Mounting Z-Axis 12V Power Supply

Wiring was never my favorite part of a project, but it needed to be done. A lot of it at that. After the latest plotter test, I picked up the next item on the to-do list: the 12V power supply for Z-axis. It was just set on the table for testing the second and third iteration of Z-axis, held only by gravity which meant it started shifting position and threatened to fall off the edge when the XY stage movement hit the table’s resonance and everything started shaking. We should mount it rigidly on some part of this machine.

My first thought was to 3D print a bracket for this power supply, and mount it to one of the aluminum extrusion beams. But then I thought it would make more sense to put it alongside X and Y axis control boxes which are combination power supply and stepper driver modules. I’ll mount the Z-axis power supply here, but I’ll hold off moving the stepper drive here as well since that would involve re-routing many more wires.

CNC 12V PSU mounted on plate below

I drill three holes in the metal panel mounted below the table for X and Y axis driver modules. Even after the 12V power supply was bolted in place, there’s plenty of room left on this panel for the Z-axis stepper driver in the future, and possibly also the ESP32 control board. This is the eventual destination for all electrical components, but one step at a time. Of course, it would help if I don’t keep changing parts of the machine…

Pen Plotting With Third Iteration Z-Axis

After third iteration of CNC Z-axis was installed, we wanted to perform a simple test. This particular assembly already had brackets to hold a spindle of some kind. We don’t know what it used to be, but measuring the hole we infer it was approximately 65mm in diameter. We didn’t have a suitable cutting tool on hand, so we reverted back to the old standby: testing it as a pen plotter.

We didn’t have any 65mm diameter pen, either, but we do have plenty of plastic bits in the form of failed and abandoned 3D prints. A few blocks were fished out of the bin and took up space so we could clamp a pen in the spindle holder. A pen could not reach the surface of the XY table, so a cardboard box and a few sheets of foam were used to raise the working surface. It’s not precise by any stretch of the imagination, but it’ll suffice for a pen plotting test.

The test plot was the ~25 minute variant of a Sawppy portrait. This file previously helped us determined UGS was not going to work in this particular configuration, and that bCNC worked better. Now we’ll feed this G-code throub bCNC to plot with the new Z-axis holding a pen.

Since the pen was clamped rigidly in the holder, and the work surface was crude with boxes and foam, the paper was not level. For one side of the sheet, the pen barely made enough contact to draw. On the opposite side, it dug deeply enough to start damaging the paper. But it did not tear, so we’re calling it unintentional embossing.

The results looked pretty good! It’s a good confidence booster before I return to more housekeeping tasks of building this machine.

Integrating Transplanted CNC Z-Axis

Bolting on a transplanted Z-axis assembly gives us a screw driven linear actuator with open-loop control via stepper motor, plus a switch for finding home position. Electrically this assembly is identical to the belt drive assembly we had wired up earlier, this second round of electrical integration consisted only of crimping some connectors on new wires.

For hardware configuration, the first stop is always to punch in part numbers to see what we get. We can tell this stepper motor is in a standard NEMA 17 form factor, but we needed to search on its part number SM42HT47-1684B to discover specs such as maximum current per phase. (1.68A) We conservatively capped our driver to a low value of 1.0A just to be safe, leaving room to increase if we need to.

The steps per revolution for this motor was unstated, so we’ll start with the assumption 200 steps per revolution typical of such motors and adjust as needed. We then measured the lead screw on this Z-axis. Since everything else on this machine is metric, we used metric measurements and it appeared to be 2mm per revolution. This maps the motor neatly into 100 whole steps per mm.

A test run with whole steps sounded very rough, so we increased the stepping up to 4 microsteps and a corresponding adjustment in Grbl to 400 microsteps per mm. This gave us smoother movement at the loss of some holding torque. We won’t know if that loss would be a problem until we start putting some heavier tools on that spindle holder.

In the meantime, we’ll start testing the same way we tested the servo Z-axis: use it as a pen plotter. Only this time we’ll have a stepper controlled screw drive Z-axis.

A New Home For CNC Z-Axis

Our hacky CNC machine project upgraded to a real CNC Z-axis courtesy of a retired CNC router project. It was a modular design built out of extrusion beams and commodity M5 fasteners, which made it easy for us to remove the Z-axis and transfer it to our project.

