Watch this video to learn about the assembly process of closed-loop CNC electronics, including component arrangement, wiring considerations, and challenges faced. Discover valuable insights and tips for ensuring proper functionality and effective shielding.
Assembly of Closed-Loop CNC Electronics: Component Arrangement, Wiring Considerations, and Challenges Faced for Optimal Functionality and Effective Shielding
In this video, I will be demonstrating the assembly process for closed-loop CNC electronics. Initially, the customer had purchased the components and intended to wire them themselves. However, they later decided to have me assemble and mount the components inside an enclosure.
Unfortunately, the spindle suffered significant damage. The collet nut became jammed at an angle on the threads, and despite delicate attempts to remove it, I was unsuccessful. To avoid causing further damage, I recommended that the customer explore alternative options, including insurance, to address the issue.
The worn-out box containing the spindle clearly displayed the extent of the damage. This particular spindle is a heavy-duty 7.5kw model.
Although the M18 strain relief cable nut assembly was also damaged, I replaced it since I would be using those nuts on the enclosure anyway.
The other component boxes showed some minor damage, but overall, the components were in good condition with only a few minor dings and no functional issues.
It's evident that the customer had started the wiring process, but after realizing the complexity involved, they decided to seek professional assistance. While I encourage customers to assemble their own electronics and mechanical systems to gain a deeper understanding of the machine, I understand that it may not be feasible for everyone, especially in time-sensitive or high-production scenarios. In such cases, it often makes more sense for a technician to handle the assembly and diagnose any issues. I would love to hear your thoughts on this in the comments section.
When transporting components with fasteners, it's important to keep in mind Murphy's Law: if a fastener can come loose, it will. The vibrations caused by the road and suspension can cause screws and nuts to loosen. Think of those vibration machines used to sort components.
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One of the most time-consuming aspects of this type of job is finding the most suitable arrangement for the components inside the enclosure. There are numerous electrical and spatial considerations to take into account. The primary concern is separating delicate signals from current-heavy and coil-wired components like motors, which emit interference. This interference can disrupt signals intended to be at specific voltage levels, such as 0 volts or higher levels like 5 volts or 24 volts. To address this issue, I arranged the components in a way that spatially separates these signals from the higher current and voltage wires, or allows them to intersect instead of running parallel. Additionally, I made sure to use shielding for all cables associated with signals and motors.
Other factors to consider when arranging the components include the location of panels around the enclosure, accessibility to various components for configuration and wiring, and the positioning of components along the edges, such as fans or vent holes.
The controller needs to have access to the removable panel section of the enclosure so that USB or Ethernet cables can be plugged in. I often need to insert the base of the electronics into the enclosure periodically to ensure proper placement. However, the limited space in the base poses a challenge, even for my thin fingers. If I were to work on many similar projects, I would need to devise a more efficient method or plan better. Prior to assembling electronics inside these enclosures, I used to create my own enclosures from wood and plan everything in CAD.
Before fastening the components to the base, I carefully consider any additional elements that need to be added. This requires thoughtful planning, as there are always components that can be easily forgotten, requiring drill holes. However, drilling leaves behind metal debris, which can be detrimental to electrical components. This challenge emerged during this build and is precisely why I create these videos in the first place.
Manufacturers and assemblers involved in repetitive jobs or assembly lines often use process routing sheets. These sheets outline the most efficient order of steps, describing each operation, its duration, and the necessary equipment. In my videos, I attempt to perform all the operations in the order I deem most efficient and straightforward. However, I often end up rearranging the clips after realizing my initial plan was flawed. This video showcases the clips in the correct order of operations, with the exception of the bus bars added after assembling the power supplies. If you pay close attention, you may notice some minor discrepancies in other clips. Nevertheless, everything comes together nicely in the end.
My intention with the orientation and placement of the drivers and power supplies is to ensure the wiring remains separate and organized. Closed-loop drivers require numerous connections, including six for the motor encoder, four for the motor, two for the power supply, and four for the controller. The encoder and motor connections need to be routed to the removable enclosure panel. Given that these cables run parallel to reach their respective locations on the machine, it is crucial for both the encoder and motor cables to be shielded. Later in the video, you will see how I terminate the shield.
