Advise on turning 4 inch rod?

unioncreek

unioncreek

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I'm making an adaptor plate for a four jaw chuck on my HF 8x12. They had some four inch round at work that they use from time to time. They let me cut some one inch pieces off to make adaptor plates with. I was turning them smooth tonight and the inside cuts like butter nice and smooth, but when I get to the outer 3/8" it's just downright hard. It will eat up a HSS tool in no time if you ake too big of cut. I'm running the lathe at 125 RPM's. Carbide cuts a little better, but still hard. The turnings get real hot and turn a bright blue if I push it too hard.

Any suggestions are greatly appreciated.

Bob
 
Hey Bob

125 Rpm may still be a little high if you are having problems?

I wonder if the steel is cold rolled? Then it will be work hardened on the outside and give you problems.


Bernie
 
I think you already have the idea of what is wrong nagging at you. Slow down. When you get out to 4" the surface feed rate is much faster than closer to the center. If you can, start hitting it with coolant. Different cutting angles might help some. Stick with the carbide.

If you can't get it to go slow enough, you can always crank the spindle by hand. I use a hand crank all the time when I am cutting threads with taps and dies. It is slow but. oh well. Everybody has to be somewhere.
 
I figured sipped was too high. 125 RPM's is the slowest the lathe will go, but I built a pulley reduction that gets it down to 40 RPM's for threading. I'll put that on to do the rest of the turning.

Thanks,
Bob
 
I haven't checked the appropriate SFM for 4" but it might not be too fast depending on the material. Do you know what kind of steel?

Ah yes, blue chips. Hot little buggars aren't they? I strive for dark amber and indigo blue -that just means the carbide is doing it's job and stands the best chance of giving you a beautiful finish. There's nothing wrong with hot chips like that.

It would be a little odd to find a 4" diameter piece of cold rolled -but not totally improbable. Cold rolled is notorious for surface tension and internal stress. That's the most likely cause of your bad finish in the outer diameter. Hot rolled stands a better chance of being somewhat normalized -and I purchase HR almost exclusively for just that reason.

Ray
 
Hi.....I had some 6" discs by 1" thick that were cut out of plate with a cutting torch (not plasma) and had the same problem. I put the discs in my wood stove overnight and it made a noticeable difference. I realize you don't have exactly the same cause of the hardness problem but the results may be the same.
 
The simple formula (using high speed steel tool) for spindle rotation is 4 times the cutting speed divided by the diameter of the bar. The cutting speed is in feet per minute and the diameter in inches. For steels the average cutting speed is 80 fpm with high speed tooling and 100 fpm for cast iron; brass and aluminum are way higher. With carbide cutting tools the cutting speed can be much higher. This is, of course, a "rule of thumb" method. In your case you should be fine at 125 rpm with carbide and light cuts.

There are a lot of steels that are cold rolled in 4 inch diameter. One of the most popular steels in industry for larger shafts is AISI (SAE?) 1045. This is a medium carbon steel which is fairly tough and somewhat of a challenge on a small lathe. It is difficult to get a really shiny finish on this material, but with patience... It does not thread well, etc.

Another popular group of shafting steels in the 4" size range are the "stress proof" line of steels. There are various brands of this stuff but it generally comes under ASTM A311. http://www.niagaralasalle.com/product-stressproof.html

These shafting steels are tough but turnable. For our gang of small lathe and mill spindles, they make a good replacement material, especially if one has access to a tool post grinder or a grinding lathe. One of the sad things about the decline of manufacturing and maintenance in the US is the disappearance of the automotive machine shops. It is still possible but not as easy to take a turned shaft to an automotive machine shop and have it ground to very close tolerance with a beautiful finish on a crankshaft lathe.

Our small machines lack the shaft horsepower of the big shop machines and most of us don't run coolant (I have the option of this on my 14" lathe, but I just don't want the mess). I have an mist style unit that I have not hooked up because I still wonder about what ends up in one's lungs. It is not often that I really see the need to flood the workpiece, just a little cutting fluid..

Good luck, just go slow and take light cuts. When you get close to the finished diameter you may wish to use a file and some emery cloth to get a good finish. Just remember to protect the ways against the grit.
 
Hi all,,,,,, Just a thought I have run into. Was the 4 inch round perhaps a pin in a former life. If so it may be case hardened. I work in a steel mill and have the occasion to get ahold of large diameter round stock upwards of 12 inch Dia. I have had a couple pins that were case hardened that cut great in the center but was like Kryptonite on the outside.
Did all the machine work on one end of a 3inch piece once making a die holder. When I flipped it around I couldn't even touch the other end. I guess that's the price we all pay when we start playing with Mystery Metal.
Just a thought.

Best Regards to all
 
If you are getting a 3/8" case on that piece of steel you have no chance of getting through it with your HF 8X12 and if you could you would eat up a lot of tooling. The best way to handle this is to heat it to around 1500 -1700 degrees this is the, cherry red you hear about,for an hour or so. You can do this with a bag of charcoal and a fan to build a "blast furnaces" heat it up and pack it in lime or I have even used a bag of Portland cement and leave it for a day or 2 this will anneal it to as dead soft as possible. This will work as long as you do not have a plated shaft.
 
Just to add to that...


The softest state for carbon steel is "spherodized". Typical recipe for low/mid carbon steel is heat to 700 for 30 hours or more and allow to air cool (which could be 6-10 hours or more for pieces with at least 1" cross segments). Air cool means sit all by itself and does not mean blow a fan on it -that will actually harden it (slightly).

Next softest state is to normalize. Heat 50 degrees over critical temperature for that material (low/mid carbon typically 1550, tool steel typically 1700) for 1 hour for the 1st one inch cross segment plus 30 minutes for each additional inch (cross segment). Cool very gradually at a rate of 60 to 100 degrees per hour. If you have a disk 1" thick by 6" diameter, the cook time is 1 hour.

BTW: Cool means 150 degrees (F) or below. Most carbon steels are still in transformation at 350-400.

No matter how you slice it, they are lengthy processes. BTW: Metal that appears red is quite low in temperature; usually about 1200 degrees (give/take). 1550 is orange/yellow. 1700 is yellow. (at least by my eyes).


Ray
 
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