Tek Circuit Computer: Sawed Hairline Fixture

This is a fixture to hold a cursor for an Homage Tektronix Circuit Computer while a tiny circular saw blade cuts a narrow flat-bottomed trench:

Tek CC - sawed cursor - Sherline setup
Tek CC – sawed cursor – Sherline setup

Each of the 123 blocks is held to the Sherline tooling plate with a 10-32 SHCS in a little aluminum pin, with another threaded pin for the screw holding the fixture on the side. The minimal top clearance provided some of the motivation behind making those pins in the first place; there’s no room for the usual threaded stud sticking out of the block with a handful of washers under the nut.

The fixture has locating slots (scribbled with black Sharpie) to touch off the spindle axis and the saw blade at the XZ origin at the pivot hole center. Touching off the saw blade on the cursor surface sets Y=0, although only a few teeth will go ting, so the saw must be spinning.

I cut the first slot under manual control to a depth of 0.3 mm on a scrap cursor with a grotty engraved hairline:

Tek CC - first sawed cursor - detail
Tek CC – first sawed cursor – detail

It looks better than I expected with some red lacquer crayon scribbled into it:

Tek CC - first sawed cursor - vs scribed
Tek CC – first sawed cursor – vs scribed

A few variations of speed and depth seem inconclusive, although they look more consistent and much smoother than the diamond-drag engraved line with red fill:

Tek CC - sawed cursor test - magnified
Tek CC – sawed cursor test – magnified

The saw produces a ramp at the entry and exit which I don’t like at all, but the cut is, overall, an improvement on the diamond point.

The OpenSCAD source code as a GitHub Gist:

