A strange "core" right along a length of bar.

Various quality-control discussions on here reminded me of my time years back as the metals-stores keeper in a company making precision screen-printing machines.

These used a lot of aluminium alloy (HE30 – I don't know its modern number) bar, and my task was cutting the blanks from stock bar of appropriate sizes.

The well-built but crudely-designed hacksawing-machine naturally left very rough sawn faces. So we were all surprised when the milling, if not the subsequent anodising, revealed a peculiar elliptical "core" or ring right through the centres of one particular batch of parts perhaps 300mm long, made from bar about 1.5 inch square.

They moaned at me until I pointed out no-one could have known until the parts were finished.

Anyone any idea what may have caused this effect, which none of us saw in anything else? Or has encountered it personally?

Interesting ideas to mull over…

Of them I am inclined to think Circlip's the most likely explanation – a heating and cooling effect.

That would explain its consistency by length and concentricity with the bar section. The section was a rectangle, as I remember 1.5 X 1.24 inches (aluminum-alloy was still being sold in Imperial sections), which difference could have influenced the core to be rather elliptical in section by depth from surface. Might be an interesting geometry and spreadsheet exercise to plot constant radial depths from a similar rectangle, to see if it gives an ellipse. That lots of trig though…

The "core" effect was uniform throughout the length, and may have been in other bars from the same batch – I have long forgotten the number of components but they were some 300+ mm long, from stock I think supplied in 4m lengths.

It was invisible on the sawn ends, hidden by the cut marks from both the metal-manufacturer's circular-saw, and certainly by the 'Kasto' hacksawing machine I operated.

An inclusion would be expected irregular in section, inconsistent in length, and not necessarily concentric with the bar, from end to end.

'

Engee – Thankyou for the reference number for the alloy.

'

The company's drawing-office did not usually bother with such niceties, often putting in the "Material" box only Alum or Mild Steel, or Stainless; leaving me as store-keeper to judge the sort from the drawing and trade catalogues. That one brush with an incorrect-edition drawing apart, no-one queried it so I must have been doing something right.

It won't be me having to worry about alloy grades though. I left that company long ago, firstly for better work and now by retiring anyway!

Just as well as it turned out, for a year later its management abruptly closed the machine-shop, with no notice; merely calling everyone into the workshop-manager's office on Friday and telling them not to come in on Monday – here's your P45s, gentlemen.

Oh, and as we've seen with many other companies behaving in that way, only just before Christmas!

A former colleague told me that the MD didn't have the guts to announce it, but left it to the Production Director. At least that was before universality of portable 'phones and e-posts so they could not use merely a cold, cowardly text message. Luckily most of the machinists found local employment with sub-contract engineering firms; ironically, making the same printing-machine parts.

Thr firm changed hands subsequently, is thriving, and rather better run. Their main customers? Computer and portable 'phone manufacturers….