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Putting the AltMill Project Back on the Burner

Hey everyone. As you guys might have seen in the November update, we are now back working on the AltMill. If you have been following along with us since 2021, you might have heard about the AltMill project.

From 2021 and 2022, there were a couple of reasons and factors that led to us putting the AltMill project on the back burner, which included:

  • Not having enough space for the development and production of the machine in our current space
  • Continued need for development and focus on the current LongMill product
  • A general decision to focus on the lower end/hobby of the market at the time

However, in 2023, we’ve now established a strong process for the LongMill and with the move to the larger building, we feel like it’s a good time to put the AltMill project on the front burner again.

Things are already moving forward with the AltMill, as we currently have 50 machines in production for our first batch. We expect parts to start arriving for assembly in the next 2 months.

What is the AltMill?

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The AltMill is a CNC router that uses ball screws and linear guides and has a 4ft x 4ft working area. This addresses the two big “asks” we get from the LongMill community for a new machine, which is to:

  • Having a larger working area
  • Getting rid of v-wheels

The AltMill focuses on the same core ideas as the LongMill, which is:

  • Be simple, affordable, and easy to maintain
  • Come with excellent support
  • Be beginner friendly

The AltMill is aimed towards:

  • LongMill users who want to upgrade to a faster, larger, and more powerful machine
  • Hobbyist, prosumer, and small business owners who want to use for small scale production work

The AltMill is a completely new machine, with basically no parts shared between the LongMill, but users will find the process of running the machine to be almost identical.

Specifications

  • 10,000mm/min rapids with closed-loop stepper motors
  • Higher rigidity with HG15 linear guides on all axis
  • Higher precision with 16mm ball screws on the X and Y, and 12mm ball screw on the Z axis
  • A working area of approximately 50″ x 50″ on the X and Y, and Z travel of approximately 6.5″ (with 4-5″ Z-clearance under gantry)

Changes to the original design

The fundamental structure, layout, and size of the AltMill between the original one we designed (More info here: https://sienci.com/2021/10/15/altmill-and-longmill-survey-results-and-development-progress/) and the one currently in production is with the linear guide choice and the frame.

The original design used SBR16-type linear guides, which had a few advantages, with the primary one being that the height that the linear guide blocks sat met up with the exact same height as the ball screw nut, making it possible to mount everyone on the same plane like shown in the picture below. In this design, we mounted everything to machined plates.

We initially avoided using “square rail” guides because of their cost and need for more careful assembly, but with our new experience working with different manufacturing techniques and other factors such as finding a well-priced supplier for the components, using rails such as the HG15 family of parts became viable.

HGH15 components

One of the main manufacturing techniques we’ve come to understand better and use is extrusions. We’ve used this technique for making the LongMill rails, LaserBeam heatsinks, and the t-track clamping system, so we now have a better understanding of the tolerances we can achieve, and because extrusion allows us to space the components as we want to, we’re able to make more rigid structures while keeping the whole machine lighter. Additionally, we can add extra features to the rail and position components where we want.

Adding features like t-slot and locations on the ends to tap holes, we are able to reduce the number of parts needed and provide more freedom in mounting different things to the machine.

We use three main extrusions in the X, Y, and crossbracing of the table that keep the machine rigid while reducing the number of parts needed to put it together.

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Switching to an extrusion-based design also helps drastically to increase machine rigidity, without increasing weight. In the LongMill MK2, we were able to increase the rigidity of the X-axis beam while simultaneously decreasing moving mass by switching from a solid ‘open channel’ angle aluminum profile to a ‘closed channel’ extrusion. This makes for a significant strength-to-weight ratio improvement, which has been the case of the AltMill’s latest design revision as well.

This is especially relevant for the case of the X-axis beam in most CNC routers, since tend to deal with very high torsion loads; twisting the beam. Closed channels (tube structures) are the most optimal shape for dealing with these loads, the closer a profile gets to becoming a perfectly round tube structure, the better it is at handling this load, and the better our machine will perform.

