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accuracy of silver steel

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lfoggy03/07/2018 07:46:14
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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?

pgk pgk03/07/2018 07:57:43
1188 forum posts
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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.

Daniel03/07/2018 08:03:06
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At the risk of demonstrating, once again, my ignorance; is that level

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

surprise

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

would soon rectify the difference. cheeky

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

Michael Gilligan03/07/2018 08:13:01
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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.

JasonB03/07/2018 08:15:45
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Posted by pgk pgk on 03/07/2018 07:57:43:

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.

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

JasonB03/07/2018 08:41:58
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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"

dsc02892.jpg

And especially for Michael that last 0.0007"

dsc02893.jpg

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

Neil Wyatt03/07/2018 08:50:29
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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

JasonB03/07/2018 08:53:39
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Posted by Neil Wyatt on 03/07/2018 08:50:29:

 

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.

Not another one, H8 is Hole, h8 is shaft. that is why the website linked to says h8teeth

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

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

Daniel03/07/2018 08:57:57
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That's what I love about this forum.

Every day is a learning day.

David Standing 103/07/2018 09:01:22
1109 forum posts
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Posted by JasonB on 03/07/2018 08:53:39:
Posted by Neil Wyatt on 03/07/2018 08:50:29:

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.

Not another one, H8 is Hole, h8 is shaft. that is why the website linked to says h8teeth

Edited By JasonB on 03/07/2018 08:54:45

Ooh, moderator to moderator handbags at dawn! teeth 2

JohnF03/07/2018 09:03:08
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697 forum posts
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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

Russell Eberhardt03/07/2018 09:04:29
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Posted by lfoggy on 03/07/2018 07:46:14:

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.

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

Russell

Andrew Johnston03/07/2018 09:10:55
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4206 forum posts
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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

Chris Evans 603/07/2018 09:13:10
1288 forum posts

Linier shafting from a bearing supplier may suit your needs.

colin brannigan03/07/2018 09:19:57
44 forum posts
1 photos

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

Mick B103/07/2018 09:27:37
799 forum posts
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Posted by Andrew Johnston on 03/07/2018 09:10:55:

...

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

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).

Michael Gilligan03/07/2018 09:27:49
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Posted by JasonB on 03/07/2018 08:41:58:

.

And especially for Michael that last 0.0007"

dsc02893.jpg

.

Thanks, Jason yes

MichaelG.

mechman4803/07/2018 10:10:39
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2164 forum posts
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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.

JasonB03/07/2018 10:23:53
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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.

Roger B03/07/2018 10:58:06
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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.

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