The modular nature also made it easy to make modifications, and as we mounted this Z-axis on our machine we could see signs of creativity by the previous owner. We’re not sure exactly what problems all of these modifications were intended to solve, perhaps we will learn as we get further on this project. For now, the focus is on exploration which means a preference for nondestructive modification until we have a better idea of what we are doing.

HAKNC bracketWhich means we’re not going to drill into aluminum for mounting holes just yet, we’ll get started with a simple 3D printed bracket for mounting this Z-axis assembly on our gantry. We would prefer to have mount it just a little bit lower, bit we were hampered by the 3D printed limit switch mount. It may get replaced later, but for now it dictates our Z-axis mounting height.

Thanks to the use of flexible aluminum extrusion beams on both CNC projects old and new, mechanically speaking it was relatively painless to transplant this Z-axis from one machine to another. Now we proceed to electrical and software integration.

A New Candidate Z-Axis From Retired CNC

We didn’t get very far with a belt drive stepper Z-axis before another candidate emerged. This is the gantry of a CNC router table, with some sort of a spindle holder and two stepper-controlled axis. The Z-axis moving the spindle holder up/down, and one of the linear axis. X or Y I can’t tell. The other axis would roll on rails and controlled via belts missing from this picture.

There’s a name on the spindle holder, and a search for Inventables CNC found their current product called X-Carve which shows some superficial similarity to what we have before us. But this one showed signs of several modifications by its previous owner. We do not have the full history of it, we just knew it was a CNC project that was left behind several months ago when its owner moved to a different city. It was given to another person, who then offered it to us because we were likely to make use of it immediately on our project.

And use it we shall, because that Z-axis looks a lot better than the one we were ready to start exploring. This Z-axis module uses a leadscrew, which we expect to offer superior precision (good) at a loss of top speed (probably less important for Z axis.) It was originally designed to be a CNC Z-axis, built with aluminum extrusion beams far more rigid than the thin folded sheet metal construction of our belt-drive assembly. Our belt-drive sheet metal Z-axis was the X-axis of a Monoprice Mini Select 3D printer, which meant it was not designed to take the kind of loads that would be necessary for CNC cutting anyway.

Let’s mount this modified Inventables Z-axis and make it work instead.

Initial Tests Of Stepper Motor Z-Axis

We have wired up our first pass of a stepper motor controlled Z-axis, with a stand-alone stepper motor driver powered by a stand-alone 110V AC to 12V DC power supply unit. All connected to a mechanical assembly that was formerly the X-axis of a Monoprice Mini 3D printer.

First test was to verify electrical functionality. The entire assembly was connected to our Grbl ESP32 controller while sitting on the XY table, and we verified there were no escapes of magic smoke. (Yay!) We then used bCNC on the laptop to command Z-axis movement, and verified the direction was correct. (The distance was not, but we can figure that out later.) At this point we were running short on time available at the shop, so we followed up the electrical test with a quick and dirty mechanical test.

The machine has a vertical aluminum beam where we had taped our sharpie markers earlier, and fastened our servo Z-axis for that series of tests. Now, with a mechanical assembly almost as tall as the beam, we’ll need to decide if we still need that vertical beam for permanent installation.

But for a temporary test while we were short on time, the vertical beam is great for us to zip-tie the mechanical assembly in place. It is crooked (not nearly vertical) but it was enough for us to gain confidence this assembly is actually going to work for us. There are still things to be figured out: a rigid mounting solution that doesn’t involve zip ties, plus Grbl parameters to correct movement distance.

But for today, we’re just happy to run through homing routine on all three axis before proceeding further.

Wiring Z-Axis Assembly To Stepper Driver

The Monoprice Select Mini 3D Printer is an impressive demonstration of how costs could be wrung out of a basic cartesian 3D printer design. We could debate whether the tradeoffs were worthwhile, but the level of integration resulting in parts count reduction is indisputable. I have extracted the X-axis from a non-functioning Mini printer intending to leverage its highly integrated mechanical assembly. But it turned out the advantageous mechanical integration was balanced by the disadvantages of electronics integration.

The Mini 3D main board is a single monolithic circuit board, with stepper motor driver chips surface mounted directly to the PCB. This meant electronics associated with the X-axis mechanical assembly could not be easily extracted and reused, and we had to use a stand-alone stepper motor driver.