// Sawing fixtures for Tek Circuit Computer cursor hairline
// Ed Nisley KE4ZNU Jan 2021
// Rotated 90° and screwed to 123 blocks for sawing
Layout = "Show"; // [Show, Build, Cursor]
Gap = 4.0;
/* [Hidden] */
ThreadThick = 0.25;
ThreadWidth = 0.40;
HoleWindage = 0.2;
Protrusion = 0.1; // make holes end cleanly
inch = 25.4;
function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);
module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes
Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);
FixDia = Dia / cos(180/Sides);
cylinder(d=(FixDia + HoleWindage),h=Height,$fn=Sides);
}
//----------------------
// Dimensions
CursorHubOD = 1.0*inch; // must match SVG hub OD
CursorThick = 0.71; // including protective layers
HairlineMin = 48.4188; // extent of hairline
HairlineMax = 97.4250;
HairlineDepth = 0.20;
PocketDepth = 0.75*CursorThick; // half above surface for taping
PocketClear = 0.25; // E-Z insertion clearance
TableOC = [1.16*inch,1.16*inch]; // Sherline tooling plate grid
BlockOC = [(9/16)*inch,(9/16)*inch]; // 123 block hole grid
BlockOffset = [(3/8)*inch,(3/8)*inch]; // .. block edge to hole center
ScrewClear = 5.0; // … screw clearance
CursorOffset = [2*BlockOC.x,0,0]; // hub center relative to leftmost screw
FixtureGrid = [5*TableOC.x,0,0]; // size in Table grid units
Screws = [ // relative to leftmost screw
[0,0,0], // on table grid
CursorOffset, // on block grid
[FixtureGrid.x,0,0] // on table grid
];
echo(str("Screw centers: ",Screws));
CornerRad = 10.0; // corner radius
Fixture = [2*CornerRad + FixtureGrid.x,2*CornerRad + CursorHubOD,5.0];
echo(str("Fixture plate: ",Fixture));
//----------------------
// Import SVG of cursor outline
// Requires our CursorHubOD to match actual cut outline
// Hub center at origin
module CursorSVG(t=CursorThick,ofs=0.0) {
hr = CursorHubOD/2;
translate([-hr,-hr,0])
linear_extrude(height=t,convexity=3)
offset(r=ofs)
import(
file="/mnt/bulkdata/Project Files/Tektronix Circuit Computer/Firmware/TekCC-Cursor-Mark.svg",
center=false);
}
//----------------------
// Show-n-Tell cursor
module Cursor() {
difference() {
CursorSVG(CursorThick,0.0);
translate([0,0,-Protrusion])
rotate(180/6)
PolyCyl(ScrewClear,CursorThick + 2*Protrusion,6);
}
}
//----------------------
// Sawing fixture for cursor hairline
// Plate center at origin
module Fixture() {
difference() {
hull() // basic plate shape
for (i=[-1,1], j=[-1,1])
translate([i*(Fixture.x/2 - CornerRad),j*(Fixture.y/2 - CornerRad),0])
cylinder(r=CornerRad,h=Fixture.z,$fn=24);
translate([0,0,Fixture.z - ThreadThick/2 + Protrusion/2]) // will be Z=0 index
cube([2*Fixture.x,ThreadWidth,ThreadThick + Protrusion],center=true);
translate(-FixtureGrid/2) {
translate(CursorOffset + [0,0,Fixture.z - 2*PocketDepth])
difference() {
CursorSVG(2*PocketDepth + Protrusion,PocketClear);
CursorSVG(PocketDepth + Protrusion,-PocketClear);
}
translate([CursorOffset.x,0,Fixture.z - ThreadThick/2 + Protrusion/2]) // will be front X=0 index
cube([ThreadWidth,2*Fixture.y,ThreadThick + Protrusion],center=true);
translate([CursorOffset.x,Fixture.y/2 - ThreadThick/2 + Protrusion/2,0]) // will be top X=0 index
cube([ThreadWidth,ThreadThick + Protrusion,2*Fixture.z],center=true);
translate([CursorOffset.x + HairlineMin,0,Fixture.z - ThreadThick/2 + Protrusion/2]) // hairline min
cube([ThreadWidth,2*Fixture.y,ThreadThick + Protrusion],center=true);
translate([CursorOffset.x + HairlineMax,0,Fixture.z - ThreadThick/2 + Protrusion/2]) // hairline min
cube([ThreadWidth,2*Fixture.y,ThreadThick + Protrusion],center=true);
/*
# translate(CursorOffset + [0,0,Fixture.z - 2*ThreadThick]) { // alignment pips
for (x=[-20.0,130.0], y=[-30.0,0.0,30.0])
translate([x,y,0])
cylinder(d=4*ThreadWidth,h=1,$fn=6);
# for (x=[-30.0,130.0,150.0])
translate([x,0,0])
cylinder(d=4*ThreadWidth,h=1,$fn=6);
*/
for (pt=Screws)
translate(pt + [0,0,-Protrusion])
rotate(180/6)
PolyCyl(ScrewClear,Fixture.z + 2*Protrusion,6);
}
}
}
//----------------------
// Build it
if (Layout == "Cursor") {
Cursor();
}
if (Layout == "Show") {
rotate([0*90,0,0]) {
Fixture();
color("Green",0.3)
translate(-FixtureGrid/2 + CursorOffset + [0,0,Fixture.z + Gap])
Cursor();
}
}
if (Layout == "Build"){
// rotate(90)
Fixture();
}

Tek Circuit Computer: Cursor Hairline

Given a machined cursor blank, clamp it into position:

Tek CC Cursor - cursor hairline fixture
Tek CC Cursor – cursor hairline fixture

You don’t want to clamp the cursor directly to the Sherline tooling plate, because the diamond drag bit would pass over two or three of those 10-32 screw holes which would, by the conservation of perversity, leave visible defects. In hindsight, I should have put a recess for an aluminum plate in there.

After a single pass at Z=-4.0 mm, add two strips of tape to protect the adjoining surface and scribble it with red lacquer crayon:

Tek CC Cursor - tape color fill
Tek CC Cursor – tape color fill

Peel the tape off:

Tek CC Cursor - tape removed
Tek CC Cursor – tape removed

Then wipe off the residue using a soft cloth wetted with denatured alcohol:

Tek CC Cursor - red cursor detail
Tek CC Cursor – red cursor detail

That looks much like the previous efforts. I’d like a more uniform trench, but I don’t know how to get there from here.

