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General Tips on LongMill Troubleshooting

Hey everyone, it’s Andy here. Over the past few years, we’ve welcomed many thousands of CNC users into our community. Of course, with any electro-mechanical machine, some degree of troubleshooting is to be expected.

For the first year and a half since the launch of the LongMill, I had taken on the large majority of troubleshooting from customers directly through email. This was an excellent experience for me as it opened my eyes to observe almost all of the issues that were possible, as well as giving me the chance to learn and communicate with customers better. Even to this day, I am regularly checking on customer tickets and working with our support team to tackle new or more complicated support issues, although it’s typically no longer my day-to-day role.

What has been interesting to see over this period of time has been not just how we collect data and information about issues over time, but also our understanding of the human nature of users when it comes to identifying and troubleshooting issues.

One of the things we’ve come to recognize is that there are a number of misconceptions to address in terms of troubleshooting the LongMill. This article covers some of my personal recommendations for helping you troubleshoot issues on your LongMill.

Our custom dashboard tracking what types of tickets we receive and the frequency of certain issues

Tip 1: Listen and look at your machine carefully

Simply listening and looking at what your machine is doing can help a lot in identifying problems. Is the machine making a weird sound? Do you hear the motors stalling? Is the machine stopping and starting irregularly? Is there a component that is slipping? Making a close observation can help identify the cause of an issue.

It’s important to note that the large majority of issues for the LongMill are mechanical. This means that for most issues, you can physically, hear, or feel issues. A few extra tips for this tip:

  • Jog your machine manually on each axis and check for smooth motion. I recommend running at the highest speed for each axis as stalling is more likely at higher speeds
  • Run your project in the air. Look for any irregularities and odd behavior.
  • Try turning lead screws and moving your gantries by hand. This can help identify looseness or binding.

Tip 2: Most issues are simple issues

The large majority of issues are caused by something simple. Always start with simple fixes first before trying something more drastic. This will save you time and give you statistically the best chance in fixing your issue.

99% of issues that our users have can be found in the Common Issues and Fixes section of our resources. I encourage everyone to read through it carefully as it covers everything that we know that may help you solve your issues. This section is updated regularly with new issues and fixes when they are found.

From my experience, users often have a tendency to jump to the conclusion that if they run into an issue, it’s a rare, complicated, or unknown issue. Sort of like being a…LongMill hypochondriac? This means that many people try to troubleshoot their issues in the wrong place and become frustrated with the machine, rather than checking the most simple reasons for issues. For example, you’d be surprised at how many people reach out to us because their machine won’t work at all because they just never turned on the machine in the first place.

Tip 3: Mechanical and electrical issues happen randomly. Software issues happen exactly the same way over and over again.

The main differentiator between a mechanical and electrical issue versus a software issue is that mechanical and electrical issues seemly happen at random and software issues happen the same way over and over again.

While mechanical and electrical issues can be caused over time by loose fasteners and connectors, wear and tear, and power fluctuations which can happen seemly randomly, software works in a series of exact pieces of code that is rigidly defined. While double-checking firmware settings and reinstalling gSender can help eliminate those as being the issue, if your issue seems random, it’s more likely to be a mechanical issue and updating or reinstalling gSender will not help.

I sometimes joke to Chris that many users use gSender as a scapegoat, as many pin their issues on gSender when they aren’t sure what’s going on. I suspect it’s because its easy to blame something that people don’t feel as comfortable with (aka the software). Sometimes it feels like gSender is messing something up randomly, however, the reality is that the vast majority of issues come from something mechanical.

If you are running into issues with gSender, additional help and documentation can be found here:

Tip 4: Static and EMF cannot cause a machine to lose steps

It is a common misconception that static and EMF can cause a machine to stall or lose steps. The main symptom of static and EMF is a complete disconnect between your machine and CNC. Issues caused by static and EMF will likely cause your machine to disconnect or stop completely. Additionally to note, due to the high draw of tools such as routers and dust collectors, its easy to mistake brown-outs for static and EMF, even though they are completely separate problems.

If your machine is losing position or steps randomly, it’s best to check out the mechanics of the machine first, as static and EMF does not cause the machine to lose its position. Use the process of elimination by turning on and off different tools and dust collectors in your shop while running your machine to identify the culprit.

Tip 5: Let us help you

Don’t forget that our technical support team is here to help answer any questions and help tackle technical issues. Sending us a message with detailed information, videos, and photos of your issue through our Contact Us page.

