Low Voltage Interface Adapter Plate

The Dell GX270 chassis has a small support plate under the CPU, evidently to support the heatsink and fan:

Optiplex GX270 CPU heatsink mount
Optiplex GX270 CPU heatsink mount

It slides neatly into those clips on the system board tray, but it’s not actually locked into position. I think that allows it to slide around a bit under the system board, providing vertical support without constraining the board’s horizontal position. Anyhow, it looked like the easiest way to support the prototyping board that will hold the low voltage interface circuitry.

By some mischance, I found a nice aluminum plate exactly the right width, so only one side needed a saw cut and squaring. Coordinate drilling four #6 clearance holes matched the support:

LV Interface Adapter Plate - drilling
LV Interface Adapter Plate – drilling

That corner of the tray had another system board retaining clip, but rather than bashing it flat, I just sawed a slit in the plate so it can slide right into position. Note the perfect alignment of that screw hole:

LV Interface Adapter Plate - retainer
LV Interface Adapter Plate – retainer

I love it when all my mistakes cancel out!

Four more holes matched the prototyping circuit board and, while I had some epoxy mixed up for another part, I fastened four standoffs over the holes. A washer under each original screw soaked up exactly enough space that the screws barely indented the case and, as if by magic, hold the support plate firmly in place:

LV Interface Adapter Plate - installed
LV Interface Adapter Plate – installed

Of course, that means I must remove the circuit board to get the tray out, but the AC interface board must also come out, so we’re not talking a spur-of-the-moment operation.

The switch in the lower left corner is the original Dell “intrusion monitoring” switch harvested from a complex metal stamping in the diagonally opposite corner of the case. It’s epoxied to the case wall, with the plunger contacting a shim epoxied to the top of the case, and will eventually disconnect the AC line power from the drive electronics: case open = switch closed = lethal power off.

ET227 Transistor: Monster Heatsink Mounting

Back in the day, heatsinks like this sat atop Moah Powah Pentium CPUs:

ET227 transistor on heatsink
ET227 transistor on heatsink

I picked it because the hulking ET227 transistor fit neatly on its backside, it seemed capable of handling 30 to 50 W of power, and I have several of them in the Big Box o’ Heatsinks. No careful thermal analysis was involved…

Mounting it on the polycarbonate sheet inside the repurposed GX270 case involved drilling & tapping a pair of 6-32 holes in one side:

ET227 Heatsink - tapping
ET227 Heatsink – tapping

That’s not rigid tapping on a Sherline, it’s aligning a hand-turned tap in the spindle bore. Sorry.

And, yeah, you’re not supposed to leave the semiconductors mounted when you’re drilling the heatsink. I figure there’s nothing I can possibly do without using a hammer that will bother that transistor in the slightest. What, me worry?

The transistor collector runs at line voltage, which means the entire heatsink will pose a lethal shock hazard. I thought about isolating the collector and failed to come up with anything I’d trust to be both thermally conductive and electrically insulating over the long term; the screw heads must be isolated from the collector plate, too.

The screws stick out below the polycarbonate sheet, just above the grounded EMI shell lining the case, so I flattened them a bit:

ET227 Heatsink - mounting screws
ET227 Heatsink – mounting screws

The simple rectangular strip to the rear of the chassis mounting clips is just slightly thicker than the screw heads, so they can’t possibly contact the case:

Chassis Clips
Chassis Clips

It gets glued to the underside of the nearly invisible sheet:

ET227 heatsink - gluing screw shield
ET227 heatsink – gluing screw shield

With Kapton tape over the heads, Just In Case:

ET227 Heatsink - mounted
ET227 Heatsink – mounted

It makes a nice linear counterpoint to the jumble of AC interface wiring:

AC Interface Chassis
AC Interface Chassis

The insulating sheet on the case lid came from the bottom of the original GX270 system board, where I think it served much the same purpose. It’s surely not rated for AC line voltages, but the thought must count for something:

AC Interface Chassis
AC Interface Chassis

More of the parts are flying in formation…

Chipmunk Feeding Zone

Mary puts damaged cherry tomatoes beside our resident chipmunk’s favorite hideout:

Chipmunk Feeding Zone
Chipmunk Feeding Zone

The critter eats them from the inside out, then tosses the shredded skins.

