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The wonderful world of gauge blocks

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Ian Johnson 124/10/2019 22:44:24
174 forum posts
50 photos

Some of you may have seen my recent posts on my new (to me) set of imperial gauge blocks.

It's not until owning my own set that I have really appreciated what a wonderful piece of engineering precision they are! Looking forward to actually using them soon, which got me thinking.......do I need a metric set? Or could I use the imperial set to get a metric measurement?

Time for a test measurement:

8mm is 0.3149" so using gauges 0.1009 + 0.104 + 0.110 gave me 8mm.

12mm is 0.4724" so using gauges 0.1004 + 0.102 + 0.170 + 0.100 gave me 12mm.

I used measurements to the 4th decimal place ignoring the 5th place, and checked with my Mitutoyo digimatic micrometer.

Looks like I don't need a metric set!

Ian

Paul Lousick24/10/2019 23:09:05
1214 forum posts
502 photos

0.4724" x 25.4 = 11.99896mm. Not exactly 12.0000mm but unless you are working in a metrology laboratory would be close enough.

Changes in temperature (even from your hands on the micrometer) will cause changes in the measuremnt. I only have a couple of gauge blocks and use them to check the accuracy of my micrometers. If it measures the same as the length of the gauge block, I then assume that other measurements will be as accurate.

Paul.

Ian Johnson 125/10/2019 01:30:29
174 forum posts
50 photos

Plenty close enough for anybody, only problem is it makes my errors more accurate!

Looking at the calibration certificate the 'Deviation of gauge length from nominal size at 20 deg C' is measured at 0.000001" that'll be one millionth of an inch crikey! I couldn't even begin to think of how to measure that in my workshop, it's never at 20 deg C anyway!

jimmy b25/10/2019 04:36:03
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537 forum posts
29 photos

I was happy with an inch set, right up to the point I saw a rally nice metric set!

Just wait until you discover how use full gauge block accessory sets are!

20191025_043227.jpg

Jim

Michael Gilligan25/10/2019 05:20:35
avatar
14249 forum posts
627 photos
Posted by Ian Johnson 1 on 25/10/2019 01:30:29:

[…]

Looking at the calibration certificate the 'Deviation of gauge length from nominal size at 20 deg C' is measured at 0.000001" that'll be one millionth of an inch crikey! I couldn't even begin to think of how to measure that in my workshop, it's never at 20 deg C anyway!

.

Our hero, Joseph Whitworth, knew a thing or two !!

Here’s an interesting read for you: **LINK**

https://archive.org/details/whitworthmeasur00whitgoog/page/n8

MichaelG.

Ian Johnson 125/10/2019 09:37:05
174 forum posts
50 photos
Posted by jimmy b on 25/10/2019 04:36:03:

I was happy with an inch set, right up to the point I saw a rally nice metric set!

Just wait until you discover how use full gauge block accessory sets are!

20191025_043227.jpg

Jim

Thanks Jim that's something else I 'need' laugh

Ian

Ian Johnson 125/10/2019 10:24:45
174 forum posts
50 photos
Posted by Michael Gilligan on 25/10/2019 05:20:35:
Posted by Ian Johnson 1 on 25/10/2019 01:30:29:

Our hero, Joseph Whitworth, knew a thing or two !!

Here’s an interesting read for you: **LINK**

https://archive.org/details/whitworthmeasur00whitgoog/page/n8

MichaelG.

Great link thanks Michael, 1877 and they knew what they were talking about, and the process of 'wringing' together two surfaces such as the more modern gauge blocks was well documented even in those days.

Interesting bit on page 39 the standard length bars are coated in 'Gold beater's skin and floated in a trough of mercury'

Fun for everyone in the home workshop!

Ian

Zan25/10/2019 14:13:04
136 forum posts
5 photos

Agreed! You just don’t realise how good the blocks are until you get a set. Mine were purchased incomplete, with about 10 missing, which I have found hunting about in auto jumbles where I also got the accessory set again it took a while to complete it again....I hadn’t thought about using them fir metric. Great idea.

old mart25/10/2019 17:30:03
790 forum posts
77 photos

I have a set of imperial ones, they have seen better days, not one would pass inspection, I had to scrape the rust off most of them. But for my purposes they are as useful as a brand new set. It is unlikely that I would ever need to measure less than 0.0005", and even a stack of half a dozen would be only that half thou down.                                   My firms inspection department had a box of slip cages, and I said, what a wonderful thing. The chief inspector replied that they are better than nothing when you are desperate.

