I recently inherited a laser cutter (an FS Laser HL40-5g hobbyist class tool) and have been trying to get it up and running. One of the first problems was the laser cooling. These lasers require water cooling, typically provided by an aquarium pump in a 5 gallon bucket of water. The pump I inherited seemed to work fine, except for one small problem:

I couldn’t find information about the pump, and that doesn’t seem like a “standard” connection that I could find in McMaster Carr. OK, perhaps it is, but I’ve got a 3D printer, and I figured it would be faster for me to print one than figure out where that piece is in the McMaster Carr catalog.

First, I needed to take a few measurements and figure out the thread spacing. Fortunately, I have a thread gauge lying around, and I highly recommend that you keep one of these handy in your toolbox.

I use OpenSCAD for my designs, and there is a module called threads that allows me to make, well, threads (surprised?). All it needs is the diameter, thread per inch, and length. I created a test print to see if I had the right dimensions and printer settings – all was in good shape:

For the hose barb, I simply wrapped some toruses around a cylinder. Again, I used the dimensions of the original to guestimate the thickness of the barbs, but didn’t bother with the asymmetrical shape of the actual barb. Putting the whole thing together and I got this:

One big difference between the actual adapter and the one I made is the underside is conical. This allows me to print the object without having to use supports. If you look closely, the hexagon also contains a “ramp-like” feature which is also intended to improve the printing quality.

Does it work? Yep. I now have a connection that allows me to use the pump. The time from problem identification through design, iteration and implementation was about half a day (perhaps less with interruptions). Perhaps I could have found the item in the McMaster Carr catalog, but there was no way I was going to get same day shipping.

One caveat with my design: it is not watertight. The threads do leak. I didn’t bother with this problem because the pump sits entirely under water, so the leaky threads results in an inefficient pump, not an ineffective one. That fits my design goals and also follows another maker mantra: don’t let perfect be the enemy of good. The design – flaws and all – allows me to move on to the next stage of getting my laser cutter operational.

For those of you who know OpenSCAD, here’s the code. The threads module is not the one that comes with the latest edition of OpenSCAD, but from here.

use <threads.scad>

difference(){
    union(){
english_thread(diameter=13/16, threads_per_inch=14,length=0.5);
translate([0,0,25.4/2+2])cylinder(d=25.4,h=3,$fn=6);
translate([0,0,25.4/2])cylinder(d1=20.4,d2=25.4,h=2,$fn=6);
translate([0,0,25.4/2+5]){
    cylinder(d=7,h=20,$fn=25);
    for (i = [0:3]){
        translate([0,0,4+4*i]){
        rotate_extrude($fn=25){
            translate([3.0,0,0])circle(1,$fn=5);
        }
    }
}
}}
union(){
    cylinder(d=4,h=50,$fn=25);
    translate([0,0,-1])cylinder(d1=15,d2=4,h=25.4/2+1);
}
}