Week 7, Computer-Controlled Machining

Objectives

Group assignment:: Complete your lab’s safety training; Test runout, alignment, fixturing, speeds, feeds, materials and toolpaths for your machine; Document your work to the group work page and reflect on your individual page what you learned
Individual project: Make (design+mill+assemble) something big

Group Assignment

Link to Group Assignment

Make Something Big

Ideas

I started by ideating on some potential things to build

Monstera pillar covers

End table

Plant table

Shadow blocker

Potting Table

Record player table

Eventually I settled on building a cabinet for my record player as right now it is sitting on a chair in my dining room which feels weird.

Concept

Since the record player is a big rectancular cube but also sitting in the corner of the room, I wanted to make it fit the corner of the room better, so I decided to make the plan view of the table octagonal so that it would be more visually interesting but also match the lines of the walls better.

I then plugged this into ChatGPT to come up with a conceptual sketch.

Prompt: sketch a cabinet for a vinyl record player. the cabinet should have an octagonal shape and a place on the top for the record player. It should have storage for the vinyl records below it. the sides of the octagon should have a cutouts that look like monstera leaves

I generally liked this concept and decided to use it as a reference to move forward.

Octagon Design Exploration

Once I had the initial concept I started exploring the concept in CAD. I used SolidWords to do the initial layouts. What became apparent from the early stages of the design was that the 45 degree joints of the octagon design were going to be a challenge to get right and also to look good.

I did some initital explorations of some joints in SolidWorks and 3D printed them just to test the concepts.

The first concept was a set of fingers that would interlock. While it worked well in 3D printing and looked really nice, it has ramps that would require 3D machining and I felt it would be annoying to program in VCarve down the line.

Then I reviewed the "50 digital joints" document that is widely available on the web for some inspiration. I was drawn to the fingertip tenons design as I thought the overlapping fingers would allow the 45 degree angle to come together. So I explored this in CAD. While sketching on this I realized that I could also add a locking bar to the design and still keep it 2D dimensional machining operation if I used a 90 degree bit on the angled side. I explored this in CAD and did a 3D print as well.

CAD of the finger tenons and locking bar design

3d print of the finger tenons and locking bar design

I liked this design so I took it forward into a full design of the cabinet. I made an octagonal floor and then made an octagonal set of inner walls. Then I drew the finger tenons and made the appropriate cuts to allow them to fit together. I explored this design for a number of hours and advanced it pretty far. Then when I showed it to my partner, she thought it looked bad, and truthfully, I did too. The overlapping figers looked messy and the shorter 45 degree faces were so puzzled out that it looked fragile and silly. So I decided not to take this forward as I didn't want to spend the time setting up the tool paths and use the material if I did not like it.

Initial octagonal center section with octagonal shape.

I took another step on this design and made the shorter 45 degree sides a little bigger. I still didn't like it and ended up abandoning it

Updated Design

I still liked the upper and lower octagons but just hated the center section. So I decided to make the center section cubic. After reviewing the 50 digital joints again, I decided that I liked the secret finger tenons as they looked easy enough to draw and did not show the ugliness of the tenon geometry.

Secret tenon joint that I used as a reference for my design. Image from opendesk.cc

I made a copy of my CAD design and set about completly overhauling the center section. I rebuilt the main walls and CADed them with intentional overlap. Then I made the cutout geometry for the tenons and extrude cut them into the front wall. Then I used the same geometry and moved it down one tenon width and made the same cut on the side. I took advantage of the symmetry of the part to mirror the tenon geometry without having to draw it over and over.

Example of the secret tenon geometry on perpendicular walls of my design

For the connection to the floor of the design I used throughhole finger tenon geometry as it would not be seen on the bottom of the cabinet.

Before I finished the CAD, I wanted to make sure that the tenon geometry would work as machined. So I extracted a corner of my CAD that had one of each of the cubic walls and the floor. Then I exported the dxfs of the 3 parts and used VCarve to create the tool paths. Then I machined them on the Shopbot and put them together.

Once they were machined I put them together and checked the fit. I found that they went together easily with a good snug fit.

Assembled corner of the design with tenon geometry.

This gave me the confidence to complete the design with the hidden tenons. I carried on with the design, adding feet on the bottom, and using tenons with dog bones (star mortises) for the holes that are hidden by the design.

CAD image showing the dogbones and radiused tenons for the blind joints.

Changed to cubic internal with octagon upper and lower Used secret finger tenons to keep a good look Update the CAD Did a test cut of just one corner to verify the fit Dog bones for through holes Missed the radius on the castles

Door

I was inspired by a record player cabinet on the web that had a hidden drawer for the records. So I wanted to add that feature to my design too. I wanted it to rotate out and have a big enough opening to allow the records to come out without twisting.