While I was busy routing wires for X and Y axis and cleaning up the tangles, Emily stepped up to handle the task of wiring this Z-axis. In the shop she found a stepper motor driver module gathering dust and got approval to use it in this project. The motor presumably runs best on 12V as that was the power supplied by the Mini’s AC adapter, but there was no existing 12V power rail on our machine to tap into. Our Grbl ESP32 controller ran on USB 5V from the laptop, which was itself running on standard Dell 19V power. The Parker ZETA4 controllers plugged directly to 110V AC and each had its own internal power supply.

So Emily also had to dig up an 110V AC to 12V DC power supply to wire up to the stepper driver. It was also gathering dust and had amperage capacity far higher than what we needed for the motor, but it was easily available so we went with it. Once everything was wired up, it’s time to test what we have.

Repurposing Broken 3D Printer X-Axis To Use As Z-Axis

It feels like a lot longer than three years ago, but that’s when I started my adventures in 3D printing with the Monoprice Select Mini 3D Printer. It was limited in print volume and print quality, but it served as a good introduction to 3D printing so I felt I understood the field enough to invest in larger and more capable printers.

My Mini was retired from active duty and sat in a box until I loaned it out to Emily for the exact same purpose of giving her an introduction to 3D printing. And just as I did, the introduction led her to purchase a larger printer and my mini went back into its box.

Now it has been pulled out of the box for a third tour of duty elsewhere. This time, I am trading it away. It is destined for local technology outreach events, and in exchange for my working but limited printer I’m receiving a non-working Monoprice Mini to tear apart. Here is my printer performing a test print to verify it still works, the final print it will perform in my possession.

MP Mini X axis

Before I agreed to this trade, I was ready to tear it apart for the sake of extracting its X-axis. That black horizontal arm is a small self-contained linear actuation unit: it has a standard stepper motor, guide rods with linear bearings, and a belt-controlled carriage. Plus a micro switch for axis homing, all inside an integrated stamped sheet metal unit.

I wanted to use this X-axis assembly as the Z-axis for our Grbl CNC project. And the timing of this trade is fortuitous, because now I’m not destroying a perfectly working printer. It is not going to be rigid enough to handle a CNC cutting tool, merely an incremental upgrade over the servo-controlled Z-axis. This allows us to take our first step towards a stepper-controlled Z-axis for our machine.

Wiring Organization With Spiral Wrap And Zip Ties

The major components of the SGVHAK CNC project now all have assigned mounted locations, the Grbl ESP32 controller board being the most recent item. No longer sitting on whatever surface is convenient, a tidier arrangement of components allow a tidier arrangement of wires.

The repurposed aluminum extrusion beams have channels that turn out to be quite convenient for running wire bundles. And as long as we stay away from the cut ends of these beams, there are no sharp corners to raise wire damage concerns. So they were stuffed into a channel, and held in place with zip ties. This may or may not be a good long term idea, we’ll find out as we go.

Under the table, there is a metal cross beam just behind the metal plate where we’ve mounted the Parker ZETA4 motor drivers. This beam is an ideal location for extra length of wire to be coiled up and zip-tied out of the way.

The leaves what we should do about the wire that can’t be conveniently tucked into an extrusion nor tied to the cross beam, and the solution is spiral wrap. The downside of spiral wrap is the time consumed in their installation, a lot of labor just winding them around and around the wire bundle. This spool was available precisely because it was so tedious to install. The owner switched to a different and easier-to-install style of cable sleeves and donated these spiral wraps to the project. It stays with the theme of building this project out of salvaged and repurposed parts, and besides, beggars can’t be choosers!

Once we’ve done our housekeeping and the wires are much neater than before, we can return to feature work.

Test Mounting Grbl ESP32 On Gantry

We now have good homes for the Parker ZETA4 driving our X and Y axis, and the laptop control console has a nice throne of its own. But we can’t start working to tame our nest of wires unless we also find a home for the prototype Grbl ESP32 controller board. Every wire on this machine leads to the controller board, so its location is literally key to the wiring puzzle.

During the test where everything was held down by tape, this controller lived atop the gantry not far from the laptop computer. This seemed to work well and there may be merit to the thought that lines for high speed digital data should be kept as short as possible. To test this plan, some very minimalist brackets were designed and printed for hooking the board on our gantry rail directly behind the laptop computer.