Since she started leaving her offerings, the chipmunk has been leaving the good cherry tomatoes in her garden untouched. We’re both astonished at how many tomatoes fit inside one chipmunk…

Rectifier Mounting Screw Tweakage

The sewing machine motor runs from 120 V AC or DC, drawing a few amps with the rotor locked, so a hulking 300 V 10 A bridge rectifier (Motorola MDA962-4, if you’re keeping score) seems grossly overrated. On the other paw, I have one, so why not?

The mounting holes pass 6-32 machine screws, but the recesses in the top seem meant for fillister head screws that I don’t have. Fortunately, I do have a lathe:

MDA962-4 rectifier - screw head adjustment
MDA962-4 rectifier – screw head adjustment

And then they just drop into place:

MDA962-4 Bridge Rectifier - installed
MDA962-4 Bridge Rectifier – installed

You can see why recessing the screw head below the top of the rectifier is a Good Thing.

That was easy…

AC Interface Chassis Mounting Clips

The Dell GX270 system board mounts on a tray, latching into small tabs, with a single screw locking it in place. The tray then slides into the metal EMI shield / case, latching onto more tabs, with a spring-loaded pair of tabs snapping into a slot under the green latch:

Optiplex GX270 - system board tray
Optiplex GX270 – system board tray

All that is well and good for a mass-production PC system board, but poses a problem for mounting anything else: there’s no room for screw heads below the tray, adhesives really don’t bond to slightly flexible aluminum sheets, and I definitely can’t do large-scale precision metal bending.

So a cheat seems in order. The general idea is to support a 6 mm polycarbonate sheet on clips that slide under the small tabs along the front, support the sheet on the rear tabs, and secure it with the screw. That’s thick enough to allow tapping holes for mounting screws, so everything else can mount to the sheet.

The sheet fits around the power supply on the right, protrudes over the rear of the tray to the back of the case (with a recess around the green latch), and clears the hinge assembly on the left. There are no dimensions, as it’s all done by eye with the Joggy Thing.

AC Chassis Shaping
AC Chassis Shaping

A drive bay EMI plug from a long-discarded PC provided some nice springy steel strips that slide neatly under those tray tabs:

Drive EMI shield
Drive EMI shield

That actually took a bit of trial-and-error:

AC Chassis mounting brackets - practice makes perfect
AC Chassis mounting brackets – practice makes perfect

My first attempts used slightly thicker steel that didn’t fit nearly as well, plus I wasn’t quite sure how wide they should be.

As with nearly all plastic doodads around here, the white plastic mounting clips / brackets come from the M2:

Chassis Clips
Chassis Clips

The two brackets in the middle of the solid model slide around the tabs at the rear corners of the tray and capture the bent-over top section below the polycarbonate sheet.

The strip in the rear goes around the screws holding the heatsink to the sheet; more on that later.

The PLA brackets get themselves glued to the sheet with IPS #4 solvent adhesive, a hellish mixture of chlorinated hydrocarbons that attacks most plastics with gleeful enthusiasm. I positioned the brackets on the tray, slobbered adhesive on their tops, slapped the polycarbonate sheet in place, and applied clamps:

AC Chassis - gluing bracket blocks
AC Chassis – gluing bracket blocks

The final bonds weren’t as uniform as I’d like, but they seem rugged enough. The lip along the rear of the tray was slightly higher on the left edge, which may have interfered with the clamping pressure; it’s obviously not a controlled dimension.

The tapped holes in the sheet accommodate screws for various bits & pieces.

All in all, that worked out pretty well…

The OpenSCAD source code:

// AC Interface sheet mounting brackets
// Ed Nisley - KE4ZNU - August 2014

Layout = "Build";		// FrontClip RearClip HeatSink Build

Gap = 5.0;					// between Build objects

//- Extrusion parameters must match reality!

ThreadThick = 0.20;
ThreadWidth = 0.40;

HoleWindage = 0.2;			// extra clearance

Protrusion = 0.1;			// make holes end cleanly

AlignPinOD = 1.70;			// assembly alignment pins: filament dia

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

// Dimensions

FC_Block = [45.0,30.0,IntegerMultiple(5.6,ThreadThick)];
FC_Retainer = [15.5,9.0,3.0,15.0];					// central section: L,W,H, inset from front

RC_Block = [30.0,25.0,IntegerMultiple(5.6,ThreadThick)];
RC_RecessOffset = [9.0,5.0,IntegerMultiple(4.8,ThreadThick)];	// X,Y,thickness
RC_SlotWidth = 2.5;

