Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
That image has desaturated red to suppress the camera’s red burnout. It looks better in the realm of pure math:
Planetary Gear Bearing – Kurled – solid model
Reducing the tolerance parameter to 0.4 produced a surprisingly rigid, yet freely turning, bearing that required no cleanup: it popped off the plate ready to roll!
The heavy lifting in the OpenSCAD source code remains emmitt’s work. I replaced the outer cylinder with a knurl and simplified his monogram to stand out better amid the diamonds. This is the affected section:
Santa delivered a pair of helmets that will require mirror mounts and a mic boom before the spring riding season kicks in. The visor has tabs that snap into sockets on each side of the helmet:
Bell Helmet Visor Mount – socket
It occurred to me that I could make an interposer between the helmet and the visor that could anchor the mic boom, with a tab for the helmet and a socket of some sort for the visor. While that’s still on the to-do list, the tab looks like this:
Bell Helmet Visor Mount
Those are 1 mm cubes on 10 mm centers, so this is a teeny little thing.
I don’t have a good idea for the corresponding socket, because those little grippers seem much too small for 3D printing, but now I have some tabs to play with:
Bell Helmet Visor Mount – OEM vs 3D Printed
The OpenSCAD source code puts the tab atop an oval base plate, but it’ll eventually stick out of the boom mount:
Turns out that I managed to crunch it, exactly as I expected: I’d added a block to the Z-axis stage that poked the home switch just slightly before the anti-backlash nut unscrewed from the top of the leadscrew, but the stage could continue moving another few millimeters.
You can see the gap just above the brass anti-backlash nut:
Sherline Z-axis leadscrew nut – top end
At that point, the nut has barely a single micro-smidgen of thread engaged; that last 0.1340 inch of travel (yeah, I measured it) isn’t usable.
Rather than put a collar around the end of the leadscrew, I opted for a brute-force block atop the Z-axis saddle nut that will slam into the bottom of the stepper motor mount just before the anti-backlash nut disengages:
Sherline Z-axis Overrun Block – rear view
A strip of tapeless sticky (double-sided tape, minus the tape) holds the block in place on the saddle nut. It’s not subject to any particular stress: as long as it doesn’t fall off, it’s all good.
I ran the stage upward until it stalled, then epoxied a new switch (with the old fluorescent tape) in place. This shows the result after backing the stage down a few millimeters:
Sherline Z-axis Overrun Block – side view
The solid model shows off the bevel that provides a bit more room for anti-backlash nut adjustment, not that I ever adjust it that much:
Sherline Z-Axis Overrun Prevention Block – solid model
Obviously, it doesn’t print in that position, but it’s easier to design it in the natural orientation and flip it around for printing.
The OpenSCAD source code:
// Sherline Z-axis Overrun Prevention Block
// Ed Nisley KE4ZNU December 2013
Layout = "Show"; // Show Build
//- Extrusion parameters must match reality!
// Print with 2 shells and 3 solid layers
ThreadThick = 0.25;
ThreadWidth = 0.40;
HoleWindage = 0.2;
Protrusion = 0.1; // make holes end cleanly
//----------------------
// Dimensions
BlockZ = 30.0; // overall height
ZLimit = 17.0; // Z travel limit
TongueX = 9.0; // beside Z axis dovetail
TongueY = 10.0;
StubX = 6.0; // behind Z axis pillar
StubY = 3.0;
BlockX = TongueX + StubX; // overall X
TabY = 3.0; // behind brass bracket
TabX = BlockX - sqrt(2)*TabY;
TabZ = BlockZ - ZLimit;
BlockY = TongueY + StubY + TabY; // overall Y
//----------------------
// Useful routines
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);
}
//- The Block
module Block() {
difference() {
cube([BlockX,BlockY,BlockZ]);
translate([-Protrusion,-Protrusion,-Protrusion]) // remove column
cube([(StubX + Protrusion),(TongueY + Protrusion),2*BlockZ]);
translate([-BlockX/2,-Protrusion,-Protrusion]) // form tab
cube([2*BlockX,(TongueY + StubY),(TabZ + Protrusion)]);
translate([0,BlockY,(BlockZ/2 - 0*Protrusion)])
rotate(45)
cube([3*StubY,2*StubY,(BlockZ + 2*Protrusion)],center=true);
translate([0,0,-Protrusion])
cube([sqrt(2)*TabY,2*BlockY,(TabZ + Protrusion)]);
}
}
//-------------------
// Build it...