Since we have components and wires soldered to the back side of our prototype control board, we need to make sure we keep a healthy distance between those exposed contacts and the very conductive aluminum extrusion beam. M3 threads were tapped in the bracket, and standoffs installed to maintain that distance.

Grbl ESP32 test mount 1

Two identical brackets were printed, with a minor lip to hook over the edge of the extrusion beam. The only thing maintaining the correct distance between these two brackets is the perforated PCB itself. Not the best plan in the world, but this is just for a test to see if all the wires would even reach and function if they do.

Grbl ESP32 test mount 2

If this location doesn’t work out, the next most logical position is on the metal plate below the table, adjacent to the X & Y axis driver modules. We’ll test this location first. And now that a location has been decided, it was time to organize some wires.

Mounting Parker ZETA4 Under Table

Adding functionality to our CNC project is fun, but every once in a while we need to stop and do some housekeeping. Such was the case for a recent work session: we need to start cleaning up our wiring. The big nest of tangles are starting to impede progress, because time we spent sorting through wires is time not doing cool things.

Real industrial CNC machine usually have a big electronics equipment cabinet in the back, made of folded sheet metal. We won’t have that, but we shouldn’t leave the Parker ZETA4 stepper motor drivers sitting loosely on the ground, either. A big metal bracket was available and repurposed as home for the beefy X and Y axis motor drivers, the Parker ZETA4.

First a few holes were drilled in the table to fasten the bracket, then mounting patterns for the ZETA4 were drilled in the bracket and tapped for fastening machine screws. There was one minor oversight: the pattern is technically upside down. The most important part of this vertical orientation is so the driver module heat sinks are oriented properly for convection cooling. Mounted upside-down will reverse the air cooling flow, hopefully the direction matters less than the fact air is flowing.

With the two driver modules fastened to the bracket, we can plan wire paths in some semblance of organization. As a bonus of this mounting, the new locations are closer to the rest of the machine giving us more slack in the wire to reach other components.

Successfully Ran Multi Hour Programs With bCNC

Once we added a crude but functioning third axis to our primordial CNC machine, we started testing it by running longer and longer G-code programs. Once we got to a test program that took roughly 25 minutes to complete, we encountered our first system failure: our computer running UGS (Universal G-code Sender) would lose its serial communication connection at unpredictable times.

As we intend to eventually run programs much longer than 25 minutes, this was unacceptable and UGS was removed from contention. We returned to the list of G-code senders in Grbl documentation and chose bCNC as our next candidate.

We are definitely giving up some nice features by moving from UGS to bCNC. We lose the ability to customize the arrangement of our control elements, and we lose the ability to preview our tool path from arbitrary directions. (We’re restricted to a few fixed projections.) But reliability is more important than eye candy, so we’re happy to give them up if it means a system that we can rely upon to run for hours.

To test bCNC, we take advantage of the fact this is an open loop system: the control board will run exactly the same whether it is attached to the salvaged industrial XY stage or not. This allowed me to run long duration tests using just the laptop and the prototype control board, away from the workshop where the machine hardware resides.

To establish our baseline: UGS is brought up to run this 25 minute test program again in the test configuration without hardware. Two attempts both failed with serial connection dropping offline at different times.

Then, using the same desktop test configuration, bCNC is brought up to run the same 25 minute test program. Five attempts ran to successful completion without losing serial connection.

Then we moved on to the challenge level: a G-code program that takes over 7 hours to execute. I would leave the laptop and prototype board running over most of a week. Every time I noticed the program had succeeded, I press “Cycle Start” again. This netted roughly ten attempts, and they were all successful. No serial connections were lost.

It looks like bCNC is the way to go. And with the new candidate software in place, attention returns to machine hardware.

Unreliable Serial Communication with UGS, Try bCNC Next

We now have a three-axis machine: aged but still robust industrial motion control linear drives for our X and Y axis, and a new but not at all robust servo holding a Sharpie marker as our Z-axis. It was enough to let us feed three-axis G-code programs and watch them in action.

We started with short programs that would take less than a minute to run, then gradually increased the complexity and duration of jobs. If we wanted to turn this into a CNC mill, it will need to be reliable and dependable for long jobs. We didn’t have enough experience to have a list of potential points of failure, we just ran ever longer jobs and watched to see what goes wrong. We knew it was going to be a process of finding a problem, fixing it, finding the next thing to fail, fix that too, and repeat.

