The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Category: Machine Shop

Mechanical widgetry

  • MPCNC: Power Supply Brick Mount

    A laptop-style power brick supplies 24 V for the MPCNC’s stepper motors, but I didn’t want it wandering around on the Basement Laboratory floor and getting in trouble, so a pair of brackets seemed in order:

    Power Supply Brick Mount - trial fit
    Power Supply Brick Mount – trial fit

    They build flat on their backs to avoid support material:

    Power Supply Brick Mount - Slic3r
    Power Supply Brick Mount – Slic3r

    The nicely rounded corners produce a very thin line of plastic on the first layer, so the model now has thicker base plates to improve the situation. A set of mouse ears would keep the tips pasted to the glass.

    The OpenSCAD source code as a GitHub Gist:

    // Power Supply Brick brackets
    // Ed Nisley KE4ZNU 2018-02-26
    Layout = "Show";
    //– Extrusion parameters
    ThreadThick = 0.25;
    ThreadWidth = 0.4;
    HoleWindage = 0.3; // enlarge hole dia by this amount
    function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);
    Protrusion = 0.1; // make holes look good and joints intersect properly
    //– Useful sizes
    inch = 25.4;
    Tap10_32 = 0.159 * inch;
    Clear10_32 = 0.190 * inch;
    Head10_32 = 0.373 * inch;
    Head10_32Thick = 0.110 * inch;
    Nut10_32Dia = 0.433 * inch;
    Nut10_32Thick = 0.130 * inch;
    ID = 0;
    OD = 1;
    LENGTH = 2;
    //– Bracket Dimensions
    Brick = [170.0,66.0,40.0]; // overall size, add details in module
    Socket = [30.0,24.0]; // IEC power socket
    Cable = [6.0,15.0]; // DC output cable ID=wire OD=strain relief
    WallThick = 3.0; // default wall thickness
    BaseThick = 4.0;
    Screw = [5.1,10.0,3.0]; // screw size, more-or-less 10-32, OD & LENGTH for head
    NumSides = 3*4;
    //———————-
    // Useful routines
    module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes
    Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);
    FixDia = Dia / cos(180/Sides);
    cylinder(r=(FixDia + HoleWindage)/2,
    h=Height,
    $fn=Sides);
    }
    //———————-
    // Models
    module BrickMount(End="Both") {
    difference() {
    union() {
    hull() // main block
    for (i=[-1,1], j=[-1,1], k=[0,1])
    translate([i*(Brick.x/2 + WallThick – WallThick),
    j*(Brick.y/2 + WallThick – WallThick),
    k*(Brick.z + WallThick – WallThick)])
    sphere(r=WallThick,$fn=NumSides);
    hull() // screw flanges
    for (i=[-1,1], j=[-1,1])
    translate([i*(Brick.x/2 + WallThick – BaseThick),
    j*(Brick.y/2 + WallThick + 2*Screw[OD] – BaseThick),
    0])
    sphere(r=BaseThick,$fn=NumSides);
    }
    for (i=[-1,1], j=[-1,1]) // remove screw holes
    translate([i*(Brick.x/2 + WallThick – Screw[OD]),
    j*(Brick.y/2 + WallThick + Screw[OD]),
    -Protrusion])
    rotate(180/6)
    PolyCyl(Screw[ID],2*WallThick,6);
    translate([0,0,Brick.z/2]) // remove center part to leave ends
    cube([(Brick.x + 2*WallThick – 4*Screw[OD]),2*Brick.y,2*Brick.z],center=true);
    if (End == "Socket")
    translate([Brick.x/2,0,Brick.z/2]) // remove cable end to leave socket
    cube([(Brick.x + 2*WallThick – 4*Screw[OD]),2*Brick.y,2*Brick.z],center=true);
    if (End == "Cable")
    translate([-Brick.x/2,0,Brick.z/2]) // remove socket end to leave cable
    cube([(Brick.x + 2*WallThick – 4*Screw[OD]),2*Brick.y,2*Brick.z],center=true);
    translate([0,0,Brick.z/2 – Protrusion/2]) // remove power supply brick from interior
    cube(Brick + [0,0,Protrusion],center=true);
    translate([0,0,-Brick.z]) // remove below XY plane
    cube(2*Brick,center=true);
    translate([0,0,Brick.z/2]) // remove AC socket
    rotate([0,-90,0])
    rotate(90)
    linear_extrude(height=Brick.x,convexity=2)
    square(Socket,center=true);
    translate([0,0,Brick.z/2]) // remove DC cable
    rotate([0,90,0])
    rotate(180/8)
    PolyCyl(Cable[OD],Brick.x,8);
    translate([Brick.x/2,0,Brick.z/4 – Protrusion/2]) // … and wire slot
    cube([Brick.x,Cable[ID],Brick.z/2 + Protrusion],center=true);
    }
    }
    //———————-
    // Build it
    if (Layout == "Show")
    BrickMount("Both");
    if (Layout == "Build") {
    translate([5,0,Brick.x/2 + WallThick])
    rotate([0,90,0])
    BrickMount("Cable");
    translate([-5,0,Brick.x/2 + WallThick])
    rotate([0,-90,0])
    BrickMount("Socket");
    }
  • MPCNC: Button Box Connector Mount