ShowPegGrid();
if (Layout == "Show")
Block();
if (Layout == "Build")
translate([-BlockZ/2,-BlockY/2,BlockX])
rotate([0,90,0])
Block();
While putting the speed wrenches in the box with the Sherline four-jaw chuck, it occurred to me that I had all the makings of a handle for Sherline’s steel tommy bars:
Sherline Tommy Bar Handle – solid model
Because these are intended for pushing, rather than twisting, I dialed the knurl back to 32 DP, reduced the depth to 0.5 mm, and ran the bar almost all the way through the handle for strength:
Sherline Tommy Bar Handles
A dab of urethane adhesive inside the handle holds the bar in place. They started out a snug slip fit, so we’ll see how well that holds the bars in place.
A tommy bar holds the spindle against the torque from the collet pusher:
Sherline CNC mill – tommy bar and collet pusher
A pair will come in handy with the three-jaw chuck the next time that one appears.
The white slab is a very early 3D printed tool from my Thing-O-Matic, made to hold the pin at exactly the proper distance from the pulley so it fits squarely into the pusher and locks it to the spindle:
Locking pin holder – spindle end view
Other folks make much nicer tommy bar handles than mine, but I’d say my 3D printed handles beat a common nail any day!
The OpenSCAD source code:
// Knurled handles for Sherline tommy bars
// Ed Nisley - KE4ZNU - December 2013
use <knurledFinishLib_v2.scad>
//- 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
PI = 3.14159265358979;
inch = 25.4;
//----------------------
// Dimensions
ShaftDia = 10.0; // un-knurled section diameter
ShaftLength = 10.0; // ... length
SocketDia = 4.0; // tommy bar diameter
SocketDepth = 40.0;
KnurlLen = 35.0; // length of knurled section
KnurlDia = 15.0; // ... diameter
KnurlDPNom = 32; // Nominal diametral pitch = (# diamonds) / (OD inches)
DiamondDepth = 0.5; // ... depth of diamonds
DiamondAspect = 2; // length to width ratio
NumDiamonds = floor(KnurlDPNom * KnurlDia / inch);
echo(str("Num diamonds: ",NumDiamonds));
NumSides = 4*(NumDiamonds - 1); // 4 facets per diamond. Library computes diamonds separately!
KnurlDP = NumDiamonds / (KnurlDia / inch); // actual DP
echo(str("DP Nom: ",KnurlDPNom," actual: ",KnurlDP));
DiamondWidth = (KnurlDia * PI) / NumDiamonds;
DiamondLenNom = DiamondAspect * DiamondWidth; // nominal diamond length
DiamondLength = KnurlLen / round(KnurlLen/DiamondLenNom); // ... actual
TaperLength = 0.75*DiamondLength;
//----------------------
// 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);
}
//- Build it
ShowPegGrid();
difference() {
union() {
render(convexity=10)
translate([0,0,TaperLength])
knurl(k_cyl_hg=KnurlLen,
k_cyl_od=KnurlDia,
knurl_wd=DiamondWidth,
knurl_hg=DiamondLength,
knurl_dp=DiamondDepth,
e_smooth=DiamondLength/2);
color("Orange")
cylinder(r1=ShaftDia/2,
r2=(KnurlDia - DiamondDepth)/2,
h=(TaperLength + Protrusion),
$fn=NumSides);
color("Orange")
translate([0,0,(TaperLength + KnurlLen - Protrusion)])
cylinder(r2=ShaftDia/2,
r1=(KnurlDia - DiamondDepth)/2,
h=(TaperLength + Protrusion),
$fn=NumSides);
color("Moccasin")
translate([0,0,(2*TaperLength + KnurlLen - Protrusion)])
cylinder(r=ShaftDia/2,h=(ShaftLength + Protrusion),$fn=NumSides);
}
translate([0,0,(2*TaperLength + KnurlLen + ShaftLength - SocketDepth + Protrusion)])
PolyCyl(SocketDia,(SocketDepth + Protrusion),6);
}
Browning Hi-Power Magazine Block – solid model – whole
The horn fits between the follower’s pegs, so that chopping the pegs off won’t increase the magazine’s capacity. Chopping the horn off without modifying the follower won’t make any difference, either. As nearly as I can tell, chopping the pegs off the follower will destabilize it enough that it’ll roll over atop the spring, but I admit to not actually trying that.
