Posts Tagged Sherline

Monthly Science: Hard Drive Mood Light Thermal Coefficient

Having that knockoff Neopixel fail from overheating prompted me to measure what was going on. Because the LEDs sink most of their heat into the package leads, the back of the LED strip should be the hottest part of the package and the Mood Light’s central pillar should be pretty nearly isothermal. Despite that, I figured I should measure the temperature closer to the back of the strip, sooo I drilled a hole for the thermocouple…

Clamp the whole Mood Light to the Sherline’s tooling plate with the pillar sides mostly square to the axes and line up the spindle 2 mm behind the LED strip:

Mood Light - aligning thermocouple hole

Mood Light – aligning thermocouple hole

The two clamp pads are CD chunks, under just enough pressure to anchor the Mood Light.

Screw the cap in place (to match-drill both holes at once) and drill a 2 mm (#46, close enough) hole down past the top LED:

Mood Light - drilling thermocouple hole

Mood Light – drilling thermocouple hole

I tucked the Mood Light into a box to ward off breezes, jammed one thermocouple into the new hole, let another float over the top platter, then forced the Neopixels to display constant grayscale PWM values (R=G=B) while recording the LED and air temperatures every five minutes:

Hard Drive Mood Light - temp vs power data

Hard Drive Mood Light – temp vs power data

That was easier and faster than screwing around with automated data collection. The data has some glaring gaps where I went off to do other things during the day.

I turned those numbers into a graph, printed it out, puzzled over it for a bit, then annotated it with useful numbers:

Hard Drive Mood Light - temp vs power data - graph

Hard Drive Mood Light – temp vs power data – graph

That first little blip over on the left comes from a minute or two at PWM 32; the cooling time constant works out to be a bit under 10 minutes. The warming time constant looks to be somewhat longer, but not by much.

Eyeballing the endpoint temperatures for each PWM value, feeding in the current measurements, and creating a small table:

VCC 5 V
Current 0.057 A
Package 0.285 W
Total 3.42 W
PWM Duty Nom Power Failed LEDs Net Power °C Rise
0 0.00 0.00 0 0.00 0
32 0.13 0.43 0 0.43 6
64 0.25 0.86 0 0.86 12
85 0.33 1.14 1 1.04 16
128 0.50 1.71 1 1.62 24
192 0.75 2.57 1 2.47 35
255 1.00 3.41 4 3.03 42

The same blue LED that failed earlier dropped out again, plus another package (on a different strip) went completely dark shortly after I clobbered the LEDs with full power at PWM 255. The Net Power column deducts the power not used by the failed LEDs, under the reasonable assumption that the total heating depends on the number of active LEDs.

All the failed LEDs worked fine when they cooled to room temperature, so, whatever the failure mode might be, it’s not permanent. The skimpy WS2812B datasheet says bupkis about a protective thermal shutdown circuit, although it specs an 80 °C maximum operating junction temperature. I’ll stipulate a 20 °C temperature difference from junction to thermocouple at PWM 255, but that doesn’t explain the first blue LED failure at PWM 85.

Methinks these knockoffs will be much happier operating in the mid-30s.

Turning the last two columns of that table into a graph (minus the PWM 0 line to let the intercept float around) looks like I’m faking it:

Hard Drive Mood Light - Temperature vs Power

Hard Drive Mood Light – Temperature vs Power

The Y intercept is off by less than 1 °C, which seems pretty good under the circumstances. The  kink at PWM 85 shows that I probably didn’t allow enough time for the temperature to stabilize after the blue LED failed.

So, in round numbers, the thermal coefficient for a dozen knockoff Neopixels on a plastic pillar inside a stack of hard drive platters works out to 14 °C/W.

The raised sine waves in the Mood Light produce a long-term average PWM half of their maximum PWM. They’ve been perfectly happy with MaxPWM = 64 pushing them barely 6 °C over ambient, so they should continue to work fine at PWM 128 for a 12 °C rise… except, perhaps, during the hottest of mid-summer days.