    This will eventually end up on a board supporting the GRBL controller box:

    Control Box - Connector Mount - Slic3r
    Control Box – Connector Mount – Slic3r

    It’s a direct cut-n-paste descendant of the old NEMA motor mount.

    The nut threads onto the connector behind the bulkhead, so you must either wire it in place or make very sure you can feed all the terminations through the hole:

    Connector Mount
    Connector Mount

    Given the previous hairball, I think in-situ soldering has a lot to recommend it:

    GRBL - Control button wiring
    GRBL – Control button wiring

    The OpenSCAD source code as a GitHub Gist:

    // Circular connector bracket
    // Ed Nisley KE4ZNU 2018-02-22
    //– Extrusion parameters
    ThreadThick = 0.25;
    ThreadWidth = 0.4;
    HoleWindage = 0.3; // enlarge hole dia by this amount
    function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);
    Protrusion = 0.1; // make holes look good and joints intersect properly
    //– Useful sizes
    inch = 25.4;
    Tap10_32 = 0.159 * inch;
    Clear10_32 = 0.190 * inch;
    Head10_32 = 0.373 * inch;
    Head10_32Thick = 0.110 * inch;
    Nut10_32Dia = 0.433 * inch;
    Nut10_32Thick = 0.130 * inch;
    ID = 0;
    OD = 1;
    LENGTH = 2;
    //– Mount Sizes
    Connector = [14.6,15.5,4.0]; // connector thread; ID = dia at flat
    Screw = [5.1,10.0,3.0]; // screw size, more-or-less 10-32, OD & LENGTH for head
    MountWidth = IntegerMultiple(2*Connector[OD],ThreadWidth); // use BCD for motor clearance
    MountThick = IntegerMultiple(Connector[LENGTH],ThreadThick); // for stiffness
    WallThick = 3.0; // default wall thickness
    StandThick = IntegerMultiple(WallThick,ThreadWidth); // baseplate
    StrutThick = IntegerMultiple(WallThick,ThreadWidth); // sides holding motor mount
    UprightLength = MountWidth + 2*StrutThick;
    StandBoltHead = IntegerMultiple(Head10_32,5); // bolt head rounded up
    StandBoltOC = IntegerMultiple(UprightLength + 2*StandBoltHead,5);
    StandLength = StandBoltOC + 2*StandBoltHead;
    StandWidth = 2*StandBoltHead;
    StandBoltClear = (StandLength – UprightLength)/2; // flat around bolt head
    Recess = StandWidth – MountThick;
    echo(str("Stand Base: ",StandLength," x ",StandWidth," x ",StandThick));
    echo(str("Stand Bolt OC: ",StandBoltOC));
    echo(str("Strut Thick: ",StrutThick));
    //———————-
    // Useful routines
    module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes
    Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);
    FixDia = Dia / cos(180/Sides);
    cylinder(r=(FixDia + HoleWindage)/2,
    h=Height,
    $fn=Sides);
    }
    //———————-
    // Model
    module MotorMount() {
    difference() {
    translate([StandThick/2,0,StandWidth/2])
    cube([(MountWidth + StandThick),StandLength,StandWidth],center=true);
    translate([-Protrusion/2,0,StandWidth – (Recess – Protrusion)/2])
    cube([(MountWidth + Protrusion),MountWidth,(Recess + Protrusion)],center=true);
    translate([0,0,-Protrusion])
    PolyCyl(Connector[OD],StandWidth,4*4);
    for (j=[-1,1]) // cutouts over bolts
    translate([-Protrusion/2,
    j*((StandLength – StandBoltClear)/2 + Protrusion/2),
    StandWidth/2])
    cube([(MountWidth + Protrusion),
    (StandBoltClear + Protrusion),
    (StandWidth + 2*Protrusion)],center=true);
    for (j=[-1,1]) // stand bolt holes
    translate([(MountWidth/2 – Protrusion),j*StandBoltOC/2,StandWidth/2])
    rotate([0,90,0])
    rotate(180/6)
    PolyCyl(Clear10_32,StandThick + 2*Protrusion,6);
    translate([0,-(UprightLength/2 – ThreadWidth/2),StandWidth/2])
    rotate([90,180,0])
    linear_extrude(ThreadWidth,convexity=10)
    text(text=str(Connector[OD]),size=6,spacing=1.20,font="Arial",halign="center",valign="center");
    }
    }
    //———————-
    // Build it
    MotorMount();
  • Baofeng BL-5 Battery Pack: Disassembly

