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/* BATHINOV-PARAMETRIC-ENGLISH-V2
by
Philippe LECA - 2015-07-24
http://www.astrokraken.fr
leca.philippe@neuf.fr
Updates :
- number of grooves calculated according to focal length
- useful ressources and comments
Very useful ressource :
http://astrojargon.net/MaskGenerator.aspx
The general rule to holes width is f/s=150-200,
where :
f is focal length,
s is hole step size.
So for telescope with 1500mm focal length the step size is 1500/150=10mm
(5mm hole, 5mm for uncut space).
If holes become too small the formula becomes 3f/s=150-200.
eg for 800mm scope you need to cut 2400/s=200 s=2400/200=12mm
(6mm cut +6mm uncut).
The angled cuts are placed at 40 degrees to each other.
*/
// general paarmeters ---------------------------
angle=22; // groove tilt angle
tmask=2.5; // thickness of the mask
tcap=2.5; // thickness of the cap's walls
daperture=80; // aperture diameter
focal=400; // focal length of the lens or telescope
bahtinovfactor=150; // usually 150 to 200
// cap parameters ---------------------------
dintcap=102; // internal diameter of the cap
dextcap=dintcap+2*tcap; // external diameter of the cap
heightcap=20; // height of the cap(=tcap if flat mask)
// for MAK or SCT : central hole and ring --------
dintcentralhole=0; // =0 if no central hole
dcentralring=0; // =0 if no central ring
// groove array parameters --------------------
widthgroove=(focal/bahtinovfactor)/2; // groove width
widthwire=widthgroove; // width of the "wires" between grooves
excessgroove=2; // number of excessive peripherical grooves (2 by default)
$fn=120;
numberdraft=floor(daperture/(widthgroove+widthwire));
numbergroove=(floor(numberdraft/2-excessgroove))*2+1;
difference(){
union(){
// CENTRAL RING FOR MAK OR SCT ===================
translate([0,0,0])cylinder(d=dcentralring,h= tcap);
// ARRAY ======================================
difference(){ // vertical array
union(){
translate([0,0,0])cylinder(d=daperture,h=tmask);
}
union(){
// half-disc
translate([0,-daperture/2-5,-1])cube([daperture/2+5,daperture+10,tmask+2]);
// groove array
for (i=[1:numbergroove]){
translate([-daperture/2,-(numbergroove+1)*(widthgroove+widthwire)/2-widthgroove/2+i*(widthgroove+widthwire),-1])cube([daperture,widthgroove,tcap+2]);
}
}
}
difference(){ // right tilted array
union(){
translate([0,0,0])cylinder(d=daperture,h=tmask);
}
union(){
// quarter disc
translate([-daperture/2-5,-daperture/2-5,-1])cube([daperture/2+5,daperture+10,tmask+2]);
translate([0,0,-1])cube([daperture/2+5,daperture/2+5,tmask+2]);
// groove array
rotate([0,0,180-angle]){
for (i=[2:numbergroove-1]){
translate([-daperture/2,-(numbergroove+1)*(widthgroove+widthwire)/2-widthgroove/2+i*(widthgroove+widthwire),-1])cube([daperture,widthgroove,tcap+2]);
}
}
}
}
difference(){ // left tilted tilted
union(){
translate([0,0,0])cylinder(d=daperture,h=tmask);
}
union(){
// quarter disc
translate([-daperture/2-5,-daperture/2-5,-1])cube([daperture/2+5,daperture+10,tmask+2]);
translate([0,-daperture/2-5,-1])cube([daperture/2+5,daperture/2+5,tmask+2]);
// groove array
rotate([0,0,180+angle]){
for (i=[2:numbergroove-1]){
translate([-daperture/2,-(numbergroove+1)*(widthgroove+widthwire)/2-widthgroove/2+i*(widthgroove+widthwire),-1])cube([daperture,widthgroove,tcap+2]);
}
}
}
}
// STIFFENERS =============================
translate([0,-widthgroove,0])cube([daperture/2,2*widthgroove,tmask]);
translate([-widthgroove,-daperture/2,0])cube([widthgroove*2,daperture,tmask]);
// EXTERNAL RING AND CYLINDER CAP ========================
difference(){
translate([0,0,0])cylinder(d=dextcap,h=heightcap);
translate([0,0,tcap])cylinder(d=dintcap,h=heightcap);
translate([0,0,-1])cylinder(d=daperture,h=tcap+2);
}
}
// CENTRAL HOLE FOR MAK OR SCT ================
translate([0,0,-1])cylinder(d=dintcentralhole,h=tcap+2);
}