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AltMill and LongMill Survey Results and Development Progress

Hi everyone. Thank you to everyone who took the time to fill out our survey. We received an overwhelming amount of responses which has helped us get a better understanding of what our users are looking for in a new machine. Here’s a bit of a breakdown and a report of what we learned from your responses.

General learnings

As expected, almost all of our respondents shared that they used their CNC machines for woodworking. Also as expected, almost all respondents expressed interest in increasing the working area of their machine.

I was very happy to see that most respondents use their machine actively, with the approximate per week usage for most users being 15-30 hours per week. About a third of our respondents who use a LongMill reported that they use their machine 20 or more hours per week, which suggests that many of our users use their machines in small-scale production.

As we get into larger machines, power becomes more of a concern. We initially were worried that people would not have access to 220V/240V power in their shops (at least in North America), but it appears around half of the respondents who chose to answer this question have access to 220V outlets. This indicates that we should consider supporting both 110V and 220V spindles in future machine designs.

Interest between the AltMill and the Extended LongMill

We see about a 60/40 split in overall interest between the two machines. For LongMill users who are interested in upgrading from a LongMill to an AltMill shared these common sentiments:

  • Want to have a more rigid machine, generally to be able to use spindles and cut faster
  • Want to have integrated limit switches or homing switches
  • Want to be able to handle larger projects and half sheet
  • Want more speed
  • Have some complaints about parts such as the v-wheels and delrin nuts

For LongMill users that are interested in extending the size of their machine shared these sentiments:

  • Heavily value the community support and affordablilty of the LongMill in its current state
  • Would like general improvements to rigidity and design of the machine
  • Want a way to tram
  • Improvements to the v-wheel and eccentric nut system

Many people indicated an interest in a spindle option for both the LongMill and AltMill. The AltMill will be designed and compatible with spindles. While we don’t currently recommend using a spindle with the current design of the LongMill’s Z-axis because of weight and size, one option we are exploring is to build the XZ axis assembly for the AltMill to be compatible with the LongMill. This should let us be able to share development efforts for the assembly across both machines. Allowing additional cross-compatibility between motors and electronics between LongMill and AltMill should also make it possible to upgrade more aspects of the LongMill as well.

Development progress (LongMill)

We’re excited to share that we’ve gotten our first batch of custom aluminum extrusions in for the new iteration of the LongMill. These rails were made for our prototyping and beta testing before starting a larger production batch.

We are planning on using custom extrusions for the next generation of LongMills. We’ll refer to them as LongMill MK2s (at least for now). The goal with this generation is to provide the same straightforward, rigid, and affordable machine at the current sizes that we offer, but allow us to provide extended versions of the machine.

I think it’s important to talk a bit about custom extrusions, as it is a big departure from our original angle aluminum design.

When we first started Sienci Labs, we found that using angle aluminum turned on its side provided a sturdy, simple, and affordable way to create a linear motion system. Given that aluminum angle extrusion was readily available off the shelf, we were able to create both small and large batches of rails quickly and easily, without worrying about custom tooling and MOQs. I would attribute this factor as an important reason for getting us to this stage in our company, as we were able to continue to scale our production as we continued to build more CNC machines.

Creating custom aluminum extrusion was always on our mind, but until recently, it was not feasible for us due to cost, and the volume we would need to make didn’t make sense at our scale. At today’s scale, we’ve learned some important things that justify making our own extrusions.

The first area to talk about would be the accuracy of rails over high volume. Since last year, we encountered a new problem. While all of the angle aluminum we had received in previous batches were made to high tolerances, we had received a new batch of material that varied in the length of each arm and angle, causing less than an optimal fit of v-wheels. This gave us an opportunity to look deeper into tolerances in extrusion manufacturing as well as performing additional quality checks to ensure each rail was made to a high accuracy. We also learned that it would be a reality that at high volumes, it would be important to ensure we tackle issues at the production side with our manufacturers, since we couldn’t trust them to make every rail perfectly unless we provided the correct specifications for the rails.

This lead us to make our own “custom” angle aluminum. Basically, we arranged production of the angle aluminum using a new die made specifically for us at a higher tolerance than the industry standard, as well as extruding the material at precision spec. With these changes, we were able to reduce the number of out-of-spec rails to near zero. This also set up a better understanding of the extrusion process and the process and costs involved in it. It also gave us a chance to work with the extrusion manufacturer to work out design kinks and set us up for future development.

Today, we use tens of thousands of pounds of aluminum a year to make our rails, way beyond practical MOQs for producing custom extrusion. We are able to spread the cost of the dies over the thousands of rails we produce to make it an affordable option as well. So financially and scale-wise, custom extrusion is a feasible option. So let’s talk about why custom extrusion makes sense, and some cons/downsides as well.

Improved performance

Designing our own custom extrusions lets us create a design that is more optimal for rigidity than angle aluminum. Chris conducted dozens of simulations and tests to find the most optimal designs for the new rails. Based on the results, we can expect 2-3 times less deflection in the rail than the original design. I would note that these are simulations, and real-life results are likely to show less of a difference since the numbers do not reflect deflection from v-wheels, linear guides, and other parts in the machine.

This is especially important as we continue the development of larger versions of the LongMill since longer rails inherently have more deflection.

