August 16, 2024
I'm in the process of upgrading different parts of my hobby CNC setup. Before I alter the system, I wanted write about the various components and summarize what worked and what didn't on my journey to this point in time.
In the Spring of 2021, I had an idea for a product that I wanted to make. After a couple shocking cost estimates and quotes from manufacturers to produce the idea, I decided to try and make it myself. One of the requirements to bring the idea to life was metal molds. I settled on aluminum because it met the heat specifications needed for baking the product and it seemed to be the easiest metal to work with on a budget. I decided that a small CNC (computer numerical control) machine would probably be the best option for making the aluminum molds.
The budget I had in mind for a CNC was roughly $1000 CAD (Canadian Dollars). I compared various CNC machines, and in the end settled on the SainSmart Genmitsu ProVerXL 4030. It's a desktop CNC that advertised it could mill/engrave aluminum. The final cost was a bit more than $1200 with shipping. The machine looked robust, had a decent work area, available upgrade options, there was a lovely community of people online, SainSmart had a good reputation, the company website was informative, and it could mill aluminum. It checked all of the boxes for me.
I was incredibly naive of what I was getting myself into though; the amount of time, effort and learning involved to operate a CNC machine was a lot more than I anticipated. I knew the learning curve would be steeper than 3D printing, but I vastly underestimated how much I would need to learn in order to mill parts. There were many contributing factors to create a successful part, such as: the rigidity of the machine, the spindle speed, holding the material, the size of the bit, the quality of the bits, the type of stock, accuracy, datums, what certain sounds mean, zeroing, work coordinates, operating temperatures, feeds, 3D CAD modeling, and a multitude of things related to the CAM software that create the actual program for the CNC to follow.
I consumed as much information as I could — I read forums, I read books, I did tutorials, and I even watched videos of professionals and amateurs milling parts in various materials. The biggest leaps and bounds came from hands-on trial and error experience coupled with the knowledge I was soaking up from various sources. Those a-ha moments when I experienced the situation or scenario I read about, or an concept clicked in my head, those were pivotal learning moments.
I often found myself watching videos of how to do something on a machine that was 100x more expensive than mine, and it seemed easy with all the fancy features that machine had. When I tried to apply it to my own setup, things didn't map over. Not all of the take-aways were applicable, but they all contributed to my understanding in small ways. Many topics depend on the machine and it's capabilities, as well as the materials and skill you have with all of the above.
While experimenting and learning, I lost track of my goal for extended periods of time. Learning was chaotic and messy. I found myself throwing various materials into the machine to see what I could make, and also experimenting with how the feeds and speeds needed to be changed for different materials. I played around with milling wood and engraved a cutting board for two friends getting married. I enjoyed milling wood, but hated the dust and mess, it was awful.
I often went on tangents that weren't applicable to my goal, but it satisfied my curiosity at the time. Whenever I put aluminum into the machine, it sounded scary compared to wood, it was not a nice sound. The floor of my home office was often covered in little metal chips. I'd occasionally find a shiny metal chip in my living room that had hitched a ride on the bottom of my foot into my safe space.
I purchased a dust boot that hooked up to the CNC spindle and a shop vacuum. That worked well to suck up any cut materials. The shop vac was actually louder than the CNC machine. Running the vacuum for extended periods of time wasn't ideal and I soon learned that shop vacs weren't designed for that use-case; I blew the motor on the shop vac and the smell of burnt materials filled my office. I decided to build an enclosure to keep the metal chips and any other materials safely contained.
The CNC lived on top of a crafting table I had in my office. It was a high table with wheels for easy movement. I decided to build a wooden box around the CNC. Nothing fancy, just a couple MDF panels glued and nailed together.
I added doors on the front, and mounted a little web cam inside so I could see cutting operations while the doors were closed. It worked really well. I loved containing the mess inside the enclosure. Switching back and forth between the GCode being executed to the web cam footage was a blast. I got such a kick out of watching the machine making an absolute mess while bringing my ideas to life.
As I refocused on my goal, I spent more time milling aluminum and honing in on the ideal feed rates and speeds for my machine. The best results were very shallow cuts and incredibly slow feed rates.
I was not able to push the feed rate faster without significantly decreasing the cut quality. The results were far below what I was hoping for with this machine. It wasn't uncommon for me to leave the machine running for 24 hours. It was agonizing to wait for tiny parts to be finished. Sometimes a mistake would happen half way through, and starting over was soul crushing.
The CNC came with a tiny 300W spindle with a 3.2mm (1/8") chuck. It was good to learn the basics and experiment with feeds and speeds, but I was also getting frustrated with the quality and duration to make parts. It was not what I had dreamed of.
One of the included options for the machine was a larger spindle holder, so you could add a bigger spindle to the CNC. I decided to upgrade the stock spindle to a 840W DeWalt DWP611 router with a 6.4mm (1/4") chuck. It was in my price point, and it was something I had seen others use in their setups. Had I known, at the time, that there was a difference between a router and a spindle I would have gone a directly to a powerful VFD spindle.
Anyways, the extra cutting power allowed me to vastly increase the feeds, speeds, and the quality of each part. Jobs that previously took 24 hours milling aluminum, now took 24 minutes. I was thrilled to see larger chips getting cut instead of little specs of aluminum.