Obviously, I should jam a thermistor inside the column and have the Arduino wrap a feedback loop around the column temperature…

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Ham It Up Noise Source Enable Switch

Some rummaging produced a tiny DPDT switch that actually fit the holes intended for a pin header on the recently arrived Ham It Up board, at least after I amputated 2/3 of the poor thing’s legs:

Ham-It-Up - noise source switch - B

Ham-It-Up – noise source switch – B

The new SMA noise output jack sits in the front left, with the white “noise on” LED just left of the switch:

Ham-It-Up - noise source switch - A

Ham-It-Up – noise source switch – A

There’s no way to measure these things accurately, at least as far as I can tell, but the holes came out pretty close to where they should be. The new SMA connector lined up horizontally with the existing IF output jack and vertically with the measured / rounded-to-the-nearest-millimeter on-center distance:

Ham It Up - noise SMA drilling

Ham It Up – noise SMA drilling

The Enable switch doesn’t quite line up with the LED, so the holes will always look like I screwed up:

Ham-It-Up - noise source switch - case holes

Ham-It-Up – noise source switch – case holes

That’s OK, nobody will ever notice.

Now, to stack up enough adapters to get from the SMA on the Ham It Up board to the N connector on the spectrum analyzer …

 

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Epoxy-filled 3D Printed Characters

Although Mary’s name in the base of the Clover Mini Iron holder was readable in person, I wondered what filling the characters with epoxy would do. A bit of tinkering produced a name plate:

Text Block - solid model

Text Block – solid model

Which is more readable in person, but magenta PETG renders it basically unreadable here:

Text Block - unfilled

Text Block – unfilled

The intent of this was not to produce a lovely name block, but to see what various epoxy fills and techniques produced. Think of this as the one you must build to throw away…

I tediously filled the first line with straight JB Weld epoxy, deliberately ruining the least functional of my 1 ml syringes to ease a strand of epoxy into each letter, then poking the goo into place with a pointed rod:

Text Block - plain epoxy fill

Text Block – plain epoxy fill

That was way tedious.

Having recently replaced the cartridge in our trusty HP Laserjet 1200, I had no qualms about step-drilling the “empty” cartridge to get the toner. For future reference, here’s where you drill into a 7115X cartridge:

HP 7115X Toner Cartridge - holes in waste and supply compartments

HP 7115X Toner Cartridge – holes in waste and supply compartments

I probably used too much toner, but one heaping pile on that wooden stick didn’t seem like a lot at the time:

Text Block - toner black epoxy

Text Block – toner black epoxy

This turned the epoxy rather thick and pasty; it didn’t ease into the letters very well at all. After the usual day, it cured into a slightly rubbery solid, quite unlike the usual rock-solid epoxy blob.

Some rummaging in the Basement Laboratory Warehouse Wing turned up two containers of aluminum powder from an Etch-a-Sketch; I mixed some into another batch of epoxy, to very little effect. With both blends, I just squished the epoxy into the letters and didn’t worry too much about slobbering any over the surface of the block.

To even off the top surface, I affixed the block to the Sherline’s tooling plate with tapeless sticky (basically double-sided tape without the tape):

Text Block - milling setup

Text Block – milling setup

Manually traversing the surface (3 k rpm, 24 inch/min) and stepping downward about 0.1 mm per pass gradually crisped up the letters. I expected the excess epoxy to vanish after going 0.1 mm or so into the top layer, but it actually required removing the entire 0.25 mm Hilbert-curve-filled surface layer to get rid of the epoxy that soaked into / through the tiny gaps. This is 0.4 mm down from the first pass, maybe 0.1 mm into the plastic:

Text Block - milled 0.4 mm

Text Block – milled 0.4 mm

With the top layer gone, it looked rather gnarly, so I applied a sanding block that didn’t do much at all: smoother, still gnarly. Spreading maybe 0.3 ml of IPS 4 solvent adhesive over the sanded surface smoothed it a bit:

Text Block - sanded and leveled with IPS 4

Text Block – sanded and leveled with IPS 4

Perhaps a topcoat of clear epoxy, along the lines of XTC-3D, would produce better results.

The small black dots in the top line are holes from bubbles in the epoxy. The missing section of the M started out as a bubble (just visible at 0.4 mm) and gradually enlarged as pieces tore out of the recess. There’s another bubble breaking the right stroke of the “y”.

The small dots in the “ley” are plastic spheres that carried the aluminum powder in the Etch-a-Sketch; they’re cross-sectioned and perfectly flat. The epoxy color is marginally lighter than the top line, but not enough to notice.

