# Machining 4140



## Armourer (Feb 4, 2018)

Hey all, I recently bought a 1.75"x4' piece of 4140 for a project of mine. This is the first time machining this alloy, and while cutting it the temperature of it got super hot. I was blown away how hot it got. Is this normal for this type of steel? Or was I turning it too fast? It machined super nice thought, the chips came off of it a nice blue colour. I will post a pic of the project in a another forum once I figure out how to now Photobucket doesnt work.....


----------



## Chuck K (Feb 4, 2018)

4140 usually creates stringy swarf for me.  If it was too hot I would slow down.  The surface speed jumps up on a large diameter like that.


----------



## seasicksteve (Feb 4, 2018)

Sometimes when it gets real hot it will harden up then it resists cutting causing more heat more hardness. I was cutting some 4140 ht yesterday tool was a bit dull and got it too hot and it work hardened


----------



## benmychree (Feb 4, 2018)

Your chips should come off blue, and if your chip breaker is adjusted correctly and you put on enough feed the chips should curl up like a spring and break off in short sections; if your tool holds up and does not quickly dull, your cutting speed should be OK.  Sometimes the curls do not want to break off; in that case, I use a chip hook, a piece of about 1/8 diameter spring steel with about a 3/4 90 deg. bend at the end and a file handle on the other with an overall length of about 16"; I take the hook and place over the curling chip and give a little tug on it until it breaks off and repeat as needed.  If speed, feed, and chip breaker are just right, the chips will continuously break off in small C shaped chips that like to go down your shirt and burn you (best to not tuck in your shirt!)   As far as heat buildup in the workpiece, the answer is coolant in a fairly large stream.  You do not mention whether the 4140 is heat treated or annealed, but that just effects how fast your cutting speed can be and if it is HT, it would generate more heat than annealed.
4140 is not difficult to machine, it just takes some technique.


----------



## 4GSR (Feb 4, 2018)

I've never had 41xx (4130, 4140/42, 4145) material heat treated or not, work harden on me while cutting.  Probably what is happening is, running too fast surface feet per minute along with too fine of a feed rate, and it's burning up your tool bit, rather it's HSS or carbide.  41xx material in the home shop is not meant to be run fast. Run at about half the SFM and RPM's as you would with mild steels and try to keep the feed rate high.

Follow benmychree's advice and you won't have any problems.


----------



## benmychree (Feb 4, 2018)

4gsr said:


> I've never had 41xx (4130, 4140/42, 4145) material heat treated or not, work harden on me while cutting.  Probably what is happening is, running too fast surface feet per minute along with too fine of a feed rate, and it's burning up your tool bit, rather it's HSS or carbide.  41xx material in the home shop is not meant to be run fast. Run at about half the SFM and RPM's as you would with mild steels and try to keep the feed rate high.
> 
> Follow benmychree's advice and you won't have any problems.





4gsr said:


> I've never had 41xx (4130, 4140/42, 4145) material heat treated or not, work harden on me while cutting.  Probably what is happening is, running too fast surface feet per minute along with too fine of a feed rate, and it's burning up your tool bit, rather it's HSS or carbide.  41xx material in the home shop is not meant to be run fast. Run at about half the SFM and RPM's as you would with mild steels and try to keep the feed rate high.
> 
> Follow benmychree's advice and you won't have any problems.


I have never had it work harden while cutting either, other than perhaps a tool has broken down at the very tip; even then, with a new carbide tip, it will cut right through the (slightly) hard spot.  BTW, 4gsr, thanks for the comment giving me credit for knowing what I am about!


----------



## pdentrem (Feb 4, 2018)

A few weeks ago, I was turning 2” 4140 18” long shafts down to 1.125” over 10” and 1.00” over 8” on the other half. I ground a HSS tool with the cutting edge at over 10 degrees of side rack, and almost 90 degrees to the axis and with a chip breaker. Started with rpm under 500, depth of cut 0.050, with 0.005 feed. I was getting dark grey to blue chips. Too fast and I got lots of chatter, so was moving the speed pot up and down on each pass. I also varied the depth of cut, while turning 4150 shafts of similar diameter and length I could go 0.100” depth, not so with 4140. Lathe is a Jet BDB-1340A with VFD. This was my recipe.
YMMV


----------



## bluechips (Feb 5, 2018)

To me if the chips coming off are blue you're turning too fast.  I like when they come off silver to slight brown and turn blue in the chip pan, then  they are carrying heat away with them...  I want the chips to look like sixes and nines.  Big fan of positive rake tooling with an adjustable chip breaker.  Just old school I suppose...


----------



## Big Bore Builder (Feb 6, 2018)

pdentrem said:


> A few weeks ago, I was turning 2” 4140 18” long shafts down to 1.125” over 10” and 1.00” over 8” on the other half. I ground a HSS tool with the cutting edge at over 10 degrees of side rack, and almost 90 degrees to the axis and with a chip breaker. Started with rpm under 500, depth of cut 0.050, with 0.005 feed. I was getting dark grey to blue chips. Too fast and I got lots of chatter, so was moving the speed pot up and down on each pass. I also varied the depth of cut, while turning 4150 shafts of similar diameter and length I could go 0.100” depth, not so with 4140. Lathe is a Jet BDB-1340A with VFD. This was my recipe.
> YMMV




4 times cutting speed divided by diameter

Cutting speed for 4140 is about 50 fpm  for HSS

So:   4 times 50 divide by 2 gives us 100 rpm.

