Earlier this year I shared with you my plans for my new N Scale Alco C-855. You can read parts one and two here and here.  I have recently started to do more work on the project  and have test printed the 3D printed parts which will extend the chassis for the new locomotive.  In this post I will share with you how they came out.

As discussed in my previous posts the chosen chassis, as modeled below, for the C-855 is going to be Con-Cor’s 4500 Gas Turbine/GE U50 chassis.

This chassis needs to be extended, as shown below, because although the C-855 uses the same trucks they are spaced further apart.

The chassis needs to be extended by 10mm and ideally in the middle over the motor.  To do this I have designed a complete replacement section that will extend the chassis and clamp the motor keeping it in the correct place.  Below is a rendering of the new parts.

These have been designed to be printed in stainless steel.  Although this metal is more expensive to get printed than plastics I didn’t want to reduce the weight of the chassis as this would have a negative effect on the locomotive’s tractive effort.  As the C-855 chassis will be longer it should now be heavier which will hopefully add to the tractive effort.  The C-855 did have 1000 more horsepower than the 4500 Gas Turbine and 500 more than the U50 after all.

The new extenders were printed by Shapeways and arrived ready to use as you can see below.

In close up shots like this you can see the layering effect caused by the 3D print process; this is more pronounced than on some other materials as the layer thickness is greater with stainless steel.  Shapeways also offer this material polished which removes these lines but as the parts will not be visible once the locomotive is complete this did not seem necessary.

A small change to the parts from the rendered view above is the introduction of wire routes.  This allows the bottom motor wire to run up between the shell and the chassis. For DC this is not necessary but for DCC the motor feed needs to be isolated from the chassis and a wire used to connect the motor to the DCC decoder.

Just to show that these really are metal, below is a photo of a basic volt meter set to measure continuity.  One of the parts has been laid across the pins.  As you can see the meter is reading 100%.

The parts will also be available in the cheaper plastics.

I did not allow any fitting gap between the motor and the new chassis parts.  Because they have been printed to such a high level of accuracy the hole for the motor is the exact same size as the motor and consequently it won’t fit.  This is easily remedied by grinding some of the inside of the chassis away. Alternatively I could have shaved down the motor casing.  I ground the inside of the parts with a flat stone in an electric modeling drill. Simply grinding the surface flat and removing the layering effect was enough for the motor to fit.

The motor now fits and I have also updated the 3D model to make the fit a bit easier.

As well as extending the chassis both drive shafts needed to be extended by 5mm as the ends will no longer reach the gears on the motor.  To do this I designed a 3D printed gear extender that will fit into the existing drive shaft gear as you can see in the rendering below.

The new part has been designed to be printed in Shapeways Frosted Detail plastics.  This is the best material to ensure the accuracy of the gear teeth.  My set was printed in Frosted Extreme Detail and below you can see how they came out.

Test fitting them into the original gears was a perfect push fit.  Below you can see one fitted into a drive shaft.  When it is time to fully assembly the locomotive I will put a small dab of super glue between the parts just to ensure they stay together although friction will do the job.

The next task is to finish the 3D model for the main body shell and set-out all the brass Additions.  My other locomotive kits have brass Additions for handrails and parts as well as 3D printed handrails but for this locomotive the only handrails will be brass.  I decided to do this because there will be lots of finally detailed handrail parts and if they are printed in plastic they are still a bit oversized and are very fragile.  With brass etching I can get decently sized handrails as well as lots of other details such as grab irons and roof top walkways.  Once I get the drawings done I will be sharing them with you.

Last weeks post was all about my designs for combining 3D printed parts and timber to scratch build a trestle bridge; you can find the post here.  The 3D printed parts have now arrived and in this weeks post I will share with you how they came out, and what the are like to work with.

The module I am building is for N Scale and has three trestles bridges although the last two are joined at one end. Below you can see a 3D computer rendering of the proposed module without scenery.

The parts of the trestle that are 3D printed are the main decks or stringers. Below is a 3D rendering of the underside from my computer model.  The cross ties you can see are guides to correctly position the top of the trestle bents (legs).