Backlit on a window, nearly all of the ugly fades away:

Text Block - backlit

Text Block – backlit

It’s definitely not presentation quality, that’s for sure, and I won’t attempt to fill the Mini Iron holder…

The OpenSCAD source code, which can also produce the soldering iron holder:

// Clover MCI-900 Mini Iron holder
// Ed Nisley KE4ZNU - August 2015

Layout = "Text";					// Iron Holder Show Text

//- Extrusion parameters - must match reality!

ThreadThick = 0.25;
ThreadWidth = 0.40;

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

Protrusion = 0.1;

HoleWindage = 0.2;

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;
Washer10_32OD = 0.381 * inch;
Washer10_32ID = 0.204 * inch;

//------
// Dimensions

CornerRadius = 4.0;

CenterHeight = 25;							// center at cord inlet on body

BodyLength = 110;							// cord inlet to body curve at front flange

Incline = 10;								// central angle slope

FrontOD = 29;
FrontBlock = [20,1.5*FrontOD + 2*CornerRadius,FrontOD/2 + CenterHeight + BodyLength*sin(Incline)];

CordOD = 10;
CordLen = 10;

RearOD = 22;
RearBlock = [15 + CordLen,1.5*RearOD + 2*CornerRadius,RearOD/2 + CenterHeight];

PlateWidth = 2*FrontBlock[1];

TextDepth = 4*ThreadThick;

ScrewOC = BodyLength - FrontBlock[0]/2;
ScrewDepth = CenterHeight - FrontOD/2 - 5;

echo(str("Screw OC: ",ScrewOC));

BuildSize = [200,250,200];					// largest possible thing

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);
}

// Trim bottom from child object

module TrimBottom(BlockSize=BuildSize,Slice=CornerRadius) {
	
	intersection() {
		translate([0,0,BlockSize[2]/2])
			cube(BlockSize,center=true);
		translate([0,0,-Slice])
			children();
	}
}

// Build a rounded block-like thing

module RoundBlock(Size=[20,25,30],Radius=CornerRadius,Center=false) {
	
	HS = Size/2 - [Radius,Radius,Radius];
	translate([0,0,Center ? 0 : (HS[2] + Radius)])
	hull() {
		for (i=[-1,1], j=[-1,1], k=[-1,1]) {
			translate([i*HS[0],j*HS[1],k*HS[2]])
				sphere(r=Radius,$fn=4*4);
		}
	}
}

// Create a channel to hold something
// This will eventually be subtracted from a block
// The offsets are specialized for this application...

module Channel(Dia,Length) {
	
	rotate([0,90,0])
		linear_extrude(height=Length)
			rotate(90)
				hull() {
					for (i=[-1,1])
						translate([i*Dia,2*Dia])
							circle(d=Dia/8);
					circle(d=Dia,$fn=8*4);
				}
}

// Iron-shaped series of channels to be removed from blocks

module IronCutout() {

	union() {
		translate([-2*CordLen,0,0])
			Channel(CordOD,2*CordLen + Protrusion);
		Channel(RearOD,RearBlock[0] + Protrusion);
		translate([BodyLength - FrontBlock[0]/2 - FrontBlock[0],0,0])
			Channel(FrontOD,2*FrontBlock[0]);

	}
	
}

module TextBlock() {
	translate([2,10,0])
		linear_extrude(height=TextDepth + Protrusion,convexity=2)		// rendering glitches for convexity > 1
//			text("Mary",font="Ubuntu:style=Bold Italic",halign="center",valign="center");
			text("Mary",font="Junicode:style=Bold Italic",halign="center",valign="center",size=20,spacing=1.05);
			
	translate([2,-15,0])
		linear_extrude(height=TextDepth + Protrusion,convexity=2)
			text("Nisley",font="Junicode:style=Bold Italic",halign="center",valign="center",size=20,spacing=1.05);
	
