Strange Hardness Problem.

[Nigel Graham 2Participant @nigelgraham2]

I modified my steam-wagon's smoke-box today, having found it was not closing fully.

I successfully re-faced the door itself, turned from some cast-iron disc or other, ohh, rather a lot of years ago, to remove a small step I thought causing the problem. .

Next I found the fixed part of the hinge was all obbley-eyed, and anyway needed the holes enlarging to compensate for the slight drop in level caused by the turning. It may have become damaged somehow.

I made each half of the hinge by brazing through-drilled mild-steel rod to a piece of angle; and it was part on the door gave the problem in trying to enlarge its pin-hole, through a tube just over 2" long.

When I tried to enlarge it, drilling free-hand with a battery drill, the drills met what appears a very hard section in the middle. I tried from both ends, but merely blunted two HSS bits on whatever they are hitting.

Could it be a hard patch?

Or are the drills skating on a tiny misalignment due to drilling the original hole from both ends?

Can anyone say what might be happening in there?

++++

I am replacing the fixed part completely – cut from solid, in fact from a bit of 25 X 10mm HRS from a scrap length of replaced miniature-railway track. All manually, including using the Drummond manual shaper to face the mounting edge faced to below the rust pits; bench-drilling the holes from marking-out, then removing the middle section by chain-drilling, abrasive-blade saw, band-saw and file. Could have milled it but probably no more quickly and certainly not more cheaply!.

'

And "obbley-eyed" ?

I learnt that from a Cotswolds farmer when walking across his land with some friends – we'd mis-read the OS map, and his directions to the lane we sought included " Cross the field and you'll come to an obbley-eyed gate…"

We were too polite to ask how we'd identify it as the right gate – after all, our error meant we'd been inadvertently trespassing.

We soon found out though – all droopy and broken, and tied up with lots of pink binder-twine.

[Nigel Graham 2Participant @nigelgraham2]

[SillyOldDufferModerator @sillyoldduffer]

I like 'oobley' – it describes so much of what I do.

My eye was caught by 'turned from some cast-iron disc or other, ohh, rather a lot of years ago'. Cast-iron is highly variable stuff, especially old cast-iron. It ranges from being carefully made to an engineering specification to an utterly vile random mix of semi-melted scrap.

Cast-iron was once the cheapest way of making a wide variety of domestic items. Most of them didn't require decent metal. It was enough that the metal poured and surfaces could be corrected with filler and paint.

Sash weights are notorious; many were made with leftovers at the end of a pour plus slag scrapings and added oddments; knocked out as cheaply as possible, and like as not chilled with a hose. The foundry didn't take any care because sash weights were never intended to be machined.

Depending on what was being made and why other castings suffer more or less the same problem. Could be good, or nasty, or mostly good with odd defects. Age matters. Before the chemistry was understood, cast-iron had distinctly local characteristics: Welsh, Scottish, and Yorkshire Iron all had different properties, and it was necessary for the customer to select from named irons like: Buffery Iron №1; Carron Iron №2; Carron Iron №3; Coed Talon Iron №2; Devon Iron №3; Elsicar and Milton; Muirkirk and innumerable local variants. Some machined well, others didn't.

The performance of cast-iron depended on impurities in the ore, coke or charcoal, flux, and on furnace time and temperature. Getting the best result was skilled work, but mysterious. Techniques that worked in Wales failed in Scotland and vice versa. By the end of the 19th century the chemistry was well understood and it was possible to produce good cast-iron almost anywhere. In the early 20th century the Americans discovered how to further improve cast-iron with Silicon and a patented thermal process. However old-fashioned methods persisted well into the 20th century, and jobbing foundries still existed in my youth, knocking out street furniture and ornaments rather than engineering artefacts.

