$fn=50;

//piston

height=40;

diameter=20;

compression_height=15; // z distance between piston top and centerline of pin

pin_radius=6;

ring_to_deck=2; // z distance from deck to ring groove

parts_gap=5; // empty distance between piston and wristpin

gap=0.04; // shrink by this much to make bolts/pins easier to fit

/////////////////////////////////////////

// END SETTINGS /////////////////////////

/////////////////////////////////////////

////////////

// piston //

////////////

module piston()

{

difference()

{

//piston body

cylinder(h=height, r1=diameter, r2=diameter, center=false);

//piston interior

translate([0, 0, (compression_height-pin_radius)/2]) cylinder(h=height, r=diameter*.75, center=false);

//wristpin hole

translate([0-diameter-1, 0, compression_height]) rotate([90, 0, 90]) cylinder(h=diameter*2+2, r=pin_radius+gap, center=false);

//rod relief

translate([0-height/1.5, 0, height+height/4]) rotate([90, 0, 90]) cylinder(h=height*1.3, r=height/2, center=false);

top_ring();

bottom_ring();

}

}

module top_ring()

{

//ring grooves

difference()

{

translate([0, 0, ring_to_deck]) cylinder(h=3, r1=diameter+1, r2=diameter+1, center=false);

translate([0, 0, ring_to_deck+1]) cylinder(h=2, r1=diameter-1, r2=diameter+3, center=false);

translate([0, 0, ring_to_deck-1]) cylinder(h=2, r1=diameter+3, r2=diameter-1, center=false);

}

}

module bottom_ring()

{

difference()

{

translate([0, 0, ring_to_deck+2]) cylinder(h=3, r1=diameter+1, r2=diameter+1, center=false);

translate([0, 0, ring_to_deck+3]) cylinder(h=2, r1=diameter-1, r2=diameter+3, center=false);

translate([0, 0, ring_to_deck+1]) cylinder(h=2, r1=diameter+3, r2=diameter-1, center=false);

}

}

//main

piston();

translate([0, 0-(diameter+pin_radius/2+parts_gap), 0]) wristpin();

///////////////////////////////

//test fittings - not for actual prints

///////////////////////////////

//wristpin in piston

//translate([0-diameter*.97, 0, ring_to_deck*5.5]) rotate([90,180,90]) wristpin();