EN3B Mild Steel is a pain or is it me?

[Chris TickTockParticipant @christicktock]

Hi, I bought some EN3B from my local metal warehouse but found it did not machine as well as EN1A on the Sherline lathe.

A year later I need to make a few simple small objects and proceeded to cut up several lengths with the parting tool. I believe I have centered the parting tool correctly and am using oil. Problem is the metal seems either not to cut or jump which leaves you a nervous wreck. I am resorting to the trusted hacksaw.

So does anyone else have similar experience and/ or any hints as to possible remedy.

I am using a HSS blade to part of is there a better metal to use?

Chris

[Chris TickTockParticipant @christicktock]

[JasonBModerator @jasonb]

With a small lathe like yours parting will never be easy unless on very small diameters with a narrow tool eg 1 to 1.5mm wide.

[Clive FosterParticipant @clivefoster55965]

Proper EN1A, 230M07 is the modern equivalent specification number, is a free cutting steel with additves to make it easy to machine. Only the leaded steels are easier to cut.

Normalised EN3B shouldn't be seriously harder to machine given sharp tools and appropriate speeds and feeds. Sherline should be up to the job with care. The major issue with manual parting off on small lathes is holding a constant slow feed rate to avoid taking too large a cut which will, at worst, stall the lathe and maybe break the tool or, at best, make things jump about most alarmingly. As you usally need to run quite slow to have the power to drive the cut the feed rate will be very small indeed. A thou or five per rev maybe. As Jason says a wide tool makes for a serious cut on a small machine.

The other issue with ordering EN steels from general suppliers is knowing what you actually get. It "should" be 070M20 but, especially if bright bar, may well be 080A15 as the certificate ranges overlap which will be harder to machine.

Clive

[Anonymous]

EN3B has a propensity to tear rather than cut. I normally run insert tooling, including parting off, on my centre lathe so that isn't much help. However, on the repetition lathe I use HSS tooling and EN3B turns ok, but not as nice as EN1A.

Andrew

[John HaineParticipant @johnhaine32865]

It is tempting to part off with the lathe running very slow. That means that the slightest jerkiness of your feed causes a dig-in, and anyway there isn't enough friction to get the material at the tool edge hot enough to cut. You may find that running the lathe significantly faster will help, then the tooth load at a given feed rate is much less and there's enough friction to soften the work at the tool edge. Use the narrowest possible tool too on your little lathe.

[Chris TickTockParticipant @christicktock]

Thanks Guys, Johns post inferring that friction heat allows the cut is a new concept for me. Is he right or is it the sharpness of the blade. A higher speed will if I am right give more torque and compensate for a blade less sharp than it should be.Adding oil may detract from the heat / friction????

I have just read something which may have a baring also that supports John's advice. As the parting tool gets nearer the centre the stock's rotational velocity deminishes. Possibly more speed is the anmswer despite the obvious concern??

Any thoughts?

Chris

Edited By Chris TickTock on 20/07/2020 21:20:06

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Chris TickTock on 20/07/2020 21:14:21:

[…]

Any thoughts?

Chris

.

Just one thought from me, Chris

John Haine is a wise man

MichaelG.

[Paul FallertParticipant @paulfallert28101]

George H. Thomas uses some ink in his book discussing the benefits of higher, rather than lower RPM and he used HSS tools. When I tried it, I became a believer and I part-off from the tool-post (front). Mostly at 300 RPM and occasionally at 600 RPM. I do have a carbide insert blade, but I usually use HSS, unless the work is hardened. I also thought GHT's experiments with a tool with a V-groove top made sense, and once I found one, it became the one to use. A slight touchup on the front edge relief and it cuts with confidence. I think they call it a "P-type" blade.

However, I do use a QCTP and dedicate one holder to this one tool. It is important to pay attentionn to the height of the tip of the blade, especially as the diameter reduces. You can see it dip on gnarly/difficult steels. The tool either stops cutting or skipping or worse; begins to dig-in. Infrequent at higher RPM for the reasons already oulined previously.

Of course, I align the tool against the face of the chuck with a rectangular piece of steel trapped between the chuck face and the side of the tool to bring the axis of the tool (not necessarily the holder) perpendicular to the lathe axis). Otherwise, the tool will bind and break as the cut goes deeper. Keep the tool stickout as short as possible, even starting-out with a short stickout and stopping to extend it as the cut goes deeper.