Simulation of an X-axis extrusion profile iteration, stress concentrations shown on right

The new AltMill’s X-axis extrusion has also been sized to be much more robust than the LongMill’s X-axis extrusion. With better linear motion components, faster cutting speeds, and more utilization of higher-powered spindles it’s important to rebalance different components of the machine to ensure there are no weak points.

The rigidity coefficients of the AltMill’s X-axis extrusion at various wall thicknesses, compared to some other extrusions

In a CNC router, you generally want to balance any deflection across all components evenly. Having a very rigid machine with a single weak component that causes it to perform poorly usually doesn’t make sense from an engineering or practical standpoint. Looking at a breakdown of various sources of deflection on the LongMill, we can see that with the exception of the V-wheels, the LongMill does a pretty good job of balancing this across major parts and sub-systems.

Since we’re now removing V-wheels from the equation in the AltMill, we now look towards some of the largest areas of deflection, since these will make up the bulk of deflection. Some of the more trivial areas such as the router mount, and deflection from the Z-axis linear bearings (MGN12 pitch deflection) can be addressed by better component selection, but the X-rail deflection stands out as an area where improvement will be needed at the design side.

Another, unrelated takeaway from looking at these charts is the variance of how much deflection the V-wheels on the X-axis contribute depending on their tuning and wear state. This can be problematic when you’ve set up your cutting parameters to fully utilize the rigidity of the LongMill (or any V-wheel machine), only to have them wear or fall out of tuning causing your rigidity to decrease and affect the quality of your project.

This isn’t to say that V-wheels aren’t more than adequate for the purposes of a hobby CNC router, but this matter becomes more of a concern when dealing with much more strenuous, repetitive projects where consistency over a long period of time is needed.

LongMill MK2 deflection breakdown by component/system

Another change not specific to the new design of the AltMill is the decision to pursue a closed-loop stepper motor system.

With regular stepper motors, the motor driver will instruct the motor to move some amount, and the controller will assume the motor has moved by that amount. If there’s nothing wrong with your machine, and you’re not running into anything that’s stopping your motor from moving, this almost always works fine.

When your motor driver instructs your motor to move some amount and it fails to move, or does not move the exact amount as requested, things get out of sync. This scenario is generally referred to as ‘losing steps’ since your stepper motor has skipped moving a few steps/increments and is not where it should be, or where the controller thinks it is. This is bad for a couple reasons such as:

  • The next toolpath your machine makes won’t be where it should be, typically meaning your cutting paths will appear ‘shifted’ in some direction
  • On a ‘moving gantry’ machine with two Y-axis motors, if one motor skips/loses steps, your X-axis will no longer be square with the Y-axis, and in serious cases you may damage parts or induce excess wear running it like this.
  • If the motors are unpowered (such as between jobs), bumping into the machine, or pulling one the router/spindle may move the motors causing them to lose position and create ‘shifts’ in your project the next time you run it.

Unlike a regular stepper motor, a closed-loop stepper motor will keep track of it’s position using a sensor known as an encoder. The sensor typically relays this position information back to the motor driver (ergo, closing the loop), to let it know if everything is in sync and motor is where it’s expected to be, or if something has gone wrong.

If something is off, the motor driver will correct for the difference, and move the motor’s position to wherever it should be. If it’s unable to, such as in the case of running into one of the travel limits, the motor driver will send an alarm signal to the controller to let it know that something has gone wrong, in order to salvage the project and prevent any sort of serious machine damage.

Closed-loop stepper motors also have some other neat benefits such as:

  • The ability to run at high speeds with reliability
  • More efficient operation (and resultantly with less heat)
  • In some cases, quieter operation

There have been a number of advances to hobby CNC technology and industrial technology in general that have made closed-loop steppers more affordable and easier to use. We’re excited to bring some of the new hardware into our designs.

Pricing

We expect the base price for the AltMill to start at $3600CAD/$2650USD, which comes with the mechanics, hardware, and electronics. This price does not include a spindle or router, but we anticipate that we’ll have something available at the time of shipping that would be suitable for the AltMill, such as a spindle package or our Sienci Router that is currently in development for around ($250 to 800CAD).