    Not much to my surprise, both Baofeng BL-5 lithium batteries went bad on the shelf:

    Baofeng BL-5 Packs - Final Failure - 2018-02-21
    Baofeng BL-5 Packs – Final Failure – 2018-02-21

    The longer traces show their original capacity, back in the day.

    Whacking a chisel into the obvious split lines broke the solvent glue bonds holding the case sections together, after which some slow prying defeated the double sticky foam tape on the cells:

    Baofeng BL-5 battery pack - innards
    Baofeng BL-5 battery pack – innards

    A closer look at the (dis)charge controller PCB:

    Baofeng BL-5 battery pack - protection PCB
    Baofeng BL-5 battery pack – protection PCB

    The other side of the PCB has no components, so what you see is what you get. The larger IC proclaims FS8205A EP050C, which may indicate a vague relation to an S8205 protection IC. The datasheet shows a 16 pin TSSOP package containing an IC for four or five cell batteries, completely unlike the 8 pin package on the PCB, but when you buy enough of anything, you can get anything you want.

    In common with all cheap lithium batteries around here, the “thermistor” terminal connects to a 10 kΩ SMD resistor steadfastly maintaining its resistance in the face of all temperature variations.

    Some probing shows one feeble cell in each pack. Perhaps a Frankenbattery built from the debris will have enough capacity for a standard ride around the block.

  • Monthly Science: BLDC Fan Characteristics

    I have often asserted, in public, in writing, that you can’t change the speed of a fan’s BLDC motor by varying its voltage, because the fan controller generates the waveforms responsible for the motor speed based on its internal timing.

    A pair of BLDC blowers recently arrived and a quick test showed I’m pretty much completely wrong:

    BLDC Blower - RPM I P vs V
    BLDC Blower – RPM I P vs V

    The data points come from this blower:

    Blower label - 24V 0.2A
    Blower label – 24V 0.2A

    The blower specs from the eBay listing:

    75MM 24V Brushless DC Blower Cooling Fan Exhaust Fan

    • Dimension:75(L)x75(W)x30(H)mm
    • Connector:2Pin-PH2.0
    • Rated Voltage: DC24V
    • Rated Current: 0.2±10% Amp
    • Rated Speed: 3800±10%rpm
    • Air flow:1.8CFM
    • Noise: 23±10%dBA
    • Bearing Type: Sleeve
    • Life: 35000 hours
    • Cable Lenght: 32cm(12.5in)
    • Weight: 75g/pcs

    The case is about 75 mm × 75 mm × 30 mm, so the generic part number seems to be 7530, with many variations. However, they all seem to resolve to the same blower with different models drawing different current at specific voltages (clicky for more dots, JPG blurriness in original):

    GDT7530S12B BLDC blower parameter table
    GDT7530S12B BLDC blower parameter table

    The blower in hand roughly corresponds to the bottom line of the 24 V section:

    • 0.21 A
    • 4000 RPM
    • 16.3 CFM
    • 1.1 inch H2O pressure
    • 43 dBA

    There’s a gross discrepancy between the eBay 1.8 CFM and the chart 16.3 CFM, but the other parameters seem within handwaving distance and, yo, it’s from eBay. ‘Nuff said.

    The graph up top shows the results with an unrestricted output opening.

    For more realistic results with some resistance to air flow, I taped a small anemometer to the blower output:

    Blower air flow test
    Blower air flow test

    Which produced:

    BLDC Blower - RPM Flow vs V - anemometer
    BLDC Blower – RPM Flow vs V – anemometer

    In very round numbers, the anemometer aperture is 400 mm², so the 9 m/s air flow at 24 V works out to 3.6×10-3 m3/s = 0.13 CFS = 7.6 CFM. Which is maybe half the 16.3 CFM spec, but they’re surely using a fancier anemometer with much lower back pressure. Close enough, anyway. Fer shure, 1.8 CFM is wrong.

