Hey everyone. One highly requested add-on for the LongMill has been limit switches. For the uninitiated, limit switches are often used on CNC machines for 1) homing the machine 2) preventing the machine from reaching the limits of its travel. If you’re interested in reading more about what limit switches are and what they can do, I recommend reading the article in the Resources.
Please note that in this post, we are using the term “limit switches” and “homing switches” interchangeably. I do understand that there is a small distinction for both, but for this application, they are basically the same.
At the beginning of LongMill development, limit switches were not a priority as a feature when focusing on beginner hobby CNCers. This primarily came down to a few factors. First was the added complexity of having limit switches, which means additional setup and assembly for the user, as well as adding to the learning curve of learning how to use limit switches. Secondly, with the LongMill set up so that crashing the machine will not damage itself, limit switches are not necessary to protect itself. For customers still adamant about having limit switches, we still provided full hardware support to plugin or wire in switches directly into the controller, which would take care of a small population of more advanced users.
For those who want to read more about community made limit switch solutions, this is a great thread to read: https://forum.sienci.com/t/homing-limit-switches/99/41
We still hold our opinion that beginner users do not need limit switches with their machine to get the full functionality of the machine, and we recommend starting out without them until a better understanding of the machine and its use is achieved. However, as our community has grown and along with that their experience, more and more users are now exploring new ways to bring advanced features to their machines. Not only that, the development of our very own gSender now allows us to integrate software and hardware more closely than ever before. With these things in mind, we’ve spent some time creating our own plug-and-play solution for the LongMill.
Creating a limit switch solution specific to the LongMill came with several challenges.
First was the lack of foresight on providing mounting points for limit switches. This simply came down to the fact that we did not integrate mounting points on the LongMill for adding limit switches. Later versions of the LongMill did come with holes and other features that could mount sensors, however, with so many different versions of the LongMill, it would be difficult to document and provide resources for installing limit switches for every single version of our machine.
Second was the voltage support of the sensors we need to use for the limit switches. We are using a variant of the LJ12A3-4-Z sensor as our limit switches, a very common and widely used sensor. However, almost all variants of this sensor are designed for a 6-36V input voltage. Although it is possible to pull 12V power from the LongBoard, the JST 4 pin connectors already integrated into the board which was designed to be used for a plug and play solution were designed for 5V only. In hindsight, it may have been a better idea to route the 12V power to the JST connectors, but this meant that we would need to purchase 5V compatible sensors, which do exist but are more difficult to source, to be compatible with the LongBoard. Our first supplier for the sensors created the proper wiring and plug set up for the LongBoard, but unfortunately, they were only able to provide 6-36V sensors which meant that we had to start looking for a new supplier.
The new design overcomes these two challenges. First of all, the mounting hardware for the limit switches will allow users to install their sensors to any version of the LongMill, as well as allowing the flexibility to choose which side of their axis they want to mount to. For example, some users may want to home from the bottom left corner of their machine and some may want to home from the upper left corner of their machine. Users only need to move their sensor from the front of the machine and remount it to the back and specify the change in the software to make the change. Second, we have re-sourced and tested a 5V variant of the LJ12A3-4-Z sensor, which will provide proper voltage compatibility with the LongBoard. This supplier will also be providing us with the proper wiring for a plug-and-play installation of the limit switches.
We expect the kit to be ready for sale and shipping around the end of August. Each kit will come with three sensors with a plug and play wiring harness which should have an installation time of around 15-20 minutes. The price for each kit will be around $60CAD or $48USD. Additional resources and software setup support will also be provided with the kit. We’ll also be publicly releasing the designs and specs for the kit for users that want to make their own setups. Please check our blog, email, and social media for further announcements.
Today’s testing of the sensors have shown repeatably of over 1 thou which should offer a very precise way to home the LongMill.
I’m excited to see the limit switch kit in the hands of LongMill users soon and look forward to seeing the rest of the development team and the community come up with ways to utilize homing on the LongMill!