The yellow comb supports the overhang that captures the tab around the magazine spring and there’s a tiny support spider inside the lower nut clearance that holds the ceiling in place:
Browning Hi-Power Magazine Block – solid model – section
The inner nut trap probably droops a bit without any support, but there’s no way to tell when it’s printed as one solid piece. That trap will hold the blob of steel-filled epoxy that secures the screw and helps prevent the block from turning, so it’s not really a nut trap and doesn’t require a precision fit. The vent tube from the top of the screw shaft gives the air and any excess epoxy an exit path.
Here’s a bottom view of two blocks, showing the support structures and the results:
Browning Hi-Power magazine – block support detail
I poked the tips of a snap ring pliers into the spider and twisted it out. The comb snaps off with fingernail pressure.
You could also print it without support by laying it flat, then glue the halves together with alignment pins. This is a bottom view:
Browning Hi-Power Magazine Block – solid model – split bottom
The OpenSCAD program has a handful of configuration settings that determine which of those blocks it produces, which components appear, and how it’s oriented.
Installed in a Browning magazine, the block looks like this:
Browning Hi-Power magazine – block in place
A detail of the bottom shows the notch capturing the spring tab:
Browning Hi-Power magazine – block detail
I think the top surface would benefit from a small bevel to ease the spring around the block, but that’s in the nature of fine tuning.
Not having heard back from my legislators yet, I still don’t know whether this counts as a readily reversible modification. I have my doubts, what with it being plastic and all, but we shall see.
The OpenSCAD source code:
// Browning Hi-Power Magazine Block
// Ed Nisley KE4ZNU December 2013
Layout = "Whole"; // Show Whole Split
// Show = section view for demo, not for building
// Whole = upright for steel or plastic
// Split = laid flat for plastic show-n-tell assembly
AlignPins = (Layout == "Split"); // pins only for plastic show-n-tell
Support = (Layout != "Split"); // no support for split
//- Extrusion parameters must match reality!
// Print with 2 shells and 3 solid layers
ThreadThick = 0.15;
ThreadWidth = 0.40;
HoleWindage = 0.2;
Protrusion = 0.1; // make holes end cleanly
//----------------------
// Dimensions
Angle = 12.5; // from vertical
SpringID = 10.3; // magazine spring curvature (measure with drill shank)
SpringRadius = SpringID / 2;
Length = 24.0; // front-to-back perpendicular to magazine shaft
Height = 18.0; // bottom-to-top, parallel to magazine shaft
// 18 = 10 round capacity
RectLength = Length - SpringID; // block length between end radii
HornBaseOD = 8.0; // fits between follower pegs to prevent shortening
HornTipOD = 5.0;
HornAddTip = (HornTipOD/2)*tan(Angle);
HornAddBase = (HornBaseOD/2)*tan(Angle);
HornAddLength = HornAddTip + HornAddBase + 2*Protrusion;
HornLength = 12.0; // should recompute ODs, but *eh*
TrimHeight = 2.5; // vertical clearance for spring clip on base plate
// OEM = 2.5
// generic A = 2.5
TrimInset = 1.5; // ... horizontal
// OEM = 0.0
// generic A = 1.5
ScrewOD = 3.0 - 0.25; // screw hole dia - minimal thread engagement
ScrewLength = 11.0;
ScrewOffset = -1.5; // ... from centerline
// OEM = 0.0
// generic A = -1.5