}

//- Build it

if (Layout == "Iron")
	IronCutout();

if (Layout == "Holder" || Layout == "Show")
	difference() {
		union() {
			translate([(BodyLength + CordLen)/2 - CordLen,0,0])
				TrimBottom()
					RoundBlock(Size=[(CordLen + BodyLength),PlateWidth,CornerRadius]);

			translate([(RearBlock[0]/2 - CordLen),0,0])
				TrimBottom()
					RoundBlock(Size=RearBlock);

			translate([BodyLength - FrontBlock[0]/2,0,0]) {
				TrimBottom()
					RoundBlock(Size=FrontBlock);
			}
		}
		
		translate([0,0,CenterHeight])
			rotate([0,-Incline,0])
				if (Layout == "Show")
#					IronCutout();
				else
					IronCutout();
		
		translate([0,0,-Protrusion])
			PolyCyl(Tap10_32,ScrewDepth + Protrusion,6);
			
		translate([ScrewOC,0,-Protrusion])
			PolyCyl(Tap10_32,ScrewDepth + Protrusion,6);

		translate([(RearBlock[0] - CordLen) + BodyLength/2 - FrontBlock[0],0,CornerRadius - TextDepth])
			TextBlock();
		
	}
	
if (Layout == "Text")
	difference() {
		translate([0,0,0])
			TrimBottom(Slice=8*ThreadThick)
				RoundBlock(Size=[80,65,8*ThreadThick],Radius=8*ThreadThick);
#		translate([-2,2,8*ThreadThick - TextDepth])
			TextBlock();

	}

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Stereo Zoom Microscope: USB Camera Mount

My stereo zoom microscope neatly filled the entrance pupil of the late, lamented Casio EX-Z850, so that a simple adapter holding it on the eyepiece produced credible images:

Thinwall open boxes - side detail - 4.98 4.85 measured

Thinwall open boxes – side detail – 4.98 4.85 measured

Alas, the shutter failed after that image, leaving me with pictures untaken and naught to take them with.

The least-awful alternative seems to be gimmicking up an adapter for a small USB camera from the usual eBay source:

Fashion USB video - case vs camera

Fashion USB video – case vs camera

The camera’s 640×480 VGA resolution is marginally Good Enough for the purpose, as I can zoom the microscope to completely fill all those pixels. The optics aren’t up to the standard set by the microscope, but we can cope with that for a while.

A bit of doodling & OpenSCAD tinkering produced a suitable adapter:

USB Camera Microscope Mount - solid model

USB Camera Microscope Mount – solid model

To which Slic3r applied the usual finishing touches:

USB Camera Microscope Mount - Slic3r preview

USB Camera Microscope Mount – Slic3r preview

A bit of silicone tape holds the sloppy focusing thread in place:

USB Camera Microscope Mount - cap with camera

USB Camera Microscope Mount – cap with camera

Those are 2-56 screws that will hold the cap onto the tube. I drilled out the clearance holes in the cap and tapped the holes in the eyepiece adapter by hand, grabbing the bits with a pin vise.

Focus the lens at infinity, which in this case meant an old DDJ cover poster on the far wall of the Basement Laboratory, and then it’ll be just as happy with the image coming out of the eyepiece as a human eyeball would be.

I put a few snippets of black electrical tape atop the PCB locating tabs before screwing the tube in place. The tube ID is 1 mm smaller than the PCB OD, in order to hold the PCB perpendicular to the optical axis and clamp it firmly in place. Come to find out that the optical axis of the lens isn’t perfectly perpendicular to the PCB, but it’s close enough for my simple needs.

And then it fits just like you’d expect:

USB Camera Microscope Mount - on eyepiece

USB Camera Microscope Mount – on eyepiece

Actually, that’s the second version. The distance from the camera lens (equivalently: the PCB below the optical block, which I used as the datum plane) to the eyepiece is a critical dimension that determines whether the image fills the entrance pupil. I guesstimated the first version by hand-holding the camera and measuring with a caliper, tried it out, then iteratively whacked 2 mm off the tube until the image lit up properly:

USB Camera Microscope Mount - adjusting tube length

USB Camera Microscope Mount – adjusting tube length

Minus 4 mm made it slightly too short, but then I could measure the correct position, tweak that dimension in the code, and get another adapter, just like the first one (plus a few other minor changes), except that it worked:

USB Camera Microscope Mount - first light

USB Camera Microscope Mount – first light

That’s a screen capture from VLC, which plays from /dev/video0 perfectly. Some manual exposure & color balance adjustment may be in order, but it’s pretty good for First Light.

It turns out that removing the eyepiece and holding the bare sensor over the opening also works fine. The real image from the objective fills much more area than the camera’s tiny sensor: the video image covers about one digit in that picture, but gimmicking up a bare-sensor adapter might be useful.