    Completely blocking the inlet with a plastic sheet to simulate the blower pulling air from, e.g., a vacuum table:

    BLDC Blower - RPM vs V - blocked inlet
    BLDC Blower – RPM vs V – blocked inlet

    The RPM varies more linearly with voltage when the blower isn’t accelerating any air.

    Some current waveform show why you really shouldn’t run fans in series to “split the power supply”, as seems common in 3D printers with 24 VDC power supplies.

    From a 24 V supply, the current drops to 50 mA every 75 ms (200 mA/div):

    BLDC 24V Blower - 24 V - 200mA-div
    BLDC 24V Blower – 24 V – 200mA-div

    From a 12 V supply, even weirder things happen (50 mA/div):

    BLDC 24V Blower - 12 V - 50mA-div
    BLDC 24V Blower – 12 V – 50mA-div

    Note that you can’t reduce the fan’s supply voltage by applying PWM to the current, as happens in essentially all 3D printers for “speed control”. Basically, PWM turns the fan off several hundred times every second, which does not modulate the voltage.

    I have no way to measure pressure, but if the 1.1 inch H2O number comes close to reality, the blower can produce 1.5 lb of clamping force per square foot. Which isn’t a lot, granted, but it might suffice for paper and vinyl cutting.

    The DRV10866 BLDC fan controller doc from TI is completely unrelated to the blower in question, but gives a reasonable introduction to the subject.

  • MPCNC: Button Box Wiring

    The wiring hairball between the control button pendant and the Protoneer board looks like this:

    GRBL - Control button wiring
    GRBL – Control button wiring

    The as-built schematic, such as it is:

    GRBL Control button wiring - sketch
    GRBL Control button wiring – sketch

    Yes, the SSR negative output goes to the Protoneer + Power Input.

    I should drive the SSR from the Motor Enable output (in the external motor control header), rather than +5 V, to let GRBL control the motors, with a manual E-Stop override. The A4988 drivers require -Enable, so:

    • -Enable to SSR -Control input (replaces GND)
    • +5 V to BRS to SSR +Control input (as before)

    The SSR Control input draws 13 mA at 5 V, suggesting I should drive the AC SSR (for the spindle motor) from the DC SSR output, rather than paralleling the two on a single Arduino output pin.

    I belatedly recognized the E-Stop BRS as an instantiation of an SCP-001-J Keter-class anomaly; it is now appropriately labeled:

    MPCNC EStop as SCP-001-J
    MPCNC EStop as SCP-001-J

    I can attest to its effect on rational thought; a molly-guard may be required.

  • J5-V2 Flashlight: Front End Rattle

    After a year of fairly light use, the lens holder (and “attack ring”) of my J5-V2 flashlight worked loose and began to rattle. The ring holding the lens in place turned out to be finger-loose, but that wasn’t the entire problem, so I removed it and looked inside:

    J5-V2 Flashlight - LED view
    J5-V2 Flashlight – LED view

    The mysterious alien egg resides on the upper-right side of the LED emitter.

    The aluminum ring holding the LED assembly in place was also finger-loose, so I unwound it to take the whole front end apart:

    J5-V2 Flashlight - front parts
    J5-V2 Flashlight – front parts

    Reassembly with a few dabs of Loctite in appropriate places should prevent future rattles.

    Given the number of … issues … accompanying this thing, I’d say it’s not been a good cost performer. The Anker LC40 and LC90 flashlights work much better.

     

  • MPCNC: Autolevel Probe, Tactile Switch Edition

    So I intended to shrink the Autolevel probe with 1/8 inch drill rod and a tactile membrane switch:

    MPCNC - Simple Z probe - pogo tactile switch
    MPCNC – Simple Z probe – pogo tactile switch

    Unfortunately, it didn’t work nearly as well as I expected, because the switch membrane requires slightly less than the 180 g of pressure that pushes the P100 pogo pin entirely into its housing, leaving no overtravel worth mentioning. The membrane switch mechanism itself has much less than 1 mm of overtravel after the dome snaps, which left me with an uncomfortable feeling of impending doom.

    I managed to figure that out before completely assembling the thing, saving me a bit of time.

    The end of the pogo pin initially sported a dot of epoxy to spread the load over the switch dome:

    Pogo pin with epoxy switch-pusher drop
    Pogo pin with epoxy switch-pusher drop

    I dismantled the pogo pin to see whether I could substitute a more forceful spring how it worked. As expected, a teeny spring drives the probe up against a trio of indentations in the brass housing. I didn’t expect the probe to have such an intricate shape, but it’s obvious in retrospect.

    The OpenSCAD code for the housing required minimal tweakage from the larger version, so it’s not worth immortalizing.