Checks & 1st Moves


Checking & Plugging In

The LongMill electronics come pre-assembled and are pretty much ready to go out of the box. Here are two things you can double-check before plugging in and powering-on.

First, check all wires going into green connectors by tugging on them. This includes the wires to the green motor connectors, green connector from the power supply, and the green connector coming from the e-stop button. Secure them using the screw terminals and a flat head screwdriver if they’re loose or the wires come out entirely.

Second, confirm the wire order for the power supply and motors. It’s important that the DC power brick has a white or red wire on the left side and a black one on the right when the screw terminal is facing you (as pictured).

For the motor connector the wires, looking down from the side with the screw heads, should be, from left to right, BLUE, YELLOW, GREEN, RED (pictured). Check if the color pattern on all four of your motor wires is correct and rearrange them if needed.

With these checks done, start connecting the motors. Track each cable from each motor to its corresponding green connector and connect it to the board. The fit of these connectors is tight but you need to be sure to push them ALL THE WAY IN so that there is good contact between the plug and the connector. Each plug on the board is labeled on the top (note that there isn’t a difference between the Y1 and Y2 plugs, the Y-axis motors can be connected to either of them).

Next, plug the connector coming from the power brick into the rear of the LongMill’s control box (pictured); wait until after it’s plugged in before plugging the AC cable on the other end into the wall.

Now connect the emergency stop button to the control box via the connector on the top. You should be able to find your e-stop button (pictured on the right) in a bubble wrapped bag in the variable box. Unclick the e-stop by rotating it then look for the red light at the top of the control box to light up to confirm that all the power wiring is coming through correctly.

Once you’ve checked that the lights are turning on, press the e-stop button to turn it back off.

Connecting the LongMill to your Computer

To manipulate your LongMill and send it files, you’ll need a g-code sender which acts as the ‘control software’ or ‘machine interface’ to your CNC. We recommend using gSender for this since it’s our own design geared towards hobby use, though there are other options you can see in our ‘Software’ resources. We’ll be using gSender as the interface for the remaining assembly.

You can download gSender here: and choose for Windows / PC , Mac, Linux, and others. If you’re not sure which type of Windows you are using, you are most likely using 64-bit.

If you get stuck at any point or want to learn more about gSender you can always reference here for more help:

Once you have gSender installed, go ahead and run it on your computer. One way is to double-click the shortcut on your desktop.

You should be greeted with a screen that looks like this.

At this stage it’s time to connect your computer to the LongMill control box via the provided USB cable and untwist the e-stop to turn on power to the machine. The USB port on the control box is on the left side.

Once that is done, hover to the top left corner of the program at “Connect to Machine”. You should see an available device to connect to and if you click it you should see confirmation of connection as well as hear a gentle hiss-and-thump noise from the machine.

Note: Sometimes it can take a moment for your computer to automatically install the drivers for the box if they’re needed. If you try to connect your machine but you cannot, you may need to manually install the drivers. You can do this by installing the Arduino IDE or you can follow the instructions on doing them manually for Windows.

With “Connect to Machine” changed to “Connected”, the plug icon turned green with a check mark, the status on the top right corner of the visualizer changed from “Disconnected” to “Idle”, and the other controls that were greyed now being activated, it’s time to take your CNC for a drive!

Try playing around with moving the machine. You can jog the machine in the direction you want within the “Jog Control” section on the right side. Choose the distance to move with each click by changing the “XY move” or “Z move” values, the movement speed with “Speed”, or just press and hold the buttons for continuous movement. gSender also has defaults for large, medium, and small movements that you can switch between by pressing the “Rapid”, “Normal”, and “Precise” buttons. It’s alive!

Note: if you installed your X-axis motor on the right side instead of the left your X movements will be flipped. If you go to ‘Firmware’ under “$3 Step direction” toggle the X-axis value and once you exit you should find that your movement has been fixed.

If you prefer inches instead of millimeters you can switch over using the gear icon on the top right of the gSender window. In these settings you’ll see a toggle to switch your units.

Things will still be a bit loose right now since we haven’t yet tuned up the movement of the machine, but tuning will be the next step and knowing how to move the machine around will be important for when we mount it to a table. While we’re here, take a moment to move each axis to each extreme while checking that the drag chains are reaching to all corners; especially for the y-axis. Don’t be shy moving around, if you hear electronic music that’s normal and if you hear a grinding noise when you hit the limits that’s normal as well.

