GP38 Body Components

Part 3 of our “Let’s Build a Train!” series deals with various body components for the GP38. This will get your ready for the assembly and electric portion of the build. Depronized (Designer of the GP38) did an excellent job of creating such an awesome engine. He even came up with a method of remote control for the GP38. But for our build we wanted to keep things simple. We just wanted to create a GP38 with a hidden on/off switch that lets you just turn it on and watch it go.

We also wanted to give our GP38 that “two tone” look by printing it in multiple colors using a standard FDM printer. We will cover how to do that here as well.

Finally, due to component choices, we ran into several issues that Depronized did not have to deal with, causing us to have to create new body components to get things to work. We have provided those as well. So, let’s continue building our train!

Here is a list of things you will need:

  1. Depronized’s GP38. You can download it on
  2. PLA filament for the main body. We used Solutech Real Red for the main part of the GP38.

3. PLA filament for the lower body. We used Silk Silver Black from Ziro.

4. Our custom body components for the GP38. You can download them here.

Printing Depronize’s Main Body Parts

From Depronize’s GP38, you will want to print the following body parts:

  • The Rear Chasis (Chassis_Aft.stl )
  • The lower tank (Tank.stl)
  • Electronics Hatch (Electronics_Hatch.stl)
  • Fan Hatch (Fan_Hatch.stl)
  • Roof Fan Covers (Roof_Fan_Covers.stl)
  • Side Vents (Side_Vents.stl)

We suggest printing them in Silk Silver Black, if you wish to reproduce our “Two Tone” look.

Getting Started Printing the Main Body

If you are not familiar with 3D printer “bridging” we highly suggest that you check out our other article, “Software: Simplify3d – Easily Bridging the Gap”.


This will help you produce a nice, solid frame with no sagging areas.

You will also need the file “Main_Body_Complete.stl” from Depronize’s download.

We printed our GP38 body in two colors using a standard single color FDM printer, using Solutech Real Red and Ziro’s Silk Silver Black.

If you would like to do the same, here is how to do it:

Printing in “two tone”

One of our members came up with this “two tone” process using our slicer of choice, Simplify3D. You can probably do this with other slicers out there, but we will be showing you how to do this using Simplify3D.

First, you need to figure out at what “height” you want to switch colors at. For us, we found the best place to switch colors was at a z height 31.38 millimeters. This is just before the front cab windows start to print vertically.

Once this stopping point has been decided, its time to get to work with the slicer. The solution to multi-color print with a single color FDM printer is simple. You need to break the print up into two files. But here is the trick: You need to tell the printer to “keep everything running” when its time to switch the filament before you begin you second print.

Using Simplify3D, you would do it this way:

  • First open the file you want to slice (in this case the GP38 body). Then go into the process you have set up in Simplify3d

  • Click on the “Advanced” tab. Then place a check mark in “Stop printing at height” checkbox. Enter the value 31.38 (That is our stopping point)

  • Click on the “Scripts” tab. You will see various scripts that tell your printer what to do before it starts to print, when its done printing, and a few other functions. You want to select “Ending Scripts”. Here would normally be the “gcode” to tell you printer to go home and shut down the heaters (extruder, bed) and turn off the stepper motors. All we want in this ending script tab are the codes G1 X0 Y0. This simply tells your printer to go home for the x and y axis but leave the height alone and leave everything running.

  • After you have made these changes, click on the “OK” button. To save the changes.
  • Now, back in the processing section, make sure your process is still highlighted. On your computers keyboard press CTRL C (to copy the process) then press CTRL V (to create a copy of the process). You will now have two processes.

You want to select the second process and again click “Edit Process Settings”

  • Click on the “Advanced” tab. Since this was a copy, you will have a checkbox in the “Stop printing at height” box. Remove that checkbox. Then place a check mark in “Start printing at height” checkbox. Enter the value 31.38 (That is the starting point for our second file)

We also recommend changing your infill setting to 100% for the top portion of the body, to make it as strong as possible.

  • Click on the scripts tab. You want to select the ending script again. You can enter all your “shut down” values again, to turn the printer off when it is done.

  • You also may want to adjust your “starting script” (things your printer would do when getting ready). Most people will want to completely remove any code in this box, depending on what type of printer you have.

When you are done with this, again, click on OK to save the changes to this second process.

Creating Your Two Gcode files

With the processes saved, you can generate your two gcode files this way in Simplify3D.

  • Click “Prepare to Print”

  • Select and highlight just the first process. Then click on OK.

  • In your preview window, you would see just the first part of your GP38 body is ready to print if you did everything correctly.

If things look good, save your toolpath to disk (the gcode). Then exit the preview mod. Time to go back and create the other file.

  • Again, click on prepare to print

  • When the process selection window comes up, select, and highlight only the second process, and click on OK.

  • If you have done everything correctly, you should see the top half of your GP38 suspended in midair, in the print preview window.

If you see this, save your second Gcode file. You are now ready to print! At this point all you need to do is: 1) print the first file with your first color. Your printer will park itself when done. Then 2) swap your filament and start your second file. The printer should pick up where it left off and give you a nice looking GP38 top!

Our Headlight assembly

We found; due to our choice of LED components (standard 3mm LEDs) the Depronize’s Headlight assembly just did not work for us. The LEDs simply will not fit next to each other. During the electrical assembly article (to come) this is critical to give you that GP38 “look and feel”. To cure that, we created our own. So from our download, you will want to print the file “Forward_light_large.stl”

It has a much larger rear compartment with larger hole sizes for the LEDs so that they properly fit.

The best way we found to print the headlight assembly, is to place it on the bed like this with automatic supports turned on inside your slicer:

The GP38 Chassis

Since we wanted to have a simple “on/off” switch to make the GP38 run, we hid it underneath the train. To do this, we created a new forward chassis plate. You want to locate in our download the file: (Chassis_Forward 001 with switch.stl) to print it:

We printed both the forward chassis as well as the original rear chassis in the silk silver black filament.

That’s it! Next time, we will get into wiring and final assembly of your GP38. So, stay tuned!

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