In any event, the hairline looks pretty good against laser-printed scales:

Tek CC Cursor - red cursor white laser decks - magnified
Tek CC Cursor – red cursor white laser decks – magnified

The new cursor is the lower one lying atop a laser-printed Pickett-style Circuit Computer:

Tek CC Cursor - red cursor yellow laser decks - overview
Tek CC Cursor – red cursor yellow laser decks – overview

Looks good enough to eat, as the saying goes …

Tek Circuit Computer: Cursor Milling Toolpath

Unlike the adhesive fixture, this setup requires a pause while milling the cursor outline to reclamp it from the front:

Tek CC Cursor Fixture - outline rear clamp
Tek CC Cursor Fixture – outline rear clamp

The trick is applying the front clamp before releasing the rear clamp:

Tek CC Cursor Fixture - outline both clamp
Tek CC Cursor Fixture – outline both clamp

Then continue the mission:

Tek CC Cursor Fixture - outline front clamp
Tek CC Cursor Fixture – outline front clamp

Because the tool path includes cutter compensation, GCMC adds entry and exit arcs to ensure a smooth transition:

Tek CC Cursor - Milling path
Tek CC Cursor – Milling path

The pix show a single cursor in the fixture while verifying the setup worked the way it should. Obviously, milling a stack of cursors eliminates a whole bunch of fiddling.

The tweaked MillCursor function from the mostly otherwise unchanged GCMC code:

    comment("Clamp on rear half of cursor!");

    local cp = {p0};                                             // enter at hub tangent point
    cp += varc_ccw([0mm,-2*p0.y,-],-hr,0,0.2mm,5deg) + p0;       // arc to tangent at hub bottom

    cp += {[p1.x,-p1.y,-]};                                      // lower tip entry point
    cp += varc_ccw([p2.x-p1.x,-(p2.y-p1.y),-],CursorTipRadius,0,0.2mm,5deg) + [p1.x,-p1.y,-];  // arc to tip exit at p2

    cp += varc_ccw([p1.x-p2.x,p1.y-p2.y,-],CursorTipRadius,0,0.2mm,5deg) + p2;  // arc to tip exit at p1

    goto([-,-,CursorSafeZ]);
    goto([0,0,-]);
    feedrate(MillSpeed);
    tracepath_comp(cp,CutterOD/2,TPC_OLDZ + TPC_RIGHT + TPC_ARCIN + TPC_ARCOUT);

    comment("Clamp on front half of cursor!");
    pause();                                      // wait for reclamping

    p1.z = MillZ;                                //  ... set milling depth
    cp = {p1};
    cp += {p0};
                                                 // exit at hub tangent
    tracepath_comp(cp,CutterOD/2,TPC_OLDZ + TPC_RIGHT + TPC_ARCIN + TPC_ARCOUT);

<<< snippage >>>

  goto([-,-,CursorSafeZ]);
  goto([0,0,-]);

Next, scribing a nice hairline with the new fixture.

Tek Circuit Computer: 3D Printed Cursor Milling Fixture

The original Tektronix Circuit Computer cursor was probably die-cut from a larger sheet carrying pre-printed hairlines:

Tek CC - genuine - detail
Tek CC – genuine – detail

Machining a punch-and-die setup lies well beyond my capabilities, particularly given the ahem anticipated volume, so milling seems the only practical way to produce a few cursors.

Attaching a cursor blank to a fixture with sticky tape showed that the general idea worked reasonably well:

Tek CC - Cursor blank on fixture
Tek CC – Cursor blank on fixture

However, the tape didn’t have quite enough griptivity to hold the edges completely flat against milling forces (a downcut bit might have worked better) and I found myself chasing the cutter with a screwdriver to hold the cursor in place. Worse, the tape’s powerful attraction to swarf made it a single-use item.

Some tinkering showed a single screw in the (pre-drilled) pivot hole, without adhesive underneath, lacked enough oomph to keep the far end of the cursor in place, which meant I had to think about how to hold it down with real clamps.

Which, of course, meant conjuring a fixture from the vasty digital deep. The solid model includes the baseplate, two cutting templates, and a clamping fixture for engraving the cursor hairline:

Cursor Fixture - build layout
Cursor Fixture – build layout

The perimeter of the Clamp template on the far left is 0.5 mm inside the cursor perimeter. Needing only one Clamp, I could trace it on a piece of acrylic, bandsaw it pretty close, introduce it to Mr Belt Sander for final shaping, and finally drill the hole:

Tek CC Cursor Fixture - clamp drilling
Tek CC Cursor Fixture – clamp drilling

The Rough template is 1.0 mm outside the cursor perimeter, so I can trace those outlines on a PET sheet:

Tek CC Cursor Fixture - Rough template layout
Tek CC Cursor Fixture – Rough template layout

Then cut the patterns with a scissors, stack ’em up, and tape the edges to keep them aligned:

TekCC Cursor Fixture - Rough template
TekCC Cursor Fixture – Rough template

Align the stack by feel, apply the Clamp to hold them in place, and secure the stack with a Sherline clamp:

Tek CC Cursor Fixture - outline rear clamp
Tek CC Cursor Fixture – outline rear clamp

The alert reader will note it’s no longer possible to machine the entire perimeter in one pass; more on that in a while.