When you send a ticket, you’re talking to:

  • One of our team members or engineers who designed a certain part of the machine
  • Someone with hundreds, if not thousands of hours of CNC experience
  • The whole technical support team, as tickets and information can be shared between all members

We also use tickets to collect data and improve the quality of our products and make adjustments to our resources.

Reaching out directly to our technical support team is typically the fastest and most reliable way to solve technical issues.

A note from Jason Kent, our Customer Support Manager

Provide as much information as possible. Information such as recent changes or updates made to the machine or software is useful to include.  When reaching out for customer support, please add images or videos relevant to the issue. While family photos are cute, images of the issue help us to diagnose your problem faster.


Tip 1) Observe the mechanics of your machine carefully, such as the sound and the movement, as mechanical issues are the most common in LongMills.

Tip 2) It’s statistically more likely that an issue is caused by something simple. Always troubleshoot by checking basic things first. Troubleshooting guides in our Resources contain fixes for 99% of issues around the LongMill and are regularly updated.

Tip 3) Understand that if the problem happens randomly, it’s most likely a mechanical or electrical issue. Software does not cause random problems.

Tip 4) Static and EMF does not cause stalling or missing steps. Static and EMF causes the machine disconnects or to stop completely.

Tip 5) Don’t forget to reach out to us directly! We can help too!

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Maintaining Linear Guides

Hi everyone. This post about maintaining the linear guides on your LongMill. We’ve had a couple of people report to us that they’ve had their Z-axis get stuck or become rough especially when they have been running over a long period of time.

I and another customer who has experienced this issue have been investigating the cause of this for a few weeks and doing more research to help customers prevent their linear guides from sticking.

I’ll just fill everyone in on our recommendation for maintaining your linear guides to ensure they work flawlessly for every cut. If you want to hear more about what we’ve done to look into linear guide maintenance, scroll down past this section to read more.

Maintaining your Linear Guides

Although the frequency of lubricating your linear guides may vary depending on the type of cutting you do and the frequency of use, we would recommend doing this procedure every 20-30 hours. However, if you experience any grinding noises or roughness in your gantry, we recommend doing this procedure more often.

  1. Wipe your linear guides with a clean cloth, paper towel, rag, or shop towel to remove any dust that may have accumulated on your linear guides. Move your Z-axis up and down if needed.
  2. Apply a liberal of machine oil or grease to your linear guides. Move your Z-axis up and down to ensure that the bearings inside have a chance to get coated Most general-purpose lubrication options should suffice. However, it is not recommended to use dry lubricants or anything with particulates such as graphite in the lubricant.

Here are some links to more into about lubrication:


We believe that most general-purpose lubricants such as the 3 in 1 oil should suffice since the linear guides are used in a relatively low speed, low load application.

These instructions are now a part of our Machine Maintenance page on our Resources.

Jumping into our other findings

One of our customers had reported having their Z-axis linear bearings seize several times, and with the help of this customer, we have investigated the issues further. Initially, this had been a fairly uncommon issue, with only 3 tickets in our system pertaining to these parts as well as a small number of users reporting this issue on our Facebook group so it hadn’t been top of mind for us to investigate. However, I guess it’s better to sort potential problems out than let them sit and percolate forever.

Based on research, the main reason for failure for linear guides is lack of lubrication. This is what I suspect happens.

  • Linear guides get coated with dust from regular use. This dust either sticks to the lubricant already on the guides and either falls off taking lubricant with it, the guides push it off, or the user wipes off dust and lubricant.
  • The chance of the ball bearings in the guide seizing goes up either due to the resistance between the balls rubbing against each other or dust making their way into the guide

To replicate the issue I first cleaned all of the grease and debris from a spare ZX gantry using brake cleaner. This provided a situation where the linear guides would have no lubrication. Then the guides were coated in MDF dust and were moved back and forth.

Although I was not able to create a complete failure of the bearings, were was a noticeable increase in friction, and over a longer period, I suspect that the bearings would be able to be coaxed into seizing.

After this testing, I applied machine oil to the guides as discussed in the section above and the linear guide returned to its original smooth movement. I believe that cleaning and relubricating the linear guides can return seized linear guides back to life, and maintaining them should ensure smooth operation for the years to come.

I hope that adding this helps improve the LongMill’s reliability and ensure that everyone’s machine keeps chugging along great!

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Launching our own T-Track clamping system

Hey everyone, I’m excited to share something Kelly and I, and the rest of the Sienci team have been working on for the last couple of months. We know that many of our customers use T-Track extrusion as a clamping/workholding system for their LongMills and other CNC machines, and we’ve learned that folks have been coming up with their own solutions based on what’s available to them.

