Mild Steel, What do I use?

Hello everyone

I’m looking for some help regarding material choices, I’m new to the hobby and bought on

eBay, shortly after buying my lathe a 20kg pack of bright mild steel. Well, this has been crap, no idea what grade it is, it wasn’t expensive and got me making chips. But now I’m looking for material to build my “Bogstandard” X2 steam engine and I want a nice grade of mild steel that will produce a good finish using carbide and HSS tooling.

What should I buy? I’m looking to machine cylinder block, crank webs, crossheads, and the eccentric cams, so I want something that’s not going to bend like a banana after milling.

Guys, I’m pretty much green in the hobby so any specifics grades, sources etc. would be much appreciated. I hear online everyone talking about these 4141 (Cousins over the water) stresses relieved steel, what is this and would this help me? Do we have an equivalent in this country?

Thanks for looking guys

Martin

For any turned work I would go with EN1A or even the leaded version that cuts even better which is EN1Apb, modern spec is 230M07 and 230M07pb. I also use this for small parts that will be milled often using it to make short square and hex parts and don't get distortion as the cuts are reasonably balanced.

You will have a job finding this spec for square and rectangular stock that tends to be EN3 or EN32B and can be had in bright or black (hot drawn) the later tends to have less problems with moving if cuts are from one side only though with care such as taking a bit off each side of bright to rough and then going back to it once it has had a chance to move to finish the part or normalising it you can avoid a lot of movement problems.

Stressproof is a brand name and there is no direct equivelant over here

Does it specify a steel block and cross head? these would often be iron or non ferrous

Hi Martin steel 4141 is not listed here and you should forget that. The easyer to machine steel is EN1A and EN1A PB The first is a straight mild steel and useful for general parts and the second is straight mild steel but with added lead which makes machining easier but has some draw backs if you are to weld etc. You should mark all materials you buy to identify whst they are. I stamp the ends and write down the length with s marker unless it is small diamiter which I use a piece of white insulation tape with info on like a flag. Other steels for other jobs when you need them. Don't forget other materials come in different standards like brass and bronze and the diferent aluminium alloys for diferant jobs. Always mark what they are eavan small useful pieces.

David

Please correct me if I am wrong ... EN1A and EN1A PB is good for turning and milling, it is not suitable for silver soldering bits together.

All the best

Derek

As said EN1A. It turns beautifully easy. For brass go with CZ121 and aluminium H30.

Hi Martin, if you are using bright mild steel, it is most likely to have been cold rolled, which alters the grain structure and causes stresses in the metals outer edges. This will happen to any grade or quality of steel, and can be cured by heat treatment at the correct temperature, which should be done uniformly and ideally in a temperature controlled furnace, and then cooled slowly but not excessively slow.

The temperature will be between 400-700 C depending on a few parameters Recrystallization Temperature of Steel. As JasonB has said, taking a little off each side at a time, will help stop bending. Hot rolled (Blue/Black) steel doesn't normally suffer form this problem though.

Regards Nick.

Edited By Nicholas Farr on 06/02/2023 09:27:39

I've silver soldered the unleaded version of EN1A quite a number of times. I use HT5 (Tenacity) flux for this even when there isn't a need for extended heating.

On the subject of stress relief, mild-steel comes in two basic forms, 'black' and 'bright'. It can be exactly the same alloy, but 'black' comes straight from the mill, where it was hot rolled. As black hot-rolled steel is allowed to cool slowly and not processed further, internal stresses caused by rolling are naturally relieved.

In contrast, the bright form is finished to a better standard by cold-rolling, but the process can trap stresses inside, which cause the metal to bend when it's cut. The advantage of Bright is the finished surfaces can save a lot of machining. But if bending is likely - as when milling notches into a large straight section - it's better to use Black.

There are many varieties of mild-steel. They're all cheap general purpose steels but the emphasis for most of them is structural work rather than machining. They can all be sawn and drilled without bother, and most can be welded. There are exceptions: mild-steels containing Lead (EN1A-Pb) machine beautifully but don't weld well. Mild-steel containing Boron for strength doesn't weld or machine well. Ordinary mild-steel, like EN3, machines moderately well, but it's a bit sticky with increased risk of surface tearing and poor finish.

