when not to use mild steel ?

Sorry Duncan for the confusion but I thought the later comments in my post would make my thoughts on the subject clear. So often we see on this and other forums, posters saying they are having problems machining some mild steel and can we help. Helping the questioner is then almost impossible as Mild Steel covers a wide range of steel grades. Therefore, if a supplier just offers Mild steel, as some do, my advice is to go and purchase from a supplier who offers steel to a meaningful spec.

To make this clear for those new to metalworking, the following is taken from the Metals4U website

"The term Mild Steel applies to all low carbon steel that does not contain any alloying elements in its makeup and has a carbon content that does not exceed 0.25%. The term “Mild” is used to cover a wide range of specifications and forms for a variety of Steel."

I will add again, my experience when making two spindles, one which was easy to achieve the required finish, whilst in the case of the second one, it was next to impossible due to using, unknowingly, two grades of steel Ever since I have always purchased to a known spec, not just Mild Steel.

Harold

Harold, we agree completely, if you'd put 'mild steel' in quotations I'd have got it first time

AjohnW, yes you can case harden 070M20 (EN3), the stuff that is described as 'case hardening steel' is 080M15, which used to be EN32. It has a tad more manganese, but less carbon. The carbon content at the surface is then increased by the case hardening process, leaving the core soft and ductile.

Video of making a boring bar, he is using the wrong chip breaker insert for that material. It should be coming off in chips, so the issues are either wrong chip breaker, wrong depth of cut and wrong feedrate. Being as it is not a really powerful lathe, he is taking small cuts and the tool geometry is therefore wrong for that particular material and job.

A finishing insert designed for small depth of cuts would have been a better choice. Most finishing insert geometries are for taking to 1mm depth of cut so are ideal for home workshops and lower powered lathes,

Neil

I mean to sort out an old Reeve's catalogue Duncan. It's about some where and thought they stocked EN3 for case hardening but not totally sure.

My interest in O1 stems from looking for a near equivalent to the very old higher carbon tool steels. I suspect that they were the equivalent of W grades which just aren't around any more. I've always been curious about the cutting edge sharpness that the can achieve. Fact or fiction ? Using oxy I notice that he went way past bright red heat and often that isn't a good idea. Well into the bright yellows from what I could see. I don't see any problem getting a section like that to the right temperature with a decent propane torch.

Decent steel - It's a pity that the old Reeve's have gone but on the other hand maybe the suppliers aren't around any more. From my TDO days I still have a booklet kicking around some where that I had to use. Branded material for specific jobs. Information gained over many years about what was best for specific jobs and no deviations allowed. Now that there are standards I suspect materials will vary 'cause there is scope for variations within them. It hard to know what companies used to get up to in this respect. They may have worked to much higher levels of precision and also at times might have added specific additional ingredients.

Oil quenching. The only thing I have ever used for that apart from once at home was a massive barrel of the stuff.

Cutting speeds - personally I don't always assume faster is better.

John

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Neil, could not see the chip breaker properly so can't really comment other than his insert has one and it does not appear to be working! I think the lathe is plenty big enough for that job (looks to be about Boxford size?) and he should be giving it a bit more, I think we agree on that.

John, You should still be able to get W grade tool steel - it is just a water hardening steel. Quench in water rather than oil. It will be significantly less stable during heat treatment and is easily cracked if you are not careful, an oil hardening or air hardening would be much easier to use depending on the application.

Mark

It does have a chip breaker on that insert, but is the wrong one for that material choice. We have lots of inserts at work with different chip breakers for this reason. As one does not do all very well. The DCMT CCMT and the TNMG range of inserts also have the best range in chip breakers. There is a valid reason for the insert makers to have such a large selection of inserts. I do alot of O1 turning in both soft state and hardened state. It is essential on a cnc to get chip control. Long strings only lead to tears. Which is why I suggest for the home workshop the best compromise is to only get finish turning inserts and not the ruffing out ones.The radius to get is either the 0.2mm or 0.4mm radius inserts. Most home machines just don't have the power or rigidity to properly run a 0.8mm radius insert or bigger. For hard turning O1 I use either ceramic inserts or CBN inserts. Some jobs I have to use CBN as the ceramic does not come in a small enough radius. With Ceramic inserts run at surface speed of 90 to 180 m/min and a depth of cut from 0.05 to 0.5 or Ø0.1mm to Ø1mm at a feed rate of 0.06mm or 2 thou per rev. Ceramics wont take interrupted cutting.