Well, we’ve created our own that serves as an excellent option for affordable and high-quality T-Track extrusion.

You can order them here: ‎

Universal 1/4-20 hex bolt compatibility

One of the key features to highlight about this new t-track system is that the profile is designed to use 1/4-20 hex bolts rather than T-Bolts that are often used in other T-Slot extrusions.

This means:

  • You can easily find and buy 1/4-20 bolts for cheap
  • You can find lots of different lengths and related 1/4-20 hardware that you can use to make your own clamps

If you want to make your own clamps/need some inspiration, check out

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Kelly designed some hold down clamps

Hi everyone. I just wanted to share some news on a new project/product we have been working on for the last couple of weeks. We are working on a new T-track work holding system to add to our host of accessories!

In the meantime, one of our awesome engineers, Kelly, has created a simple hold-down clamp design that can be used for all sorts of CNC stuff. We are also sharing the link so that you can copy and modify the design to fit your needs:

If you want to download the STL files, we also posted the design on Thingiverse:

We’ve designed these clamps to be made from plywood and use standard 1/4-20 hardware. Knobs can be 3D printed or milled as well.

As mentioned before, we are currently working on our own t-track as well. One of the biggest selling points of the new extrusion will be designed to fit the head of standard 1/4-20 hex bolts, which means that you can find the bolts you need for any of your workholding needs from your local hardware store. No special hardware needed!

We are expecting to have t-tracks available for purchase in the next month or so!

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Things to consider when making a longer LongMill

One of the most frequently asked questions is “Can you make a bigger version of the LongMill?” Well the short answer may be “yes”, but there are many other considerations that you should to consider.

Screw whip

Screw whip, or “whip” refers to when a rotating rod wobbles or flexes, which is exacerbated by the length of the rod, the speed of the rotation, or how off balance the rod is. The LongMill 30×30 uses a 8mm diameter steel leadscrew that is approximately 1030mm long. At the speeds that the NEMA 23 motors turn at and the length of the lead screw are such that the effect of a properly assembled machine are minimally affected by whip.

When you start to go longer in lead screw length, the effects of whip become more pronounced to the point where you will either need to increase the diameter of the screw or use a lower motor speed, both of which present different challenges and downsides.

There are different lead screw designs that can be used for this application, but may need modification with bearings, mounting feet, couplers, and motor mounts.

Motor speed

For practical purposes, it is best for the machine’s speed to increase proportional to the size of the machine. For context, the Mill One with a work area of around 258mm x 185mm has a maximum speed of 1800mm/min. The LongMill on the otherhand, comes has a maximum speed of 4000mm/min, more than double the speed of a Mill One but also significantly larger.

It is important for a machine to offer faster speeds to accommodate for a larger size machine as doing large jobs at a slow speed would take forever. Typically, you can run a LongMill 2.5x the speed of a Mill One, which means that a project that takes 30 minutes to do on a LongMill would take 1 hour 15 minutes to complete.

If you want to run the machine faster, you will likely need to provide more power to your motors as well. You can do this by increasing current and voltage supplied to your stepper motors, which may also need upgrading your power supply and motors to support the changes.

Luckily the LongBoard controller can support higher voltages and current with a larger power supply, but you will still need to consider upgrading the stepper motors (rated for up to 2.8A).

Rail rigidity

The longer your rails are, the more flex you’ll have if you don’t fully support or reinforce the rail. While the Y-axis is easy to do, as all you need are more feet to support the rail, you may want to consider adding additional reinforcement to their X-axis rail which is a free-floating part.

Without modifying the rails, you may experience more deflection, which will need to be combated by decreasing your cutting speeds.

The other consideration to make is how straight and parallel your rails are. Aluminum extrusion is relatively straight due to the process used to manufacture them. However, deviance in straightness increases the longer your rails are. This also applies when considering if your rails are skewed as well.

For some deep dive into rail design and FEA, make sure to check out this post on the forum:×3-angle-gantry/693/5


A larger machine cost more to ship, as there are restrictions on how large shipments by courier can be. This can vary region and country, which limits the ability to transport the parts for the machine, which is why we don’t offer longer rails for the LongMill. That being said, you can typically find 2×2″ and 3×3″ angle aluminum from most metal supermarkets as it is a standard material.


