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Inductive Limit Switches – Production Update

Hey everyone here’s an update on the development of the inductive limit switches for the LongMill! If you haven’t read the last post, you can read it here:

I know a lot of people are excited about this kit, and I assure everyone we’re working really hard on this. Over the last couple of weeks, we’ve been working on a couple of different things, including video and written info and content, continual testing, assembly instructions, packaging, and the supply chain for the kit. We are now waiting on our first batch of sensors and a couple of other parts to arrive from our manufacturers, and we will be starting packing and assembling the kits as soon as parts start to trickle in. All of the parts for the kit have been ordered and are expected to arrive in mid-September. We expect to start shipping kits a couple days after we’ve received all of the parts. Kits will be $60CAD or around $48USD each.

Our initial timeline for this project was to have a product released at the end of August. However, we had a minor setback due to some changes in part price and availability from one of the sensor suppliers that we initially ordered and tested samples from, so we have acquired samples from two additional suppliers, one of which we’ve fully tested and have decided to move forward with to use for production.

Some a bit more specifics that we’re working on to provide users include information about using different workspace coordinates, returning to a certain part of your job after a power outage or shutoff, and using jigs, which should add some extra tricks and functionality users can add to their machines.

Making your own

As promised in the last post, here are some instructions on making and assembling your own mounts and sensors if you prefer making your own over buying the kit from us.

Please note that these instructions are still in development, and additional resources and videos will be available for users soon. These instructions should help the general user population if they wish to make their own mounts and sensors.

Choosing sensors

The sensors we recommend using are:

Model: LJ12A3-4-Z/BX

NPN Detection

Detection distance: 2mm-4mm

Normally open

Supply Voltage: 5V* 

Choosing the correct voltage option is very important, as this particular type of sensor is more commonly available in a working voltage of 6-36V, which requires additional wiring to make work with the LongBoard. For using higher voltage sensors, you may need to use either the 12V auxiliary power from the board, 24V from the power supply, or from an external power source. That being said, I highly recommend sourcing the 5V variant of the sensor as this will make installation much more simple.

There are many variations of the LJ12A3-4-Z/BX, as well as other M12 sized barrel sensors that come in different lengths. In my experience, most seem to be more than accurate enough for this application, with a repeatability of 1 thou or better.

Most sensors also come with a set of nuts and washers, which can be used for mounting.

Making the mounts

All mounts can be 3D printed. The models can be found on our public Onshape document for the LongMill. The models can be found under Electronics -> Limit/Homing Switches. Right click on the model to export as an STL or your preferred 3D model file format.

These parts can be printed with most FDM printers. If you’re interested in reading about our 3D printing process, please check out this post. I would recommend using a higher infill for these parts since a more rigid part generally helps mounting.

All of the mounts use a pair of M3 heatset inserts. CNC Kitchen has a couple of videos on using threaded inserts on 3D printing that are awesome which talk about them in general as well as how to install them.

For our application, we found a fairly inexpensive and commonly available insert that works great. A drawing of the insert can be found below.

Here is an exploded view of the inserts.


Assembling the mounts

Here is a view of everything assembled before mounting to the machine.


And here is the exploded view:


Attaching to the machine

The mounts slide onto different areas of the machine as shown in the images below. Use the M3 screws to secure them. You will need to position the sensor to a position that lines up the tip (usually blue or orange) with the gantry you are sensing for. Loosen and adjust the mounts as necessary.


Although the sensors for our kit will come with pre-wired JST connectors with a 2.5m wire for running through the drag chain, it’s likely that off-the-shelf options will not. You will likely need to extend the wires to be able to run the wires through the drag chains.

The LongBoard comes with ports to connect limit switches via JST4 connectors or with the detachable screw terminal block. Here is a diagram of wiring the inductive sensor using the screw terminal. Note that the 5V and ground lines are shared between all of the sensors, and each black signal wire is connected to their separate axis.


More info on wiring can be found on our resources for limit switches.

Firmware settings

Once your sensors are installed you may need to update your firmware settings to enable the limit and homing functionality. A full outline of all of the related firmware settings can also be found in our resources.


I hope that this information helps some of our more ambition users who don’t want to wait to get a kit from us set up limit switches on their machine. I also hope that this will give you guys a head start in exploring all of the functionality in adding limit switches to your design. Over the next couple weeks, our team will continue developing the resources for the installation of the switches, so I highly recommend staying in tune on our social media and our blog, and check back on our resources page to check for updated resources!