Accuracy of steels stock

[Robert Smith 24Participant @robertsmith24]

I recently ordered a length of 1/2 inch diameter round steel bar, EN16T to make a new small end pin for a model steam engine. On checking the dimensions when it arrived, I was surprised to note that the diameter was 4 thou under the nominal size. Is this usual? Is there a source of accurately sized stock?

[Robert Smith 24Participant @robertsmith24]

[JasonBModerator @jasonb]

Bright bar is often a little undersize and not always perfectly round. Either turn from larger stock or use PGMS but that is EN1A

[Martin KyteParticipant @martinkyte99762]

If you need steel to dimension then either silver steel or precision ground is wht you require.

regards Martin

[Anonymous]

It is well within the looser tolerances for drawn bar. For diameters from 10mm to 18mm my supplier normally supplies h10 tolerance, ie, a maximum of 0.07mm. Tolerances are always negative, mostly for economic reasons. I've just measured some offcuts of EN3:

1/4" diameter – undersize by 1 thou

1/2" diameter – undersize by 1.5 thou

1" diameter – undersize by 2 thou

I would normally expect drawn bar stock to be 1 to 2 thou undersize. So 4 thou is pushing it a bit, even if still within the limits. Who was the supplier?

Same as ordinary steel silver steel is not always the same. I've bought 1/2" silver steel that was 1 thou undersize. In contrast Coventry Grinders quote a tolerance of ±0.00025" for 1" diameter and smaller.

Andrew

[Robert Smith 24Participant @robertsmith24]

Many thanks for the responses. It does seem I have purchased a length which is just within tolerances so it will have to be consigned to the stockpile. I will order some 5/8 inch stock and machine it down.

The supplier by the way was the Bay of Evil.

[Tony Pratt 1Participant @tonypratt1]

Posted by Robert Smith 24 on 16/08/2022 14:35:01:

Many thanks for the responses. It does seem I have purchased a length which is just within tolerances so it will have to be consigned to the stockpile. I will order some 5/8 inch stock and machine it down.

The supplier by the way was the Bay of Evil.

As far as I know eBay don't supply anything?

Tony

[Robert Smith 24Participant @robertsmith24]

To clarify, the steel was purchased from a supplier on E Bay.

[Swarf, Mostly!Participant @swarfmostly]

Good afternoon, all,

Just about within topic:

Regarding silver steel, it was part of my upbringing that silver steel, being centreless ground, could often be trilobar, not perfectly round. So it would always measure the same 'diameter' with a micrometer but would reveal its trilobar shape if rotated between centres and clocked with a dial gauge.

I've never actually tried it – has anyone else? Is it an urban myth?

I've always regarded silver steel as 'too posh' for mere shafting.

Best regards,

Swarf, Mostly!

[Anonymous]

Posted by Swarf, Mostly! on 16/08/2022 16:05:10:

…silver steel, being centreless ground, could often be trilobar…

As I understand it that could be true, in the early days of centreless grinding when the process wasn't always well controlled. Now I would expect silver steel from any reputable suppler to be round to a high degree of accuracy. Lacking a proper roundness meter (*) I think the best way to check for roundness is to rotate the stock in a V-block on a surface plate using a DTI or indicator to measure out of roundness. I don't think that rotating between centres will give results that are easy to interpret.

Just tried the V-block and DTI method on a length of 25mm silver steel. Barely a needles width variation on a 0.01mm dial, so around 0.001mm? The DTI needs to be close to the V-block or one can get more than a 0.01mm variation just my varying the force pushing the rod into the V-block.

Andrew

(*) If I ever win Euromillions big time a proper metrology laboratory will be part of the new workshop

[Anonymous]

Posted by Robert Smith 24 on 16/08/2022 14:35:01:

…supplier by the way was the Bay of Evil.

I do sometimes buy steel from that source, but only for fixtures and formers. I don't expect it to be to any particular tolerance or to be consistent in machining so wouldn't want to incorporate it into a model. This lump of steel was bought via Ebay to make a former for a rolled chimney:

As you can see the finish is inconsistent:

Acceptable for a former but not for a model part.

Andrew

[Author]

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