The OpenSCAD source code:

// USB Camera mount for Microscope Eyepiece
// Ed Nisley KE4ZNU - August 2015

Layout = "Build";                    // Show Build Mount Cap

//-------
//- Extrusion parameters must match reality!
//  Print with 2 shells

ThreadThick = 0.25;
ThreadWidth = 0.40;

HoleWindage = 0.2;

Protrusion = 0.1;           // make holes end cleanly

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

inch = 25.4;

Tap2_56 = 0.070 * inch;
Clear2_56 = 0.082 * inch;
Head2_56 = 0.156 * inch;
Head2_56Thick = 0.055 * inch;
Nut2_56Dia = 0.204 * inch;
Nut2_56Thick = 0.065 * inch;
Washer2_56OD = 0.200 * inch;
Washer2_56ID = 0.095 * inch;

BuildGap = 5.0;

//-------
// Dimensions

//-- Camera

PCBThick = 1.1;
PCBDia = 24.5;
PCBClampDia = 23.0;

KeySize = [IntegerMultiple(27.6,ThreadWidth),IntegerMultiple(9.5,ThreadWidth),IntegerMultiple(PCBThick,ThreadThick)];
KeyOffset = [0.0,1.5,0];

CameraOffset = 22.3;                    // distance from eyepiece to camera PCB

WallThick = 4.0;

EyePieceOD = 30.0;
EyePieceLen = 30.0;

BodyOD = EyePieceOD + 2*WallThick;
BodyLen = CameraOffset + EyePieceLen - 5.0;

echo(str("Body length: ",BodyLen));

CapSocket = 10;
CapLen = CapSocket + WallThick;
CableOD = 3.7;

echo(str("Cap length: ",CapLen));


echo(str("Total length: ",BodyLen + CapLen));

NumScrews = 4;
ScrewAngle = 45;

NumSides = 6*4;

//-------

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);
}


//-------
// Components

module LensMount() {
    
    difference() {
        cylinder(d=BodyOD,h=BodyLen,$fn=NumSides);
        translate([0,0,CameraOffset])
            PolyCyl(EyePieceOD,EyePieceLen,NumSides);
        translate([0,0,-Protrusion])
            PolyCyl(PCBClampDia,(BodyLen + 2*Protrusion),NumSides);
        for (i=[0:NumScrews-1])
            rotate(ScrewAngle + i*360/NumScrews)
                translate([(BodyOD/2 - 1.5*Head2_56/2),0,-Protrusion])
                    rotate(180/4)
                        PolyCyl(Tap2_56,10.0,4);
    }
}

module CamCap() {
    difference() {
        cylinder(d=BodyOD,h=CapLen,$fn=NumSides);
        translate([0,0,WallThick])
            PolyCyl(PCBDia,CapLen,NumSides);
        translate(KeyOffset + [0,0,(CapLen - KeySize[2]/2 + Protrusion/2)])
            cube((KeySize + [0,0,Protrusion]),center=true);
        if (false)
            translate([0,0,-Protrusion])
                PolyCyl(CableOD,CapLen,8);
        else
            translate([0,BodyOD/2,(CapLen - CableOD/2 + Protrusion/2)])
                rotate([90,0,0])
                    cube([CableOD,(CableOD + Protrusion),BodyOD],center=true);
        for (i=[0:NumScrews-1])
            rotate(ScrewAngle + i*360/NumScrews)
                translate([(BodyOD/2 - 1.5*Head2_56/2),0,-Protrusion])
                    rotate(180/4)
                        PolyCyl(Clear2_56,(CapLen + 2*Protrusion),4);
        
    }
}

//-------
// Build it!

if (Layout == "Mount")
    LensMount();

if (Layout == "Cap")
    CamCap();

if (Layout == "Show") {
    CamCap();
    translate([0,0,CapLen + 5])
        LensMount();
}
if (Layout == "Build") {
    translate([-(BodyOD/2 + BuildGap),0,0])
        CamCap();
        translate([(BodyOD/2 + BuildGap),0,0])
        LensMount();
}

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DC Motor Mounting Plate

The Squidwrench Power Wheels Racer needed a mounting bracket for its DC motor, so Matt handed me a precut steel slab and some drawings. I did a manual layout to get a feel for the sizes:

Motor Mount - dye layout

Motor Mount – dye layout

Yes, it’s slightly rhomboid & irregular on the sides; it’ll be welded to a U-channel. The front edge is the straightest and I scribed a perpendicular datum line over on the right, from which to measure the motor center point.