Inspiration of a hidded drawer from Kithe

I did a layout of the drawer with a mix of 2D and 3D sketches. I tried to hide the hinge inside the main volume of the design, but I could not figure out how to get the hinge laid out to keep it from interfering. So I decided to use a standard door hinge from a hardware store. I modelled the hinge in my CAD and did an assembly to check interferences. The first time I sketched it, it crashed.

Initial hinged door exloration that resulted in a CAD crash.

Then I updated the design to be a little bit taller to accomodate teh 12.5" opening that I need for the records. I also needed a way to make the stops. So I made some extrusions on the rear of the drawer to give it a foot to hold the drawer level when it closed and wings to lock it out on the top when the drawer is opened.

Cutaway view of the rear plane of the drawer showing the foot and the wings that keep the drawer in line.

Toolpaths

With the design sorted out it was time to build. I started by going to the Lowe's to get some plywood. I wanted to get something with a good finish, so I chose some maple hardwood panels. Since the 3/4" sheets were 90$ a sheet, I opted to go for 1/2" thick sheets. Then to get it into my car, I had to have the workers cut it down to 39" x 48" sheets. Since I had done the design with 3/4" thick in mind, I had to update all of my CAD. Fortunately, I had used parametric design principles and had used equations to define the thickness of the elements. So, when I made the change the design mostly snapped back into place. There were just a few sketches that I needed to repair and I was good to go.

Then it was time to do the tool paths. To start, I created drawing sheets in SolidWorks that were the size of my wood sheets, and placed all of the components to try to nest them as tightly as possible.

Sample of the layout drawings I did in SolidWorks

Then I saved these as dxf files and imported them into VCarve software to do the toolpaths.

Sample DXF

In VCarve I opened a new file and set the stock material to the size of the boards that I had including the thickness. Then I went through each of the features and assigned toolpaths too them. I would start with holes if there were any, then do the blind pockets, then the through pockets and finally the cut profiles. For the cut profiles I added tabs so that the parts would not move. Then I exported the tool paths and started the cut using the Shopbot software. For most of the machining I used a 1/4" upcut bit running at 18000 RPM and at 9ips speed.

Cutting

I started the cutting by securing the plywood to the spillplate. For all of my cuts I used screws in the corners of the wood where it would not contact the cutting path.

Then I installed the bit, and zeroed it to the table bed (not the top of the material). I did this using the alligator clip and the zeroing plate that came with the machine. Once the Z-zero was set I would then drive the head to a suitable origin point a little bit in from the lower left corner in Y and X and then zeroed the X and Y in the Shopbot software.

Then I would load the cut file and walk through the prompts, confirming that the machine was zeroed. When prompted I would turn on the spindle lockout and turn the spindle on on the pedastal. Then I would keep my hand near the spacebar while I watched the cut start.

If the cut went well, I would have parts in 5-45 minutes depending on which cut file I was running. However, it was not all smooth sailing. I had a few problems on my very first cut. One problem was that I setup the cut files in VCarve on a 48" x 48" sheet instead of a 39" x 48" so 2 of the parts had parts missing. On that same cut I also accidentally put a screw right in the middle of a cut path and snapped a bit.

Broken bit after I screwed up a toolpath and crashed into a screw.

Fortunately the fix was easy. I updated the stock size, moved the parts around on the sheet to make them fit and re-ran the parts.

I also had another small problem where the bit did not cut all the way through the parts, so I had to adjust the depth of cut from .500" to .520" and that solved the problem.

Once the problems were fixed, I went and ran all of the parts.

Assembly

Once the parts were cut it was time to assemble. I started by sanding all the parts. They all had rough edges and I used an orbital sander to take them down. I also used files to knock down other rough edges or nasty spots and a drill to chase the holes in the dogbones.

I then started with the bottom and went up. I installed the legs to the lower bulkhead and used a rubber mallet to tap them into place. Then I took the 4 sides and puzzled them together into a cube before placing them on the floor of the cabinet. Then I gently tapped the walls in place with a mallet until the were all in place. Then I took the upper bulkhead and placed it on top of the cube of side walls. The top did not fit perfectly as the edges of the cube were not pulling in together very well. So I had to pull the sides together and lightly tap them withe the mallet to get them started. Eventually, I was able to get the tabs on the top to slot into the upper bulkhead, and tapped them all down to get the main structure finished. The joints were tight enough that I need no other fasterners or glue to hold it all together.

I then used a similar technique to assemble the record drawer. I puzzled it together and used the mallet to pound them into place.

Then I added the lenses for the LEDs. I took a piece of 9mm thick acrylic and used the laser to etch a frosting on the plastic. Then I used the Shopbot to router the lenses. Then they were pressed into the cube in the slots that I had designed for them.

