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$795.00
Our Closed-Loop Stepper Motor Kit is designed for existing LongMill lovers and DIY CNCers looking for the benefits of a feedback loop system that auto-corrects motor missteps and deviations from commands.
***This is not available for exchange if you have already purchased a LongMill. It is an entirely new product and must be purchased separately.***
For Vortex Rotary Axis closed loop motor upgrade, please purchase it here.
Switching to closed-loop stepper motors from open loop NEMA 23 motors on your LongMill means more reliability. The main difference between the systems is that open-loop motors lack positional feedback making them prone to “skipping steps” under load. With closed-loop motors, the feedback system helps monitor motor position which enables self-correction, improved accuracy and operational efficiency. The addition of the SLB-EXT Closed-Loop Controller sets up “dual homing” which allows your CNC to square the X and Y axis to one another through limit switches.
This kit is compatible with MK2 and MK2.5 versions of the LongMill, any size. It is not compatible with LongMill MK1. The kit can be used with non-Sienci Labs CNCs, but we will not offer support.
This product has a lead time. View current lead times.
***New to CNC? Read to ensure a successful start!
***Our products are subject to the USMCA and are not affected by the 35% tariff on Canadian goods. Read how we are handling the situation.
***We will be shipping to US customers with UPS option only.
This kit is compatible with the following LongMills:
***It is not compatible with any size MK1 version of the LongMIll.***
The kit can be used with non-Sienci Labs CNCs, but we will not offer support.
| Weight | 22 lbs |
|---|---|
| Dimensions | 24 × 12 × 6 in |
What’s included in each kit:
Some images are 3D renders of products. May not be exactly as shown. Some photos may contain items for illustrative purposes, such as routers or CNCs.
Motor Specifications
48V 10.4A Power Adapter Specifications
This power supply is not rated for countries with 220 voltage. A transformer of 500 watts or more is required for operation.
Measurements
Will you be selling the closed loop stepper motors on their own?
Yes, we do plan to sell the closed-loop motors on their own. Watch for upcoming announcements. If you own an AltMill and need replacement/spare parts soon, please contact us on this page.
Will you have installation instructions for my specific CNC machine (Shapeoko, Onefinity, OpenBuilds, X-Carve etc)?
No, we will only have instructions for LongMill MK2/MK2.5 machines. Although our team will try their best to provide information, technical support will be limited for third-party machines and accessories.
Furthermore we cannot guarantee that third-party accessories will be compatible with the SLB-EXT controller, please see our SLB manual (it applies to the SLB-EXT as well) to check if your accessory can be hooked up to the controller.
What’s the difference between a closed-loop stepper system and an open-loop stepper motor system?
With open loop motors, a command is sent to the motor driver, and the motor driver tells the motor to move some amount. Whether or not the motor actually moves that exact amount is unknown to the rest of the system. If there is some sort of resistance, disturbance, or obstacle in the way that prevents the motor from spinning its intended amount, the motor will ‘skip steps’ and will essentially lose track of where it thinks the motor is.
With closed-loop motors, a command is sent to the motor driver, and the motor driver tells the motor to move some amount, while simultaneously monitoring the position of the motor using a sensor. If the motor position is lagging behind where it is expected to be, the motor will receive more power to ensure that the motor gets to the specified position without any skipping. In the case where the motor is somehow obstructed from spinning entirely, it will enter an ‘alarm’ state and shut off power to prevent any damage. The motor driver will communicate back to the machine controller to let it know that something has gone wrong, and the controller can halt the entire system to prevent any sort of damage.
Aside from no potential for loss of position, there are a few other benefits of closed-loop stepper motors:
Items such as our Closed Loop Stepper Motor Kit are covered under our 60-day warranty. Learn more.
| 5 star | 90% | |
| 4 star | 5% | |
| 3 star | 5% | |
| 2 star | 0% | |
| 1 star | 0% |
Only logged in customers who have purchased this product may leave a review.
Alan Jones (verified owner) –
This was the best addition to my third-party CNC. It worked perfect and Gsender software was icing on the cake.
Daniel K. (verified owner) –
Huge upgrade. It was easy to change out. Had a couple hiccups that were my fault. I did not correctly run the setup file, but was able to fix things by doing some research. Overall the kit is an easy upgrade and definitely worth the money.
Bob I. (verified owner) –
The ability to home and rely on settings/memory is a big plus
Paul J. (verified owner) –
I have been using the Longmill Mk2 since the spring of 2025. I had no experience with CNC but the resources available both with Scienci and other available internet sites made the learning curve easy. The v-wheels and open loop motors however made it quickly clear that any projects requiring accuracy or increased speed would likely end in frustration. The closed loop motors have allowed for greater speed, accuracy and zero wasted projects. The v-wheels remain a problem but by sticking to the correct speeds and feeds and with timely maintenance the Longmill is a good machine and the closed loop motor kit is a must for any projects requiring accuracy.