NutOD = 5.6; // hex nut dia across flats
NutThick = 2.4; // ... then add 50% to trap for thread engagement & epoxy
NutOffset = 6.0; // ... base height from floor
VentDia = 2.0; // air vent from back of screw recess
PinOD = 1.72; // alignment pins
PinLength = 6.0;
PinInset = 0.6*SpringRadius; // from outside edges
echo(str("Alignment pin length: ",PinLength));
NumSides = 8*4; // default cylinder sides
Offset = 5.0/2; // from centerline for build layout
//----------------------
// Useful routines
function Delta(a,l) = l*tan(a); // incremental length due to angle
// Locating pin hole with glue recess
// Default length is two pin diameters on each side of the split
module LocatingPin(Dia=PinOD,Len=0.0) {
PinLen = (Len != 0.0) ? Len : (4*Dia);
translate([0,0,-ThreadThick])
PolyCyl((Dia + 2*ThreadWidth),2*ThreadThick,4);
translate([0,0,-2*ThreadThick])
PolyCyl((Dia + 1*ThreadWidth),4*ThreadThick,4);
translate([0,0,-(Len/2 + ThreadThick)])
PolyCyl(Dia,(Len + 2*ThreadThick),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);
}
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);
}
//----------------------
// The magazine block
module Block(SectionSelect = 0) {
CropHeight = Height*cos(Angle); // block height perpendicular to base
echo(str("Perpendicular height: ",CropHeight));
difference() {
union() {
intersection() {
rotate([Angle,0,0])
hull() {
for (i=[-1,1])
translate([0,i*RectLength/2,-((Length/2)*sin(Angle) + Protrusion)]) cylinder(r=SpringRadius,
h=(Height + 2*(Length/2)*sin(Angle) + 2*Protrusion),
$fn=NumSides);
}
translate([0,0,CropHeight/2])
cube([2*SpringID,3*Length,CropHeight],center=true);
}
translate([0,-Height*sin(Angle),Height*cos(Angle)])
resize([SpringID,0,0])
intersection() {
rotate([Angle,0,0])
translate([0,0,-(HornAddBase + Protrusion)])
cylinder(r1=HornBaseOD/2,
r2=HornTipOD/2,
h=(HornLength + HornAddLength + Protrusion),
$fn=NumSides);
cube([2*SpringID,Length,2*(HornLength*cos(Angle) + Protrusion)],center=true);
}
}
translate([0,ScrewOffset,-Protrusion]) // screw
rotate(180/6)
PolyCyl(ScrewOD,(ScrewLength + Protrusion),6);
translate([0,ScrewOffset,NutOffset]) // nut trap in center
rotate(180/6)
PolyCyl(NutOD,1.5*NutThick,6);
translate([0,ScrewOffset,-Protrusion]) // nut clearance at base
rotate(180/6)
PolyCyl(NutOD,(1.1*NutThick + Protrusion),6);
translate([SpringID/2,-((Length/2)/cos(Angle) - TrimInset),-Protrusion])
rotate(180)
cube([SpringID,2*TrimInset,(TrimHeight + Protrusion)],center=false);
if (AlignPins) // alignment pins
for (i=[-1,1])
rotate([Angle,0,0])
translate([0,
(i*((Length/2)*cos(Angle) - PinInset)),
(CropHeight/2 - i*2*PinInset)])
rotate([0,90,0]) rotate(45 - Angle)
LocatingPin(PinOD,PinLength);
translate([0,(ScrewOffset - NutOD),-Protrusion]) // air vent
rotate(180/8)
PolyCyl(VentDia,(ScrewLength + Protrusion),8);
translate([0,(ScrewOffset + VentDia/2),ScrewLength])
rotate([90,0,0]) rotate(180/8)
PolyCyl(VentDia,(NutOD + VentDia),8);
if (SectionSelect == 1)
translate([0*SpringID,-2*Length,-Protrusion])
cube([2*SpringID,4*Length,(Height + HornLength + 2*Protrusion)],center=false);
else if (SectionSelect == -1)
translate([-2*SpringID,-2*Length,-Protrusion])
cube([2*SpringID,4*Length,(Height + HornLength + 2*Protrusion)],center=false);
}
NumBars = floor((SpringID/2)/(5*ThreadWidth));
if (Support) { // add support structures
for (i = [-NumBars:NumBars])
translate([i*5*ThreadWidth,
-((Length/2)/cos(Angle) + TrimInset/2 + ThreadWidth),