For most purposes I use Bright EN1A-Leaded because it's easy to machine and the good pre-prepared finish saves time. However, I switch to Black whenever stress bending might cause trouble. Not often, because most of what I make is stubby.

Buying metal I recommend reading the specification looking for words like 'free-cutting' and 'good machinability'. After early bad experiences I avoid scrap because modern manufacturing chooses alloys with no regard to amateur recycling. The machinability of scrap ranges from excellent to diabolically difficult, and a unlucky batch can completely confuse beginners. Three things go wrong in a workshop and it's best for beginners to de-risk when they can:

1. machine worn, faulty or needs adjustment. Includes blunt tools and other annoyances
2. operator error. There's a lot to learn, including what to do about problem 1!
3. difficult material. Bad news in combination with a wonky machine and trainee operator. Good news; it can be avoided by buying metal known to easy to machine.

Don't dismiss scrap though: give it a try after learning the basics. Knowing how good metal behaves makes it much easier to adapt to more difficult materials later.

Dave

Forgive me if I repeat what has already been said, or you already know, but whilst difficult or poor steels may not be easy to work alot will also depend on the machine and the skill of the operator. The grinding of the tool and setting it up is vital, even the best steels will not work well if the machine is wrongly set or the tool blunt or badly ground. There are many books on these subjects, those in the the "workshop practice series" are under £10 each, No 34 on lathe work and No 35 on milling are a good start, No 42 The Metal Workers Data book and The Model Engineers Handbook by Tubal Cain (the real One, Tom Walshaw) these 2 are NEVER far from my hand. Good Luck and Best Wishes. Noel.

You can silver solder both EN1A and EN1A pb, provided you don't overheat the EN1Apb and boil the lead content but you are only likely to do that if using OA or OP, propane on it's own should be OK unless it's very small sections which can overheat. No problems with EN1A as there is no lead in it.

Edited By JasonB on 06/02/2023 10:28:17

Hi Martin,

Your 20kg pack will be EN3, machines well with Aluminium ##GT inserts which are very sharp.

En1A machines much better with hss, the down side being an increased tendency to rust.

Round BMS is only round-ish though it is rounder than Black.

I cheat and use ground round steel for shafting of any length.

Rapid Metals are modeller friendly especially if you call in when you can check out the off cuts bin. They also due postal.

I think you will find SAE 4141, like the more common 4140, is a high tensile alloy steel along the lines of chrome moly, and thus not easy to machine for model purposes. Usually used for high-load industrial shafting and gears etc.

1144 is the usual "stress proof" steel some US model makers like to use for delicate crankshafts in model IC engines etc but not at all necessary for general modeling use.

Jason, you must boil the lead as lead melts at 200 to 300degs and silver solder flows at approx 690 degs

Bernard, lead may melt at those temperatures but it's boiling point (turns to vapour) is about 1750deg C so at normal silver soldering temps it will be OK.

Boiling point

You may get a small amount of unalloyed lead on the surface of the steel mixing with the solder that can give a slightly weaker joint so it can help to have a bigger gap so the lead is diluted by the larger volume of solder

Edited By JasonB on 06/02/2023 15:13:04

Yes, I've not seen orthogonal sections from our usual suppliers. However, it seems to be available e.g.

**LINK**

I wonder if it is more popular in industry these days due to CNC operations. I'd certainly choose it in preference to EN3 for machining.

Rod

You have been able to get hex from several suppliers to the ME trade (good for nuts and hex head screws/bolts for a number of years but I tend to prefer to mill it and square heads these days as you get clean crisper corners. Plus the ME suppliers tend to keep imperial and BA not metric that I mostly work with these days

The other sections will probably need 3m or 6m lengths to be purchased, your link only sell EN1A in round so although it is probably made still hard to find

Edited By JasonB on 06/02/2023 16:42:02

We don't know where you are but if in the UK, you are very unlikely to find the American grades Hopper suggests!

The EN-series is an old British industrial standard, but the modern identities like 230Mxx are essentially the same materials under international trade-standard names.

It may not matter so much for a small engine run only occasionally on compressed-air or low-pressure steam; but it is normal practice for parts running on each other to be of different materials; so you may as well start in that way.

