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:
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:
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:
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:
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);
}
