"One Perfect Part at a Time"


Halloween Thought

I have discovered I might have all that I need to die happily in my machine shop. Well, almost. It’s that “almost” that will keep me alive in the long run. Just one more tool then I will die happy. It may be the “just one more tool” that keeps me alive forever. What do vampires know about immortality? HA! All that awful yucky blood and stuff…

It’s bad enough when I nick my finger.  I have a cute little scar on the back of my left hand middle finger where earlier this year I let a 10,000 rpm end mill remove some flesh.  CSI (Crime Scene Investigators) would have enjoyed figuring out what happened at the scene of the accident from reading the resulting blood splatter. <’ulp…>

Ninety nine point nine percent of the time I practice safe workshop.  That’s ok as long as the last tenth remains minor. The vampires can stay in their dark places, thank you.

Small Stuff

I am still in lust for the smaller projects. I had a discussion with a caller about machine tool size. I admitted I liked some of the larger machine tools, but I have no projects that can justify them. Mostly I cannot justify the very high cost of the tools or the materials. I’m just in my comfort zone where I am.

I have been doing some recent machining so small I have to wear one of those dual lens magnifying hoods to see the work.  When I push it up or take it off, I always feel amazed at how tiny the work is that I was doing. I think it is a lot of fun doing miniature machining.

There is a trade-off between modeling something very small for display and making something very small that will actually operate properly. This includes various heat engines and other thermodynamic equipment. Thermodynamics does not scale down well in small size engines. It isn’t the heat is too much for the small size. The problem is usually there is not enough heat to do the proper work. It is the expansion of hot gas that provides the driving force.

Electric Power

For that reason electrical powered models are very popular. Electrical motors scale very well into some very small sizes. Some high performance electric motors get hot, but it is not the heat that makes them function. It is magnetic force that does the work. The heating is a waste product of inductive losses in the metal containing the magnetic force as well as a lot of other very heavy scientifically calculated reasons.

The advance in batteries (smaller, lighter, more powerful) and special high powered magnetic materials in motor cores are creating a whole new world of model aircraft and other machines now powered by the rotary action of electric motors. With electronic controllers, high power poly phase miniature motors are now the state of the art. Brushes are no longer required on small DC motors (but are still heavily used because of low cost.)

Model makers will see a lot more use for these new smaller motors and control systems.

Scale Effect

Working on the small size project also requires more accurate machining. A twenty inch part may only need to be accurate within twenty thousandths (0.020”). A one inch scaled down part would have to be accurate to within one thousandths  (0.0010”) to have proportionally the same tolerance. Proportional tolerance becomes impractical at some point but the point made is that very close but reasonable tolerances are required as projects get smaller. Careful and skilled work is required by the micro machinist. That’s what small size hobby machining is all about; taking the time and effort to make the best parts possible with available skills and machines. Making it smaller doesn’t make machining it easier. All the rules still apply.

Especially the one that says, “Have fun no matter what the size.”

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