Because the AltMill uses a frame structure to ensure the whole machine is level and square, we are planning to have specially-made table legs that can be added to the machine to allow the AltMill to be its own standalone bench, eliminating the need for users to need to build a bench like the LongMill. We expect this addition to come as a kit for around $150-300.

Other accessories (and necessities) such as T-tracks and dust shoes will be available specific to the AltMill near the time of launch as well. Most accessories that currently exist for the LongMill system of CNC routers will be compatible – this includes things like the LaserBeam, Vortex Rotary Axis, and any of the future add-ons that pair with the upcoming SuperLongBoard controller.

Users will need to provide a wasteboard (3/4″ MDF) to be mounted on top of the machine.

Production

The AltMill is already in production and we expect the first batch of parts to arrive at the end of December. We expect to have our first working machine in February. We are ordering enough parts to build 55 AltMills and expect to yield a minimum of 50 units in this batch. We expect to have units start shipping in March or April.

50 units is a pretty small batch to start with at our scale, but since we’re not sure how much demand we’ll see for the product, we’ve decided to keep the number pretty low. I think even if we only sold 50 machines, since they are fairly simple and use a lot of off-the-shelf parts, we can keep them supported on a small scale as well. My expectation in the long run however is to be able to ship and sell around 1000-2000 AltMills per year.

Ordering

We expect to start pre-orders sooner or later based on the demand for this machine. Basically…

  1. If people want to give us their money right away and pre-order now, we will set things up so that can happen. This would be the ideal situation since it would be less risky to invest in this new product for us financially, but be the most uncertain for the customer on when they would be getting their machines.
  2. We launch the pre-order when we have a fully working machine so that people can see what it looks like and have more confidence in a specific launch date.
  3. We start to sell and ship once we get all of the parts in and the design is complete. There would be a short wait time as we build and pack machines.

Let us know what you think. If you’re interested in ordering an AltMill now, please fill out the survey below.

FAQ

Technically not an FAQ, but more of an anticipated FAQ…

  • Will the AltMill be compatible with a spindle?

Yes, we actually believe most customers will want to default to a spindle to take advantage of the AltMill’s higher speed and rigidity. We will be working on a spindle or higher-powered router option at the time of shipping that will be able to be used with the AltMill.

  • Can I upgrade my LongMill to an AltMill?

No. Because this is a completely redesigned machine, there will be little to no parts shared between the two platforms.

  • I want to pre-order an AltMill right away. Do I need to put down a deposit?

At the current time, we are planning to ask customers to pay the full price of the machine upfront once we decide to open up pre-orders. You may change or cancel your order at any time before your machine ships.

  • Do I need to assemble the AltMill?

The major parts of the AltMill such as the X-axis rail and Y-axis rails will come pre-assembled, but will have some basic assembly to help keep shipping costs low. We expect set up for an AltMill to take around 2-4 hours with a basic set of tools.

  • Will there be a 4×8 AltMill?

At this time, and for the near future we will only be offering a 4×4 AltMill. It’s possible we may look into creating a 4×8 variant of the AltMill much later on.

  • Will there be an ATC (auto tool change) spindle/system for the AltMill?

It’s not in our immediate plans to offer an ATC system for the AltMill, however, this is something that could be possible much later on as we continue development on the Sienci Router project. In the short term, it will likely be possible to integrate such a system on your own since the AltMill’s controller will run grblHAL firmware which supports more advanced tool-changing features needed for these systems to function.

  • Will I need to connect a computer to control the AltMill?

The short answer is, yes. The AltMill will need to be tethered to a computer at the time of launch. That being said, some of the development to move the computer onto the board or for us to provide a separate computer module applies that we’re working on with the SuperLongBoard for the LongMill, so we expect at some point, we’ll have a more integrated system for the AltMill. Currently the options we are assessing are expected to cost around $200-300.