The parts have been printed by Shapeways in their White Strong & Flexible material and below are some photos of how they look when they arrived.

The three photos above show the short trestle stringers from the left hand side of the module.  The images below are the three parts that make up the large trestles to the right of the module.  The longest span from the front of the module has been split in two to make it easier to print and ship.

As you can see in the image above, none of the sections are straight, so having them 3D printed allowed me to ensure the trestle followed the correct path and landed at the right spot on the other side of the module.  As expected, the accuracy of the 3D printed parts was perfect, and when I laid the parts over a scale drawing I had printed out, they were a spot on match.

To join the two ends of the long trestle section together, I designed a finger joint into the middle.  Each stringer is made from four timbers. So as you can see in the image below, with the top section, I lengthened the middle pair and shortening the outside pair.  This was reversed on the connecting section.

Because I wanted a good tight and strong fit I did not allow any tolerance between the parts intending them to be held in place by friction as well as glue.

In the test fit below you can see they fitted very well.  To permanently fix these parts together I used tacky wood glue (white glue) in the joint, push fitted them together on a flat surface and left them overnight.

Although this material has a nice roughness to it which helps it look like timber the shocking bright white color does not. This is very easily resolved and in the same way I colour my timber for the rest of the trestle.

A have done this several times before as I have scratch built timber trestles before, although entirely out of wood, such as the one below.  This is part of the James Canyon Trestle on the Golden State Model Railroad Museums’ massive N Scale layout.  You can see more shots of it in the gallery here.  This trestle is made from bass wood and was stained rather than painted.  I used Woodland Scenics‘ Burnt Umber C1222 to stain the timber and black weathering powder at the intersections.

A good supplier of Bass wood is Black Bear Construction who specialize in scale lumber and jigs for making trestles in all scales.

Because the bass wood is stained rather than painted the hue of the colour can easily be varied depending on the amount of stain you use.  I also recommend staining all your timber before building the trestle, this is much easier than trying to get a brush into all those tight spaces.

For my new trestles I am using balsa wood.  This is not as strong as bass wood but I have a good supply and I was able to cut all the required scale sizes at Model Railway Solutions here in the UK.  It was partially because balsa is not as strong as the bass wood that I decided to 3D print the main deck or stringers; at this scale the WS&F material is much stronger than wood.  Surprisingly dispite its softness, balsa wood is a hard wood. Hard woods and softwoods are designated from the family of tree not from a hardness test.

Again I used a stain, or in this instance, I used American Walnut wood dye from Colron.

As with the balsa wood, the WS&F material is very absorbent to paints and stains and sucks up the color.  A small amount on a brush when touched to the WS&F will cover a big area and just about seeps through to the other side.  As with the bass wood trestle, you can get different hue effects by altering the amount of stain or dye applied.  Below are some shots of the stained decks or stringers.

In hindsight, I should have stained the two long trestle sections before I glued them together.  The tacky wood glue I used forms a barrier that the stain will not penetrate or cover,  so at the joint there are some white spots as you can see below.

However this can easily be covered with brown paint and weathering, so when finished it will not be visible, but this is a good reason for staining all the parts first which I did with all the rest. Construction could then begin.  Below are some shots of parts of the smaller trestle in place. It is not finished yet as there are still lost of braces and details to add, but it gives you a good idea of how the 3D printed parts and the balsa work together.

I now have a lot of bents to make and landscape to form to complete the trestle which will keep me busy, but I will share my progress with you in the coming weeks. This module will be finished for this year’s NMRA (BR) annual convention in Derby later this year and will be part of the Gosport American Model Railroad Group’s layout Solent Summit.  Maybe I will see you there.

With 3D printing becoming more and more useful in the model railroad world I have started to look at the scratch built projects I am working on and wonder how I can use 3D printing to do the same job.  This has been great for projects which need complex parts or very bespoke and detailed items.  But sometimes simply making them with a 3D printer can take some of the enjoyment out of model making.  A good example of this is bridges, or to be more precise, timber trestles.  I have always enjoyed scratch building trestles using real wood and in this post I am going to share with you how I have combined 3D printing and real timber to scratch build a new trestle.

