Introduction: Automated Bottle Cutter
The Bottle Upcycler is a machine that transforms empty glass bottles into drinking glasses. We were inspired by the elegance of artisanal glassware and the opportunity to make "trash" destined for the recycling bin into something beautiful.
This is a video of The Bottle Upcycler in action. The bottle breaks at 1:53, at which point the lighter is turned off and the platform on the right-hand side starts pulling the bottle apart.
The machine works like a low-speed lathe, turning the bottle as different operations are carried out on the glass. To crack the bottle, it is first scored, then heated, flash-cooled, sanded and finally broken.
The user presses a button corresponding to each step in the cutting process. The button press signals our microcontroller to move the pieces necessary for the operation into the right places.
The following steps detail our testing, mechanical system, software, and electrical system. The mechanical system consists of the track, clamps, scoring/sanding wheel, and the flame activator.
Step 1: Preliminary Testing
At the beginning, we did a lot of research into what methods would work best to cut a bottle. After collecting glass bottles of various ranges and sizes, we tested different methods of conducting the following processes on them: scoring, cooling, heating, and sanding.
For scoring, the options that we identified were a carbon steel wheel, a diamond scribe, and a file. We found that a clean score line was necessary for a break with no unwanted fracture lines. The carbon steel wheel gave us this, while the diamond scribe was not sharp enough and the file did not provide a clean enough line.
For cooling, we identified compressed air, water, and ice as our options. Water worked well, so we figured there was no reason that we needed to use ice, which would be difficult to store and dispense. Compressed air also worked well, and we were planning on using it until we realized that having a heat source near a compressed can would be dangerous.
Our heat source options were a blow torch, lighter, colder torch, cigar lighter, wire cutter, and candle. The blow torch turned out to be out of our price range, so we didn’t even end up testing it. The lighter worked well, but it would be difficult to activate mechanically compared to the push button cigar lighter, which worked equally well. The wire cutter and candle both did not provide enough heat to the bottle.
Our options for sanding were using a file, Dremel or sandpaper. After testing, we found that a file provided edges that were too rough, a dremel was too hard to control in addition to being out of our price range, and sandpaper worked great, although we were worried about going through a lot of it.
Step 2: Track
The track design from this model was based off that of a lathe. Threaded rods, some actuated by hand and some actuated by motors, were used to move platforms back and forth. The system was modeled in SolidWorks and once the design was finalized, the platforms were laser cut out of Delrin and the threaded rods were attached with locknuts.
The purple platform is stationary and holds the main set of threaded rods, and the motor and hand cranks that control them.
The blue platform is stationary and holds the main set of threaded rods as well as the motor that turns the bottle.
The red platform holds the lip of the bottle and is moved back and forth by the motor on the purple platform. The motorized threaded rod goes through a tapped hole, while the other threaded rod goes through a clearance hole.
The green platform holds the sanding, scoring, heating, and cooling mechanisms and moves back and forth by the hand crank on the purple platform.
The orange platform holds the heating mechanisms and is moved back and forth by the left hand cranked threaded rod.
The yellow platform holds the sanding and scoring mechanisms and is moved back and forth by the right hand cranked threaded rod.
Step 3: Clamps
This system uses two different clamps, one around the lower body of the bottle and the other inside the lip.
The clamp around the lower body of the bottle was designed and machined out of laser cut Delrin, a threaded rod, rubber strips, an aluminum rod, and shoulder bolts. The wide oval-shaped arms allow for a range of bottle sizes to fit in the machine. The original design intent was that all the joints were pin joints, so to tighten the clamp, only the wing nut on the threaded rod would have to be adjusted. In tightening this, the arms holding the rubber-lined circular clamps would compress the bottle. As these arms moved down, the linkages would move along the spinner arm. However, it turned out that there was too much slop in the system for this to work properly and provide a stable spinning mechanism. To correct for this, the clearance hole that the threaded rod went through in the spinner arm was tapped, so that to adjust the clamp, the threaded rod had to be spun as well as the wing nut.
The clamp inside the lip is a bottle stopper that was purchased from an online vendor. Clamping is accomplished when the upper arm of this piece is turned and a screw compresses a rubber stopper. This clamp rotates freely in a bearing.
Step 4: Scoring
The score line is an important part of the system, as a neat line translates to a clean break. The score line stress weakens a small area, making it susceptible to crack propagation. Having a clean and straight score line is crucial to a clean break in the glass. The glass scoring wheel spins freely in its mount as it comes in contact with the rotating bottle and creates a score line.
The sanding operation is the final step in the process. It serves to deburr the cut edge to prevent cuts and weaken sharp edges. The sander rotates down and straddles the lip of the cut bottle edge. As the bottle rotates, the edges get chamfered. The sander is a small v-shaped aluminum part with sandpaper adhered on the inside edges where the bottle contacts. Unfortunately, the sanding mechanism was not ultimately part of the operations completed by the Upcycler due to alignment issues.