All change! Today, my local foundry is a high-tech operation using centrifugal casting and other advanced methods. Their main customer is aero-space. Outside, the foundry looks like an ordinary commercial building. Inside, the workspace is clean and tidy. I suspect the furnaces are all electric to eliminate impurities. No-one wears a cloth cap or shovels coke. Minimum Order Quantities in the low thousands – the firm aren't interested in small jobs or rabbits!

So, unless bought to a specification, cast-iron is unreliable stuff. I suspect Nigel's door contains a hard slag inclusion. Try a masonry or carbide drill on the inclusion, and then go back to HSS for accuracy.

My scrap-box has some cast-iron slabs recovered from a big night-storage heater. Apart from a really tough outer skin about 3mm thick, it machines well. Unfortunately for some purposes, it's impossible to clean, leaving black marks like a pencil. Must have an unusually high carbon content, maybe to make the iron more fluid when melted, or perhaps to increase the slabs thermal capacity. A clever chap knew why that particular cast-iron was selected, I can only guess. He didn't plan for it to be machined 50 years after the heater was first installed!

Dave

 

 

 

Edited By SillyOldDuffer on 29/04/2021 10:48:52

[Nigel Graham 2Participant @nigelgraham2]

Ah – I should have been clearer.

It was the hinge screwed to the door that contains the hard (?) part – and that is fabricated from mild-steel.

Not the cast-iron door. That machined very well though revealed a couple of small blow-holes.

'

Although I forget the source of the cast-iron, I think it was probably a scrapped machine part. I know architectural castings were usually cheap and cheerful, and items I have tried turning were like Swiss cheeses. One I hoped to use for the pistons was far too porous, but good for making a weight to hold the boiler's "stoking-shoot" (the original name) lid closed. I once tried sawing an old sash-weight, and it was too hard even for the hefty 'Kasto' hacksawing machine I used at work at the time.

One of my old text-books gives a recommended recipe for iron suitable for large machinery frames etc. It uses selections by quarry as you show – but each ton of mixture is 15cwt of various new irons , plus 5cwt of "best selected scrap".

Modern foundries are a far cry from that.

Back around 1980, my Somerset- based caving-club replaced its old central-heating / hot-water boiler, which had a massive cast-iron heat-exchanger, and the Club Secretary of the time took it away. He, Bob Drake, was Managing Director of the Bristol foundry (I forget its name) whose more unusual commissions included the replica engines for S.S. 'Great Eastern' that had recently come home.

We asked Bob if his foundry can use the iron.

"No", he replied, "It will all go back to the refiners along with our own scrap. We don't know what's in that boiler iron, and our customers need metal of known and consistent quality. "

IKB – and his foundry-men and machinists – would no doubt have been delighted with known and consistent iron!

[Bill DawesParticipant @billdawes]

I remember in my days as an apprentice during my machine shop experience that turning cast iron could be a pain, it had hard glass like bits in it, could well have been glass mixed in the scrap iron that went into the cupola, we had our own foundry. Castings were much more frequent then (late 50s) largely replaced with fabricated parts now.

Bill D.

[Bill DawesParticipant @billdawes]

And drilling and boring was a nightmare, hard bits and blow holes, i had to drill well undersize, straighten it out with a boring bar and then finish bore or ream. Must have caused the poor fitters a problem they were that hot coming off the lathe the cold bore must have well undersize. Scraping out was the order of the day, scrapers there's a lost art.

The components mentioned were large hubs for centrifugal fans.

Hope none of the old Alldays & Onions fiitters are reading this!

Bill D.

[Nigel Graham 2Participant @nigelgraham2]

Some rolled steel angle can be bloomin' awful too, especially it seemed the stuff that used to be used for bed-frames.

Hard bits in cast-iron might not have been glass mixed with the scrap but silica from poorly-refined raw iron – same compound as glass though, and just as hard.

Anyway, I was asking why it was bright mild-steel, not cast-iron, that was blunting my drills. Yet I am pretty sure I had made the component originally by drilling through the length of solid rod, not from tube.

[Author]

Posts