OpenSCAD source code: Ball-drilling fixture for mini-lathe three-jaw chuck

Lathe Ball Fixture.scad

// Lathe Ball Drilling Fixture
// Ed Nisley KE4ZNU 2020-11

/* [Layout options] */

Layout = "Build";					// [Build, Show, Body, Jaws]

BallDia = 10.0;           // [5.0:0.5:25.0]

/* [Extrusion parameters] */

/* [Hidden] */

ThreadThick = 0.25;
ThreadWidth = 0.40;

HoleWindage = 0.2;

function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);
function IntegerLessMultiple(Size,Unit) = Unit * floor(Size / Unit);

Protrusion = 0.1;      // make holes end cleanly

inch = 25.4;

ID = 0;
OD = 1;
LENGTH = 2;

//* [Basic dimensions] */

Chuck = [21.0,100.0,20.0];                        // chuck bore, OD, jaw length

Jaw = [Chuck[LENGTH],15.0,12.0];                  // jaw free length, base width, first step radius

JawInclAngle = 112;                               // < 120 degrees for clearance!
JawAngle = JawInclAngle/2;                        // angle from radius

WallThick = 5.0;                                  // min wall thickness

Kerf = 0.75;                                      // space between clamp blocks

ClampSides = 8*(2*3);

ClampBore = BallDia/2;                             // clear bore through clamp

ClampAngle = asin(ClampBore/BallDia);              // angle from lathe axis to clamp front

Plate = [ClampBore,
         BallDia + 2*WallThick + 2*Jaw.z,
         Jaw.x];

LegendDepth = 1*ThreadWidth;

ShaftOD = 3.6;                                    // sample shaft

ShowGap = 1.5;


//----------------------
// Chuck jaws
// Real jaws have a concave radiused tip we simply ignore

module ChuckJaws(l=Jaw.x,r=10) {

  for (a=[0:120:240])
    rotate(a)
      linear_extrude(height=l)
        translate([r,0])
          difference() {
            translate([Chuck[OD]/4,0])
              square([Chuck[OD]/2,Jaw.y],center=true);
            for (i=[-1,1])
                rotate(i*(90 - JawAngle))
                  translate([-Jaw.z/2,0])
                    square([Jaw.z,2*Jaw.y],center=true);
          }
}


//----------------------
// Clamp body

module ClampBlocks() {

  difference() {
    cylinder(d=Plate[OD],h=Plate[LENGTH],$fn=ClampSides);         // main disk

    translate([0,0,-Protrusion])                                  // central bore
      cylinder(d=ClampBore,h=2*Plate[LENGTH],$fn=ClampSides);

    for (a=[0:120:240])                                           // kerf slits
      rotate(60 + a)
        translate([Plate[OD]/2,0,Protrusion])
          cube([Plate[OD],Kerf,2*Plate[LENGTH]],center=true);

    translate([0,0,BallDia/2 * cos(ClampAngle)])                  // ball socket
      sphere(d=BallDia,$fn=ClampSides);

    for (a=[0:120:240]) {                                         // legend
      rotate(4.5*360/ClampSides + a)
      translate([Plate[OD]/2 - LegendDepth,0,Plate[LENGTH]/2])
        rotate([0,90,0])
          linear_extrude(height=LegendDepth + Protrusion,convexity=10)
            mirror([0,0,0])
              text(text=str(BallDia," mm"),size=2.5,spacing=1.20,font="Arial:style:Bold",halign="center",valign="center");
      rotate(-4.5*360/ClampSides + a)
      translate([Plate[OD]/2 - LegendDepth,0,Plate[LENGTH]/2])
        rotate([0,90,0])
          linear_extrude(height=LegendDepth + Protrusion,convexity=10)
            mirror([0,0,0])
              text(text="KE4ZNU",size=2.5,spacing=1.20,font="Arial:style:Bold",halign="center",valign="center");
    }
  }

}

//----------------------
// Clamp with jaw cutouts

module ClampBody() {
  difference() {
    ClampBlocks();
    translate([0,0,-Protrusion])
      ChuckJaws(l=Jaw.x + 2*Protrusion,r=BallDia/2 + WallThick);
  }
}


//----------------------
// Lash it together



if (Layout == "Body") {
  ClampBlocks();
}

if (Layout == "Jaws") {
  ChuckJaws();
}

if (Layout == "Build") {
  ClampBody();
}

if (Layout == "Show") {
  ClampBody();

  color("ivory",0.2)
    ChuckJaws(r=BallDia/2 + WallThick + ShowGap);   // move out for E-Z viewing

  color("red",0.4)
    translate([0,0,-Jaw.x/2])
    cylinder(d=ShaftOD,h=2*Jaw.x,$fn=ClampSides,center=false);

  color("white",0.5)
    translate([0,0,BallDia/2 * cos(ClampAngle)])  // ball socket
      sphere(d=BallDia,$fn=ClampSides);

}

More details on my blog at https://wp.me/poZKh-9zB