Mary wants more light directly around the needle of her Kenmore Model 158 sewing machine, as the existing light (a 120 V 15 W incandescent bulb tucked inside the end housing) casts more of a diffuse glow than a directed beam:
The end cap fits snugly around the bulb, but I thought a pair of 10 mm white LEDs, mounted side-by-side and aimed downward at the cover plate, would work. Of course, plugging a pair of white LEDs into a 120 VAC socket won’t work, but some judicious rewiring and a new 12 V DC wall wart will take care of that.
The bulb has a dual-contact bayonet base, with both pins isolated from the shell and connected to the non-polarized (!) line cord through the power switch. I didn’t know it was called a BA15d base, but now I do.
A 12 V automotive brake/taillight bulb (type 1157, I think) pulled from the Big Box o’ Bulbs has a slightly different pin arrangement that keys the filaments (which are not isolated from the shell) to the surrounding reflector:
So I conjured a mockup to see if it would fit, using 2-56 screws to mimic whatever hardware might be practical:
The solid model shows how it all fits together:
The two tiny ruby-red pins represent filament snippets in alignment holes, barely visible in real life:
I glued those pieces together, using a tiny machinist’s square as a jig to keep them perpendicular:
Some random 10 mm LEDs served for testing:
It actually fit pretty well, ignoring the fact that the LEDs point 90° from the intended direction (so I could see how the holes came out inside the pivot, honest), and lit up the area quite well, but it’s such a delicate affair that removing the entire socket and replacing it with a dedicated metal bracket / heatsink for two high-power SMD LEDs will be better.
The OpenSCAD source code:
// Adapter for LEDs in Sears sewing machine lamp socket
// Ed Nisley - KE4ZNU - January 2014
Layout = "Show"; // Build Show LEDTab LEDPlate ShellMount
//- Extrusion parameters must match reality!
// Print with 2 shells and 3 solid layers
ThreadThick = 0.20;
ThreadWidth = 0.40;
HoleWindage = 0.2; // extra clearance
Protrusion = 0.1; // make holes end cleanly
Gap = 2.0; // spacing between Show parts
AlignPinOD = 1.70; // assembly alignment pins: filament dia
inch = 25.4;
//----------------------
// Dimensions
//-- LED mounting plate
LEDDia = 10.0; // LED case OD
LEDFlangeOD = 10.7;
LEDPlateThick = 2.0; // mounting plate thickness
LEDMargin = 2.0;
LEDSpaceOC = LEDDia + LEDMargin; // LED center-to-center distance (single margin between!)
LEDTabLength = 15.0; // base to screw hole center
LEDTabThick = 4.0; // tab with hole for mounting screw
LEDTabScrewOD = 2.0;
LEDTabWidth = (3.0*2) + LEDTabScrewOD;
LEDMountHeight = 25.0; // estimated mounting screw centerline to bottom of LEDs
//-- Lamp base adapter
// hard inch dimensions!
