Most Efficent Air Blast for Cutting Steel

99% of my paying work is cutting aluminum (flood), but I still sometimes need to make a steel part. I am still very much a hack/hobbiest in skill level when making steel parts.

Yesterday I was cutting some 4140HT with 1/2 AlTiN and 1/4 (coating unknown, but probably AlTin) end mills. I was getting lots of blue chips, but the 1/2 would certainly start to give a dull glow that under dim shop lights was barely visible. I gerry rigged up an air blast that came off my CNC wood router and bungee corded it to the side of my liquid coolant system. The parts looked better (although they weren't bad before) and the mills no longer started to glow. The stock didn't seem to be getting excessively hot in either case. Now I am sure my cut should have been optimized somehow to reduce heating up of the mill (the edges did not break down), but I don't make enough steel parts to justify spending a lot of time "just getting the feel for it." I plug numbers into an SF calculator and run it. Then I make a few adjustments to speed or feed over ride if necessary so I get good looking chips and eliminate or reduce anything else bad I notice.

My plan is to setup a semi permanent air blast on a sliding mount like my liquid coolant system. I figure for the amount of steel parts I make (mostly shop tools) the air blast is the easiest way to get the jobs done.

Now all of that is just background. I don't really need affirmation of it. Its what I did. It worked.

My question is: Is there any particular air nozzle design that might make more efficient use of the air? Maybe a laminar flow design that gives a consistent cone of air without a lot of waste air swirling away before it hits the tool? I have three machines with air seal spindle and two others that use some air. I'd like to not worry about exceeding the capacity of my refrigeration dryer or having the air compressor cycle to often when I am using the air blast. The better answer of course is to get a bigger compressor and a bigger air dryer in the shop and just don't worry about it. The real answer is I can't afford to throw money at every problem. LOL.

Regardless of whether or not I can find a more efficient nozzle design, I also plan to build a ball mount with nozzle slide so I can quickly and easily point the air nozzle directly at the cut at the right distance to encircle the mill with the blast and clear the chips.

I'm not interested in a vortex tube. They use WAY to much air for my shop.

Not much to add but my first and only thought was if the dryer capacity is a concern to tap off the air blast line prior to the dryer, if plumbing another line isn't too much of a hassle. A little entrained moisture will further aid in cooling and I assume still not shock your cutter. You could use this for general shop use as well and save the dry air for where it's required.

JCByrd24 said:

Not much to add but my first and only thought was if the dryer capacity is a concern to tap off the air blast line prior to the dryer, if plumbing another line isn't too much of a hassle. A little entrained moisture will further aid in cooling and I assume still not shock your cutter. You could use this for general shop use as well and save the dry air for where it's required.

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I thought of that. Its a decent idea. I use a few tools that probably don't care about dry air if I keep them well oiled. I also found myself once a little frustrated when I had to do some air system repairs that would have been easier if I had air, so I added one quick couple before the shutoff valve a couple years ago. As you hit on though adding another air line over to that machine would be a bit of a chore. It might in the long run be the most efficient solution, but in the short run I've got parts to make and deadlines to meet. Fortunately not steel parts at the moment.

If you've got flood coolant available when cutting Al, why not use it for the steel? Don't forget that the HT will need a somewhat lower cutting speed than soft steel!

We have through the spindle air plumbed through all of our machines, turns on/off with M code.
When running dry, you are not so worried about cooling the tool, as you are removing the chips from the cutting areas. If you are cutting dry correctly, most of the heat comes off with the chip.

Mark Rand said:

If you've got flood coolant available when cutting Al, why not use it for the steel? Don't forget that the HT will need a somewhat lower cutting speed than soft steel!

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Won't that result in shattered carbide? Or were you also suggesting switching over to HSS?

Bob La Londe said:

Won't that result in shattered carbide? Or were you also suggesting switching over to HSS?

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You can run coolant while cutting steel with carbide, even hardened steel, with little to worry about. I do all my machining dry but I know several people that hard-mill tool steels up to 62HRC under coolant with no issues at all.

Mark Rand said:

If you've got flood coolant available when cutting Al, why not use it for the steel? Don't forget that the HT will need a somewhat lower cutting speed than soft steel!

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Like Bob LL said.. You must like shattered carbide, or running slow...

Carbide can take heat, it can take TONS of it.. Lots and LOTS of heat, CRAZY HEAT..
Look up crucibles someday, you may see the word CARBIDE involved.

What carbide can not do is rapid heat cycling. Ever had a glass brownie pan shatter
on you by hitting it with cold water when it was still hot? Same thing..

Heat.. No problem..
Cold.. No problem..

Going from hot to cold quickly... BIG BIG problem..

An endmill. Generates a lot of heat when its cutting. Just behind the
cutting edge on the inside of the flute.. At 3000rpms, that piece of carbide
with coolant is cycling from HOT!!!! to COLD!!!!! 3000!!!! times a minute.
50 times a SECOND!!!! That is some rapid Cooling and Heating..

Now how big of a swing in temp are we talking about??? This isn't a brownie
pan in your oven.... At what temp does steel glow? At what temp can you see
it glow brightly in a lit room? Well over 1000F.. 1000F plus degree swing
a few thousand times a minute..

Now what temps are we actually talking about?? The dark purple stuff on an endmill
TiAlN, or AlTiN, or whatever the hell they want to call it this week comes into play
at 1400-1700F or so.. It gets harder than the underlying carbide and slicker than
snot (The clear kind, not the gross black booger you pulled out of your nose after grinding
all day).