The project I am currently working on is a module for the Gosport American Model Railroad Groups N Scale layout.  The module, called Warsash Wye, is five feet long and one foot deep and has a ‘U’ shaped river running through it. Below is a computer model of my module and you can see the river bed at the bottom.

As the railroad passes through the module it crosses the river twice and also has a diverging line that splits off and runs out of the back of the module.  Below is a plan view showing the track centers.  The diverging line also crosses the river before entering a rock tunnel.

I wanted to create a scene similar to the famous Keddie Wye trestle, which is near the California and Oregon border, but using timber instead of steel.   As with the Keddie Wye the diverging tracks leave the turnout directly onto the trestle high above the river.

There are all sorts of ways to make a timber trestle but the fundamentals are always the same.  There is a main deck or floor that the track is fixed to; it is made from timber sat on a pair of timber stringers which run the length of the trestle.  The stringers are then supported on sets of timber legs called bents.  The bents are spaced at typically 14′ intervals and braced together with horizontal timbers called girts and diagonal timber bracing.

In the computer model below I have placed typical bents in the correct place leaving gaps where the river runs through.  These gaps will have bridge sections built into the trestle. Where the two trestles run together the bents will be twice as wide supporting both parts.

Very little of the trestle is straight, by design, and to accurately space out the bents the set out would normally be fairly complicated.  But with the computer it is a fairly simple operation.  Each line extending off the drawing below represents a change in the radius of the trestle deck.  At the end of each line is the center of the curve.  By using this geometry I can set out all the bents so they are all perpendicular to the stringers in the computer model.

I have made curved trestles before and one of the issues I had was ensuring the bents were all evenly spaced and perpendicular around the curve.  Even though I have set this trestle, out on the computer when it comes to making it there is still a chance of getting the spacing wrong, so to make this trestle easy to build I am going to 3D print the stringers and scratch build all the bents out of timber.  The girts and bracing will also be made from timber

Doing this has several advantages.  Firstly, by 3D printing guides onto the stringers I can ensure all the bents will be set out correctly.  Secondly, curved stringers can be complicated to make and 3D printing them will greatly decrease the construction time and increase accuracy.  Thirdly, as this module will be regularly transported around, having the stringers made from one piece will help protect the trestle by strengthening it, as well as ensuring it holds up to the biggest rolling stock and locomotives we have.

Normally the stringers are made from three or four timbers with packers between them.  Considering that this trestle is for N Scale and also to give them strength I have made the stringers solid along their length instead of making the packers intermittent.  Below is a cross-section through the stringers.  I have also modeled the bolts that run through the stringers at the pack locations.

The two stringers are tied together by the guides as shown in the images below, the stringers are shown upside-down.  These have been positioned so the top bent timber, known as the top cap, fits between them.  In the image below there is a triple set of guides.  This is because at this location there will be a double bent as this will be where the trestle crosses the river.

I have also notched the end of the stringers so they will lap over the end of my bench work. My track is laid on top of a cork road bed and when the trestle is fitted in place the top of the trestle will be at the same level as the top of the cork allowing a smooth transition.  Below you can see a close up of where the trestle will meet the bench work and a double bent.

With all the geometry worked out and all the bolt details and notches modeled the parts which will form the trestle deck can be separated out and sent off to be 3D printed.  Because the largest part of the trestle will be very long I have split it in two.  Where the two ends are to be joined together I have designed them so they will finger together for strength.  You can see one of these connections at the bottom right of the image.

These parts have now been 3D printed in Shapeways’ White Strong & Flexible material.  I chose this material because it will be, as the name suggests, strong.  It is also fairly cheap as it’s Shapeways’ basic material.  The level of detail is not as high as their other materials but for my purpose that is not a problem as the top will be covered with track and I want it to have a weathered wooden look rather than a crisp finish.

These parts have now been delivered and in next week’s post I will show you how they came out and what I did to make them look like timber, blending them into the rest of the trestle.