Then I got a piece of 3mm acrylic and laser cut a backer for the LEDs. This was made to be a little longer than the lens and with some cutouts for the wires. Then I placed a strip of WS2812 LEDs on each piece of the black acrylic and taped them into place inside the cube.

Since there were 2 strips I then soldered wires between the Dout of the first strip to the Din pin of the second and also connected the power and ground. When the wiring was complete I hotglued the strips in place behind the frosted lens.

I completed the assembly by installing the drawer. I rotated the drawer through the holes in the bulkheads and moved it into place. Then I place 2 pieces of 3mm acrylic under the face of the drawer to hold it in the correct position. Then I installed the hinges with a cordless drill, being careful to tighten them sequentially. The hinge locked down in place and worked the first time.

LEDs

The initial concept was to make a the LEDs a Vu meter and have a microphone listen to the record player and display the sound intensity. However, it took longer for the cutting and assembly, so I opted to just have it run an ambient rainbow cycle for now.

I used a XIAO ESP32C3 and put it on a breadboard. I then plugged the wires from the LEDs into the breadboard to connect power, ground, and Din to pin D5 on the board. Then I uploaded the sample code from the Adafruit Neopixel library and commented out all of the effects except for the rainbow cycle, and changed the data pin number and the number of LEDs to 56 as there are 28 LEDs on each of my strips.

Rainbow Cycle
// A basic everyday NeoPixel strip test program.

// NEOPIXEL BEST PRACTICES for most reliable operation:
// - Add 1000 uF CAPACITOR between NeoPixel strip's + and - connections.
// - MINIMIZE WIRING LENGTH between microcontroller board and first pixel.
// - NeoPixel strip's DATA-IN should pass through a 300-500 OHM RESISTOR.
// - AVOID connecting NeoPixels on a LIVE CIRCUIT. If you must, ALWAYS
//   connect GROUND (-) first, then +, then data.
// - When using a 3.3V microcontroller with a 5V-powered NeoPixel strip,
//   a LOGIC-LEVEL CONVERTER on the data line is STRONGLY RECOMMENDED.
// (Skipping these may work OK on your workbench but can fail in the field)

#include <Adafruit_NeoPixel.h>
#ifdef __AVR__
 #include <avr/power.h> // Required for 16 MHz Adafruit Trinket
#endif

// Which pin on the Arduino is connected to the NeoPixels?
// On a Trinket or Gemma we suggest changing this to 1:
#define LED_PIN    6

// How many NeoPixels are attached to the Arduino?
#define LED_COUNT 60

// Declare our NeoPixel strip object:
Adafruit_NeoPixel strip(LED_COUNT, LED_PIN, NEO_GRB + NEO_KHZ800);
// Argument 1 = Number of pixels in NeoPixel strip
// Argument 2 = Arduino pin number (most are valid)
// Argument 3 = Pixel type flags, add together as needed:
//   NEO_KHZ800  800 KHz bitstream (most NeoPixel products w/WS2812 LEDs)
//   NEO_KHZ400  400 KHz (classic 'v1' (not v2) FLORA pixels, WS2811 drivers)
//   NEO_GRB     Pixels are wired for GRB bitstream (most NeoPixel products)
//   NEO_RGB     Pixels are wired for RGB bitstream (v1 FLORA pixels, not v2)
//   NEO_RGBW    Pixels are wired for RGBW bitstream (NeoPixel RGBW products)


// setup() function -- runs once at startup --------------------------------

void setup() {
  // These lines are specifically to support the Adafruit Trinket 5V 16 MHz.
  // Any other board, you can remove this part (but no harm leaving it):
#if defined(__AVR_ATtiny85__) && (F_CPU == 16000000)
  clock_prescale_set(clock_div_1);
#endif
  // END of Trinket-specific code.

  strip.begin();           // INITIALIZE NeoPixel strip object (REQUIRED)
  strip.show();            // Turn OFF all pixels ASAP
  strip.setBrightness(50); // Set BRIGHTNESS to about 1/5 (max = 255)
}


// loop() function -- runs repeatedly as long as board is on ---------------

void loop() {
     // Fill along the length of the strip in various colors...
    //colorWipe(strip.Color(255,   0,   0), 50); // Red
    //colorWipe(strip.Color(  0, 255,   0), 50); // Green
     //colorWipe(strip.Color(  0,   0, 255), 50); // Blue

  // Do a theater marquee effect in various colors...
    // theaterChase(strip.Color(127, 127, 127), 50); // White, half brightness
    //theaterChase(strip.Color(127,   0,   0), 50); // Red, half brightness
    //theaterChase(strip.Color(  0,   0, 127), 50); // Blue, half brightness

    rainbow(10);             // Flowing rainbow cycle along the whole strip
    //theaterChaseRainbow(50); // Rainbow-enhanced theaterChase variant
}


