Its good to have a CO2 fire extinguisher handy in a shop that uses CBN inserts.

[Flynth]

why would you need cbn on aluminum? HSS is good enough.

I should've clarified. I machined aluminium previously(a day or two before) with hss. There were aluminum chips in the pan.

Then on the day described in my post I was hard turning hardened steel. Specifically I was turning down the 2.5mm hard layer on a piece of scrap hydraulic rod to get to the metal below to use for my project.

I machined the aluminium with a big hss drill (42mm - about 1.5in). So I had to feed carefully not to spin the taper iny tailstock. This resulted in lots of very wide and thin aluminium ribbons on the bottom of the pan.

In the photos the yellow "stream of fire" is hardened steel chip made by a CBN insert. It was fine for good 10 minutes or so. Perhaps the chip had enough time to cool on its way to the bottom.

When you machine hardened steel with cbn the chip most often swirls and goes in the direction opposite the chuck making a neat pile of "steel wool" in front of the tool post(that steel wool can catch fire too, but everyone knows that). This is the chip on my photos.

However, sometimes instead of swirling to the side a very long stream like chip forms going straight down. It looks really beautiful, but it must have hit those aluminium ribbon chips and ignited them.

Hmmm.... I use PCD for aluminum, it's amazing. I thought CBN was for super alloys and super hard steels? Anyway, I bought a few and had nothing but a bad time with them. Am I using them wrong?
More on topic, I love to turn titanium, but the horror stories are always running in the back of my mind. I know there are very "specialized" extinguishers for Ti? Is it Co2? Are you running crazy high rpm? I would think the same feeds/speed are for CBN as carbide and a bit more?

Indeed it is. Sorry for confusion. As mentioned cbn was for steel and aluminium chips were leftovers of a previous machining session.

I always considered CBN out of my reach as a hobbyist with moderate budget, but these days one can buy those Chinese CBN inserts with just one edge very cheaply. I paid $8 for two if I remember correctly. The first time I used it on hard steel, just wow, I understood how people felt when carbide was introduced first. With proper feeds and speeds it machines effortlessly with very little force of the tool (I do take very light cuts as per recommendations - 0.07mm/under 3 thou max).

I never tried PCD (on aluminium of course). I always assumed my lathe/mill will not go fast enough.

Yes all metal burns and at higher temps than most organic things. In the photos above note how bright the chip is.
The material I watch the most when machining is titanium. Won’t turn it until the chip pan is empty. It’s a fire waiting to happen. I won’t say what to put the fire out with, please research it yourself. I will say don’t use water. I watched a safety vid years back that showed a lathe chip pan full of titanium burst into flames. Fire was short lived but at such high temps warped the ways beyond repair. If I can find the vid I’ll post it.

I heard about titanium too.

I used to burn pure magnesium in chemistry lab as a kid in school. Also I saw some YouTube ignite magnesium chips. So probably one should also be careful of leaving magnesium chips in the pan and then throwing sparks on them

As for "all metals burn", yes you're 100% correct. Anyone who saw steel wool burn can confirm.

 

[Flyinfool]

Most of us have seen steel burn. Burning the steel is what makes a cutting torch work. You use the flame to get it hot and then add a jet of pure O2 to ignite the steel, and that burning steel is what keeps the cut hot enough to continue the cut through the part.

As for extinguishers, If you can find one $$$ Halotron is the best. Halotron is what is used in big dollar computer rooms because it will not destroy anything if it is used. Not because it is best at putting out the fire but it will not destroy what you are trying to save from the fire. Chemical extinguishers are VERY corrosive not just to what was burning but everything around that the dust can get to. CO2 works well but comes out at extremely cold temps which can cause things to warp and crack due to shock cooling.

 

[snoopdog]

Good post, and I've learned a few things. But, let me interject this. How many of us are flirting with potential disaster from the residue of cutting oil, and say, kero, in our chip pan. I think I'll buy another extinguisher.