Ease of assembly

The new extrusions also include additional features that will make it easier to assemble and require fewer parts. For example, by including tapped holes on each face of the extrusions, users will be able to mount the rail to the gantry plate without any brackets. Each rail also has a t-slot, so all drag chain components can be mounted without additional tapped holes. Overall this will reduce the number of fasteners needed, the number of unique fasteners, as well as assembly time and complexity.

Improved scalability

Although time will have to tell, we expect that the new rails will be easier to produce at a larger scale. Since we already need to custom manufacture our own angle aluminum, lead times for both the angle aluminum and custom extrusion are the same. Since the custom extrusion requires less machining, we expect it to be slightly easier and less expensive to process the rail after it has been extruded. Also, since the rail requires less parts and a lower number of unique parts to put together the overall machine, it will save time and effort in sourcing and purchasing as well.

We are also working on cutting and tapping rails in-house, allowing us to have more flexibility in the sizes and variations in the machines we produce as well.

Less production flexibility and a step away from replicability

Since angle aluminum is a fairly universal product that can be purchased off the shelf, a determined maker should be able to replicate the rail design of the LongMill and make their own custom machine from scratch. It would be much more difficult to replicate the new custom extrusion, as the costs to produce a small number of rails are incredibly high. This, I feel, is a step away from the openness of the platform. We will continue to fully open-source the designs as we have always done, but part of the open-source movement is considering the replicability of the product. This was an important consideration when we started this development, and these are some considerations and why we made this step:

  • The number of people who make their machine from scratch is incredibly low. While there are people who use the LongMill design to make their own machine, making the designs available for this purpose serves a very small population.
  • The net benefit of having a simpler, better machine that is more easily scalable provides more benefit in our goal to make CNC accessible to beginners than to have a machine that can be made from scratch.
  • Most people who make modifications to their machines generally do it after they purchase and assemble a manufactured kit. Continuing to make the design public will continue to support people who wish to simply modify a kit
  • Building a machine from scratch generally costs more and will not perform better than a stock LongMill. We have extensively optimized the design and put an insane amount of thought and consideration to the quality of each part. Parts such as the couplers, Delrin nuts, and even the 3D printing filament are all custom made specifically for us at a higher tolerance than off the shefl components. Since we work within high volumes, we are also able to take advantange of economies of scale that do not come with buying parts in small numbers. Because of this, I believe that folks who want to build a machine from scratch would only benefit if they plan on making extensive changes to fit a specific need, or are doing it for the fun of making the machine. There are of course other designs and options that people can build besides the LongMill that lend itself in being made from scratch.

Backward compatibility

While the rails have been designed to be as backward compatible as possible, and many of the old LongMill parts can be used on the new rails, this brings up another important debate, which is “is it better to take apart and modify an old LongMill to put new parts on it, or is it better to buy a new one?” This is what I think.

First of all, if you already have a LongMill and are happy with the current size of it, I believe that keeping it the way it is and continuing to use it is the best option. While the newer versions of the LongMill will perform better, not only does the current version work well already, the extra cost to switch over parts isn’t worth the extra performance you may get. Instead, investing in other things, such as better tooling, software, and materials for projects may give a better return on investment. It should also be noted that the price of the MK2 LongMill will be higher than the current LongMill, so that we can account for changes in material prices, cost to build the machines themselves, and inflation.

If you are wanting to upgrade the machine to a larger size, then the debate gets a little more tricky. If you take apart your old LongMill to swap in new rails and lead screws, you’ll be left with a lot of leftover parts. Instead, it may make more sense to sell the LongMill and buy a whole new machine instead. So the formula would go:

(Cost to buy a larger LongMill – Price you sell your old LongMill) v.s. Price of the upgrade

I personally like the idea that instead of having this be an opportunity for a new user to scoop up a used LongMill at a discount so that they can get into the CNC hobby and prevent having a bunch of unused parts lying around. The net number of machines is one instead of two.

Of course, we will offer both an upgrade kit and full kit options to customers. These parts are interchangeable between all generations of the LongMill:

  • Motors and electronics
  • Lead screws, couplers, and nuts
  • V-wheels, fasteners, and eccentric nuts
  • XZ gantry assembly
  • Drag chains

Development progress (AltMill)

We’ve completed the baseline CAD design for the AltMill and are currently in the process of having our first prototype machined. We expect the parts to arrive in mid-November. This will be our first fully functional prototype which will be used to test performance and make design changes.

Next steps

We’ll be talking about next steps for sales and beta testing of these products. If you wish to sign up for beta testing, please fill out our survey:

LongMill/Extended version of the LongMill

We are waiting on a couple more parts to arrive to start building working versions of the LongMill MK2, at which point we’ll be contacting and working with beta testers.

Parts that we are still working on making include:

  • Steel Gantries
  • Feet and Z axis mount
  • Thicker lead screws (for larger versions of the LongMill)

We expect the first two parts to be ready in the next 2-3 weeks, with the thicker lead screws arriving in about a month.


The prototype parts are currently in production. We will be building one single prototype and putting it through the paces. Once we’re happy with the performance of the machine, we’ll be opening up pre-orders for beta testers. We expect this to happen around the end of the year or start of 2022.