A Baldwin DT6-6-2000 in HO – Body Shell Part 3

In last week’s post, I promised to share some progress with my HO Scale Baldwin DT6-6-2000 body shell and, so far, things have gone well.

The locomotive body, as pictured below, was originally drawn for my N Scale model which can be found here.  This means the bulk of the drawing work has already been done.

However, as this new model will be for HO scale, roughly twice the size, some of the details can be improved or enhanced.

There’s also scope for removing material from the shell to potentially reduce the overall cost.  What I mean by this is reducing the wall thickness of the model.  For example, the 3D printer I use to make my shells can print a rectangle of plastic which is only 0.6 mm thick, and when this is scaled for N scale at 1:160 the plastic translates to 96mm thick.  So I designed the sides etc. of the shell to be about 96mm thick, but when this is printed at HO scale, which is 1:87, they come out at 1.10mm thick, which is almost twice as thick as it needs to be.  Previously I would work through the model and thin all the walls down;  I used to do that for other HO models as the price of the 3D print was based on the volume of material used. However, the method of calculating the cost has changed and there are some different rules depending on the print size.  One is to do with the space the print takes up in the printer, or ‘Machine Space’, and as this is a fairly large print it’s calculated that way and a small change in the volume has no effect.  A big change in volume, such as the shell being solid, would mean the volume would be used to calculate the cost and it would be higher.  But for us it’s ‘Machine Space’, so I can leave the bulk of the walls as they are.

There’s also the issue of strength.  The bigger a section of ‘Wall’ is, such as the side of a shell, the more flexible it will become.  By increasing the thickness, the ‘Wall’ section will become more rigid and overall the shell will become stronger.  Considering this is an HO locomotive and the couplings are attached to the shell and not the chassis, I want it to be strong to withstand the impact and pulling forces of a heavy train.  So leaving the walls thicker is an advantage.

Getting back to the details, in the last post I showed the shell split in half with the chassis fitted inside, and I needed to connect the two together.

By increasing the material behind the coupler pocket I’m able to create an area for the chassis lug to fit into.  The chassis is shown in gray.

As you can see below the chassis lug has a hole in it which is 3.5mm in diameter so I’ll probably use a bolt to hold the chassis to the shell.  I can indent a hexagonal hole in the top of this new section so the bolt nut becomes captured and unable to turn.  It could even be glued in so the bolt can easily be tightened from below.  With one at each end, this will be sufficient to hold both parts together allowing the locomotive to be picked up from the body shell.

At each end, and on either side, the original DT6-6-2000 has air vents close to the walkway.  On the N Scale version, these were simply reproduced by recessing the shell to show the steel frame and the mesh, as shown below.

But for the HO version, I’ve removed the material to allow an etched brass mesh to be placed behind the frame.  This etched part will be on the ‘Brass Additions’ for this model so it only needs to be fitted.  The inside of the shell will be recessed for the mesh so the position will be correct, and it won’t catch on the chassis.

I’ll also be adding other etched brass parts to this model such as grab irons.  The N scale version had the grab irons molded as part of the shell but the HO version will have the mounting holes only, as shown below, 3D printed into the shell.

The etched brass handrails and grab irons will be made from 0.5mm brass and will have locating holes for easy and accurate assembly.

I have more details to improve and add over the next week, but something that only occurred to me today, and which I’ve decided to add, is the ability to add Preci Models DCC auto uncouplers directly to the locomotive.  Preci Models make a kit to automate a Kadee coupling, allowing it to be opened and closed via the DCC decoder as demonstrated in the video below.

I’ve fitted several of these to HO and OO locomotives with great results, but each time I had to modify the chassis or truck to mount the motor and it took a lot of fine-tuning.  I had particular trouble with HO locomotives such as the EMD GP7 and F7 because the truck is very close to the pilot, which doesn’t allow room to mount the motor.  But the DT6-6-2000 has plenty of room and I can design a pocket for the motor and a route for the actuating string.  This will not be a requirement but a great addition, as it will allow the locomotive to uncouple anywhere on the layout.  And as the DT6-6-2000 was designed as a transfer locomotive from railyard to railyard, this is ideal.

This is the perfect stage to add details and parts to the model.  Does anybody have anything else they would like to see added to the HO DT6-6-2000, or RT-624 which will be following right behind, either 3D printed or in etched brass?  Please use the contacts page to let me know.

Next week I’ll have more progress on the shell to share with you and hopefully my solution for mounting the Preci Models uncoupler.