Neil

I've sort of concluded finishing inserts are the best for me on a Boxford but it just happened that way as I didn't want to buy large inserts. They are ok on a mini lathe. I do wonder if max rad has something to do with rigidity of the whole set up though. I had no problem using the usual brazed tip large rad carbide tools on a Raglan. The ML7 I had which was pretty "loose" didn't like them at all. I've never tried them on the Boxford. They were also ok on brand new horrible combined mill lathe where the mill sits on the headstock. They had pretty obviously used a low tensile cast iron for making that.

I can't find anyone who lists W grade steels. O1 is no problem. I can ask next time I pass the place I usually get ferrous stuff from. It might not be the same any more though going on comments about the life of parts from a clock restorer. He reckoned it was something to do with the way the original iron was made. What he was suggesting was that parts that did last 100 years or more no longer did anything like that made with modern equivalents. He had a small stock of extremely old stuff and reckoned he had proved the difference with that.

Speed - I always bear in mind that lots of turning has been done on lathes that can't even get near 1000 rpm so if I have problems I always see what happens if I slow things down. I do get more torque that way as well.

John

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Edited By Ajohnw on 04/10/2016 11:19:36

AjohnW,

from what I can glean, W just means water hardening. Give Carr's a ring on 0121 522 6789, if they can't help they will know a man who can. However if what you want is a small quantity of very hard steel, then Tubal Cain used to reckon that old files were harder than silver steel. You do of course have the problem of softening them before you can machine them

It's more to try for lathe tools Duncan than anything else. Curiosity. I'll bear Carr's in mind.

Tubal Cain's comment fits in with many others in different areas. That's why I am curious. I have used HSS's at work that will obtain a much sharper edge than what seems to be about now as well. All branded though. I have a fair selection of old branded HSS toolbits. Buy a lathe and they often come with lots if some one is giving up. Rather than use those I tend to buy new tool bits.

When I did the bearings on my ML7 is made a very small scraper out of an old 3 square file. It was extremely sharp. More like a razor. The one I made in training really needs hollow grinding again. Not sure if it's me or the grinder but I don't seem to be as dexterous as I used to be doing that sort of thing. Probably lack of practice. Now the weather is cooling my workshop is more likely to get up and running again. I need something small to grind that has suitable rests in that so suspect that will be the first job.

John

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I think it's largely down to habit that i can remember all of the imperial steel codes, yet the modern numbers seem confusing to remember, when theres a letter suffix attached it's much more catchy.

Clearly the suppliers are keeping it because it works. It might not necessarily tell me anything about the steel, but if i can remember a name then it does it's job.

Michael W

W and O are mostly North American designations.

In general terms:

O grades = oil hardening = gauge plate

W grades = water hardening = silver steel.

We ran a very detailed article on hardening W and O steels in MEW, which all applied to gauge plate and silver steel (one of my hardest ever edits as I had to translate every temperature from Fahrenheit to Celsius and then check them all again).

American drill rod although being similar to silver steel lacks (manganese?) content that helps minimise distortion.

Neil

It looks to me that there isn't a modern equivalent of O1 or silver steel but they are still around due to their usefulness.

The high carbon content of silver steel is supposed to help it obtain sharp edges. O1 has tungston in it. Guage plate may have too but there seems to be some variation.

The W's from what I can find out should be plain carbon steels going up to rather high carbon levels.

Tubal Cain I think points out that carbon steel is harder than HSS as is file steel but only up to a certain temperature which means using very low cutting speeds.. Getting out his heat treatment book to check - he does. I think I've seen comments that sulphur can cause problems and this is the reason for some constituents of alloy steels. Might explain the clock refurbisher's problem.

John

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