HS_Insulation = [80.0,16.0,2.5];
HS_Hole = [8.0,40.0];					// screw clearance dia,on-center

// 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,

module ShowPegGrid(Space = 10.0,Size = 1.0) {

  RangeX = floor(100 / Space);
  RangeY = floor(125 / Space);

	for (x=[-RangeX:RangeX])
	  for (y=[-RangeY:RangeY])


// Front clips

module FrontClip() {

	difference() {

		translate([0,(FC_Retainer[3] - FC_Block[1]/2),(FC_Retainer[2] + FC_Block[2]/2)])
			cube([(FC_Block[0] - 12*ThreadWidth),FC_Retainer[1],FC_Block[2]],center=true);

		translate([0,FC_Retainer[3] - FC_Retainer[1]/2,FC_Block[2]/2])


// Rear clips

module RearClip(Hand="Left") {

HandSign = (Hand == "Left") ? -1 : 1;

	difference() {

		translate([0,RC_RecessOffset[1],RC_RecessOffset[2] + RC_Block[2]/2])
			cube([RC_Block[0] - 2*RC_RecessOffset[0],

		translate([HandSign*(RC_Block[0]/2 - RC_RecessOffset[0]),



// Heatsink bumper

module HeatSink() {

	difference() {

	for (x=[-1,1])



if (Layout == "FrontClip") {

if (Layout == "RearClip") {

if (Layout == "HeatSink") {

if (Layout == "Build") {
	for (x=[-1,1]) {
		translate([x*(Gap + FC_Block[0])/2,(Gap + FC_Block[1])/2,0])
		translate([x*(Gap + RC_Block[0])/2,-(Gap + RC_Block[1])/2,0])
			RearClip((x == -1) ? "Left" : "Right");
	translate([0,-(RC_Block[1] + HS_Insulation[1]/2 + 3*Gap/2),0])

IEC Power Socket Mount

The original Kenmore Model 158 sewing machine used a two-wire line cord:

Kenmore 158 - terminal block
Kenmore 158 – terminal block

In light of my modifications, grounding the frame seems prudent. The heap produced a long IEC extension cord with screw-mounting ears on the socket end that fit neatly into the GX270’s rear panel area occupied by two PCI cover plates, so a bit of Quality Shop Time seemed in order.

The GX270’s carcass yielded a complex bit of sheet metal that held the hard drive and a few other odds & ends, with some clean right-angle bends in exactly the right places:

Dell drive bracket - intact
Dell drive bracket – intact

Some bandsaw work removed the gimcrackery:

Dell drive bracket - first bandsaw pass
Dell drive bracket – first bandsaw pass

More bandsawing produced a rough outline:

Dell drive bracket - second bandsaw pass
Dell drive bracket – second bandsaw pass

Sawing to length, removing the small flanges, and squaring the sides:

Dell drive bracket - squaring edges
Dell drive bracket – squaring edges

I traced the existing PCI cover tabs, bandsawed the outlines, and filed to suit:

Dell drive bracket - basic outline
Dell drive bracket – basic outline

They look a bit ragged, but fit well enough:

Dell drive bracket - trial fit - interior
Dell drive bracket – trial fit – interior

From the outside, it looks like it grew there:

Dell drive bracket - trial fit - exterior
Dell drive bracket – trial fit – exterior

The divider between the PCI slots succumbed to tin snips and a bit of filing. The tabs climbing over the bottom edge come from the internal EMI shield covering the entire back surface.

A bit of coordinate drilling and manual milling produced the IEC socket outline

Dell drive bracket - drilling and milling
Dell drive bracket – drilling and milling

Which looks pretty good from the inside:

Dell drive bracket - IEC socket - interior
Dell drive bracket – IEC socket – interior

And great from the outside, if I do say so myself:

Dell drive bracket - IEC socket - exterior
Dell drive bracket – IEC socket – exterior

Match-drilling a #6 clearance hole below the hole in the clamp arm, then ramming a self-tapping case screw into it, provides a convenient grounding point for the sewing machine cord:

IEC Socket Mount - ground screw
IEC Socket Mount – ground screw

The chassis lid has two matching holes for those screw heads, which would ordinarily hold the two PCI cards in place. I could remove the clamp arm, but it doesn’t get in the way of anything.

I loves me some Sherline mill work…