CNC Journey

I'm in the process of upgrading different parts of my hobby CNC setup, and before I alter the system, I wanted to write about the various components and summarize what worked and what didn't on my journey up until this point in time.

Machine

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) milling 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, several 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.

A lot to Learn

I was incredibly naive of what I was getting myself into; 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.

Many factors are required to create a successful part, such as: the rigidity of the machine, the spindle speed, holding the material, fixtures, 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.

Hands-on

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 a 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.

Experiments

While learning I lost track of my goal of milling aluminum, and for extended periods of time I went on unrelated tangents experimenting with various add-ons, such as a drag knife and laser cutter. It satisfied my curiosity at the time, but they were minor distractions.

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.

Enclosure

Milling wood produced a lot of dust, and milling aluminum left tiny little flakes around my office. I'd occasionally find a shiny metal chip in my living room that had hitched a ride on the bottom of my foot. I purchased a dust boot to suck up any debris. It worked well to collect lightweight 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 are not 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 ditch the dust boot and build an enclosure to keep the metal chips and any other materials safely contained. Nothing fancy, just a couple MDF panels glued and nailed together.

I added doors on the front and it worked really well for containing the mess inside the enclosure. After operations were finished, I would easily vacuum up the debris. I mounted a little web cam inside so I could see cutting operations while the doors were closed. 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.

Spindle

As I refocused on my goal, I spent more time milling aluminum and exploring the feed rates and speeds that could work well for my machine. I struggled to produce parts at the rate and quality I wanted. The results were far below what I was hoping for. In fairness it wasn't all on the machine, as a big factor was the operator (me) and my understanding/skill with the tools I was using — as you can see in the photo below, that bit could be shortened significantly to reduce chatter. At the time, I didn't understand that, and the results I was getting were not what I had dreamed of. It was so slow and the goal of rapidly making parts felt so far away.

It wasn't uncommon for me to leave the machine running for 24 hours. Patiently waiting for tiny parts to be finished. Sometimes a mistake would happen half way through, and starting over was soul crushing. I wanted to push the feed rate faster and I needed to increase the cut quality, but I couldn't figure out how to do it with the current setup.

I did managed to successfully make the first version of two mold halves for the original idea I had, along with some other really basic parts, but it was taking a really long time to do anything. I was curious if a bigger spindle/router would help alleviate some of my pains.

The tiny 300W spindle that came with the machine was good to learn the basics and experiment with feeds and speeds, but my growing frustrations with the quality and durations led me to explore alternate options. One of the included options for the machine was a larger spindle holder, so I could add a more powerful 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 online. At the time, had I known there was a difference between a router and a spindle, I would have gone a directly to a VFD spindle for rpm control, torque, reduced noise, and cooling.

More power

Very quickly it became clear that the extra cutting power was going to be a big win. The new router 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 would spin up to high speeds, I'd close the doors, and 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, and I wasn't paying attention to my cut paths. My clamps were directly in the cutting path. The machine demolished one clamp and significantly chewed into the part 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.

Relay hack is essential for a router

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.

Noise and Heat

The router is 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. For the first time ever, I had aluminum melting to the milling bit. Possibly because my router was spinning too fast, not taking aggressive enough cuts, the cut aluminum was not getting cleared out of the cutting path properly, not being cooled correctly — maybe all of the above.

Coolant

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.

Inspiration

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 with minimal input from me. I wanted to be hands off with the doors closed. I began brainstorming how I could seal the wooden enclosure for using liquids (link to blog post).

Will it work?

I wasn't sure if this idea would work with my machine, so I tried to keep expenses 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 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 coolant up through a series of clear flexible tubing to the CNC spray nozzle.

Filters

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. No duct tape, but I think MacGyver would be proud. 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.

It works, sorta

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 made little splash covers to protect the limit switches and provide a roof over the router and steppers motors. I added a second relay switch to toggle the coolant pump when the router was turned on and off. I added additional metal kitchen mesh to the top of the salad bowl to filter chips before they reached the inline filter.

I kept using this setup for the better part of year, despite a number of mishaps. The biggest pain was after 30 or 40 minutes of continuous operation, the inline filter was prone to getting clogged and caused coolant to overflow the sides of the metal bowl. Turns out, I incorrectly placed the inline filter and the low pressure flow wasn't ideal. Unfortunately once I realized my mistake I was already designing the new coolant system, so I left it and suffered for a period of time.

I once made the mistake of closing the enclosure doors for a couple weeks and when I came back and opened the enclosure, it was incredibly humid inside, and a lot of the CNC parts looked corroded — screws, the shaft of the router, and other random parts. No airflow inside, coupled with the residual coolant on the walls wasn't the ideal environment for certain metals.

The coolant setup has introduced a new anxiety to my CNC operations - a fear of overflow. I quickly added a secondary power switch for the coolant pump, so it could be manually shut off during jobs. The constant monitoring of coolant levels, and toggling the coolant pump off and on as needed to maintain levels, is annoying and stressful. I briefly enjoy hands off operations for the first thirty minutes of a job, but after that it is full time baby sitting. There is definitely room for improvement.

Next Steps

This hacked together hobby setup is less than perfect, but it works for now. I love that I can make metal parts on this inexpensive machine, but I also struggle with it's limitations.

• update chip filters — this will allow for longer operating periods, less anxiety, more fun and joy [DONE]
• circuit for detecting low and high coolant levels [IN PROGRESS]
• add a separate pump and circuit for manually cycling the reservoir liquid [DONE]
• move the hose line to the second pump, use a recoil hose and spray nozzle [DONE]
• air blast hose for cleaning parts coming out of the machine [IN PROGRESS]
• replace the T-tracks with a large fixture plate / add large fixture plate [DONE]
• airflow in the enclosure
• replace all of the chasis screws [IN PROGRESS]
• replace the semi-open plastic reservoir bin with a sealed container [DONE]
• update the controller board for coolant control, door alarms, and a 4th axis
• move all electronics into a new box
• add more structural support to the machine for rigidity
• consider using heavy duty linear rails with carriage blocks
• add more height to the Z-axis
• replace wood enclosure (water damage) with metal, open bottom with generous slopes for drainage and chip collection
• slide doors open or up — swing doors drip coolant on the floor or chips fall out
• larger workarea
• removable side panels for larger pieces, or maintenance
• have thick safety windows on the enclosure to see inside
• replace router with water cooled VFD spindle — more power and bigger chuck - quick change would be ideal
• tool height probe
• offset library for tool changes
• add an auger for chip evacuation