Upload gcode files automatically from Simplify3D to OctoPrint


Some slicers, like Slic3r, have a built-in feature that allows you to send gcode files directly to OctoPrint’s queue without saving and uploading manually. I wanted this feature in Simplify3D.

Someone must have done this already, right?

Kinda. there are a few solutions I found, but they have some disadvantages:
cURL – using cURL to send a POST request to OctoPrint’s REST API via the additional terminal commands for post processing in Simplify3D. This works, but it has a security flaw. A pretty big one – Simplify3D includes the post processing command inside the Gcode file, and the command for cURL contains the unique and secret API key for your OctoPrint server.
This means that ANYONE who has access to the interface (let’s say you opened a port in the router and made it accessible from anywhere) can download files in the queue WITHOUT LOGIN, open them, read the API key and take full control over your printer.
Not good.

The content of a Gcode file sent with cURL

scp – what about copying straight to the machine? well, yes, it works. We are not using the API so no key is required and if you set up ssh keys, you wont need to enter your username and password.
The problem with this is that we are moving files behind OctoPrint without talking to the application, this means that in order to see our file in the queue and print them, we must refresh the webpage.
Not what I’m looking for.

A better solution

From the other examples we learn that we can’t have the API-key in the command and that we must talk to the server (i.e. use the API). This brings one thing to mind – a script!

After some googling and learning a bit about REST and python, I wrote this simple script :

import requests
import sys
requests.post('', files={'file': open(sys.argv[1], 'rb')}, headers={'Host': '', 'X-Api-Key': 'XXXXXXXXXXX'})

The “local” in the url can be changed to “sdcard” in order to save the files on the SD card.
In order to use the script for your setup, replace the IP with your server’s IP and the API-Key with the one for your server (can be found in OctoPrint’s settings under API).

After testing that the script works on its own, it was time to insert it to the post-processing box in Simplify3D.


Note that because I put the script in the Simplify3D folder, the program needed to be run as administrator to run the script (took me a while to figure that one out). You can put it anywhere else and not have this problem.

We can see that there’s no key in the post processing command, let’s see if that’s the same in the file:

The content of a Gcode file sent with python script


Additional features

Once you realize that you can run arbitrary scripts after the file saves, you can do pretty much anything. The REST API allows you to fully control the printer and local commands work fine. I haven’t found any use for other functionalities at this point, but I saw some people who wanted the file to be removed from the computer once uploaded or maybe start the print when the file uploads or run a special Gcode sequence. Not a problem, a quick look at the documentation¬†and you’ll find commands for anything in the interface and a lot more.

OctoPi – Remote Control 3D Printing

Leaving a 3D printer unattended is not very smart, especially a homemade one. If you’re lucky, you’ll only mess up a print and waste some plastic. If you’re less lucky, you can cause some damage to the printer or worse, burn down your house!

This is where OctoPrint comes in. OctoPrint is a free 3D printer web interface. It includes a password protected interface with live video stream, time-lapse capturing, G-Code viewer, Terminal interface, Temperature graphs, motor and temperature control buttons, and more.
This means you can SEE what is going on in real-time and stop the printing or send some code to the printer if necessary. This is a huge convenience, I no longer have to go and check that everything is OK, I can do it from my phone.
Moreover, I can slice on any computer and send the G-Code from anywhere in the world. If I don’t have a computer with slicing software, I can even link OctoPrint to a local installation of CURA and slice remotely! now that’s amazing.

I work with two computers, a desktop and a laptop. Although OctoPrint gives me the freedom to send and monitor prints from any computer, I didn’t like the idea that my printer has to be permanently connected to one of them. I wanted the printer to be independent, autonomous. I didn’t want to have to leave my computer on or not be able to reset it is something else needed it.
A dedicated computer is a massive overkill, It takes up a lot of space and it costs too much for what it does, I was looking for a more mobile solution so that I could move the printer and still have all features available. I wanted the printer to be an all-in-one solution.
After a short search I found OctoPi, A Raspberry Pi image with OctoPrint and everything¬†built-in, maintained by Guy Sheffer. This means I can mount a RPi on the printer and have the interface and all of its features and settings no matter where the printer is set or on which computer I’m currently working.

OctoPi also provides a GUI for a touch screen to be mounted on the printer, I have no need for this right now, but maybe I’ll add one in the future.

Raspberry Pi mounted on the printer. Excuse the cabling - i'm still working on that.
Raspberry Pi mounted on the printer. Excuse the cabling – i’m still working on that.

If you’ll notice, the USB cable is made of two cables, there are two reasons for this. One, the Arduino’s USB port is facing downwards and a straight jack would be pressed against the desk and apply force on the Arduino – not good. I used some scrap L shaped USB-B cable I had from an old scanner to prevent this. And two, the RPi and the Arduino are powered via two different power sources and both regulate the voltage seperately. This means that their operating voltages aren’t 100% identical. If I connect the RPi to the Arduino via regular USB cable, the RPi would supply its regulated 5V to the Arduino, making the Arduino receive power from two different sources – also not good. For this reason I cut the 5V line of the USB cable, thus connecting the + and – data lines and sharing ground (important!) without supplying power.
I didn’t cut the cable to length because I’m not completely sure this is the final position of all components. there are more to be mounted.

Working with a RPi meant i can use the GPIOs to make the printer smarter and add features I need (see the relay in the picture? more on that in a future post)