Spray gun nozzles.
I'd bought one of these 15 dollar spray guns a while ago to try it out and spray some latex.
But the instructions advised against spraying latex. The gun sat on a shelf for some time and I got interested again when we did a medium facelift in our bathroom and decided to paint the two pine doors when the weather turns nice enough to do it outside this year.
The internet says that you can drill out the nozzle on the cheap gun, thin the latex a bit, and get good results. The internet also says that instead of drilling out the nozzle from 1.4 mm to 2.0 mm I could buy replacement nozzles that would fit the gun.
I ordered a 1.7 mm and a 2.0 mm nozzle from China. When they arrived they didn't fit because the thread number was the same, but the threads were a bit larger than the original. They are some sort of stainless steel.
The internet told me how to change the gear train to cut metric, and I followed the chart numbers. But the threads were close to the shoulder of the nozzle, and my external threading bit just wouldn't fit. I bought this set because I wanted an internal threading bar because the tool my dad had ground only allowed me to thread a short distance.
The design of this tool let me cut very close to the shoulder, and the carbide insert worked great to cut the stainless. I used a HSS parting tool to deepen the thread relief groove next to the shoulder, then I turned down the OD before the threads and used the same tool to cut off the existing threads. Then I locked the half nuts, and threaded the nozzle by turning the chuck by hand.
On the second nozzle I used power. I also changed my technique a bit. I found that my right hand wants to turn the lathe's power switch in the right hand direction and whether that's muscle memory or habit I don't know. I do know that that habit caused a minor crash against the shoulder of the second nozzle when I went forward instead of reversing as I had intended. I then changed to using my left hand to reverse, and that seemed to work out very well.
It went this way:
Skim cut by hand rotation of the chuck.
Reverse until the tool is clear.
Zero the dial.
Advance the feed a couple of thou.
Cut the threads and stop the feed.
Repeat until the threads will fit where they have to go.
I learned a lot about metric threading, and I found out as expected that using a HSS parting tool to cut stainless was a bit tough because it took a bit of extra pressure before the bit dug in and started cutting.
Something we don't ever seem to talk about. What did it cost?
The HVLP gun cost 15 dollars.
The two replacement nozzles cost around 30 dollars but each nozzle was a complete set of the long part, the nozzle and the nozzle cover.
The carbide threading set cost 41 dollars.
And maybe two hours total standing at the lathe.
I was talking to a friend who asked whether the additional investment in the 15 dollar tool was worth it. Hmm. After thinking about it, I returned to Harbor Freight and bought a 75dollar HVLP spray gun. It was an easy rationalization. :)
And much like the old saying that if you only have a hammer, then every problem looks like a nail, if you have machine tools, then every problem can be solved by using them. Except that every problem really can be solved by using machine tools.
Disclaimer. I am not a real machinist, and I rarely figure out what speed and feed I should be using. It is very satisfying to create something that does what you need it to do by using machine tools and your skills.
STxAR addendum: If you machine you are a machinist. You may not be a pro, but you aren't a button pusher either. Us "figure it out on our own" guys are just like the fellows that did the same thing in the past. Eating trig tables and squirting out parts....