Friday, March 12, 2021

Guest Post, part 2


Next project 
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. 
Power reverse. 
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. 

Take care, 

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....


  1. Up here the trades are just effed. Years ago an organization formed to lobby the provincial gubbimint to decertify the trades. It would make Alberta more competitive in the international markets, dontchya know. Not having to pay journeyman's wages, and train those expensive apprentices. They were basically set on fire and run out of town, so they just went on with it unofficially and below the radar.

    My neighbour is a tin basher that does residential HVAC. He is a full blown journeyman that can make metal do beautiful and wonderful things - and he rails at the declining presence of journeymen in the trade, who are being replaced by 'installers'. Installers can put a new furnace and air conditioner in your house as long as everything is simple and straightforward. But if there are any problems... they are just hooped.

    I think our future will redeem the tradesmen... or we will all be sitting around, trying to make the cheap Chinesium stuff work...

    If I ever grow up I want to be a machinist.

    1. I was an apprentice electrician in the mid 80's. Our drywall and painting guys were mostly Mexicans. They didn't speak English, but were masters at their craft. When oil hit $18 a barrel, the housing market just croaked. I went back to college and finished up an electronics degree. Now, every tradesman down here is Mexican. I've been on construction sites where Spanish is the language, or it doesn't get done.

      I blame the folks that pushed the college degree as the doorway to a good job. When you get folks that were poor in school going to college, they had to invent easy degrees for them, and those easy degrees cost what a real one does, but won't pay squat after you graduate. Now, all degrees are easy, as long as you spout the party's mantra. And bridges collapse....

      I trust the Mexican tradesmen more than anyone. They are sharp. And they aren't afraid to sweat and get dirty. Old traits most folks had. Traits I consider important.

    2. My dad was a tradesman STxAR... and he pushed the college/university route for all he was worth. When he was a kid, if you finished high school you could get a modest middle class job. Those that bailed out early went into the trades. If you had a college or university degree you were on easy street the rest of your life.
      I get that immigrants can do good work, but we don't have jobs for our own kids anymore. Given the ever sprialling affirmative action... I worry about the future and our kids. There are some really horrible issues facing our young adults, and a steady, meaningful job would go a long way to help solve them.

    3. STxAR and Glen. Mike Rowe has expressed my thoughts far better than I could.
      I dropped out of college and only regretted going there in the first place.
      To be fair, I wasn't mature enough, and the affordable choice of a large Philly school was a bad idea.
      Even in 1970 the college had gone leftward, and was an example of how things were going to go.

  2. Glen. I think being an amateur machinist has given me the best of both worlds.
    I've not had to grow up and these tools are some wonderfully big toys!
    And after some thought, machine tools are much like our boyhood toy sets from way back. They are complicated, they teach us useful things, and they will hurt you if you use them in the wrong way.

    1. I never looked at machine tools as a giant erector set. But it is....

      Wise words John, really good stuff.

  3. A lot of wisdom there, John.

    STxAR, I love reading these. I only understand about 20% of it, but it is fun trying to figure it out.

    1. Thanks for stopping by. I do the same for folks that I only get about 20% of their content too! It's good to be exposed to new things. As long as they are wholesome....

    2. TB. Thank you. I spent a summer once working in a small machine shop as a parts robot.
      I learned some machining, and I did learn a lot about mass production.