ShellOD = 0.600 * inch; // dia of metallic shell
ShellOAL = 0.66 * inch; // ... total length
ShellInsert = 7/16 * inch; // ... length engaging socket
ShellSides = 4*4;
BulbOD = 0.75 * inch; // glass bulb
BulbLength = 1.14 * inch;
InsulOD = 0.485 * inch; // insulating stub around contact pins
InsulThick = 0.070 * inch; // ... beyond end of shell
ContactOD = 2.0; // contact holes through base (not heads)
ContactOC = 0.300 * inch; // ... center-to-center spacing
BayonetOD = 0.080 * inch; // bayonet pin diameter
BayonetOffset = 0.125 * inch; // from end of metal base
LampOAL = InsulThick + ShellOAL + BulbLength;
echo(str("Overall Length: ",LampOAL));
//-- Miscellany
//----------------------
// 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,
$fn=Sides);
}
module ShowPegGrid(Space = 10.0,Size = 1.0) {
Range = floor(50 / Space);
for (x=[-Range:Range])
for (y=[-Range:Range])
translate([x*Space,y*Space,Size/2])
%cube(Size,center=true);
}
//-- Tab for screw mounting LED holder
// AddLength remains below Z=0 for good union
module LEDTab() {
difference() {
linear_extrude(height=LEDTabThick)
hull() {
circle(d=LEDTabWidth);
translate([LEDTabLength/2,0,0])
square([LEDTabLength,LEDTabWidth],center=true);
}
translate([0,0,-Protrusion])
rotate(180/6)
PolyCyl(LEDTabScrewOD,(LEDTabThick + 2*Protrusion),6);
for (i=[-1,1])
translate([LEDTabLength/2,i*LEDTabWidth/4,LEDTabThick/2])
rotate([0,90,0]) rotate(180/4)
PolyCyl(AlignPinOD,(LEDTabLength/2 + Protrusion),4);
}
}
//-- Plate holding LEDs
module LEDPlate() {
difference() {
union() {
linear_extrude(height=LEDPlateThick)
hull() {
for (i=[-1,1])
translate([i*LEDSpaceOC/2,0,0])
circle(d=(LEDDia + 2*LEDMargin));
translate([0,(LEDFlangeOD/2 + LEDTabWidth/2),0])
square([LEDTabThick,LEDTabWidth],center=true);
}
}
for (i=[-1,1])
translate([i*LEDSpaceOC/2,0,-Protrusion])
rotate(180/12)
PolyCyl(LEDDia,(LEDPlateThick + 2*Protrusion),12);
for (i=[-1,1])
translate([0,(i*LEDTabWidth/4 + LEDFlangeOD/2 + LEDTabWidth/2),3*ThreadThick]) rotate(180/4)
PolyCyl(AlignPinOD,(LEDTabLength/2 + Protrusion),4);
}
}
//-- Bulb shell mounting adapter
module ShellMount() {
difference() {
union() {
cylinder(r1=InsulOD/2,r2=ShellOD/2,h=(InsulThick + Protrusion),$fn=ShellSides);
translate([0,0,InsulThick])
cylinder(r=ShellOD/2,h=(LampOAL - LEDMountHeight + LEDTabWidth/2),$fn=ShellSides);
}
translate([0,ShellOD,(InsulThick + BayonetOffset)]) // bayonet pin hole
rotate([90,0,0]) rotate(180/4)
PolyCyl(BayonetOD,2*ShellOD,4);
translate([0,ShellOD,(InsulThick + LampOAL - LEDMountHeight)]) // LED mount screw hole
rotate([90,0,0])
PolyCyl(LEDTabScrewOD,2*BulbOD,6);
translate([0,0,(InsulThick + ShellOAL + LampOAL/2)]) // slot for LEDTab mount
cube([2*ShellOD,(LEDTabThick + 2*Protrusion),LampOAL],center=true);
for (i=[-1,1]) // contact pin holes
translate([i*ContactOC/2,0,-Protrusion])
rotate(180/6)
PolyCyl(ContactOD,2*LampOAL,6);
}
}
//- Build it
ShowPegGrid();
if (Layout == "LEDTab")
LEDTab();
if (Layout == "LEDPlate")
LEDPlate();
if (Layout == "ShellMount")
ShellMount();
if (Layout == "Show") {
LEDPlate();
translate([-LEDTabThick/2,(LEDFlangeOD/2 + LEDTabWidth/2),(LEDTabLength + LEDPlateThick + Gap)])
rotate([0,90,0])
LEDTab();
for (i=[-1,1])
# translate([0,(i*LEDTabWidth/4 + LEDFlangeOD/2 + LEDTabWidth/2),(LEDPlateThick + Gap/4)])
rotate(180/4)
cylinder(r=AlignPinOD/2,h=Gap/1,$fn=4); // fake the pins
translate([0,(LEDFlangeOD/2 + LEDTabWidth/2),(LampOAL - LEDTabWidth/2)])
rotate([0,180,0]) rotate(90)
ShellMount();
}
if (Layout == "Build") {
translate([0,LEDDia,0])
LEDPlate();
translate([-10,-(LEDMargin + LEDTabWidth),0])
rotate(-90)
LEDTab();
translate([10,-(LEDMargin + LEDTabWidth),0])
ShellMount();
}
The original doodles for the bulb dimensions and adapter layout:
The Smell of Molten Projects in the Morning 