This week I’ve been working on the Alco C-855 project and I’ve assembled the chassis using the 3D printed metal chassis extenders.  In this post I will share with you how I did it.

You can read about the design for the metal and plastic parts for the extenders in my earlier post which you can find here.  The metal chassis extenders are required because the donor chassis, taken from a Con-Cor model of a GE U50, is not long enough for the huge Alco C-855.  The chassis extenders, pictured below, have been 3D printed in stainless steel.

To start with the donor chassis is stripped down so only the two main metal parts are left.  It is best to remove any moving parts when cutting the chassis as metal filings can get into the gears and bearings causing damage at a later date.

The two parts pictured above, along with the new sections, are ready to be marked for cutting.  I like to use a permanent marker to shade in the areas that need to be cut, as you can see below.

Once I was happy with the marked areas I used a hack saw to cut the unwanted chassis sections out.  I will be providing instructions when these parts are released for sale with dimensions for where to cut.  Once removed the chassis sections looked like this.

To fit the parts together I used a superglue but an epoxy will work just as well.  Because the parts are designed to fit together along a step it is fairly easy to get them in the right place. However it is still possible to fit them together at a slight angle so I recommend using straight edges as guides.  I used the back of a metal ruler for a base plate and my metal square as a side.

I started with the top section and, as this is a test piece, I only glued one side first.  In the photo below you can clearly see the difference in size between the new section and the part that was cut out.

Before I glued the other side of the top section together I wanted to check things were going right so I test fitted in the lower section of the chassis with the motor. As you can see from the photo below there was a slight problem.

The motor appeared to be sitting too high in the lower part which looked to be preventing the top section from coming down squarely.  However after further inspection the motor was found to be in the correct place but the top section was a bit too thick.  This was caused partly by the rough surface on the unpolished stainless steel, and also because the superglue added a layer of thickness between the parts.  This was easily resolved by grinding down the underside of the chassis extender.  I used a sanding stone in a Dremel-style tool and removed some of the thickness as you can see below.  Interestingly the stainless steel is much harder than the metal used for the original chassis and it took a bit if working The metal got incredibly hot but the superglue joint held up with no problems.

With the extension part modified the motor section now fitted properly, so I glued the other end on using the same metal square and ruler.

The gap you can see in the picture below at the top of the right hand joint is because I slightly over-cut the chassis. However that is not problem as the step below is the part which correctly positions the extension.  I later filled this gap with more superglue.  I used the Gel Control Superglue made by Loctite which is perfect for jobs like this as you get a bit of working time before it dries and, being a gel, it will not run.

Before moving on I also did some squareness checks as you can see below..

Now the top section was complete I could position and glue in the motor section.  You may have noticed I left the top and bottom sections of the chassis bolted together throughout most of this.  I did this to help ensure everything was in the correct place, particularly when it came to fitting the motor section.  As it happened I did cut the lower front chassis section a bit short and if I had glued the whole bottom section together tightly it would have been too short.  However as the chassis parts were bolted it all worked out well and below is the chassis glued together.

Next I refitted the trucks and other internal parts ensuring there werre no metal fillings in any of the moving parts. I lubricated the motor, gears and drive shaft bearings and also put a strip of Kapton tape over the top motor brush connector.  It was ever-so-slightly touching the metal of the chassis extender and, as I proved in my prevision post, these stainless steel parts conduct electricity very well.  If this locomotive was going to be run as a DC locomotive this would be great but it will be DCC so I needed to isolate the motor.

Although the chassis extenders are great conductors the fact that I used superglue for the joints helped to form a perfect electrical barrier, so to ensure I get the benefit of all the power pickups, I bridged the chassis extenders using the original bolts, as you can see below.

The two nearside bolts are in plastic sleeves so they don’t touch the top section of the chassis but conduct power from the bottom section.  The bottom section is connected to the right hand rail and the top is connected to the left.  To complete the test I also fitted a DCC decoder and the lighting and function wires are simply taped to the chassis for later use.

The longer mechanism had no problem navigating some S bends and small radius turnouts on my switching layout.  I will also do a few tests on a bigger layout this week with a train in tow to see how it performs and I will share a video of that with you.

Below you can see some side by side comparisons between an original Con-Cor U50 chassis and my extended C-855 one.  The original chassis weighs 170g (5.99 ounces) and the extended one weighs 186g (6.56 ounces).  The C-855 did have 500 more horsepower than the U50 so this extra weight will help with traction.

I have now made some modifications to the chassis extension 3D model drawing to fix the issue I had with the first build. I will do one more test print before I make them available,, just to confirm that everything will fit together without modification.

The next step for the C-855 is to finish the 3D model for the shell and brass Additions.  Once I get them drawn up and ordered from the printer and etcher I will share them with you.