Dealing with screws and nuts to mount many of these components can be frustrating, time-consuming, and susceptible to loosening due to vibration. I may consider using standoffs with clips instead, although the varying hole sizes may not permit it.
To raise the controller to a level where the USB and Ethernet connections can be accessed from the removable panel, I created spacers. I designed these spacers to provide maximum structural support. Since the controller has solder points near these holes, I had to adjust the diameter of the area around each hole to optimize contact area. Using HDPE material, I made these spacers on the lathe. I happen to have plenty of this material in my workshop.
The terminal blocks I mentioned earlier were added after the components had already been assembled. It was challenging to drill into the area, and I had to ensure the other components were protected from metal chips to prevent damage. Planning is crucial in such situations.
In a previous video, I used zip ties, and some concerns were raised in the comments, particularly regarding the cut ends. Rest assured, I listened to your feedback. It's worth noting that I also use UL listed zip ties. After all, with my years of experience in this field, I cannot fathom why plastic zip ties would require UL listing. I don't believe non-UL listed ones are conductive or possess sharper edges that could damage wires. Perhaps the UL listing relates more to their longevity and material composition.
To please the inquisitive folks out there, UL listed zip ties are used for safety and strength in their intended applications. The UL listing ensures that the material does not emit harmful toxins when burned or heated.
In a previous video, I soldered a perfboard with headers to provide a convenient way to connect ribbon cables. Ideally, I should make PCBs for this purpose, but soldering on perfboards is not too challenging. This particular connection is between the controller and the drivers for the pulse and direction signals.
My trusty Knipex wrench comes in handy for making ribbon cables. I often mention these wrenches in my recent videos because I genuinely love using them. I even provide a link in the description for those interested, which may earn me a commission. It's fantastic to see innovation in this segment of the tool industry.
Some closed-loop drivers label their power terminals as AC on each terminal, indicating compatibility with both DC and AC inputs. However, it's essential to be aware of the required voltage level for the AC input if you choose to utilize it. These drivers usually do not display polarity on the terminals marked AC. In the video, I show that the positive terminal is typically located near the motor coil connections, but it's always prudent to confirm this with your specific driver model.
Now it's time to create cables for the encoders. Each cable requires connectors on both ends, resulting in a total of 48 wire ends to be soldered. This process involves splaying out the wires, twisting them together, soldering the connections while ensuring they remain intact, heating heat shrink tubing over the soldered ends (without forgetting to add it before soldering), and finally covering the entire set of connections with larger heat shrink tubing.
I had to insert the base of the electronics into the enclosure multiple times to mark the opening for the controller.
Vevor, or "Vee-vor" (I'm not certain about the pronunciation), is a company that has been providing a wide range of industrial equipment. They reached out to me to review one of their products, and I chose a magnetic drill that utilizes a magnet to stay in place while drilling. I received this drill for free, but I will provide an unbiased review. In hindsight, I realize that opting for a punch and die set might have been a better choice, but the magnetic drill still performed adequately for creating the holes I needed. However, there are a few caveats to be aware of.
You may have noticed that the first hole I drilled using a hole saw was not ideal. I knew I needed at least 15mm of metal beneath the electromagnet of the drill to ensure proper holding, and I should have used the correct tool instead of a hole saw. Unfortunately, I didn't have a 3/4" rotobroach on hand at the time, so it became an interesting experiment.
To secure the tools, the mag drill employs a Weldon-type shank with two flats on the shaft, into which the tool shank is inserted. Two set screws keep the tool in place, and there is no play in the fit.
While the drill's ways, which constrain vertical movement, were not tight enough initially, I needed to adjust the gib. The instructions stated that the gib was pre-tightened at the factory. The adjustment involves three long set screws with jam nuts to prevent loosening over time and movement of the ways.