The baseplate pretty much fills the entire Sherline tooling plate. It sports several alignment pips at known offsets from the origin at the center of the pivot hole:

Tek CC Cursor Fixture - touch-off point
Tek CC Cursor Fixture – touch-off point

Dropping the laser alignment dot into a convenient pip, then touching off X and Y to the known offset sets the origin without measuring anything. Four screws in the corners align the plate well enough to not worry about angular tweakage.

The OpenSCAD source code as a GitHub Gist:

// Machining fixtures for Tek Circuit Computer cursor
// Ed Nisley KE4ZNU Jan 2021
Layout = "Show"; // [Show, Build, Cursor, Clamp, Rough, Engrave]
/* [Hidden] */
ThreadThick = 0.25;
ThreadWidth = 0.40;
HoleWindage = 0.2;
Protrusion = 0.1; // make holes end cleanly
inch = 25.4;
function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);
module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes
Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);
FixDia = Dia / cos(180/Sides);
cylinder(d=(FixDia + HoleWindage),h=Height,$fn=Sides);
}
//----------------------
// Dimensions
CursorHubOD = 1.0*inch; // original Tek CC was hard inch!
CursorTipWidth = (9.0/16.0)*inch;
CursorTipRadius = (1.0/16.0)*inch;
CursorThick = 0.5; // plastic sheet thickness
CutterOD = 3.175; // milling cutter dia
CutterDepth = 2.0; // … depth of cut
CutterLip = 0.5; // … clearance under edge
ScribeOD = 3.0; // diamond scribe shank
StudOC = [1.16*inch,1.16*inch]; // Sherline tooling plate grid
StudClear = 5.0; // … screw clearance
StudWasher = 11.0; // … washer OD
CursorOffset = [-2*StudOC.x,0,0]; // hub center relative to fixture center
// must have even multiples of stud spacing to put studs along centerlines
BasePlateStuds = [6*StudOC.x,2*StudOC.y]; // fixture screws
echo(str("Stud spacing: ",StudOC));
CornerRad = 10.0; // corner radius
BasePlate = [2*StudWasher + BasePlateStuds.x,2*StudWasher + BasePlateStuds.y,5.0];
echo(str("Base Plate: ",BasePlate));
EngravePlate = [5*StudOC.x,1.5*StudOC.y,BasePlate.z];
echo(str("Engrave Plate: ",EngravePlate));
TemplateThick = 6*ThreadThick;
LegendThick = 2*ThreadThick;
Gap = 3.0;
//----------------------
// Import SVG of cursor outline
// Requires our hub OD to match reality
// Hub center at origin
module CursorSVG(t=CursorThick,od=0) {
hr = CursorHubOD/2;
translate([-hr,-hr,0])
linear_extrude(height=t,convexity=3)
offset(r=od/2)
import(file="/mnt/bulkdata/Project Files/Tektronix Circuit Computer/Firmware/TekCC-Cursor-Mark.svg",center=false);
}
//----------------------
// Milling fixture for cursor blanks
module Fixture() {
difference() {
hull() // basic plate shape
for (i=[-1,1], j=[-1,1])
translate([i*(BasePlate.x/2 - CornerRad),j*(BasePlate.y/2 - CornerRad),0])
cylinder(r=CornerRad,h=BasePlate.z,$fn=24);
translate(CursorOffset + [0,0,BasePlate.z - CutterDepth])
difference() {
CursorSVG(CutterDepth + Protrusion,1.5*CutterOD);
CursorSVG(CutterDepth + Protrusion,-CutterLip);
}
translate(CursorOffset + [0,0,BasePlate.z - 2*ThreadThick]) { // alignment pips
for (x=[-20.0,130.0], y=[-30.0,0.0,30.0])
translate([x,y,0])
cylinder(d=4*ThreadWidth,h=1,$fn=6);
for (x=[-30.0,130.0,150.0])
translate([x,0,0])
cylinder(d=4*ThreadWidth,h=1,$fn=6);
}
for (i=[-1,1], j=[-1,1]) // mounting stud holes
translate([i*BasePlateStuds.x/2,j*BasePlateStuds.y/2,-Protrusion])
rotate(180/6)