(TrimHeight - ThreadThick)/2])
color("Yellow")
cube([(2*ThreadWidth),(3*TrimInset),(TrimHeight - ThreadThick)],center=true);
translate([-SpringID/2,-((Length/2)/cos(Angle) + 2*TrimInset + ThreadWidth),0])
color("Yellow")
cube([SpringID,(2*ThreadWidth),(TrimHeight - ThreadThick)],center=false);
translate([0,ScrewOffset,0])
for (j=[0:5]) {
rotate(30 + 360*j/6)
translate([(NutOD/2 - ThreadWidth)/2,0,(1.1*NutThick - ThreadThick)/2])
color("Yellow")
cube([(NutOD/2 - ThreadWidth),
(2*ThreadWidth),
(1.1*NutThick - ThreadThick)],
center=true);
}
}
}
//-------------------
// Build it...
ShowPegGrid();
if (Layout == "Show")
Block(1);
if (Layout == "Whole")
Block(0);
if (Layout == "Split") {
translate([(Offset + Length/2),Height/2,0])
rotate(90) rotate([0,-90,-Angle])
Block(-1);
translate([-(Offset + Length/2),Height/2,0])
rotate(-90) rotate([0,90,Angle])
Block(1);
}
A Home Shop Machinist article (A Speed Key for Your Four-Jaw Chuck, p 67 Nov-Dec 2013, David Morrow) showed some lovely knurled steel knobs. These 3D printed knobs aren’t nearly as pretty, but they do much the same thing:
Sherline Knobs – in 4 jaw chuck
The solid model resembles the illegitimate offspring of a wine bottle and a pineapple:
Sherline Knob – solid model
The knurling comes from aubenc’s Knurled Surface Library v2. I ran off a prototype (on the left), then tweaked the dimensions to get the final version on the right:
Sherline Knobs – knurl depth variation
Being that type of guy, I define the knurl in terms of its diametral pitch, compute the diamond width & length to fit in the available space, then hand those measurements to the knurling library… which recomputes everything and decides on one less diamond than I do: NumSides has a Finagle Constant of -1 to make the answer come out right. We may be using a different diameter or something, but I haven’t deciphered the source code. It’s parametric out the wazoo, as usual, so you can spin up what you like, how you like it.
Anyhow, a 24 DP knurl with 1.0 mm depth looks and feels pretty good; the XY resolution isn’t good enough for a 48 DP knurl around that knob diameter. The diamonds don’t come out as crisp and pointy as crushed steel knurls, but they’re OK for my fingers.
Doing half a dozen doesn’t take much longer than doing a few, because there’s a 20 second minimum layer time in effect and those things don’t have much plastic, so now I have one for the hold-down clamps and another for Show-n-Tell sessions:
Sherline Knobs – M2 platform
I chopped a 5/32 inch hex key into five 15 mm lengths with a Dremel cutoff wheel, then filed both ends flat and broke the edges. The hex stubs were a press fit in the hex holes, so I finger-started them, grabbed the hex in the drill press, aligned the handle below, and rammed the stub about 5 mm deep. The final depth comes from jamming the wrench into the chuck and pressing firmly, so the stubs project exactly as far as possible:
Sherline Knobs – hex key inserted
One might quibble about the infill on the end; one may go adjust one’s own printer as one prefers.
There’s 0.1 mm more HoleWindage than usual, because these holes must fix a hex shaft, not a circular pin, and the corners need some clearance. They came out a firm press fit: exactly what’s needed.
They’re no good for final tightening of those chuck jaws, but that’s not their purpose…
The Smell of Molten Projects in the Morning 