I used flooded coolant, really makes a difference in tool life and surface finish.


Grind in a good chip breaker to roll the chips and avoid long stringy razor blades.  Safer and makes cleaning out the chip pan easier.

Back in my job shop days if I noticed a guy running a lathe and making long stringy razor blades I would stop his work and give him a talk on chip breakers.    Many years ago in another nearby shop a lathe operator had his Achilles tendon cut by a long razor blade chip.  Needless to say that shop got some tool grinding lessons.

Once you master HSS then move up to carbide.


----------



## Big Bore Builder (Feb 6, 2018)

Armourer said:


> Hey all, I recently bought a 1.75"x4' piece of 4140 for a project of mine. This is the first time machining this alloy, and while cutting it the temperature of it got super hot. I was blown away how hot it got. Is this normal for this type of steel? Or was I turning it too fast? It machined super nice thought, the chips came off of it a nice blue colour. I will post a pic of the project in a another forum once I figure out how to now Photobucket doesnt work.....




I have machined a lot of 4140 in my life.  It is easy to work with if you follow the rules.     Cutting speed in FPM, calculate proper RPM, use of HSS or Carbide, rigidity and horsepower of lathe, coolant, etc.     Spent many an hour on a big 30 inch Monarch making 4140 shafts in a large job shop.  The lathe had a 5 ton bridge crane over head with two hooks to give you an idea of the size of work pieces.

Give us more info on your setup.    Speeds and feeds, how are you grinding the tooling, etc.  Photos are worth a thousand words.

Try imgur for photos, much better than the old photobucket and real easy to use.  https://imgur.com/


----------



## Big Bore Builder (Feb 6, 2018)

The most important rule in Machining is:       

 RPM equals 4 times the cutting speed divided by the work piece diameter.

The crusty old school machinists way back in the 1800's developed this simple formula along with many others.  And they gave us the cutting speeds in feet per minute for various materials and tool bit types.

It works both forward and back ward.  Use it to calculate the work piece rpm, in the above postings, the speed for a certain diameter shafting.

Or use it for calculating the tooling speed, such as for a 1/2" end mill in the vertical mill.

It is easy to derive this formula, I will put it up if any one wants to see the methodology. 

Find the old South Bend Book "How To Run A Lathe" and read.    Everything is in the book!

Like General George Paton said:    "Rommel, I read your )*&^%$# Book"


----------



## 4GSR (Feb 6, 2018)

If you want to get more exact, use 3.14 instead of 4.  Sorry.


----------



## pdentrem (Feb 6, 2018)

60 to 200 sfm with HSS cutters. 3-4 times that with Carbide.


----------



## Big Bore Builder (Feb 6, 2018)

4gsr said:


> If you want to get more exact, use 3.14 instead of 4.  Sorry.



You know, it is guys like you that make us old timers reluctant to post anything.      Pi was rounded off to 4 many years ago as the old timers wanted simple calculations to do in the head.

Anyway, even if you use 3.14 (which is not an accurate description of Pi) you will not have a gear in your lathe that will match exactly the calculated RPM.     

A 10 to 20 per cent error in speed calculation really does not make any difference.   It is the gross mistakes that the formula helps to avoid, like running at 500 RPM when you really should be nearer 100 RPM.

For your reading pleasure I have deleted my posts and I have placed you on my ignore list.


----------



## woodchucker (Feb 6, 2018)

bluechips said:


> To me if the chips coming off are blue you're turning too fast.  I like when they come off silver to slight brown and turn blue in the chip pan, then  they are carrying heat away with them...  I want the chips to look like sixes and nines.  Big fan of positive rake tooling with an adjustable chip breaker.  Just old school I suppose...


That's interesting coming from a screen name of bluechips.


----------



## benmychree (Feb 6, 2018)

bluechips said:


> To me if the chips coming off are blue you're turning too fast.  I like when they come off silver to slight brown and turn blue in the chip pan, then  they are carrying heat away with them...  I want the chips to look like sixes and nines.  Big fan of positive rake tooling with an adjustable chip breaker.  Just old school I suppose...


With HSS tools that is true, with carbide positive rake tools, tools survive longer with blue chips right off the cut.  I am old school too!


----------



## pdentrem (Feb 6, 2018)

A Machinery’s Handbook is a must, either printed which works even if the power goes out or the online version. Anyone can use an online calculator like this one. See below. 
As the diameter is reduced the rpm can go up. After making 21 pounds of chips, I only had the sharpen the HSS once. I was going from 2” down to 1.135” and 1.02” prior to finish grinding. At 4” diameter any where from 50 rpm to just under 200 rpm depending on where in the range of cutting fpm you want to try.

http://www.custompartnet.com/calculator/turning-speed-and-feed


----------

