Trouble turning hot rolled steel!

[blockmanjohn]

Hi, I am attempting to turn a flywheel from 1018 hot rolled steel. The finished dimensions are 4.25" diameter by .750" thick. I bought this grade of steel because it was half the price of cold rolled.

I have never tried turning hot rolled before, and it has been a nightmare. It is chipping the tips on my inserts almost as fast as I can replace them. HSS seems to just wear down rapidly. The finish is terrible and very inconsistent. I have varied the feed rate and depth of cut to no avail.

Is there something I am doing wrong or should I just bite the bullet and buy a blank of cold rolled?

Thanks in advance, John.

 

[mcostello]

What speed are You running?

 

[blockmanjohn]

I was running 400RPM with .005 feed rate. I tried slower speeds, but nothing faster. John

 

[mikelkie]

I'm not familiar with the hot rolled steel 1018 , in RSA we have hot rolled steel called wm300
used for die set bases etc. it quite soft and hardens where welded. I turn up to 200mm (8 in)dia
with a insert at high speed with exellent finish but facing not too good but acceptable
i use neat cutting oil squirted on

 

[blockmanjohn]

Thanks for the reply. What do you mean by high speed? John

 

[Brian Rupnow]

The mill scale on the outside of hot rolled 1018 is very tough. You need a sharp tool and a fairly large depth of cut to get thru that outer black coating. Once you are thru it (about .5 mm thick) it should cut very easily. You appear to be using HSS tooling, so a high speed is not necessary. Lets do the math. Cutting speed in feet per minute is 80 fpm. At 4.25" diameter x 3.1416=13.25" Divide that by 12 and you get 1.1 foot . So---If you turn that piece at 70 rpm the surface will be travelling at 77 foot per minute. Slow your lathe down to approximately 70 to 75 rpm.

 

[blockmanjohn]

Well I put in a new insert and raised the speed to 725 rpm. I can't believe the difference. It cut smoothly and left a mirror finish while turning the diameter. The facing cuts were decent but no where near the diameter cuts. I don't know why that is, so if some one does, please let me know. I never realized how important speeds are.

Thanks for the lesson, John.

 

[ALEX1952]

Hi
When you take a facing cut the surface speed is constantly reducing as you travel to the middle, so for us compromises have to be made, I generally don't use power feed when facing I prefer to "feel" the cut. C.N.C. machines used in high end production are often able to alter the speeds and feeds as they progress therefore tuning the process.

 

[ALEX1952]

Hi
Me again I agree with Brian Rupnow about a heavy first cut, this is common practice in manufacturing mill scale is very abrasive but also the actual skin of the bar can be exceptionally hard to the point that it can't be turned or milled you must get under the skin. I've even taken an angle grinder to it to preserve my tooling.
A word of caution when you break the skin it will move! flat surfaces will bend and the geometry of a turned surface will change, if this is going to be an issue the material will need normalizing which takes all the stresses out after the first cuts, the skin must be broken all over first or it will move again when you break another skin, don,t worry about getting near to finished form just get rid of the skin. Unfortunately we used a blessed great furnace not sure how to do it as a D.I.Y process.
Years ago slip manufacturers would rough machine all over then store them outside for a long period and let the stresses sort themselves out and it is still reckoned to be the best method for slips, but is no longer required since the advent of carbide slips.

 

[Andy Munns]

Another option is a water finish - Had a problem finishing a crankshaft - Low Carbon steel with finish issues at textbook speeds on a heavy lathe. Old timer showed me how to set up a broad nosed tool and use a slip stone to hone a flat on tool face parallel with surface. Run lathe at extremely slow speed with fine cut and lots of water/coolant. Not quite a ground finish but only needed a fine final polish with wet and dry. Takes ages.

 

[ALEX1952]

What you are describing is almost a burnished finish except you are taking a cut, put very simply the tool is blunt and pressed against the surface and lubricated to achieve a mirror finish generally used for bearing surfaces as it also makes the surface more dense but not much use for making good a poorly turned finish. A cheat I sometimes use is to start the cut in the centre of the face and feed out, obviously rough out first conventionally then light cuts feeding out to finished size, goes against everything taught but gets the job done sometimes!

 

[Andy Munns]

On water finish - I neglected to detail that the oil stone rubs between tool and job, but the gap between tool and job is adjusted so that oil stone leans in at top, and therefore produces on the tool a tiny flat that is 'wider' than the feed rate per turn. A tiny facet on the end relief angle is also produced, which means that the tool is not really blunt. A tiny shaving is produced, almost dust-like. (I have seen these small oil stones marketed as a 'souvenir stone' - These are indispensable for this work, plus other jobs like taking the sharp edge off a new drill to stop grabbing into brass, etc.).

 

[bluejets]

Hi, I am attempting to turn a flywheel from 1018 hot rolled steel. The finished dimensions are 4.25" diameter by .750" thick. I bought this grade of steel because it was half the price of cold rolled.

I have never tried turning hot rolled before, and it has been a nightmare. It is chipping the tips on my inserts almost as fast as I can replace them. HSS seems to just wear down rapidly. The finish is terrible and very inconsistent. I have varied the feed rate and depth of cut to no avail.

Is there something I am doing wrong or should I just bite the bullet and buy a blank of cold rolled?

Thanks in advance, John.

Maybe try this...vertical shear tool.

 

[ALEX1952]

The oil stones are called "India" stones and come in a variety of sizes all about 4"/100mm long x 1/2"/12mm in section, and are readily available in variouse grades.

 

[goldstar31]

Yes, 'India stones are made by Norton. I use them prior to finish honing of the tools .
Arguably, the best results are Black Arkansas ones but mine are the white variety.

Today, things can be speeded up with the use of diamond wheels and synthetic diamond pastes.

This is when some of us old geysers get out that cheap Stent or not so cheap Quorn tool and cutter grinder. I bought- or intended to buy a decent or more decent 1/6th HP 2880 rpm motor and found it attached to a fabricated from steel Stent tool and cutter grinder. All wrong according to the book about steel against steel but it works and for £100, who cares?
I'm still looking for a replacement motor for the Quorn but have settled for a salvaged one from a washing machine- a twin tub!


Cheers


Norm

 

[ALEX1952]

I find the Arkansas stones a bit soft but there again everybody has their favorite.

 

[goldstar31]

Point taken but my Arkansas stones were courtesy of my wife who was a Fellow of the Royal College of Surgeons, now sadly deceased.

 

[ALEX1952]

Sorry I did not intend it as critisism just an aside.

 

[goldstar31]

Excellent contributions
Thanks

Norm

 

[chrsbrbnk]

a sort of tangential approach would be use L1011 a free machining steel the slightly higher price per pound is still way cheaper than a bunch of chipped carbide inserts