PolyCyl(StudClear,BasePlate.z + 2*Protrusion,6);
translate(CursorOffset + [0,0,-Protrusion]) // hub clamp hole
rotate(180/6)
PolyCyl(StudClear,BasePlate.z + 2*Protrusion,6);
translate([2*StudOC.x,0,-Protrusion]) // tip clamp hole
rotate(180/6)
PolyCyl(StudClear,BasePlate.z + 2*Protrusion,6);
for (i=[-2:2], j=[-1,1]) // side clamp holes
translate([i*StudOC.x,j*StudOC.y,-Protrusion])
rotate(180/6)
PolyCyl(StudClear,BasePlate.z + 2*Protrusion,6);
}
}
//----------------------
// Show-n-Tell cursor
module Cursor() {
difference() {
CursorSVG(CursorThick,0.0);
translate([0,0,-Protrusion])
rotate(180/6)
PolyCyl(StudClear,TemplateThick + 2*Protrusion,6);
}
}
//----------------------
// Template for rough-cutting blanks
module Rough() {
bb = [40,12,LegendThick];
difference() {
CursorSVG(TemplateThick,1.0);
translate([0,0,-Protrusion])
rotate(180/6)
PolyCyl(StudClear,TemplateThick + 2*Protrusion,6);
difference() {
translate([bb.x/2 + CursorHubOD/2,0,TemplateThick - bb.z/2 + Protrusion])
cube(bb + [0,0,Protrusion],center=true);
translate([bb.x/2 + CursorHubOD/2,0,TemplateThick - bb.z])
linear_extrude(height=bb.z,convexity=10)
text(text="Rough",size=7,spacing=1.00,font="DejaVu Sans:style:Bold",halign="center",valign="center");
}
}
}
//----------------------
// Template for aluminium clamping plate
module Clamp() {
bb = [40,12,LegendThick];
difference() {
CursorSVG(TemplateThick,-1.0);
translate([0,0,-Protrusion])
rotate(180/6)
PolyCyl(StudClear,TemplateThick + 2*Protrusion,6);
difference() {
translate([bb.x/2 + CursorHubOD/2,0,TemplateThick - bb.z/2 + Protrusion])
cube(bb + [0,0,Protrusion],center=true);
translate([bb.x/2 + CursorHubOD/2,0,TemplateThick - bb.z])
linear_extrude(height=bb.z,convexity=10)
text(text="Clamp",size=7,spacing=1.00,font="DejaVu Sans:style:Bold",halign="center",valign="center");
}
}
}
//----------------------
// Engraving clamp
module Engrave() {
difference() {
hull() // clamp outline
for (i=[-1,1], j=[-1,1])
translate([i*(EngravePlate.x/2 - CornerRad),j*(EngravePlate.y/2 - CornerRad),0])
cylinder(r=CornerRad,h=EngravePlate.z,$fn=24);
translate(CursorOffset + [0,0,-Protrusion])
CursorSVG(CursorThick + Protrusion,0.5); // pocket for blank cursor
translate(CursorOffset + [0,0,-Protrusion])
rotate(180/6)
PolyCyl(StudClear,EngravePlate.z + 2*Protrusion,6);
translate([2*StudOC.x,0,-Protrusion])
rotate(180/6)
PolyCyl(StudClear,EngravePlate.z + 2*Protrusion,6);
hull() {
for (i=[-1,1])
translate([i*1.5*StudOC.x,0,-Protrusion])
PolyCyl(2*ScribeOD,EngravePlate.z + 2*Protrusion,8);
}
}
}
//----------------------
// Build it
if (Layout == "Cursor") {
Cursor();
}
if (Layout == "Clamp") {
Clamp();
}
if (Layout == "Rough") {
Rough();
}
if (Layout == "Engrave") {
Engrave();
}
if (Layout == "Show") {
Fixture();
color("Green",0.3)
translate(CursorOffset + [0,0,BasePlate.z + Protrusion])
Cursor();
color("Orange")
translate(CursorOffset + [0,0,BasePlate.z + 10])
Rough();
color("Brown")
translate(CursorOffset + [0,0,BasePlate.z + 20])
Clamp();
color("Gold")
translate(0*CursorOffset + [0,0,BasePlate.z + 40])
Engrave();
}
if (Layout == "Build"){
rotate(90) {
Fixture();
translate([0,-((BasePlate.y + EngravePlate.y)/2 + Gap),EngravePlate.z])
rotate([180,0,0])
Engrave();
translate(CursorOffset + [0,(BasePlate.y + CursorHubOD)/2 + Gap,0])
Rough();
translate(CursorOffset + [0,(BasePlate.y + 3*CursorHubOD)/2 + 2*Gap,0])
Clamp();
}
}

