Air flow switch holder

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This is the OpenSCAD code to create a wafer air flow sensor (and backflow preventer) to hold a microswitch to stop the laser from firing if the exhaust flow stops. Dimensions have been set to match the exhaust nozzle. The current version of the header doesn't quite match, even though the nozzle was reverse engineered from it.

This was printed on 5/1 and it has some issues.

  1. The arms which hold the switch body interfere with the flap plate.
  2. The flap plate axis of rotation could be lowered to improve the balance.
  3. The thickness of the wafer can be increased to reduce the warpage of the piece.

Model was redesigned on 5/5:

  1. Switch holder moved to side from top center
  2. Flap axis of rotation lowered
  3. Up arrow added
  4. Thickness increased from 3 to 5 mm
  5. Wire holes relocated 180°

You can find the stl file here File:Airflow-switch.stl


/*
exhaust airflow detector
safety interlock for cheap Chinese laser at Hac DC
This switch is a lug style wafer for insertion between the exhaust collector and the exhaust nozzle on the back of the laser chassis.
  When the exhaust fan is running and air is flowing the switch will operate to allow the laser to fire.  This switch is upstream of
  the exhaust fan so air will leak into the exhaust stream, not exhaust leaking out into room air.
James Sullivan
5-5-17, v2
OpenSCAD version 2015.03-1 

--dimensions from mating exhaust nozzle--
nid=60;     //nozzle inner diameter
nod=80;     //nozzle outer diameter
mod=100;    //maximum outer diameter
sh=30;      //step height
sw=5;       //step width
oah=50;     //over-all height
tlw=3;      //top ledge width
bcd=46.8*2; //bolt circle diameter
bhd=3.6;    //bolt hole diameter
fw=12;      //foot width
fh=15;      //foot height
fod=108;    //foot outside dimension, from outside edge to outside edge
fid=(nid+nod)/2;//foot inside dimension, from inside edge to inside edge
*/
fid=60;  //flange inner diameter, same as nid
fod=80;  //flange outer diameter, same as nod
bhd=3.6; //bolt hole diameter
bcd=93.6;//bolt circle diameter
thick=5; //thickness of flange - originally 3, but warped when removing from printer bed
flap=3;  //thickness of flap - originally 3, but warped when removing from printer bed
hph=bhd*2;   //hinge pin height above center line, i.e. butterfly offset.  Reduce to make switch more sensitive.  Increse to make switch more stable. - originally 10
sfw=fid-thick*2; //switch flap width - originally sqrt(fid*fid-4*hph*hph)
shd=2;  //switch hole diameter
shp=10; //switch hole pitch, i.e. center to center spacing of mounting holes on microswitch
srh=12;  //switch roller height, i.e. height above switch hole centerline where switching action occurs
sbw=6;  //switch body width
nfw=5;  //nut face width
nt=1;   //nut thickness
$fn=80;

difference(){ //wafer body
    union(){
        cylinder(d=fod,h=thick);    
        for(ang=[0,90]){
            rotate([0,0,ang]) hull(){  //lugs
                translate([bcd/2,0,0]) cylinder(d=3*bhd, h=thick);
                translate([-bcd/2,0,0]) cylinder(d=3*bhd, h=thick);
            }
        }
        translate([sfw/2+thick/2,0,thick]) rotate([-90,0,0]) cylinder(d1=shd*1.6,d2=0,h=shd*2);//up direction arrow head
        translate([sfw/2+thick/2,0,thick]) rotate([90,0,0]) cylinder(d=shd*0.8,h=shd*2); //up direction arrow shaft
    }
    translate([0,0,-thick/2]) intersection(){ //bore
        cylinder(d=fid, h=2*thick);           //circular top and bottom
        cube([sfw,fod,thick*4],true);         //vertical left and right
    }
    for (angle=[0:90:270]){ //bolt holes in lugs
        rotate([0,0,angle]) translate([bcd/2,0,-thick/2]) cylinder(d=bhd,h=thick*2);
    }
    for (angle=[235:5:245]){  //wire holes through flange
        translate([0,0,thick-flap/2]) rotate([0,90,angle]) cylinder(d=1,h=bcd/2);
    }
    translate([0,hph,flap/2]) rotate([0,90,0]) cylinder(d=1,h=bcd+4*bhd,center=true);  //hinge pin axle hole
} //end of wafer body
translate([-thick/2-sfw/2,0,flap/2+srh]){   //switch holder
    difference(){
        union(){
            cube([thick,shp+3*shd,3*shd],center=true);//mount flange
            color("blue") translate([0,0,-srh/2-flap/4+thick/2-3*shd/4]) cube([thick,shp+3*shd,srh+flap/2-thick-3*shd/2],center=true); //support for mount flange
            translate([-thick/2,0,-shd*2]) cylinder(d2=shd*1.6,d1=0,h=shd*2.0);//flow direction arrow head
            translate([-thick/2,0,-shd/2]) cylinder(d=shd*0.8,h=shd*2.0); //flow direction arrow shaft
        }
        for (dy=[-shp/2,shp/2]) {
            translate([0,dy,0]) rotate([0,90,0]) cylinder(d=shd,h=2*thick,center=true);   //bolt holes
            for (angle=[0:120:240]){
                translate([-thick/2,dy,0]) rotate([angle,0,0]) cube([nt*2,nfw,nfw/sqrt(3)],center=true); //nut sockets
            }
        }
    }
}

translate([0,fid/2+bcd/2+bhd*2,0]) difference(){    //flap disk
    intersection(){   //bore
        cylinder(d=fid-0.5, h=flap);  //circular top and bottom
        cube([sfw-0.5,fod,flap*2],true);    //vertical left and right
    }
    translate([0,hph,flap/2]) rotate([0,90,0]) cylinder(d=1,h=bcd+4*bhd,center=true);  //hinge pin axis
}