For the first hole, I initially planned to create a pilot hole, but the subsequent tool I used did not have a guiding point. I understand that many of you might have concerns about this, and I agree that a hole saw is not the appropriate tool for this application. An annular cutter would have been a better choice. Unfortunately, the annular cutters I had started at 7/8", while I needed a 3/4" hole. This put me in a difficult situation. Additionally, I was supposed to have at least 15mm of metal beneath the magnet coil, which was not the case. As a result, this attempt did not go smoothly.
The tool I used for the first hole was a standard hole saw, not an annular cutter. Clearly, not the best idea.
To position the drill correctly, I used a smaller bit to reach the correct position.
Interestingly, the thread of the hole saw matched perfectly with the Weldon shank adapter for the chuck.
Now it's time to find some thicker metal in my shop since I had forgotten about having a metal table (getting old has its downsides!).
Oh, there's the metal table I forgot I had!
Despite the mishap with the first hole, I persisted and continued using the hole saw, thinking that the additional metal thickness would provide better holding.
With confidence in the mag drill for the remaining holes, I proceeded to arrange the connectors on the panel. The middle bolt is where the shielding will be connected.
Spoiler alert: the remaining holes I needed to make turned out fine. It would have been helpful if the drill had come with a steel plate for drilling on thin metal.
I made a mistake in a couple of drill locations. Although the measurements and lines drawn on the panel were correct, I accidentally added a crosshair to the wrong line. I had to make adjustments later, resulting in more space between the motor connectors. If the space had been too small, I would have caught the error before drilling.
Now I need to find the right-sized tool for these connectors. A 7/8-inch tool is slightly too small, while a 1-inch tool would place the two mounting holes too close. I decided to use the 7/8-inch rotobroach cutter, which is similar to an annular cutter but with a different shank. Fortunately, the rotobroach has the same thread as the hole saw, which is a feature I appreciate since I can use my existing tooling.
The drill on the mag drill ways is adjustable, allowing for raising or lowering the drill to accommodate longer tools. I initially considered using the rotobroach with its own shank inserted into the chuck, but I wanted to minimize any potential runout. By adding the chuck and then attaching the rotobroach with its long shank, I could reduce any minor runout.
The cut came out well, but there was a slight lip, which is normal. Interestingly, I noticed less of a lip when using the hole saw. These lips are easily removed with a deburring tool.
The connector had just enough material to be tightened into the chuck. However, one of the connectors got pushed out during the process. Additionally, the small section of the connector clamped by the chuck is slightly flexible, making it challenging to achieve a secure grip. Nonetheless, I managed to fit all the connectors.
You can observe the movement of the mag drill, indicating that the full magnetic strength wasn't achieved due to the limited thickness of the metal beneath the magnet. Despite this, the magnetic force was still sufficient to create the holes, although I remained cautious throughout the process.
I'm using a lift table, which I had forgotten about, and its metal body is thicker than what I was previously using. Although it doesn't meet the recommended 15mm thickness, it provides more stability. Some of you may notice that I'm not using a punch or pilot hole for pin guidance. I only used the pin to position the drilling at the crosshair on the panel.
In this clip, it's easy to see if there is any visual runout. Fortunately, I don't see any. While I might measure the runout at a later date if I need to work within specific tolerances, it's unnecessary for this project. However, I did notice one thing—the drill's magnetic base oscillated during some holes. This caused the holes to be slightly out of round, more like rounded triangles. This may have been due to the oscillation, but remember, I didn't have the recommended 15mm of metal beneath the drill, and it seems this drill works best with annular cutters.
I needed to use progressively larger drills for the smaller connector holes. It would be more convenient to have a stepped drill for this purpose, which would make my life much easier.
Here is the final panel with all the holes. The lips are more apparent at this angle, and I used a dull twist drill to improve the edges on the holes that needed it.
This angle clearly shows the marks left by the base of the drill. Although I wiped the bottom of the drill for each hole, the circular marks correspond to the coil of the electromagnet. The magnet generates significant heat, and I learned that leaving the drill on the surface with the magnet engaged can cause these marks. If I only activate the magnet during drilling, no marks are left on the surface.
I'm using a 5/16 bolt to create a shield screw terminal. While a #8 screw alone can serve as a screw terminal, I believe converting a bolt into a screw terminal provides a more professional appearance.