Our first problem: the G-code sender UGS running on the control console laptop. In the middle of running a job of approximately 15 minutes, UGS would drop serial connection. The machine stops moving and UI shows “OFF-LINE”. This is not just annoying, it is plainly unacceptable in a machine that might be expected to run for hours.

And there’s another possibly related problem with UGS serial communication: it was not able to connect to Grbl ESP32 if the dev board was connected at boot. We could work around this by unplugging the USB cable to ESP32 and reconnect, but this is rather inconvenient.

We could put up with the startup connection issue if that was the only problem, but randomly halting in the middle of a long job is unacceptable. So UGS is out of contention, and we return to the Grbl G-code sender list to find a replacement.

The next candidate: bCNC.

Quick Fabrication For Servo Z-Axis

Soldering up components for a test run at the workshop, I ran out of time to implement something to actually attach to the end of the Z-axis servo. While I was setting up all the components with copious amounts of tape, I asked Emily for help. She has repeatedly demonstrated skill at creatively building a solution in very short time using whatever parts were on hand. The most important episode of this skill saving our bacon was when she fabricated a steering servo bracket for SGVHAK rover.

As I was focused on routing wires and taping them in place, I didn’t watch the magic happen first hand. But I was amazed when Emily walked up less than 15 minutes later with a bracket with parts clearly made of 3D printed plastic. There was not enough time to print such a thing… “How did you do that so fast?”

As it turned out, she drew from a box of rejected & failed 3D prints that was sitting in the back of the shop. The parts were not printed for this project, but their residence in the fail pile made them candidate raw material for today’s quick fabrication. Once Emily installed the Sharpie marker holder to our servo Z-axis, our plotter can lift its pen!

Emily rigging up Sharpie holder for Grbl ESP32 Z axis servo

But as we found out very quickly, the lift is not clean. This cheap micro servo has a lot of slop which made it difficult to position it at a height that will make good contact with the paper when down and stay clear of the paper when lifting. Instead of ending a line cleanly, the pen would make a short diagonal mark as it lifted.

No matter, it was enough for us to continue testing this system. We started feeding it increasingly longer programs to see what breaks down first. Our answer: UGS, the G-code sender program running on our control console laptop, was the first to fail.

This Test Run Made Possible By Tape

Completion of soldering circuits for hardware control switches seemed like a good place to take a break and test. It’s fun to keep the momentum going, but it’s also important to stop and verify the work done so far. Off to the shop we go to set things up!

The jury-rigged nature of this prototype test is evident. While I had put a bit of time into building a nice shelf for the computer, none of the other pieces received such attention. Eventually there’ll be an enclosure for the ESP32 running Grbl. A circuit board of the dev module plus all of its associated circuitry, much like the official Grbl ESP32 board. But that board has room for Pololu stepper drivers like those on a 3D printer, and we don’t need that for our Parker motors. That will happen later. For this test, I found a piece of scrap acrylic and taped it to the top extrusion beam to serve as table for the perforated circuit board.

In fact, tape is the dominant element in this test. In addition to the ESP32 platform, tape is held the battery pack for Z-axis servo. Plus all the wires, as it’s not yet clear how we’d want to run wiring for this system. The Parker ZETA4 drivers are still sitting loosely on the bottom shelf of the table, they need to be properly mounted eventually. Once these drivers and the ESP32 are mounted, we will need to consider how to best run wiring to minimize chances of wires getting in the way of our work piece.

In the meantime, everything is held out of the way with tape. Tape tape tape.

Aside from the computer, about the only thing not held by tape was the servo I intended to use to test Z-axis, which received a small 3D printed bracket. However, I ran out of time at home before I could devise something to attach to that servo output shaft.

For that I had to call for help, and Emily answered.

Wire Up Hardware Control Switches

After wiring up for Z-axis servo control, I turned my attention to the remaining empty quadrant of the prototype board.

At the moment I have a small laptop running a G-code sender acting as the CNC control console, from which I can access all functionality of Grbl. The ESP32 port of Grbl also offers a built-in web interface, which is a great choice for compact machines that don’t want the overhead of a full computer. Both of these control options have a communication delay, so some things are better handled by hardware switches for immediate feedback.