The original doodle with some notions and dimensions that didn’t survive contact with reality:

Cursor Fixture doodle
Cursor Fixture doodle

I have no idea why the Sherline tooling plate has a 10-32 screw grid on 1.16 inch = 29.46 mm centers, but there they are.

Homage Tektronix Circuit Computer: Laser Printed Scales

Given the proper command-line options, GCMC can produce an SVG image and, after some Bash fiddling and a bank shot off Inkscape, the same GCMC program I’ve been using to plot Homage Tektronix Circuit Computer decks can produce laser-printed decks:

Tek CC - laser - detail
Tek CC – laser – detail

Pen-plotting on yellow Astrobrights paper showed how much ink bleeds on slightly porous paper, but laser-printing the same paper produces crisp lines:

Tek CC - laser - yellow detail
Tek CC – laser – yellow detail

Laser printing definitely feels like cheating, but, for comparison, here’s a Genuine Tektronix Circuit Computer:

Tek CC - genuine - detail
Tek CC – genuine – detail

Plotting the decks on hard mode was definitely a learning experience!

Obviously, my cursor engraving hand remains weak.

Tek Circuit Computer: Cursor Hairline Scraping

Engraving a PETG sheet with a diamond drag engraver on the Sherline and filling the scratch produces a good-looking hairline, but there’s a tradeoff between having the protective sheet pull the paint out of the scratch and having the crayon scuff the unprotected surface. This time around, I scribbled the crayon through the protective film, let it cure for a few days, then scraped the surface to level the paint and see what happens.

First, an unscraped cursor:

Tek CC - Cursor red lacquer - plain - overview
Tek CC – Cursor red lacquer – plain – overview

Peeling the transparent protective film:

Tek CC - Cursor red lacquer - plain - partial peel
Tek CC – Cursor red lacquer – plain – partial peel

The hairline is solidly filled:

Tek CC - Cursor red lacquer - plain - peeled
Tek CC – Cursor red lacquer – plain – peeled

Scribbling another cursor the same way, then scraping the protective film to flatten the shredded edges:

Tek CC - Cursor red lacquer - scraped - overview
Tek CC – Cursor red lacquer – scraped – overview

The hairline remains filled, but not as completely:

Tek CC - Cursor red lacquer - scraped - partial peel
Tek CC – Cursor red lacquer – scraped – partial peel

A closer look:

Tek CC - Cursor red lacquer - scraped - peeled
Tek CC – Cursor red lacquer – scraped – peeled

Scraping the crayon off the film removes a substantial amount of paint from the hairline, but, on the upside, the protective film does exactly what it says on the box and the PETG surface remains pristine.

Both hairlines are, at least eyeballometrically, Just Fine™ for their intended purpose.

Tek Circuit Computer: Water Test

So the question came up: “Exactly what happens when one of those things gets wet?”

Which obviously requires an experiment:

Laminated Tek CC vs Water - start
Laminated Tek CC vs Water – start

That’s the mis-cut top deck revealing why GRBL really needs four digits after the decimal point, but, other than that, it’s perfectly representative of the genre: heavy paper, good ink, nicely laminated in plastic.

Prediction: water should seep into the paper, dissolve the ink, maybe delaminate the plastic, and generally make a mess.

Which is exactly what happens:

Laminated Tek CC vs Water - finish
Laminated Tek CC vs Water – finish

User Advisory: your shiny new Homage Tektronix Circuit Computer is not waterproof, so don’t use it in the sauna!