But then, realizing I’d have to mill the central hole anyway, I did what I should have done from the beginning and lined it up on the Sherline:

Motor Mount - Sherline laser centering

Motor Mount – Sherline laser centering

With the part zeroed at the center, everything has polar coordinates. The bolt holes are #10 on a 50 mm BCD, which is G0 @25^[45+90*i]. Rather than writing & debugging a program, I did it all by feeding manual instructions into the interpreter; the i gets typed as 0, 1, 2, and 3 by clicking on a previous command, backspacing, and retyping, which is both faster and easier than it sounds. The holes are drill cycles: G81 Z-7 R1 F30

This being steel on a Sherline, the rule of thumb that says you can drill at 100x the drill diameter (in inch/min or mm/min, as appropriate) at 3000 RPM gets derated by at least factor of 10. I settled on 30 mm/min for a #10 drill (0.194 inch = 4.9 mm → 500 mm/min = hogwash) after trying the first hole at 50 mm/min:

Motor Mount - bolt holes

Motor Mount – bolt holes

The least horrible way to cut out the hole for the motor mounting boss involved chain drilling to excavate the most steel with the least effort. These center drill points are at G0 @14 ^[15*i] with i in [0..23]:

Motor Mount - chain center drilling

Motor Mount – chain center drilling

I drilled every even hole #27, then every odd hole #28, both at 50 mm/min, to get a thin web:

Motor Mount - chain drilled

Motor Mount – chain drilled

Then helix-mill downward with a 1/8 inch end mill at 1 mm per pass:

Motor Mount - helix milling

Motor Mount – helix milling

That started at 14 mm from the origin to match the hole circle: G3 I-14 F100 Z-1

Then I switched to a 3/8 inch = 9.5 mm end mill to bring the hole up to size, ending with G3 I-12.75 F300

Motor Mount - center hole milled

Motor Mount – center hole milled

A trial fit showed the hole was slightly off-round, probably due to a few mils of backlash in both axes, and slightly too small, because that’s how I wanted it. Flipped back-to-front, reclamped, recentered, ran the cutter around at 12.75 mm to clear the ovalness, then crept out to 12.8 mm, and it was all good:

Motor Mount - test fit

Motor Mount – test fit

That’s an easy fit with maybe 0.1 mm = 4 mil radial play around the boss. Better than that, I cannot do.

Lacquer thinner stripped the layout dye and it’s ready for welding:

Motor Mount - with motor

Motor Mount – with motor

Reminders for next time…

The drill feed on a rigid machine with plenty of spindle power is 100 x (drill dia) @ 3000 RPM. On the Sherline, in steel, 10 x dia is optimistic. Aluminum feeds run higher, but don’t get stupid.

Re-centering to the accuracy required for this job is a matter of noting the coordinates where the cutter kisses the perimeter across a diameter along each axis, adding the coordinates, dividing by two, moving to that position, and zeroing the origin. Do that in X, Y, X, and Y and it’s good enough. You could automate that with a touch probe, of course. Hand-turning the spindle with the cutter in place to feel it kiss the workpiece is fine, but use the same cutting edge on both sides of the diameter.

Figure the chain drill diameter thusly:

  • Pick a reasonable drill diameter; #10 is about as large as you want on a Sherline
  • Drill circle dia = final milled hole diameter – drill dia – 2 mm, round down to lower integer
  • # holes = π x DCD / drill dia, rounded down to lower integer
  • Hole angle = 360 / # holes
  • Hole radius = DCD / 2

Wisely is it written that a man with a CNC milling machine has many friends.

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Sony HDR-AS30V: AKA-SF1 Skeleton Frame Latch Repair

My Sony HDR-AS30V is an action camera, but requires an external case / frame to mount it on anything. Here’s the camera inside its AKA-SF1 Skeleton Frame atop my helmet:

Sony HDR-AS30V camera on bike helmet - inverted

Sony HDR-AS30V camera on bike helmet – inverted

Four 1 mm tall ramps on the inside of the black base (the part just above the yellow sled) snap into 2.6 mm square sockets in the skeleton frame surrounding the camera. For an unknown reason(s) that surely involves applying forces I don’t remember, an opposing pair of those ramps broke off, leaving the other pair to loosely hold one end of the camera in place.