By default Grbl ESP32 supports four physical switches, in the order of their pin assignment they are:

  1. Feed Hold: On many CNC, this completes execution of the current G-code command but holds off running the next one. Some machines can pause mid-command but this is not guaranteed. Axis motion stops, but spindle does not. This is a good way to have a machine pause, useful for example when the operator wants to visually check to make sure position and upcoming commands look reasonable.
  2. Cycle Start: Begins executing the loaded G-code program. Also used to resume execution after Feed Hold.
  3. Reset: This commands an immediate stop, of everything. Unlike Feed Hold, it will not wait for the current command to complete. It will also turn off spindle in addition to axis motion. Since it is an immediate cutoff of execution, the controller ends up in an unpredictable state. There’s no resuming after a reset. The machine has to be re-homed and all coordinate offsets recalculated.
  4. Door: Designed to be wired up to a door open detection switch so the machine can take actions to ensure operator safety. On some machines this is effectively a Feed Hold, others treat it as an emergency Reset, most machines treat it as somewhere in between. I don’t know yet how Grbl reacts.

All four are designed for normally-open switches that activate upon closing the circuit to ground. For reasons I don’t understand, these switches don’t use the ESP32 internal pull-ups and require external pull-up resistors. Normally-open switches don’t necessarily make sense for a situation. For example, reset is usually wired up with a series of normally closed switches and, if any of them should open, the machine halts. But this is easy to address in the physical circuit.

Another concern for these switches is that they tend to have long runs of wire. (Such as  the aforementioned reset switch.) Long wires have a nasty tendency to act as an antenna picking up stray signals. So a real board would require opto-isolation to avoid triggering from line noise. But again, this is a prototype board missing the full set of protective features.

After I wired up jumpers for playing with these four switches, I made a small piece of label to remind me which pin is which. Then it’s time to bring the results of this prototype soldering session to the shop and run a few tests.

Z-Axis Servo and Battery Box

I plan to take advantage of a feature in Grbl ESP32, where a RC hobby servo can take the place of a stepper motor for any supported axis. It won’t be nearly as precise, or have the same range of motion, but it’s a good option for specific situations including tests.

The first part of this task was, obviously, to find it in the code repository and know how to compile with this option active. The second is to wire up my ESP32 dev board to emit the 1-2 ms RC control signal at its 3.3V output and convert that to a 5V signal courtesy of the USB port. Then it’s time to connect a servo.

But not directly, because USB doesn’t supply very much current and would not be a good source for servo motor power. Tasks with high stress or moving quickly will draw more than what USB can supply and cause voltage level to sag. Possibly causing the ESP32 to brown out and restart which would ruin everything.

What I needed for a servo test was a separate power supply. I started digging through my collection of salvaged AC to DC power transformer bricks looking for one in an appropriate voltage range before I decided I was overthinking things. This isn’t going to be the long term solution, it’s just for a short test. I don’t need a long term power source.

RC hobby servos are originally designed to run off 4.8-6V of a four-cell pack of batteries, tracing its lineage back to the age of NiCad radio receiver packs. This is roughly the same voltage as a commodity AA battery cell, so I pulled from my stock of 4xAA battery holders (*) for this test. They even have an integrated on/off switch for convenience.

The ground wire was connected to the servo ground wire as well as ESP32 ground. Servo power wire is supplied by this 4xAA tray, and servo control signal from the 3-pin servo header of the prototype controller board. And finally, the servo gets a 3D printed bracket to clip on to the gantry structure’s 40mm extrusion beams.

The Z-axis test arrangement is now complete. But before I wrap up this session of perf board soldering, I wired up provisions for hardware control switches.

(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

Wiring For Both Options Of Z-Axis Motion

Strictly speaking, it was not critical to add a shelf for the little laptop used to control everything, but it is very nice to resolve the constant irritation of pausing what I wanted to do just to find a place to set it down. It should speed up future tinkiering of this machine, and the next step in that process is to wire up Z-axis capability.

In hindsight I should have packed the X (lower left) and Y axis (lower right) components a little closer together, but learning these lessons this is why we build prototypes. There isn’t quite enough room to duplicate the same pin layout for Z in the upper right, but then again, I don’t really need to. I’m not interfacing with an existing Parker Motion Control product, the Z-axis will be different.