We believe that the sizes offered for the LongMill are optimal in terms of price, performance, and usability. However, we encourage folks to build their own machines if they choose to, which is why we provide all of our design files open and updated for free:

On the other hand, there are a lot of things that need to be considered in terms of building a longer version of the LongMill which can add to the cost and complexity of the machine. There’s a reason why costs can go up exponentially as size goes up as well. There is also a strong case to be made to avoid expanding this design without significant modification or purchasing a pre-made, larger machine as well.

For those who want to do larger pieces without modifying their machines, consider looking at putting your materials in diagonally, or using “tiling“.

We hope you enjoyed this read, or even inspired you to mess around with our LongMill design. In any case, we hope you share with the community what you learn and what you build.

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Surfacing the Wasteboard on Your Longmill

Want to learn to surface your wasteboard?

  1. Surfacing your wasteboard helps level the surface in relation to your machine. This means that if you have bumps or uneven surfaces on your wasteboard, or if your wasteboard is higher on one side that the other, surfacing will even out and flatten the board.
  2. Cleans off old marks and scars, leaving you with a new, clean surface to glue, clamp, and mount your workpiece.

Check out our newest video that covers how on Youtube:

For more info and surfacing code for all LongMills, visit our resources page:

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Check out these new instructables on modding your Mill One

Troy, a.k.a tmbarbour has put out some really cool instructables on adding some new functionality to the Mill One! You might know him from his Add Homing Switches to a Sienci Mill One CNC project, and he’s made some other cool changes to his machine.

Easy Z Axis Probe for Your CNC Router

This instructable walks you through adding a Z axis probe to the Mill One using the built in pins on the CNC V3 Shield. This makes it a lot easier to automate the process of finding the Z height of your workpiece.

Add an Arduino-Based Optical Tachometer to a CNC Router

Knowing the RPM of your spindle can help you get more consistent results out of your Mill One. Not only that, it’s a cool little add on that’s fairly inexpensive and fun to make. Troy’s instructable covers everything you need to know to make your own.

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Sienci Mill One Air/Oil Mist Coolant System

There’s been talks and photos of different coolant systems on the Sienci Mill One Group over the last few months, but this is the first full guide I’ve seen on setting it up on a Mill One. Check it out here:

So why a coolant system? Well, when it comes to cutting aluminum, one of the biggest challenges is to keep the end mill from clogging with aluminum chips that weld themselves due to the heat created by friction. Aluminum has a fairly low melting point, making it a material susceptible to this.

There are a few methods to make sure you don’t damage your end mills. One is to make sure that the chips you’re creating are large enough to carry the heat created away from the cut. This is where using a single flute aluminum bit works well, since the single, large flute creates larger chips than what a 2 flute or a 4 flute would typically do. This works great with most jobs, and typically you won’t reach those temperatures. However, with long jobs that can take several hours, some sort of cooling is nice to have.

Andrey’s method of using a mist coolant system is commonly used in industry on large, industrial machines. It uses a blast of air, mixed with a stream of vaporized coolant, pointed toward the end mill to lubricate and cool the part and the tool. Unlike flood cooling, which uses a stream of liquid coolant that sprays at the tool, mist cooling requires far less coolant, and if properly set up, a lot less messy.

If you’ve had this mod in mind for your Mill One, check it out!



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What is backlash?

With any screw driven mechanical positioning system, there is often some degree of slop or “backlash“, including the one used in the Mill One. To explain further, backlash occurs when there is a gap between the threads of the nut and the lead screw and the nut is allowed to move within the gap which is present. With most people, the level of precision that the Mill One provides is more than enough, but for those who want to push their machine further, or want to need their Mill One extremely high precision work, this is an important topic to discuss.

We tested the backlash on our ACME nuts by attaching a dial indicator to the Mill One’s gantry and running the gantry back and forth. We chose a point to call zero on the dial indicator, and moved the gantry past zero, moved it back, then moved back even more, and then moved it forward again. The gap between the zero and where the needle landed was our backlash. A better explanation can be found here:

We tested this way for both a brand new stock ACME nut, as well as after running for many cycles. We ran the gantry back and forth for about 8 hours, with an additional load simulated by using bungee cords as to wear the nut as far as possible.

The results of this test, are as follows:

  • Brand new stock ACME nut: 0.001″ or less in backlash
  • Stock ACME nut after 2-3 hours: 0.002″to 0.003″ in backlash
  • Stock ACME nut after 6 hours: 0.003″ in backlash
  • Stock ACME nut past 8 hours: 0.003″ in backlash

Based on these results, we can see that the backlash of the ACME nut had gone from just under 0.001″ to around 0.003″. Just to put that into perspective, 0.003″ is approximately the thickness of a sheet of paper. For most projects, this is a great level of precision. But for something like PCB milling, where the width of each trace can be less than 0.006″, 0.003″ is a big number.

