Blue Chips, Carbide, and Taking Out the Heat in the Chips

[BobWarfield]

There's an excellent thread over on PM about blue chips and carbide tooling:

http://www.practicalmachinist.com/vb/showthread.php?t=154429

The point they're making, that the blue chips take the heat away from the workpiece, is a point I've tried to make, but people are skeptical. The amazing thing is that with the right tooling, you can do this very nicely on little home machines like my 9x30 lathe, or the flycutter on my mill. It's only appropriate for carbide. For HSS tooling, straw color is about as hot as you'd want it, and you're not pulling the heat out in the chips in the same way. It's also only relevant to steel since aluminum doesn't turn blue!

To give an idea, when I flycut the steel table for my disc sander, these are typical of the chips I was getting and their color:

I was using a brazed carbide tool for the operation. Could've done with better chip formation, but the brazed carbide tool is not the ideal geometry for flycutting as we've discussed elsewhere. On the lathe, I would be getting perfect blue 6's and 9's.

You do have to be careful because those little blue devils are hot! You want closed collar, no pockets or cuffs, really good eye protection, and maybe a hat too. I'd also keep on eye on where they're landing. Don't know if they could start a fire, but oily rags and blue chips seem like they ought not to be allowed to get together.

OTOH, after a fly cutting pass, the surface of the steel was not even warm to my touch. I used very little coolant either, just a little heavy sulfurized cutting oil, one good swipe with a brush at the beginning of each pass.

Cheers,

BW

 

[Philjoe5]

Bob,

I've experienced the same thing turning a 4" diameter CRS flywheel blank at 540 rpm on my 10x22 lathe. Lots of blue chips but the toolbit stays sharp. It's just a cheap brazed carbide tip unit. ;D

Cheers,
Phil

 

[tattoomike68]

I have read that with the newer faster mills running dry shops are saving money and still enjoying good tool life.

Coolent can be messy and running parts washers can be a hot and dirty job.

 

[BobWarfield]

Bob,

I've experienced the same thing turning a 4" diameter CRS flywheel blank at 540 rpm on my 10x22 lathe. Lots of blue chips but the toolbit stays sharp. It's just a cheap brazed carbide tip unit. ;D

Cheers,
Phil

Dang Phil, when you say blue you mean BLUE!!!

Tattoomike68, I am always fascinated to read about dry machining. As you say, coolant is a real pain. There are guys building total containment enclosures so they can run full flood coolant on the CNC conversions. That just seems like a whole lot of mess and trouble to go through.

Apparently drilling is one area where you just gotta have some coolant, but at least it could be a little less crazy than full flood.

I just got a Bijur mist unit off eBay. It's incomplete, I have to make a nozzle, but I'll be trying that in lieu of flood when I need a little coolant. Mostly I'll be trying to run dry where possible.

Cheers,

BW

 

[rake60]

Interesting Thread!

The color of the chip tells you something about the temperature of the steel at
the cutting point of the tool. A blue chip is getting hot.
Carbide and carbide tipped brazed bits, require that heat to plasticize the steel
then push it off the base material.

I've seen many infrared photos and model picture that explain that.
Such as this one:

As that model shows, most of the heat is going into the chip.

A blue chip from a HSS tool or drill bit is a warning signal.
That tools useful life is about to end.

Mike mentioned the new High Speed Milling cutters.
I do not have the HP to use them at home, but use them at work almost
daily. A 2" cutter with 3 carbide inserts has no problem taking a 1/4" depth
of cut in 4140 steel. It's run dry, faster and is much quieter than anything I've
ever used before. The work piece stays cool. The cutter never gets too warm
to handle. I wouldn't be reaching into those chips!

Rick