One major downside of the router, I soon encountered, was I had to manually turn it on before I started a job; I'd reach into the enclosure, flick the power switch on the router, the router spun up, closed the doors, then press start on the computer to run the job. This also meant that if something went wrong during a job, the router would continue to spin even though the controller had stopped the machine. Not ideal.
Not even a day later after installing the new router, I setup the machine to mill a new job. I wasn't paying close enough attention to my cut paths and the placement of my clamps. The machine demolished one clamp and was half way through a second clamp before I realized something was wrong. Hitting the emergency stop button on the controller prevented the machine from advancing through the remaining clamp, but the router was still on and spinning, sitting flush against the clamp it had chewed half-way through. I shut off the router, and immediately started searching for solutions.
I saw that others had hooked up a relay switch from the CNC controller to toggle the router power and that was a reasonably quick fix (see blog post). That allowed the controller to start and stop the router just as it had done before with the stock spindle. Doing a similar modification to the speed control on the router wasn't something I wanted to do, nor spend time looking into.
The router was tremendously loud compared to the stock spindle. I felt self conscious running the machine now and worried my neighbours might hear it. Keep in mind this machine is in my home office in a townhouse. I added 5cm (2") thick styrofoam to the inside of the enclosure to help reduce the noise. It muffled the sounds, but it also insulated the enclosure and prevented heat from radiating out. It wasn't a major issue because I wasn't running jobs for extended periods, thanks to the increased cutting power. It did get warm in the enclosure, but not something I felt I needed to address at that time.
Another problem related to the extra cutting power surfaced though. For the first time, I had aluminum melting to the milling bit. Either because my router was spinning too fast and not taking aggressive enough cuts, and/or the cut aluminum was not getting cleared out of the cutting path properly.
I used compressed air to clear the cutting path, and that helped, but it didn't do much for cooling the bit. My router was spinning really fast (16,000RPM +) on it's lowest setting. The other downside with the air was the compressor was louder than the CNC machine, and it often would blow the circuit breaker causing the CNC to shut off.
What worked really well was occasionally spraying cutting fluid on the part being milled. It almost completely eliminated the aluminum build up on the milling bit. I'd crack open the enclosure doors while the CNC was running and spray cutting fluid on the part. It was terrifying to stand there with the doors open, putting my hands near this cutting contraption. Just imagine sharp aluminum chips flying towards you, fluid spattering all over, wincing and cowering behind your safety goggles for fear that a bit spinning at 20,000 RPMs might break off and find it's way into your body. It was the last thing I wanted to be doing, but it was working.
The sporadic nature of when I would spray the cutting fluid on the part, wasn't consistent enough to produce reliable results. It was too hands on, prone to error, and once again I had metal chips creating a mess on the floor. Every time I opened the enclosure doors I wondered if there was a better and safer way. I had seen videos of professional machines using large quantities of liquid coolant flooding the part, and that's what I wanted to try. That looked like something that could run continuously without me needing to babysit it. I wanted to be hands off with the doors closed. I began brainstorming how could seal the wooden enclosure for using liquids (link to blog post).
I wasn't sure if this idea would work with my machine, so I tried to keep expensese to a minimum. I lined the interior of the enclosure with 3.2mm (1/8") plastic sheets - thinner would have also worked. Overlapping them where I could so liquids wouldn't get out. I used a heat gun to shape the plastic underneath the cnc machine, forming a primitive a basin that would drain towards the center. I regretted using the plastic as soon as started trying to shape it. It bent, warped and expanded in ways I couldn't anticipate. If I hadn't spent so much money on the sheets of plastic I would have tried using sheet metal instead. I added a PVC drain to the center of the table, and from there the liquids would pass through a filter underneath, and into a reservoir. A fish pump in the reservoir then pushed water up through a series of clear flexible tubing to the CNC spray nozzle.
The chip filter underneath the CNC was made of random kitchen supplies cobbled together; a strainer and a metal salad bowl with a hole drilled in the bottom. I added an inline water filter from the hardware store, to capture smaller partciulate before it got back to the reservoir. I connected it all together with PVC pipe, plumbers putty, thread tape, and PVC glue. It's the ugliest damn thing I've ever made, and I'm embarrased to share it, but it was perfect to experiment with. I tested all the connections with small buckets of water, fixed any leaks, and then quickly jumped into full operation with bio-lubricant.
My budget coolant setup worked well enough that I could see and hear differences in the cutting performance. I no longer had aluminum getting gummy on the milling bits, I wasn't opening the doors to fiddle with the machine, and the machine didn't seem affected by all of the liquids spraying everywhere. I added additional finer filters to the top of the metal bowl to catch smaller chips before they reached the inline filter.
The setup worked well enough that I kept using it, despite a number of mishaps; after 30 or 40 minutes of continuous operation, the inline filter was prone to getting clogged and caused coolant to overflow the metal bowl. Operating the CNC with the coolant on introduces a horrible sense of anxiety as I constantly monitor coolant levels.
I once made the mistake of closing the enclosure doors for a couple weeks and when I came back and opened them, it was incredibly humid inside. All of the CNC chasis screws looked corroded, and so did the shaft of the router. No airflow inside and coupled with the residual coolant on the walls isn't the ideal environment for certain metals.
This hacked together hobby setup is less than perfect, but it sorta works. I love that I can make metal parts on this inexpensive machine, but I also struggle with it's limitations.