accuracy of silver steel

My current project requires a length of accurately ground 10mm diametre steel bar and ideally I want a 12cm long piece, bang on 10mm, straight and parallel. I've got 6 lengths of 10mm silver steel from various sources and have been surprised at how variable they are in size when measured accurately, ranging from 9.970mm to 9.998mm. The 9.998 piece is suitable but its not parallel and tapers from 9.998 at one end to 9.990 at the other over 30cm. This is still OK for my needs but I wonder what the typical tolerances on ground silver steel bar are.

Is it possible to buy more accurate and consistent ground steel bar?

The supplier ought to have their tolerances published.

**LINK**

For instance claims H8 tolerances which would appear to be too lax for your needs. Whether a Co like that grinds their own or buys in might determine their capability of sorting through to making a rod to your tolernaces.

At the risk of demonstrating, once again, my ignorance; is that level

of precision even possible outside of a sterile, clean room environment ?

I would hasard that holding the thin end in one's hand, for a couple of minutes,

would soon rectify the difference.

Your project sounds interesting though (re the Harley), hope you post some photos.

Silver Steel is 'centerless ground' and is sometimes not as accurate as one might hope.

PGMS (precision ground mild steel) is [or at least was!] ground between centres.

Good Stainless Steel rod appears to be available, to the printer & scanner manufacturers.

MichaelG.

That would indeed be very lax, try h8 which is for rods not H8 which is for holes

Just unwrapped and measured some 10mm PGMS, used the imperial mic as I prefer the feel of that over the digital (metric) one.

10mm = 0.3937" and on both ends I measured 0.3937"

And especially for Michael that last 0.0007"

Afraid I don't have anything that will measure to 100,000ths or 1 micron like the OP but as said if it did it would not measuer the same now as it did when I took the photos as the shed is starting to get some sun on it. A taper of 0.00008" over 12" is not a lot.

Edited By JasonB on 03/07/2018 08:46:02

Edited By JasonB on 03/07/2018 08:51:58

As has been said PGMS is good.

Silver steel has the reputation of sometimes being 'lobate' (like a 50p piece) as well because of the centreless grinding.

H8 for 10mm shaft is up to 27 um undersize so allowing for you not having a temperature controlled toolrom (like Jason does ) the 0.970 might just be in tolerance.

Neil

Not another one, H8 is Hole, h8 is shaft. that is why the website linked to says h8

EDIT H8 is plus 0.027 not undersize, h8 is 0.027mm undersize 

Edited By JasonB on 03/07/2018 09:17:25

That's what I love about this forum.

Every day is a learning day.

Ooh, moderator to moderator handbags at dawn!

Hi have a look at Parker Steel web site **LINK** they sell Stubbs SS which was generally acknowledged as “the best” some time back, the tolerance was always size +0 to - .0005”

Have to say I have purchased some SS that I find dubious in quality so not try to stick with Stubbs

John

Err, "bang on" is not possible. What tolerance do you really need?

Russell

Accuracy depends upon the source. A couple of industrial suppliers quote a tolerance of 0/-0.015mm for silver steel up to 25mm diameter. I've just measured a 16mm diameter length chosen at random; it's within 0.003mm of size and a variation of less then 0.002mm end to end and round the diameter. Either the measurement technique is wrong or the supplier isn't up to scratch.

The issue of lobes is one of the great ME old stories. Sure enough in the early days of centreless grinding there were some issues with trilobal results to do with the regulating wheel; constant diameter but not a fixed centre. But any reputable manufacturer sorted out the issues long ago; think 50+ years.

Andrew

Linier shafting from a bearing supplier may suit your needs.

.........................Makes note of "lobate" for future use

More than that, I think - my grandpa was a centreless grinder for BSA in WW1 (Reserved Occupation) and his view from remembered conversations with older family members was that the technique could produce results as good as the best. Of course, tolerances like the OP's may not've been on the agenda in those days.

And when I was working at a dial gauge manufacturer, PGMS came in long lengths with no centre holes I ever saw, so I thought that was centreless ground too.

Bars for threadrolling at another shop I worked in were routinely bar-turned (think rotating centreless roller-box) from scaly black bar to a couple of tenths (say 5 um).

.

Thanks, Jason

MichaelG.

Jason; is your mic a 'Shardlow' . I have a dual scale one that I bought when I was apprentice back in 1963- 55 yrs ago now, & still have it, in decent nick too.

George.

Mitutoyo 0.0001" one about 35yrs old. It was my brothers when he started work but he gave it to me when he went from BL to BMW.

Despite having said I don't have anything that will measure to 1 micron I do infact have one of their digital mics that displays to 0.00005" or 0.001mm but don't find that as accurate to use as the thimble has a friction rather than ratchet drive and it's a bit larger and unbalances so i find I can't get very consistant readings.

I had a length of 'Lobate' 2mm silver steel a couple of years ago. I'm not sure of the supplier, possibly RC in Luxembourg.

This, after lapping to 1.97mm, would not enter a lapped hole that a 1.98mm pin gauge passed through. When I rolled a length on the surface plate with a ground V block the irregularity was audible. The pin gauge was quiet.