[John HaineParticipant @johnhaine32865]

I once borrowed a very thick book on workshop technology that went into great detail about machine tools and how they work. It was there that I found the explanation of the cutting mechanism. Basically the "sharp" tool creates a very small volume of the material being cut at its edge which is under great pressure, causing it to heat up and become plastic. Then the sharp tool can more easily shear the material off. A blunt tool has too large a contact area and therefore not enough heating. Of course if the tool gets too hot it can soften, so coolant may be needed. Carbide tools are much harder and have better high temperature performance so can cut even though the edge may be more rounded, provided the speed is kept up and the cut isn't too small – but need a more rigid machine. If you add coolant to the carbide edge it may reduce the heating effect so it doesn't cut as well, and even cause the tool to fracture through thermal shock.

That's what the book said anyway, as I recall. But it does explain for me why speeding up the parting operation makes it easier and why there seems to be less of a problem with "built up edge" on ali at higher speeds. And why carbide tools seem to behave better at high revs and quite fast feeds.

[Nigel Graham 2Participant @nigelgraham2]

Sorry, but I find that puzzling and I wonder what classes of machining the book describes though it is clearly in the professional realms, possibly having to consider very high production rates to very tight tolerances in very awkward alloys .

Yes, the tool can cut only by shearing the material, but surely if cutting steel means even a few microns thickness having to be softened, the chips at least would be momentarily incandescent, coming off rather like grinder sparks?

So assuming sharp condition, how come carbon-steel files, hacksaws, taps and tin-snips cut steel without turning up their toes at the first few slivers of swarf? All these use basically the same action – they shear the metal, and at very low speeds but relatively high "feeds" .

Modern NC machine-tools using carbide inserts of the right form and grade for the metal being worked, can operate at very high rates, but they also use very powerful floods of coolant.

Conversely I have found that "can" is not the same as "should", and carbide tips are just as happy, giving good results, at the fairly moderate speeds and feeds my second-hand ML7 is accustomed to. An HSS tool can give a better finish but there a lot of variables to consider, not least matching a carbide tool to the metal more than to the machine, or grinding a steel tool properly, and one's own skill at setting and operating a manual machine-tool.

=

Going back to the original question, EN3B or its modern equivalent is amenable to most machining operations, but it is not especially free-cutting, and seems tough rather than hard. It is possible to obtain a good finish on it but not as easily as on the free-cutting grades. However, it can be welded, which is not advised for the leaded steels. (Welds in leaded steel can be brittle, I believe).

[Lee RogersParticipant @leerogers95060]

It's the task that makes a power cross feed worth having. It's the constant smooth feed that makes the difference but the set up must be spot on.

[Martin Hamilton 1Participant @martinhamilton1]

EN 3B is always going to be more difficult on Sherline, on a Sherline it also depends on the type & method you use for parting. I use the Sherline rear mounted inverted HSS T shape parting tool which is also only around 1mm wide, this parts like a dream on my Sherline. I also sometimes use a 1.5mm carbide insert parting tool mounted on the front side of the lathe for convenience if i have my QR toolpost already mounted. Depending on what material i am parting off with this tool, aluminium, brass or EN1 steel part pretty good, other steels need more care. The rear mounted inverted HSS parting tool wins hands down on a Sherline.

Edited By Martin Hamilton 1 on 21/07/2020 14:58:12

[Steve CrowParticipant @stevecrow46066]

Like Martin, I also use the Sherline rear mounted blade and inserts for convenience. Works a treat.

As somebody has already mentioned, it pays not to be to cautious with speeds and feeds. I still sometimes lose my bottle and get the hacksaw out though!

Are you using EN3B round bar? Just asking because I only use it when I can't get EN1A in square, flat or hex.

[Nigel McBurney 1Participant @nigelmcburney1]

Regarding EN 3b for most purposes it is best to AVOID using it, though it is used on some full size boiler work ie stays and studs,it does not machine well,it tends to tear. I have a S7 and a Colchester master and it does not matter what tooling is used,you have to be really careful to achieve a reasonable finish. Regarding parting off it was usual practice to use halve the normal speed,though higher speeds could be used on brass.Very good results can be obtained with EN 1A freecutting leaded steel,though it is best not use it in welded construction,though higher speeds can be used ie over the normal 100 ft per min for the softer steels,En1A is a better general use steel,with free cutting properties ,I do not stock any en3b , En 8 ,a tougher steel I use for vintage engine studs studs and always have a stock in my metal rack, En 16 is good for replacing the bent shafts and pins for farmers equipment,though I never weld it, my welder mate always said dont weld anything tougher than en8 ,unless you are a skilled welder.

[Chris TickTockParticipant @christicktock]

Appreciate all posts very helpful. I need to look at the rear mounted parting tool and try to avoid buying EN3B in future.

Thanks Guys

Chris

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