A Baldwin DT6-6-2000 in HO – Trucks Part 2

In last week’s post, I shared with you the first steps in the HO Baldwin DT6-6-2000 project and I ended with the image below showing my 3D model of the truck centers which hold the gears in place. You can find the post here. The reason for modeling the truck centers was to allow me to work out how to reposition the gears to allow the axels to be positioned differently.  The trucks are asymmetric and I need them the other way around.

In this week’s post, I’ll share with you my solution to solve the issue.

Inside the truck centers, in the original configuration, are 5 gears, as shown below.  The green gear at the top connects to the worm gear at the end of the drive shaft.  This drives the large blue gear which turns the center and right axels, shown in black.  The center axel then transfers the rotation through the three red smaller gears to the left axel.

Because I need to move the center axel to the left, the gearing will need to be rearranged and ideally, reusing the same gears would make sense, but that wasn’t possible as you can see below.  By swapping the red and blue gears over, all the axels are connected but there’s a big gap between the green gear and the red, so another gear needs to be added in.  The purple gear is the same size as the red.  But this configuration has another issue in that the blue gear is too big for space.  Looking at the outline of the truck center you can see the shape was tapered above the blue gear’s original position and that would not be possible in the new location.  The part would either become too thin and weak or project up and hit the chassis.

So, as an extra gear was unavoidable, I decided to make four extra gears, as shown below, and remove the blue gear completely.  The four new purple gears are all the same as the red ones.  To allow space for the new configuration of the red gears, the top of the truck center will also need to be extended, but that’s okay as there’s room between the truck center and the chassis.

Both sides of the truck chassis can now be properly drawn with the new gear holes set out.

The four new gears have been modeled inside a cage to make them one printed part, even though they don’t actually touch the cage.  This reduces the cost of the 3D print.  These parts will be test printed in Shapeways Smooth Fine Detail Plastic material for accuracy.

As well as the trucks I also had to model the Bowser chassis to see if it needed to be modified in any way to fit inside the shell.  The green section is the existing circuit board, with an 8 pin DCC socket.  The black section is the motor with its two brass flywheels.  Everything else is metal.

The shell, taken directly from my N Scale version looks like this.  I’ll be refining some of the details as they don’t need to be so big for HO, and replacing some with brass parts, such as the grab irons.  I’ll also be making the grills at the bottom of each nose section from a fine brass mesh.

 With the shell split in half you can see the chassis inside and it’s a good fit, with nothing requiring modification on the chassis.  As the DT6-6-2000 is longer than the original body shell for this chassis I can update the new shell to utilize the original shell and fixing points.

Next week I’ll have some progress on the shell to update you with and once the test truck arrives I’ll share that as well.

A Baldwin DT6-6-2000 in HO – Trucks Part 1

Ever since I released my N scale kit for the DT6-6-2000 in 2014 I’ve been planning to release it in HO scale. The project has had a few challenges getting started but finally, it’s underway.  And the first place to start is the chassis.

As with the N Scale version, I’ll be using a ready-to-run chassis to make things easier, and more reliable.  I’ve chosen the Bowser Alco C628/C630.  It comes with a big central motor, two flywheels and lots of weight, which will be ideal for a model of a DT6-6-2000.  It also has a circuit board with a DCC socket which I also intend to use.

This particular chassis came from a Canadian Pacific C630M and has different trucks to the Commonwealth trucks used on DT6-6-2000, but when I purchased the locomotive I assumed the wheel arrangement was in the same asymmetric positions with different side frames.  However, despite appearances, the wheels are evenly spaced.

But the good news is I was able to order a set of Commonwealth trucks from Bowser with the correct asymmetric wheel arrangement.

They’re a direct replacement in the chassis and now I’m at the right starting point.

The main difference between the Alco C-628/C-630 and Baldwin DT6-6-2000 chassis is the asymmetric trucks are facing the other way.  With the N Scale Atlas chassis, the truck gear tower is in the middle so they can simply be fitted facing the other way.  But with the Bowser trucks, the gear tower is at one end.  Luckily the front and rear wheel sets are already in the right position.  The DT6-6-2000 has an overall wheelbase of 54’9″, as you can see in this original blueprint below.  (Clicking on the image will make it bigger).

Converting that to Metric and HO scale works out at 191.8mm which is exactly the wheelbase the new chassis has, so it’s all good apart from the fact that the center wheel is in the wrong place.

The good news is the truck side frames are separate from the truck centers which hold the gears in place.

My plan is to 3D print some new truck centers with different gear spacing allowing the side frames to be refitted around the other way.  I’ve already drawn the truck centers with the original gear spacings.

My next step is to work out the new gear spacings which I’ll share with you once complete.  Then I can turn my attention to the 3D printed body shell.

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.