get back to the chassis and finish working out how to modify it to fit in.  Once I have done that I’ll have another update for you.