In this picture, the left ramps (one visible) are missing, leaving a square-ish gray scar that’s nearly indistinguishable from the reflection on the intact ramp on the right:

Sony HDR-AS30V Skeleton Mount - broken latch ramps

Sony HDR-AS30V Skeleton Mount – broken latch ramps

Surprisingly, the round head of a brass 0-80 machine screw fits neatly inside the square socket on the frame; they’re a bit more than 1 mm deep. The approach ramps visible below the sockets guide the latches on the base:

Sony HDR-AS30V Skeleton Mount - frame sockets

Sony HDR-AS30V Skeleton Mount – frame sockets

So I figured I could just shave off the remaining two latch ramps, drill four holes at the proper spots, and replace the plastic ramps with metal screws.

I clamped the skeleton frame to the Sherline’s tooling plate, aligned it parallel to the X axis, put the laser spot dead center in the square socket, then snapped the base onto the frame. The laser spot shows where the drill will hit:

Sony HDR-AS30V Skeleton Mount - laser hole alignment

Sony HDR-AS30V Skeleton Mount – laser hole alignment

A carbide drill did the honors:

Sony HDR-AS30V Skeleton Mount - 0-80 hole drilling

Sony HDR-AS30V Skeleton Mount – 0-80 hole drilling

That’s a #55 = 0.0520 hole for 50% thread, rather than the proper 3/64 = 0.0469 hole for 75% thread, because that’s the closest short carbide drill I had; an ordinary steel twist drill, even in the screw-machine length I use on the Sherline, would probably scamper away. The hole isn’t quite on the sloped bottom edge of the base, but it’s pretty close.

The first hole didn’t emerge quite in the center of its ramp scar:

Sony HDR-AS30V Skeleton Mount - hole position - interior

Sony HDR-AS30V Skeleton Mount – hole position – interior

Which made sense after I thought about it: the ramp tapers to nothing in the direction of the offset, so the hole actually was in the middle of the matching socket.

Threading the holes required nothing more than finger-spinning an 0-80 tap:

Sony HDR-AS30V Skeleton Mount - tapping 0-80

Sony HDR-AS30V Skeleton Mount – tapping 0-80

The feeble thread engagement didn’t matter, because those mysterious tabs-with-slots (possibly for tie-down strings?) just above the holes were a perfect fit for 0-80 brass nuts:

Sony HDR-AS30V Skeleton Mount - reassembled

Sony HDR-AS30V Skeleton Mount – reassembled

The screw heads extend into the sockets, hold the frame solidly in the base, and make it impossible to pull out. Although the frame still slides / snaps into the base, that seems like it will wear out the sockets in fairly short order, so I’ll unlatch the frame (with the yellow slide latch on top), open it up, ease it into position, and then latch it in place. That was the only way to remove it from the original latches, so it’s not a big deal.

I should add a drop of epoxy to each of those nuts and perhaps fill the screw slots with epoxy to keep them from abrading the plastic inside the sockets. Maybe a dab of epoxy on the heads, followed by latching the frame in place, would form four square pegs to exactly fill the sockets.

This was a straightforward repair that should not have been necessary…

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HP7475A Plotter: Never Throw Anything Out

Our Larval Engineer stopped by, on her way to a half-year co-op job out around Route 128, and devoted a few days to merge-sorting / triaging her possessions. Having shown her the HP 74754A plotter project, she later dropped a bag o’ stuff on my desk without comment:

HP7475A - My old pens racks doodles

HP7475A – My old pens racks doodles

The perforated pen holder stuck to the plotter case (hey, it would still fit!) in front of the carousel with a bit of foam tape on an angled bracket you can’t quite see. It held 15 pens at the ready: I really used that plotter.

The doodle on the yellow sheet sketches a bulky adapter between the spindle nose thread on the Sherline CNC mill and a plotter cartridge. The flange-less pen body might just fit into the spindle bore, but I remember concluding that machining pen bodies or adapters wasn’t worth the effort. Now it’s a simple matter of some OpenSCAD source code and a few hours of hands-off production, so perhaps I should re-think that.

No dates on anything, but I got the Sherline in 2004. The pen holder probably dates back to the late 80s, shortly after I got the plotter. Most likely, I gave her the bag o’ stuff and told her to make something interesting; it could still happen…

 

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