Tuning Movement

With the machine together and moving, it’s time to tune its movement before we attach it to its work surface. Most of these tuning steps will be the same ones you’ll use when performing maintenance on your machine.

Like other CNCs, and especially for hobby-grade machines, parts need to exist that can cancel out cutting inaccuracies by compensating for wear over time and the initial user assembly. For the LongMill these parts are the v-wheels, eccentric nuts, and the anti-backlash nuts. We chose these parts because they’re commonly available and easy to use once you become familiar with them. Let’s start with the v-wheels and eccentric nuts.

Recall that during assembly each steel gantry was fitted with one set of firmly bolted v-wheels and another set of loosely attached wheels with eccentric nuts, these loosely bolted ones are the ones we’ll be returning to to finish tightening them up. For the Y-axis these are the top v-wheels (pictured) and for the X-axis these are the bottom. We’ll work on these one plate at a time.

Eccentric nuts are ‘eccentric’ or ‘off center’ nuts and this means that by turning them you can change the gap between the v-wheels attached to them and the fixed v-wheels on the other side of the rail. We call this ‘tensioning’, a system where the wheels can clamp onto the rails enough to not move around loosely but still create smooth motion. You can see below what it looks like when an eccentric nut is all the way open (largest gap between wheels) and all the way closed (smallest gap between wheels) for both the Y and X-axes.

To perform ‘tensioning’ the idea is to loosen the M5 bolt with an Allen key far enough that you can rotate the eccentric nut (picture 1) all the way ‘open’ as the starting point. Then, turn the nut whichever direction you choose to close it slightly (picture 2) and re-tighten the M5 bolt with the Allen key (picture 3). For the opposite Y-axis you can access the wheel bolts by lifting up the drag chain. At this point you’ll want to check both the wheel you just tightened as well as its static wheel on the opposite side of the rail. Whichever wheel is on top will always be harder to spin, but ideal tensioning is when the lower wheel is able to barely turn when you use your fingers to rotate it.

You’ll likely need to repeat *loosening, turning the nut slightly, tightening, then checking the wheels* a couple times for each wheel pair until you reach the right clamping force. Take your time to slowly approach the right point rather than over-rotate the eccentric nut and put too much force on the wheels. Also, know that the wheels don’t need to be 100% perfect to have a well-operating machine so if you feel like you’ve gotten close enough then feel free to move on to the next step. If you need more help visualizing how to do this you can watch our video:

Once you’re done tensioning the wheels on all axes you should find that it’s still easy to rotate each lead screw with your hands but if you grab the steel gantry it shouldn’t move around on the rail. It might be a bit loose moving the plate back-and-forth and that’s the next step when tuning.

With the v-wheels tightened down, go around and finish bolting down the remaining anti-backlash nuts; there’s one on each Y-axis and another on the X-axis. Recall the method for doing this when you did it for the Z-axis where you alternate making a couple turns onto one bolt and then the other until they’re both tightened down fully. If you twist hard onto just one bolt while the other one is loose it can twist the anti-backlash nut and misalign it to the lead screw.

Lastly, let’s check for backlash. The term ‘backlash’ refers to the difference between where the machine thinks it is and where it actually is due to components being worn out. Since your anti-backlash nuts are brand new it’s likely that they fit really well with the ACME lead screws, this means that trying to wiggle each plate along its rail should have no looseness.

As you use your machine the nuts will wear out and develop a looser fit with their lead screws, something you’ll feel as a jiggling looseness on that axis. This is why each nut is secretly two nuts with a bolt between them. This allows the anti-backlash nuts to compensate for backlash due to wear and keep your machine accurate for a long time. Think of this like how zipping up your pants keeps them fitting nicely on your waist.

You’ll find these bolts in the spots pictured for the X, Y, and Z-axes. For now just turn them until they cross the gap and make contact with the other side. With time, come back to them and give the bolt a 1/4 turn if it’s feeling like the plate is getting loose side-to-side.

Y-axis nut tensioning (mirrored for other side)



With all the tuning complete, we can move on to mounting your LongMill and starting to cut with it! If you’re planning on using your machine for especially precise cutting, also consider checking out the ‘movement tuning’ feature built-in to the calibration section of gSender:

To keep your clothes from potentially snagging in the next section, clip on the 3D printed ACME nut covers to both front feet (pictured). These act to cover over the bolts and are an extra safety precaution.