// Some functions of our own for creating animated effects -----------------

// Fill strip pixels one after another with a color. Strip is NOT cleared
// first; anything there will be covered pixel by pixel. Pass in color
// (as a single 'packed' 32-bit value, which you can get by calling
// strip.Color(red, green, blue) as shown in the loop() function above),
// and a delay time (in milliseconds) between pixels.
void colorWipe(uint32_t color, int wait) {
  for(int i=0; i<strip.numPixels(); i++) { // For each pixel in strip...
    strip.setPixelColor(i, color);         //  Set pixel's color (in RAM)
    strip.show();                          //  Update strip to match
    delay(wait);                           //  Pause for a moment
  }
}

// Theater-marquee-style chasing lights. Pass in a color (32-bit value,
// a la strip.Color(r,g,b) as mentioned above), and a delay time (in ms)
// between frames.
void theaterChase(uint32_t color, int wait) {
  for(int a=0; a<10; a++) {  // Repeat 10 times...
    for(int b=0; b<3; b++) { //  'b' counts from 0 to 2...
      strip.clear();         //   Set all pixels in RAM to 0 (off)
      // 'c' counts up from 'b' to end of strip in steps of 3...
      for(int c=b; c<strip.numPixels(); c += 3) {
        strip.setPixelColor(c, color); // Set pixel 'c' to value 'color'
      }
      strip.show(); // Update strip with new contents
      delay(wait);  // Pause for a moment
    }
  }
}

// Rainbow cycle along whole strip. Pass delay time (in ms) between frames.
void rainbow(int wait) {
  // Hue of first pixel runs 5 complete loops through the color wheel.
  // Color wheel has a range of 65536 but it's OK if we roll over, so
  // just count from 0 to 5*65536. Adding 256 to firstPixelHue each time
  // means we'll make 5*65536/256 = 1280 passes through this loop:
  for(long firstPixelHue = 0; firstPixelHue < 5*65536; firstPixelHue += 256) {
    // strip.rainbow() can take a single argument (first pixel hue) or
    // optionally a few extras: number of rainbow repetitions (default 1),
    // saturation and value (brightness) (both 0-255, similar to the
    // ColorHSV() function, default 255), and a true/false flag for whether
    // to apply gamma correction to provide 'truer' colors (default true).
    strip.rainbow(firstPixelHue);
    // Above line is equivalent to:
    // strip.rainbow(firstPixelHue, 1, 255, 255, true);
    strip.show(); // Update strip with new contents
    delay(wait);  // Pause for a moment
  }
}

// Rainbow-enhanced theater marquee. Pass delay time (in ms) between frames.
void theaterChaseRainbow(int wait) {
  int firstPixelHue = 0;     // First pixel starts at red (hue 0)
  for(int a=0; a<30; a++) {  // Repeat 30 times...
    for(int b=0; b<3; b++) { //  'b' counts from 0 to 2...
      strip.clear();         //   Set all pixels in RAM to 0 (off)
      // 'c' counts up from 'b' to end of strip in increments of 3...
      for(int c=b; c<strip.numPixels(); c += 3) {
        // hue of pixel 'c' is offset by an amount to make one full
        // revolution of the color wheel (range 65536) along the length
        // of the strip (strip.numPixels() steps):
        int      hue   = firstPixelHue + c * 65536L / strip.numPixels();
        uint32_t color = strip.gamma32(strip.ColorHSV(hue)); // hue -> RGB
        strip.setPixelColor(c, color); // Set pixel 'c' to value 'color'
      }
      strip.show();                // Update strip with new contents
      delay(wait);                 // Pause for a moment
      firstPixelHue += 65536 / 90; // One cycle of color wheel over 90 frames
    }
  }
}

I finished the LED installation by sticking the breadboard to the bottom of the bottom bulkead and ran the power cable out the back of the cabinet so it could be plugged in.

Installation and testing

I moved the cabinet into the corner where the vinyl player sits and get it a test. I loaded the drawer with records and tested that it indeed was the right size to give full access to the collection and I had plenty of space for my adequate collection of albums.

Then I put the top on the cabinet which is another octagonal board without and holes and placed the record player on top of it. In future I will wood glue the top onto the upper bulkead, but left it loose for now until the whole device was validated. Then I plugged in the LEDs, put on a Christopher Cross album and invited my family to take a look. They were suitably impressed and my wife even appreciated it too.

Files

3D CAD

STEP file of the first joint exploration

STEP file of the finger tenon joint exploration

STEP file of the original octagonal design with finger tenons

STEP file of the as built cabinet

2D CAD