Over the last few months we have been testing anti-backlash nuts on the Mill One, which “preloads” two sides of the ACME nut to eliminate the gap which causes backlash. Using the same tests, the anti backlash nuts manage decrease backlash to less than 0.001″, greatly improving its accuracy. This resulted in parts coming out with much better dimensional accuracy, with tolerances of +/-0.002″ (0.05mm) or better being easily achievable.

Here’s an example of a test cut we milled from some brass:

Because of these good results and since the upgrade is simple to do and fairly inexpensive, we have created kits to allow users to install their own anti backlash nuts. You can order a kit here: We’re really happy to make this upgrade available to let users take their projects to the next level. We will continue to do tests with the anti backlash nuts with a variety of projects, so make sure to check out the blog to find out more!


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Turning the Mill One into a 3D printer


3D printers technically ARE CNC machines because they use “Computer Numeric Control” systems, but when it comes to CNC routers we start to see some major differences between the two types of machines.

Almost all consumer facing 3D printers are FDM (Fused Deposition Modelling) 3D printers, laying down layer by layer of molten plastic to create 3D objects. They use a variety of mechanical systems to move a nozzle which extrudes out the molten plastic to build up that object.

CNC routers work in a similar way, except starting with a block of material and removing material using a rotating cutting bit until you’re left with a object.

Before we dive into how the Mill One was converted it’s important to point out some major differences between CNC routers and 3D printers.

The most important is the differences between the mechanical intent of these machines. CNC routers experience huge amounts of force during milling and rely heavily on the stiffness of the mechanical systems to maintain accuracy. This makes them significantly heavier and slower than a 3D printer. 3D printers on the other hand need to move the extruder nozzle quickly, and because they are relatively lighter than a router or spindle, the mechanical systems lighter and are much more nimble.

While there are several 3D printers which can act as a CNC milling machine, due to the different mechanical requirements of each machine, they are either slow at 3D printing or underpowered as a CNC router. It’s up to the customer to choose if they want a machine that can do one thing really well, or a few things so so.

Regardless of this fact, we still went ahead to see what would happen if we turned the Mill One into a 3D printer!

The first step to modding the Mill One into a 3D printer is to find the right electronics. We had a RAMPS 1.4  control board on hand so we chose to use this. The RAMPS 1.4 has all the sockets and pins needed to control all the periphery devices of a 3D printer (like a hot end, extruder, homing switches). You can find newer, more powerful control boards with many more features that the RAMPS, but the RAMPS is fairly easy to find and can be found inexpensively online.

We followed this dossier to help me wire the RAMPS together and wired the 3 motors which power the X, Y, and Z axis, as well as a spare extruder we had lying around from the old, out of commission Tevo Tarantula. It was quite busted, and some hot glue was to put it together.

Next we made a hotend mount on Onshape ( to mount the hotend and set that up as well. We printed it out on the 3D printer.

As for the hotend, we bought a E3D Volcano hotend clone online for a few dollars. It works pretty well, although if you do use this hotend, make sure to use the fan included otherwise it will clog.

Last thing to do is upload the firmware to the Arduino Mega in the RAMPS 1.4. We used this tool to configure the firmware, which will help you configure the firmware to match the rest of your hardware. It took a bit of trial and error to select the right settings. You can also change some of the settings through the EEPROM settings in Repetier Host (the gcode sender/slicer) we used, in case you need to fine tune things.

Installing the firmware is as easy as selecting the right port and device on the Arduino IDE, extracting the downloaded firmware ZIP file, and opening the Repetier.ino file. Simply click “upload” and the firmware should install onto the Arduino.

There’s a couple more things we could add, like a part cooling fan, homing switches, heated bed, etc. However, we wanted to keep things simple and just prove that it was possible to turn the Mill One into a 3D printer. All in all, the Mill One did a decent job at printing out this little low poly Pikachu. You can see there is some blobbing, which can be fixed with fiddling with retraction settings, and we can improve the pointiness of the ears by adding a part cooling fan.

In comparison to a regular 3D printer, the Mill One is a little bit slower and a little bit louder, but it can still produce high quality prints because the mechanical systems are more rigid and more precise. It was a really fun modification to make and the total cost in parts, had we purchased everything new would be around $60, making it a pretty inexpensive mod as well.

Until next time…