I've employed this method in a previous customer electronics build. The screw only needs to establish good contact with the enclosure's body, which is connected to earth ground. The bolt's head is flattened to ensure proper contact with a spade terminal that terminates the cable shield. I then drill and tap for a #8 screw, which will secure the spade terminal in place.
This board serves as an interface for the controller's inputs. It allows you to connect limit switches, proximity switches, or any other on/off type of input, regardless of the input device's voltage. I'm using this board because the customer utilizes proximity switches that require 24 volts to operate. If I were only using the controller, the switches could only be connected to 5 volts. This additional board provides a great solution.
Finding a cost-effective, large enclosure with a fan mount and ventilation openings has been challenging. As a result, I had to create them myself. I decided to make multiple holes for fan air circulation, allowing the customer to add a filter if desired. These holes are symmetrically and radially placed, while still maintaining a reasonable structure so that a filter can be sandwiched between the fan and the enclosure's side.
Initially, I used a hole diameter that matched the distance from the inner circle to the outer circle. Then, I selected a hole diameter that fits between the four larger holes while leaving enough space for structural integrity. I opted to create pilot holes this time to provide guidance for the rotobroach and add stability, preventing any anxious moments. This was a good decision since I only had the thin side of the enclosure as the metal for the electromagnet.
The drill did come with two annular cutters, but unfortunately, they were both the same size, and neither was suitable for this application. Nonetheless, I believe this drill offers good value for its features, even without the included annular cutters. Additionally, the annular cutters that were provided have pins, similar to the hole saw.
On the bottom of the enclosure, I drilled ventilation entry holes. My intention was for the air to flow from these ventilation holes and exit through the location of the fan if a filter is not used. Since these vent holes are positioned underneath the base of the electronics, if a filter is used with the fan, I suggest rotating the fan to allow air to enter from that location. This setup creates positive pressure inside the enclosure, keeping dust and debris out.
I located the holes where the spindle cable and VFD power cord will enter the enclosure. I used an M18 cable strain relief bulkhead nut for this purpose.
The cables now need to be connected to the drivers and the controller input board.
There were a total of 61 solder points connecting the cables to the connectors. Most of the solder points were small cups, making this quite a time-consuming task. I'm not sure which is more tedious—the cables or the connectors with their small cups. Altogether, there are 48 solder points for the encoders, 321 for the motor cables, and 61 for the connectors, totaling 141 solder points in the entire build.
I added three M18 cable strain relief nuts to the removable panel. One nut is for the main power cord, another for the E-Stop cable and button, and an extra one for any additional needs the customer may have.
Typically, unless the customer specifically requests the E-Stop button to be mounted on the box, I provide it as a cable and button so that the customer can position the button where it is most accessible. The enclosure is often not situated in a convenient location, and the E-Stop button should be within quick reach in case of dangerous situations or machine malfunctions that could cause harm to the operator or the workpiece.
Here, I'm connecting the two main systems—the VFD (Variable Frequency Drive) and the power supply's protective earth ground—to the enclosure to ensure proper functioning.
To verify the functionality of the power supplies, I perform a test of their DC output. This test is conducted with the drivers disconnected to ensure their safety, just in case any power supply outputs an unexpected voltage.
This test ensures continuity between the shield terminals and the enclosure's ground. It is essential to establish proper grounding for effective shielding.
In this machine, the Y-axis and A-axis are slaved together. The two motors on the right side should move at the same rate. To achieve this, several factors must align: both drivers (A and Y) must be set to the same amps and microsteps, and the steps per unit, velocity, and acceleration need to be set the same in the motor turning section of the control software.
Next, I test the proximity switches and their connection to the controller and input board. One helpful feature of the input board is that it includes LEDs to indicate the status of each input. The LEDs illuminate to indicate whether the proximity or limit switch is engaged or disengaged.
Finally, it's time for the final wiring and testing of this electronics assembly—the VFD power and the VFD to spindle cable. However, I approach this test with caution. Remember that the spindle collet nut was jammed at an angle, and I didn't want to keep the spindle running for more than a fraction of a second due to potential imbalances or the risk of the nut flying off and causing damage.