As a result, the JST-XH connectors have been simplified from a 4+3 arrangement to a single 6-pin arrangement. 4 of the pins are the same: a pair of open-drain signals for step and direction. The remaining two pins are for a normally-open switch to home the Z axis stepper control.

But there’s another twist to the Z-axis: a feature of Grbl ESP32 is the ability to use a RC hobby servo for any axis. It requires changing a few #define in the source code and recompiling, something I could do on the little laptop who now has a shelf. I thought a servo-actuated Z-axis would work well as a first test of system functionality, before I go through the effort of building a more functional stepper-controlled Z axis.

But I couldn’t use the same pin for both, because an open-drain circuit is the wrong way to send a control signal to a servo. Instead, a separate transistor was rigged up so the ESP32 control signal (3.3V) can emit a 5V servo signal. The signal pin and ground are exposed via a separate 3-pin header.

The 5V source for the control signal came from the USB port connected to the little laptop. Ideally there’ll be some opto-isolation for the control signal, but this will suffice for a prototype. However, it will not be enough to power the servo motor, which will require its own power source.

A Shelf For CNC Console Computer

The first thing I wanted to address after a wobbly (but successful!) first run was placement of the control console computer. I didn’t have a good place to set the tiny laptop down. The machine may not look like it would take up the entire table, but once machine’s range of motion is accounted for, there’s not a whole lot of space left. During the test run, the laptop was literally on the ground next to the table. It would be useful to have a dedicated computer shelf.

The shelf was designed in two parts. The right side could be bolted to the end of an extrusion beam, but the left side didn’t have that luxury. I thought I would design it to clip on to the extrusion beam, but the first draft hooks were far too aggressive. I had to trim them back with a saw before I could fit the piece around the beam.

HAKCNC computer shelf overly agressive claws

Both hooks installed and ready to host the computer. The right hand hook was printed with the final filament from one spool and start of another spool of PLA. Even though I ordered from the same vendor (Monoprice) they have apparently changed vendors or specification and the new spool filament is visibly different.

HAKCNC computer shelf in place

At first glance this design may appear to be heavily cantilevered, with most of the weight on the front of the hook placing great stress on the mounting points. This is only true when the laptop lid is closed. When the lid is open, where this shelf mounts on the beams is actually very close to the center of gravity of the laptop.

It still needs to be able to accept some weight, though, since there’ll be physical forces as I type on the keyboard and use the trackpad. But PLA is plenty strong for this application, with very little flex even when I rest my wrists on the computer.

This shelf is probably not permanent, but it is nice to have a convenient shelf to hold the laptop while I figure out how to work the rest of this machine.

A Wobbly First Draft Of Z Axis Gantry

We had a few final bits of goofing off without a Z-axis before starting to build a real one. Two beams available for construction were found to be exactly the same length as the width of our table, so they were natural candidates as the main horizontal gantry structure. Now we could use arbitrary lengths for the vertical support beams bolted to either side, because they could drape past the edge and below the table surface. Not only does it give us complete flexibility on what height to mount our main horizontal beam, we also gain the option to reinforce the beam with brackets bolted to the bottom of the table.

Once the drilling and bolting started, however we found a few unexpected problems.

A small problem was that while our horizontal beam is exactly the width of the table, we also had a black plastic moulding surrounding the edge of the table. Actually dropping the beam below the table surface meant cutting interfering pieces of plastic away. Which we could do, but we don’t need to do so just yet so that’s been deferred.

A more significant problem was that one of the two holes of a bracket overlapped with the existing metal structure of this printer table. If it lined up exactly with the horizontal parts of the metal, we could drill a hole through it just as we did the wooden parts. Unfortunately it partially overlapped with some vertical members of the support structure, which would severely weaken the table if we drilled into it. We chose not to drill, but it also meant there were only two bolts instead of four fastening our gantry to the table.

This meant we ended with a less rigid gantry than we had originally hoped. It is pretty good left-right (parallel to machine X axis) but front-back (machine Y axis) is weak. We’ll have to add more reinforcements before we get serious about cutting material, but in the meantime it is the best Z-axis yet for pen plotting.

So Emily created a program that draws a gift for our enthusiastic supportive online cheerleader. This was the machine’s first run with nontrivial G-code, and its success cleared the way to further refinement of this machine.