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Why is my silver steel undersize

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BOB BLACKSHAW18/01/2020 18:08:07
262 forum posts
59 photos

I'm using silver steel for a axel, and have reamed 5mm on two pieces of brass bar which are the standards for the steam crane I'm making. Having found a slight play when together I measured the silver steel and its .03mm undersize. I have measured all of my silver steel from 10mm to 3mm and all measure undersize, why is this ? I now have slight play and a bit annoyed as I will have to turn the axel to fit the standards or find the correct 5mm size. My question,is all silver steel undersize.

Bob.

Andrew Johnston18/01/2020 18:17:46
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5106 forum posts
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The only time I’ve seen undersized silver steel it was from a cheap supplier. Normally one would expect it to be on size to better than 0.01mm.

Andrew

Paul Kemp18/01/2020 18:21:11
376 forum posts
18 photos

That's a little more than a thou. What are you measuring it with? I have just measured a piece of 3/8" with a Starret 0-1 mic and its bob on 0.375. As you say all the bits you have you have measured are undersize maybe it's your instrument?

Paul.

JasonB18/01/2020 18:25:26
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Does sound like your equipment if everything is undersize.

What spec was the reamer H7, H8 or something else?

AJS18/01/2020 18:33:25
34 forum posts

Have you measured the finished size of your reamed hole, or are you assuming it's 5.00mm?

Bill Chugg18/01/2020 18:34:32
966 forum posts
6 photos

Bob

Just checked my Hercules and mine is spot on 5mm. I buy all my materials from Joe at Maccmodels.

Is it possible that the material is sized correctly and it is the reamed holes that may be a tad oversize ? Fortunately if so, there is enough matl onthe standards to soft solder in a bush.

Bill

Neil Wyatt18/01/2020 19:11:34
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My silver steel is all ex-stubs and is fine.

The brand is now owned by T&A and their specs are HERE

Under 1" the tolerance is +/-0.00025"

Is it possible there's an issue with how you are measuring? Place two pieces side by side and see if they measure 0.03 or 0.06mm undersize. If its still about 0.03 then you have a zeroing or measuring technique error.

<edit>Some interesting comments on tempering at that link.

Neil

Edited By Neil Wyatt on 18/01/2020 19:13:22

Emgee18/01/2020 19:21:20
1344 forum posts
212 photos

I bought some Stubbs ss recently in 10mm and 5mm, both sizes were within quoted tolerance for ss in those sizes, that is +0 -.015mm
I don't have calibrated measuring instruments but when needed have some decent slips for checking the readings obtained.

The problem with fits is that H7 will give oversize and so the less than full diameter for the spindles will result in running clearance greater than required.

Emgee

Edited By Emgee on 18/01/2020 19:25:10

jimmy b18/01/2020 19:23:24
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568 forum posts
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I get mine from here they say h8 tolerance

Jim

BOB BLACKSHAW19/01/2020 10:46:06
262 forum posts
59 photos

Thanks for the replies.

I have checked my four callipers, one is a Mitutoyo and three micrometres with slip gauges so I am confident that they are correct, they all read the same on the silver steel as .025 undersize, I also put two together and .05 undersize. All of my silver steel reads .02 t0 .025 under, I brought the steel from a well known seller on this site, so I shall try another supplier as suggested by Jim. The hole size is correct by making a plug a fraction under 5mm to fit the bush which I done this morning.

I also noted that the 8mm rods from old printers are undersize by .08mm which I've used for axels and made bushes to fit,any reason why?

Bob

peak419/01/2020 11:14:16
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Posted by BOB BLACKSHAW on 19/01/2020 10:46:06:

....................................

I also noted that the 8mm rods from old printers are undersize by .08mm which I've used for axels and made bushes to fit,any reason why?

Bob

Maybe because they are 5/16";

7.92mm = 0.3118"

5/16"=0.3125" only 7 tenths of a thou different

Where were the printers made?

Bill

Edited By peak4 on 19/01/2020 11:14:43

BOB BLACKSHAW19/01/2020 11:47:39
262 forum posts
59 photos

I have no idea where the printer was made I got it from a charity shop as not working but I have had another printer in the past the same 7.92mm, nether thought about imperial size as everything now is metric.

Bob

Mike Poole19/01/2020 12:03:57
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2311 forum posts
52 photos

As much computer hardware is specified by the Americans then much of it is imperial standard sizes. Most of the fasteners in a PC are American threads.

Mike

Ian P19/01/2020 14:34:30
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2299 forum posts
93 photos

Printer rods are 7.92mm diameter so you are obviously reading those correctly.cheeky

Ian P

lfoggy20/01/2020 21:00:53
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102 forum posts
9 photos

I had a similar issue a while back. i wanted a piece of 10mm silver steel, ideally in the 9.99 - 10.00mm range. I had all sorts of pieces of 10mm silver steel and most varied from 9.97 to 9.99mm. Also some were not exactly round ! I have found 'precision ground mild steel' to be more consistent and nearer to nominal size. In the end I extracted a beautiful piece of precision gound steel measuring 10.00mm from an old piece of laboratory equipment.....

 

Edited By lfoggy on 20/01/2020 21:04:23

Howard Lewis20/01/2020 21:56:22
2715 forum posts
2 photos

It is possible that your Silver Steel is not round, but is lobed. So it would measure undersize when measured on a diameter, but be a snug fit in a truly round hole, although actually only making contact at three points.

If the bar was reamed with a reamer, firmly held in the Tailstock, it is possible that the reamer was a gnats whisker off centre for some reason. If it was, then some of the cutting edges would act like a boring bar, to produce an oversize hole. It is a good idea for the reamer to float so that it can follow the pilot hole without any external constraint to pull it off centre.

Howard.

Andrew Johnston20/01/2020 22:19:27
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5106 forum posts
594 photos

Lobing as a result of centreless grinding has the interesting property that the diameter measured at any two points (with a micrometer for instance) is constant. But the material is not round. Think the 50p piece if you're in the UK. Any half decent grinding company ought to have this issue under control.

Andrew

BOB BLACKSHAW21/01/2020 17:38:06
262 forum posts
59 photos

I float ream when using the tailstock so I know that the hole is correct to size, and the rods are round as they measure the same at two points. I never trust the tailstock or the tailstock chuck as I always find that the hole is oversize, but I'm only using these Chinese made ones, I would like to get a Jacobs chuck but will this improve the hole size? the tailstock is good using a feeler gauge on two points.

Bob.

Andrew Johnston21/01/2020 20:27:36
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5106 forum posts
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Posted by BOB BLACKSHAW on 21/01/2020 17:38:06:

.......and the rods are round as they measure the same at two points.

Not necessarily so, a part can have constant diameter without being round.

Andrew

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