As I don't have a lathe (yet, anyway) and there is a nice ready-made air assist head available, I bought one from cnsigntech on eBay:
As you can see, it comes with a threaded hole for the air supply. I asked the seller what the threading was, and they replied that it's 5mm. They didn't state the thread pitch, but it looks like common M5x0.8 threading. This would likely be easier to obtain in a country where metric is commonly used. It's a little trickier in the United States. However, as it happens, this is surprisingly close to a 10-32 thread. Close enough that it's not going to bind for the thin engagment here.
So, where do I find miniature threaded to hose barb adapters anyway? As it turns out, my local hobby store, Hobby Hangar, has such things in stock. I had a choice, use a $2 10-32 pressure fitting (Du-Bro Cat No. 540, comes with a gasket, nice touch), or spend $6 on a nice blue anodized in-line fuel filter that happens to use an M5x0.8 thread (Central Hobbies part # BCSIFF) and just use the male threaded end.
I'll also need some air hose, something nice and flexible.
One obvious choice is aquarium tubing from the local pet store.
Another choice is vacuum line from the local auto parts store.
I'll also need a way to hook this up to my air source. I decided to use an ordinary quick-disconnect air compressor fitting, screwed to a hose barb connector, using the back panel of the laser cutter as a bulkhead to panel mount it.
It turns out that Home Depot doesn't offer threaded hose barb connectors by themselves, so I picked up a "hose repair kit" that contains one, along with a male quick-disconnect that will thread onto it. You'll notice that the hose barbs are not the same size. Since I may want to move a fair amount of air, I decided to do part of the run with larger-bore tubing, then just the end run with the small tubing that will fit on the cutting head. This means I'll need two more items:
The parts pile yielded up this "Thera-Band" elastic tubing, originally designed for resistance exercise equipment, acquired cheap from Electronics Goldmine.
At the same auto parts store where I picked up the vacuum hose, I also found this handy tubing adaptor that allows connecting different-size tubing. Just what I needed!
Here it is, all hooked together. A little teflon tape on the threads discourages leakage.
The original head mounting bracket wouldn't fit the new head, so I tried hand carving one with a Dremel tool. It was slow going, and the result wasn't very satisfying. So the inaugural project on the new milling machine was to clean up the screw slots some.
Here's the new head mounted in the laser cutter. It turns out that It sticks out more from the rail than the original one, so I'm going to have to make a new bracket for the mirror that moves it a corresponding amount. The new head also has a longer focal length lense than the original, so the cutting table is now too high as well. I went ahead and removed it, as it was designed to hold small pieces of plastic for engraving, and I want to use more of the available cutting area anyway.
Here's the new air supply port on the back of the machine. It turns out there was already a hole in a useful place (originally used to access a screw for the gantry). It was a little smaller than I needed, which I remedied with a chassis punch.
Since the new head will require a new mirror bracket, and another method to hold objects to be cut at the correct height, I haven't yet given the new air assist system a tryout. I'll need to realign the optics once the new mirror mount is fabricated and installed, then I can give the new air assist system a test drive.