A Dummy Chassis For an Atlas C-628 or C-630 Shell Part 2

A few weeks ago I shared with you my designs for a dummy chassis and trucks for all those spare Atlas N Scale C-628/C-630 shells, you can find the post here.  In this post I will show you how the 3D printed parts came out and how they all fitted together.

Below is a rendering of the finished assembly including power pickups and lighting board.

Alco C-628 Dummy Chassis Render 6

The power pickups will be in the form of axle wipes as shown in the rendering below.

Alco C-628 Dummy Chassis Render 10

All the parts, with the exception of the circuit board clip, are printed in Shapeways’ Frosted Ultra Detail material and once cleaned I sprayed them with a basic locomotive black.


The wipes are made from 1mm wide phosphor bronze strips.  This material is ideal for wipes as it is strong, flexible and has excellent electrical conductive properties.  To make the wiper I cut four strips of phosphor bronze; two measuring 27mm, one at 8mm and one at 6.5mm.


Before I soldered anything together I test fitted the parts, as shown below.  The 6.5mm long strip is the cross-piece, it is slightly longer than it needs to be but I will trim it once I have soldered the parts together.  The cross-piece will fit under the two main wipers. I repositioned the parts and marked the main wipers where the parts intersected with a cutting knife.IMAG0591

I then soldered the first two pieces together ensuring they where perpendicular to each other.  I didn’t solder the other wiper strip on at this point because if it is not in the right place it will not slide between the wiper guides on the truck adding unnecessary drag on the axes.


To get the other wiper in the correct place I added some solder to the cross strip end then I positioned the first pieces in place.  Then I placed the second wiper in place and very quickly used the soldering iron to join the two parts.  This has to be done quickly because as the phosphor bronze has great electrical conductive properties this also means it conducts heat very quickly.  The FUD material has a low melting point so if the iron is left on the joining for too long the phosphor bronze will start to sink into the truck.

IMAG0594 IMAG0595

Once the parts are joined they can be removed again and the solder joints can be renforced if required.  The cross strip can also be trimmed back; if it sticks out too far it may snag the center wheel set.  The last part to add on is the 8mm strip which needs to be soldered to the center of the cross strip.  Ideally it wants to be parallel with the wipers but it can be at a slight angle as again, if the iron spends too long on the joint the heat will quickly travel through the phosphor bronze strips and release the other joints.


Once all the joints are soldered the 8mm strip needs to be bent up by 90° ensuring, as shown below, that the cross strip is above the 8mm and wiper strips.


After another quick test fit the wiper assembly can be glued in place. For this I like to use Loctite’s Gel Control Super Glue, because it is a gel and so will not run all over the parts and it also gives you about twelve seconds to position the parts before it sets.


The super glue only needs to be applied under the center strip, the main wipers need to be able to flex.

IMAG0599Once the wipers are fixed in place the 8mm strip will now project up through the slot in the truck next to the bolster pin hole.  This will now become the contact point to attach the wires.


The next step is to fix in the wheel sets, the center set will be electrical neutral as it does not touch either of the wipers.  However it is still recommended to install it in the same orientation as the other two, that is to say that all three wheel sets have their electrically isolated wheels on the same side.  Although my 3D printed trucks have been designed to have the wheel sets fitted from the underside, the two outer wheel sets can be fitted from above, this will cause the wipers to flex naturally without being bent to get them in.


Once fitted and the wheel sets have been checked to see if they move freely they are ready to be fitted onto the chassis.


When pushing the bolster pins into the chassis be carefull not to break the chassis.  Once the trucks are fitted thin wires can be soldered to the contact points which will be poking through the crescent shaped slots in the chassis. At this stage I realized that only 8mm for the last strip made it a little bit tricky to solder the wires on, so on the next chassis I will make that strip 12mm long.  Even with all the parts assembled the chassis is extremely light and needs to be weighted to both improve the electrical contact with the rails and to ensure the locomotive will stay on the track.  Again I have used old motorcycle wheel balancing weights which are smaller than car ones and are ideal for N Scale.


I also filled the fuel tank with weights which made the chassis the ideal weight overall.  The clip which holds the circuit board is made from Shapeways White Strong & Flexible material.  It is a lot cheaper to print than the FUD because it is a coarser material, this is ideal as the parts don’t need any visible detail.  The two halves are the same as each other and clip together securing the circuit board in place between them.  The assembly then clips into the chassis above the fuel tank.  The wires can then be soldered to the circuit board as shown below.


The next step is to mount the shell, below you can see a pair of Alco C-628 locomotives in the Monon livery. One is powered and one is the dummy. I would have asked if you could tell which one was which but I think my mistake with the truck colour gives the game away!

IMAG0612 IMAG0613 IMAG0614

Both locomotives light up in the same way, the final step is to run them on a layout and I will share with you how that worked out in a later post, but for now Merry Christmas.