Bright vs mild steel and 'bananaring'

Could you advise me please chaps, as you perhaps know, from a previous post, I am planning to mill an I beam out of 1/2 square bar.

I've looked for suitable material on eBay but so far not found any stocks of 1/2" square in mild steel, to the length I need, 1m (plenty of 12mm which is unfortunately, just under size).

Most seem to offer bright mild steel which if I am correct, is 1) tougher to mill and 2) more likely to banana.

Is this correct? If so, could anyone recommend a reasonable cost supplier who could supply the material I need, please?

I think in one of my previous posts, a kind poster gave a link to a shop on eBay, but they don't seem to have it either.

Ideally I'd like to keep cutting to a minimum hence buying the correct 1/2 square stock, rather than buying an oversize piece and milling it down therefore (hopefully) keeping the banana's to a minimum.

Cheers

Edited By Chris Hammond on 23/01/2017 16:13:41

Any Gate manufacturer will have 12mm sq black bar.its dirt cheap look for a local place and call in

Hi Michael, sorry, I think I was editing my original post just as you replied. Yes, plenty of 12mm around, but it's a touch undersize (.7mm). I do think it will make a difference, tiny as that measurement is, as it will mean all the brackets which rivet to the beam will also have to be undersize.

Thanks for the suggestion though. It's good to keep in mind for future reference.

Edited By Chris Hammond on 23/01/2017 16:24:58

Chris

I remember you asking about how to machine the I beam in another post.

Something that may not have been mentioned before to reduce the banana effect when machining is to normalise the steel beforehand. Get it red hot let, let it soak at the red heat and allow it to cool slowly. At this time of the year, you could put the steel in your fire while it is good and hot and leave it there overnight.

Dave
The Emerald Isle

You can still get 1/2", act. 13mm square, but you will have to go to the yard and check. I know this 'cos I've bought it in error, not that it mattered at the time. I think it is from when we went metric and the rolls were not altered. Black MS will be best for your job.

Best to use hot rolled black steel. It won't go banana shaped when machined. Black steel is usually slightly over nominal size, to allow for the corners not being square.

I've got some 16mm square hot rolled in stock - as it's way cheaper to buy the standard 6m length than mess about buying shorter lengths. Whereabouts are you?

Andrew

mkmetals sell 1/2" ground stock by the metre. This will not bend when machined. Up to you if you want to pay the price of £32/m.

Black bar is black because it is rolled when hot and cools at a rate that usually keeps internal stress low. Bright bar is usually bright because is has been rolled cold but this induces internal stresses that can result in the bending often seen when it is machined. Ground flat stock is an oil hardening steel that is annealed then ground to size. It is more expensive than plain steel but if time is money as in industry it can end up being a time saver.

Martin

Even if you did come across 1/2" black bar it will likely have rounded corners so as I said in the other post mill it out of the next size up which is 16mm.

It is probably not quite so nice to machine as bright but is still best for the job.

Don't know if you saw my post yesterday in teh workshop progress thread but I showed some parts that are 5mm finish thickness, I cut them from a mixture of old 1/4" and new 6mm black bar that I had in stock. I also had 5mm black bar but chose the thicker material. They have not moved.

Thanks for the advice, guys.

steamdave - great idea, one big problem, we don't have a fire! Mum and dad do, so I can use that if need be.

Gordon, I don't think I know of any yards around, but will look. Good idea.

Andrew, I am in Coventry, years ago, I could have walked into the city and found 100s of engineering firms, big ones too, like Alfred Herberts, sadly, they have all gone. Nothing left.

Martin, definitely not going to pay £32/m.... I would want gold or platinum wrapping for that!

Gosh Jason, that's terrific work.

Great point about the rounded edges, so yes, 16mm it is I think. Going over to the workshop progress thread now to have a nose....

Jason, quick question, what's pickling? I guess it's soaking the metal in something, but what, why and how long for?

The black scale can be a bit abrasive on tools so is best removed before machining.

I use "brick cleaner" from the local builders merchant, a soak in that for about 1/2hr is usually enough to cause the scale to flake off, maybe a bit longer if the scale is very heavy or the acid getting old. Quick rub with a small wire brush can also help.

Once the scale is off rinse in water to remove any acid, dry and give a quick spray of WD40 so it won't start rusting.

It is also good as a pickle to remove the oxide after silver soldering and will also shift Tenacity/HT flux.

Don't do it inside as any fumes can make other metal rust.

I use Rapid Metals in Redditch but they have a branch in Coventry - I've found them very helpful and well priced. If I'm looking for something in particular I phone and ask but then I'm a newbie and not that discerning .... http://www.rapidmetals.co.uk/

Hi Chris, you may be able to do a little less machining by getting some 16 x 10mm bar for your "I" beam. These people do it and you can have some cut to length if you don't what a full 4.1M of it. **LINK** Just select cut to size in the select box and click on add enquiry. I don't know if they only do a minimum order value though, but it may be worth an inquiry.

Regards Nick.

Thanks Jason. I will add this to my list of useful tips and do this when I get started (hopefully in a week or two!).

Phil, thanks for this, they are about 4 miles from me, so I'll give them a call and see what they have.

Hi Nick, thanks for the advice, that sounds like a good plan to save a lot of machining.

Thanks again guys.

That would be a big fire grate to take a 1 metre length. I put the odd casting in my woodstove but even that is 18" maximum.

I am firmly in the camp of those recommending hot rolled (black) bar. Attempting to use cold finished (bright) bar and anneal it is unnecessarily complicated and expensive. If you have a cutter with carbide inserts, I would not bother pickling the bar to remove rust. I suspect the brick cleaner mentioned is hydrochloric acid. Its fumes will corrode any steel nearby. For a source of hot rolled bar check out the shops doing ornamental iron work. They might have some drop about the right size and would save cutting charges.

Rapidmetals at Coventry (Bedworth) are very good used a few times.

I think you will have a banana problem wether black or bright. I remember years ago when we milled out some pieces of 6" by 4" 36 long to make some narrow track fork lift arms. They were to be welded each side of some 1/4 plate, just couldn't get them straight. After numerous attempts we modified the customers design and built the whole thing from welded pieces. Had to tack and weld alternate sides and pieces to keep them straight along with thermal stress relieving. After we had created half dozen of these pieces we had it sussed.

I know the sizes are a bit industrial but it is makes you expect the worse when you do things as a model engineer. Just because it is smaller doesn't mean the problem won't crop up.

Cannot see any problem getting 1/2 square m/s regular ME suppliers stock it, forget about black steel its blacksmith material,not all mild steel bananas when cut on all sides it varies batch to batch,rectangular seems to be worse than square particularly key steel, just anneal by heating to red and cool slowly. Another approach where there is a wider selection of available material specs is to machine round bar to the shape required ,leaded en 1A produces a super finish,or if a tougher material is required then free cutting en8 is just the job, with virtually no distortion , i remember reading in Model Engineer back in the 1970s of a exhibition winning model engineer who liked stainless steel motion on locomotives, his approach was to machine it from stainless round as it machined easier than rectangular section and had a wide choice of free cutting s/ steel specs, getting it right takes longer and more patience but worth it in the end.