Both the scoring and sanding mechanisms are mounted on a single platform perpendicular to the main track. A DC motor with a potentiometer rotates the scoring arm into place once the bottle is cut. The scoring wheel is permanently mounted and thus constantly scores the bottle as long as it is rotating. The single platform for the two operations simplifies the motor control and maximizes space. The original design had both the scoring and sanding arms rotate into place, but difficulties with scoring wheel alignment and force applied led us to switch designs. The perpendicular platform on which the scoring and sanding mechanisms are mounted is moved in manually by turning threaded rods until the scoring wheel is contacting the bottle.
Step 5: Heating
The heating mechanism works by having an arm on a motorized lead screw press down on the button of a butane cigar lighter. There is a second rod parallel to the lead screw to prevent the arm from rotating. The lower platforms clamp the lighter and hold it in place. The top platform and side supports have places where captive nuts can be embedded to lock them in place and keep the entire system together. The bottom platform interfaces with the lead screws on the system track. This system was custom made for a specific lighter out of laser cut Delrin.
Step 6: Cooling
After the bottle is heated evenly along the score line, we intended it to be flash cooled with water flowing from a tube onto the heated line. Water was chosen as a cooling mechanism because it was both plentiful and easy to obtain and store. Our other options, including compressed air, ice and liquid nitrogen were either more expensive, required extensive support systems or both. Our water system involved storage in a 5-gallon bucket and flow actuation using a solenoid valve. The solenoid valve had a separate mount apart from the main system and runs to the main system via 1/2 inch tubing. Tubing is mounted to the lighter platform on the main system allowing the water flow to be directed on the scoreline over the top of the bottle.
After testing, we decided not to use the water cooling system because the scoring and heating was enough to consistently break the bottles. Also, because the solenoid valve had a high current demand it was hard to run off our Arduino.
Step 7: Electrical
Our mechanical design involved using three motors. Restrictions on the Arduino Uno’s digital pin output power made it a necessity to use motor drivers. We had two different types of motor drivers.
Single Direction Motor Driver
The motor used to spin the clamp only needed to spin one direction. The figure for the single direction motor driver is shown below. The single direction motor driver consists of a transistor, a diode and the motor. The transistor is turned on with a PWM pin from the Arduino, which allows us to set the speed of the motor. Since the motor acts as an inductor, the diode is needed so that when the current through the motor is shut off, the voltage across the motor does not spike.
Bidirectional Motor Driver
The other three motors in our system need to run in both directions. The bidirectional motor control circuit is shown below. It is similar in concept to the single direction motor driver. It uses a L293D chip which is used to create an H-bridge and drive the motor.
We control the entire system using a combination of switches and buttons. They are powered off of the Arduino 5 V and gnd pins. The potentiometers in the system are used as switches representing either a one or a zero. There are four motors and two potentiometers. Each motor is mapped to a number between 0 and 3, so the switches can be set to pick which motor to control. One button is used to change the current motor to the one designated by the switches and the other button is used to control the direction of that motor and whether it’s off or on.
Step 8: Software
The buttons are attached to the two interrupt pins of an Arduino Uno, so whenever they are pressed, they interrupt the loop and change the motor state. Interrupts can only be attached to 0(digital pin 2) and 1(digital pin 3).
An interrupt is attached using the line:
attachInterrupt(inputpin, responseFunction, Trigger);
The buttons are used to rapidly change which motor is being controlled by the buttons and the direction of the motor being controlled.
The motors are controlled by setting the PWM pins to the appropriate speed using analogWrite. For the bidirectional motors, the direction is set by setting one of the digital pins high and one low, then switching it for the other direction.
If you're curious about what the Arduino code looks like, we'd be happy to send it to you!
Step 9: Final Thoughts
If we were to continue work on this Bottle Upcycler, there are a few improvements we'd like to make. First, there are some mechanical improvements which would help the machine run smoother. we would like to use acme lead screws rather than threaded rods because all of the platforms could be moved in and out faster. We would have taken more care in machining and construction because some parts are slightly misaligned which worsens their performance. Currently the bottle is supported by clamps on either end and once the bottle is cut, it sags down in the middle which makes it difficult to sand. It would be much better to have a third support in the middle so that the bottle remains in the same place throughout the whole process.
Next, there are some improvements which could be made for the safety of the machine and those operating it. Currently, the lighter mechanism will remain on if power is disconnected from the machine. The only way to shut off the lighter is by backing up the lead screw. This creates a dangerous environment in case of emergencies. Currently the Bottle Upcycler is supported by two thin plates on either side of the machine and it rocks back and forth as the bottle spins. An attached base plate would allow the machine to sit in one place.
I worked with this project with my three good friends, Gaby, and Mary2. Communication was a key component in this project, and it really helped that we were all honest with each other and took each other's concerns to heart. If you have an idea just go for it and implement it. Along those lines, don’t be afraid of failure, make mistakes early and often. Rather than spending a ton of time wondering if something will work and trying to perfect it, just create it and see if it works. You have nothing to lose!