Arthur Petch (verified owner) –
After installing the kit on my FoxAlien (FA) 8040 I found it worked really well.
This weekend I connected my “office” computer that lives next door and removed the small CNC dedicated laptop. This required using the Ethernet connection instead of the USB which while rather difficult to set up (mostly due to my forgetting connections and not reading instructions carefully) works quite well. When using the Ethernet connection moving the spindle around was initially jerky but that seemed to fix itself after I restarted it all.
There are several benefits that installing and using the kit have generated: it helped me improve the CNC stepper motors; allows me to do my Vectric Aspire design work and use gSender to apply the generated GRBL files without greater ease and comfort; declutterred my CNC work space; allowed me to bring my 24 inch CNC dedicated monitor closer so I can better see the gSender software (at age 78 my eyesight is less than optimal).
Most importantly the kit has done this without my having to upgrade the entire CNC, which while okay did come with some cost-saving shortcuts that bothered me as I learned more about CNC technology.
My next step will probably be to get the rotary accessory and use the A axis that was not available when dependent on my FA controller.
Louis Flores (verified owner) –
Best upgrade I could have done. My MK2.5 runs fast quiet and very smooth
Stephen Stoner (verified owner) –
I debated about doing this due to the cost but am extremely pleased with the results and very happy I did!! The additional power, precision and control options really take it to the next level!! If I had had the choice in the beginning, I would have purchased the new version of the long mill of course as it incorporates many great new features, but I am still very pleased with the MKII that I have. As I don’t use it a lot and am still learning it is a perfect solution for me.
Please keep up the good work and best wishes to Chris on his new endeavors, I really appreciated his input and videos and will miss his insight.
Benjamin (verified owner) –
I’ve been really happy with the closed loop motors. Being able to try more aggressive speeds without worrying that something will slip and offset the rest of the job is really nice. It seems like they take more power when sitting idle than the open loop motors? After the upgrade, the automatic switch that start my dust collector always stays on, now, instead of only turning on when the router gets turned on, so it seems the power usage overall with the new controllers and motors is higher; but that makes sense given they can move faster and more reliably.
Jeremy K. (verified owner) –
The closed loop upgrade is amazing as well as Sienci’s service as always. Keep up the good work. Jeremy
David Rackley (verified owner) –
This really improved the performance.
Thomas C. (verified owner) –
The closed loop stepper upgrade is a nice improvement to a very fine CNC!
Anthony M. (verified owner) –
I’m very happy I decided to convert my onefinity buildbotics machine using the SLB-EXT closed loop kit. the premade wiring bundles were very nice and the 48v closed loop steppers are a big improvement!
Byron (verified owner) –
Works great my machine is a lot quitter and stable
Dave R. (verified owner) –
I’m very happy with the Closed Loop Stepper Motor kit. The machine is quieter and faster and seems to move with more precision.
Borys Koba (verified owner) –
Kit looks good, however documentation has errors and gaps. Installation took longer and more hassle than it should have. Required Tech Support to complete.
Michael H. (verified owner) –
Although I installed the motors and SLB-EXT on another manufacturers CNC machine (Lead 1515), it has worked flawlessly. I configured and operate the machine after installation as an Altmill 4X4 (done for compatibility reasons with Vectric and I also use Gsender). The only item I had to physically alter in the kit was the cable chain, just needed a different size and length to accommodate my installation specifics. Am greatly satisfied with the kit.
Stephen N. (verified owner) –
Really nice kit! I was able to put it on my cheap ttc-h80 that I was never able to use was a poorly though out kit starter project. Wished I would have known before this journey. I was able to adapt everything and the project are coming out nice. Setup was a breeze with your software. I will be buying additional products in the near future. The only downside side I did not like was the motor connections.
Scott (verified owner) –
Fairly problematic getting it to work. Still have issues to work thru. Long mill 2 30×30
Peter Monaco (verified owner) –
My LongMill 48×30 has made a noticeable difference in both smoothness and overall performance. Motion feels more controlled, rapids are stronger, and I no longer worry about lost steps during longer jobs.
Paired with the new AutoSpin — which has been rock solid for over a year of testing — the machine feels far more refined and dependable overall.
The only challenge I’ve run into has been occasional motor-related troubleshooting within Vortex, but narrowing things down has been manageable and the reliability of the closed-loop system itself has been solid.
Overall, this upgrade makes the 48×30 feel more capable and closes the gap to my Altmill. Highly recommended for anyone looking to improve consistency and peace of mind. Only negative I would say is if it eliminated the v-wheels and added linear rails. But sounds like the MK3 has these newer features.
Stanley G. (verified owner) –
The
Closed loop upgrade has been a true delight to use. It has fixed some of the intermittent problems the open loop system was exhibiting I have not had any dropouts or ruined projects since the upgrade. Highly recommended a tool length sensor is the only other add on that I have added which has made multi bit projects much more reliable.