In a model steam engine, typically the -

- cylinder, valve-chest are of cast-iron or gunmetal,

-piston and slide-valve often gun-metal; piston-rod and valve-spindle normally of a free-cutting stainless-steel

- cross-head is of cast-iron running on steel guide-bars (mild-steel is fine),

- eccentric straps and sheaves vary from design to design but can be of mild-steel running on gun-metal or cast-iron, or gun-metal on mild steel, with no set rule as to which partner is of which metal. Usually the strap would use the bronze or steel due to the thin sections.

- connecting rod(s), linking parts, for mild-steel. Normally one-piece each.

- crankshaft of mild-steel (built-up usually - they can be machined from solid if you like a challenge), with gun-metal big-end and journal linings.

- small parts like lubricators and drain-cocks can be machined from brass bar.

"Gun-metal" is a type of bronze, and one variety is lead-bearing for better machining and running characteristics.

'

Bronze cylinders excepted, these choices are pretty much as was the industrial practice we are replicating.

Look in the ads on here and in the two magazines for materials stockists supplying the hobby, for all those metals I have listed.

I'd advise against buying steel from the DIY building-supplies merchants. It is fine for its intended purposes but not cheap, and not best for precision engineering. It can be used in some areas of large-scale model projects, but with care to match metal to purpose and process.

.

On a general point, EN1A is easier to machine to a fine, accurate finish than is EN3B (or their modern equivalents for both); but as others have said the crucial point is in the operating! So good tool-grinding and setting, and appropriate cutting speeds and feeds.

As others have said, using "pre-loved" steel is a gamble! A clue to its suitability, if salvaged from a scrapped machine, is to consider its original purpose. I have used old cable-drum tie-bars, ostensibly "just" mild-steel, and they proved some of the least machinable stuff I have found! A carbide tool just ripped its surface but I obtained a finish sufficient for a static part later painted, with an HSS tool carefully ground.

'

On tooling...

Some swear by carbide insert tool - and often swear you need run the machine very fast for it to work but I have not found that necessarily true. These tools are made for very fast cutting on modern, massive industrial machines but they still work at modest rate. They are expensive though, and fraught with difficulties because they come in more varieties than Heinz foods, by their designed trade uses.

Some swear by HSS tooling, and for a beginner (or anyone really) this is often the better and certainly far more economical option. It is easy to sharpen with a reasonably good off-hand grinder, and writers like Harold Hall have published designs for simple tool-rests to enhance such a machine for the purpose. Good machining exercises, making them, too!

Some use either HSS or insert tooling according to purpose, and there are times when either is better than the other for the particular operation.

I've just posted a couple of updates to my James Coombes thread. Several instances of machining round stock to square or rectangular section which not only allows easily obtainable free cutting round material to be used but also save s on having to set up these sections in a 4-jaw and the resulting interrupted cuts as most of the material is turned round.

At the risk of derailing the thread, if your "Bright Mild Steel" was diffgicult to machine, how did you go about it?

What tooling did you use? HSS properely ground, mounted at centre height, and using the right speeds and feeds should provide quite acceptabl results,.

Carbide tips can give very good finish, so mabe some other factor is causing your problems?

What feeds, speeds, and depth of cut are you usaing?

Are the gibs set correctly?

Is there no undue play in the bearings?

Boasting, using a Diamond (Tangential) HSS tool with a feed rate of 0.0025" (0.06 mm) per rev at a surface speed of 100 fpm ( 30 M/min) the finish, particularly on facing, is very good...

HTH

Howard

Hello Guys

Thank you so much for all the detailed replies on the various types of mild steel. I'll have a look into the EN1A and the leaded type and see how I go with this.

I noted that there were a few questions asking why I hadn’t thought of cast iron for some of the engine parts, its just a matter of experience or lack of it, and the need of time to source materials.

I live in a very rural area on the west coast of Scotland and delivery is a premium for materials.

I’ve spotted a few vendors on here and I’ll have a look at their stock list, also in I’m looking for a chunk of PB square stock to machine a new leadscrew nut for the cross slide on my Warco GH1230. From the factory it’s  got a horrifically machined chunk of brass, I think.

Thanks for all the input guys I really appreciate all the help.

Martin

Edited By Martin Currie on 09/02/2023 08:40:44