So.. In my experience, you hit a *Break* point.. Where coolant just means busted carbide.
Shut that coolant off and you can get really stupid.. On a MILL.. On a lathe, you are in
a mostly constant cut, you are only going to get that thermal shock once per pass... Once
every 5, 10 or 30 seconds.. Depending.. Not 50+ times PER second.

On a lathe. Interrupted cut.. You can see the same thing.. No need to turn the speed way
down, just turn off the coolant until you get into a stable consistent cut. It really
does work. *There are also other ways to deal with an interrupted cut, I like, if I can, a
single pass, low feed, high DOC, and try to get the nose into just where the part is going
to be round.. Single pass to get past the interruption.

So.. That is why you sometimes don't use coolant.. If you insist on using coolant in
all of your cutting, then I hope I hope I'm quoting against you.

Air moving slow enough to be in laminar flow wont do anything.

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Cole2534 said:

Air moving slow enough to be in laminar flow wont do anything.

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I was not aware that adequate velocity precluded laminar flow, but I guess I should have said pseudo laminar flow. I did say "cone" rather than line. Much like some types of water hose nozzles create a very low angled cone from the tip of the nozzle when you crank up the flow rate. Some much better than others. Almost always those that do not have center control valve/pin.

Bob La Londe said:

Won't that result in shattered carbide?

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Only if you apply the coolant to an already hot end mill.
We use flood coolant all day long every day on our cnc mills cutting anything from 1018 to A2 without "shattering" our tools.
Sure there are times when I use air instead of coolant, like on steel that has a rockwell higher than 45 or so.

1hp is equal to about 746 watts
.
if you doing heavy cutting using 10hp thats 7460 watts thats means heat (like having 5 electric room heaters on making about 25,000 btu of heat)). a lot of heat. its ends up in chips and cutter and the part. bigger machines its normal for part and cutter to be in a cloud of steam from hot coolant.
....coolant cools. and coolant often is temperature controlled to +/-1F on many machines. air blast often varies much more in temperature 20F or more temp changed is common with air blast. that changes part size as its temperature changes. flood coolant not only carries chips away it carries heat away relatively fast or more effective.
.
machinibility rating of steel is around 0.5 to 0.8cubic inch per hp per minute
aluminum around 2.0 to 6.0, literally machining steel can generate 10x more heat than machining aluminum

DMF_TomB said:

1hp is equal to about 746 watts
.
if you doing heavy cutting using 10hp thats 7460 watts thats means heat (like having 5 electric room heaters on making about 25,000 btu of heat)). a lot of heat. its ends up in chips and cutter and the part. bigger machines its normal for part and cutter to be in a cloud of steam from hot coolant.
....coolant cools. and coolant often is temperature controlled to +/-1F on many machines. air blast often varies much more in temperature 20F or more temp changed is common with air blast. that changes part size as its temperature changes. flood coolant not only carries chips away it carries heat away relatively fast or more effective.
.
machinibility rating of steel is around 0.5 to 0.8cubic inch per hp per minute
aluminum around 2.0 to 6.0, literally machining steel can generate 10x more heat than machining aluminum

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And that answered the question, or helped in ANY way.... How?

DMF_TomB said:

1hp is equal to about 746 watts
.
if you doing heavy cutting using 10hp thats 7460 watts thats means heat (like having 5 electric room heaters on making about 25,000 btu of heat)). a lot of heat. its ends up in chips and cutter and the part. bigger machines its normal for part and cutter to be in a cloud of steam from hot coolant.
....coolant cools. and coolant often is temperature controlled to +/-1F on many machines. air blast often varies much more in temperature 20F or more temp changed is common with air blast. that changes part size as its temperature changes. flood coolant not only carries chips away it carries heat away relatively fast or more effective.
.
machinibility rating of steel is around 0.5 to 0.8cubic inch per hp per minute
aluminum around 2.0 to 6.0, literally machining steel can generate 10x more heat than machining aluminum

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Dude, what fucking world are you living in where this answers the guy's question IN ANY WAY?

Well if you write down enough and sound knowledgeable you get at least partial credit on essay questions.

Thanks guys. I have used flood cutting steel with micro endmills at (relatively) high speed, but they don't throw coolant away from themselves like larger mills do. I did some 4140HT embossing dies a while back, and I did all the detail work with 1/16 and 1/32 ball mills at 24K with flood... and didn't tell anybody. Some of those cuts would run all day. Actually its part of why I am using 4140HT for some current tools I am making for the shop. I had it left over from that job. Otherwise I'd probably just use some 1018 which, inspite of what some folks say, seems to cut quite easily for me. I have made other tools with 1018. Its ok. Just doesn't last forever.

I just haven't had that luck on my bigger (bigger for me) Hurco KMB1 mill. I have almost instantly destroyed mills with it when trying to run flood coolant 1/2 inch or larger mills. Running recommended speeds and feeds within the HP of the machine. Its got a 5HP 4 pole Leland spindle motor, and Hurco rates the machine at 4HP. In my SF Calculator I set the spec for the machine at 3HP with a linear power curve. Its actually much better than that, but I try to start out conservative. I had better luck almost immediately by backing off feed and speed, and increasing the cutter engagement with a hand applied layer of oil on the part. I still ate mills up, but I could run a while first.

The try at air the other day seemed to make everything better which started my path down this rabbit hole. I do appreciate everybody's feedback.

Based on what some of you had said I might be able to run flood, by running more nozzles with a more powerful coolant pump to keep a mountain of coolant around the mill (like I can on the smaller high speed machines with smaller cutters), but it wouldn't be very practical on a knee mill with a table top enclosure. It would spray more coolant around the shop than would flow back into the tank at any given moment.

Well, most of you have given me something to think about. Thanks guys.