Edited By old mart on 25/10/2019 17:33:45

robjon4426/10/2019 10:37:45
111 forum posts

Hi all, some 60 years ago during my turning apprenticeship I took my turn through the toolroom working on a shaping machine of truly Victorian style! All of the turners, millers & shaping machine operators had a box of out of calibration gauge blocks & I still have & use mine to this day. A quick check reveals 1 off 3" 20 off 0.2" - 0.95" 50 off 0.05"-0.2" despite having a hard life over all these years a quick random check with a Mitutoyo 0-1" micrometer could not reveal any error as great as 1 tenth of a thou! On a shaper (I have an Acorntools 7" if machining a surface with shoulders steps & troughs they are very handy even if it becomes necessary to alter the angle of the tool itself to reestablish tool height with a gentle touch on the appropriate block, I have a shaper gauge which came with the machine.

Another useful adjunct (is that a word?) is a 2" length off HSS ground with a chisel edge to stand on block(s) if you still mark out workpieces, ie mark out, clamp in vice, machine down to line, jobs a good un'. It is not necessary to do any of these tasks to a tenth of a thou but more to save that most precious commodity of all, time.

Bob H.

Howard Lewis26/10/2019 11:52:31
2442 forum posts
2 photos

Gauge Blocks, (Slips Jo Blocks or whatever you choose to call them ) are superb pieces of measuring kit.

used in conjunction with a Height Gauge and a Finger Clock, or DTI, they allow measurements to be taken that would be difficult, and more accurate, using other methods and equipment.

Even if they are out of calibration, they are probably more accurate than our measuring kit can show.

BUT, always use the 0.1 protective slips, to prevent wear of the actual Gauge Blocks.

And don't hold them too long, if you want absolute accuracy. Most are accurate at 20 degrees C.

Howard

IanT26/10/2019 12:21:42
1363 forum posts
137 photos

Interesting Bob - I also use a "Shaper" Gauge (although I call mine a Transfer gauge). They are certainly very useful for some Shaper operations (I also have an Acorntools 7" ).

They can also be handy for other (non Shaper) work but don't seem to be very well known by home machinists. (e.g. gauging gaps, setting up temporary reference points/levels etc). I guess you actually have to have one to find other uses for it? However, I must admit that I try not to use my gauge blocks directly with sharp tooling (perhaps I'm being over cautious? ). I generally prefer to set the gauge from an existing reference point or surface plate ('off-work' ) using a height gauge or mic. I guess that since I've 'calibrated' my larger mics using the blocks - that is an indirect use of them though. smiley

Of course, provided the tool isn't disturbed, any finish cut(s) on a sharper can be set very simply just using an indicator and one of those movable arms with a mag base. However, it is sometimes awkward to measure work (without removing it) and the transfer gauge is often handy then (as can also be a depth mic). But maybe I should find more uses for my 'precious' blocks too....

Regards,

IanT

Accurate Downfeed

Edited By IanT on 26/10/2019 12:23:34

Ian Johnson 126/10/2019 14:53:23
174 forum posts
50 photos

Yep definitely one of the more versatile pieces of kit. Every machinist should have a set.

I rapidly found out when stacking the blocks to a metric size that the most important range (in inch sizes) is 0.0001 to 0.0009, so one bit of advice if buying a second hand set make sure that range is complete.

Ian

Tim Stevens26/10/2019 16:10:50
avatar
1101 forum posts

Ian J - A gauge block which is one tenth of a thou thick? Are you sure?

My set has a series of blocks which are 0.1001, 0.1002, 0.1003 etc. Much less frail.

Cheers, Tim

Ian Johnson 126/10/2019 21:17:36
174 forum posts
50 photos

Oops! Yes it should be 0.1001 etc

Mike Poole26/10/2019 21:51:36
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2187 forum posts
52 photos

The passion for dimensioning drawings for models using fractions of an inch is I feel ridiculous, a sixtyfourth of an inch is 0.015625 so most people are going to call it 15 or 15 and a half thou and the rest is lost using practical tolerances and home workshop equipment. A set of gauge blocks is not able to accurately produce a size involving a sixtyfourth but for practical purposes it’s not going to matter but it’s going to bother anyone with CDO ( that’s OCD but with the letters in the right order).

Mike

IanT26/10/2019 22:01:51
1363 forum posts
137 photos
Posted by Howard Lewis on 26/10/2019 11:52:31:

BUT, always use the 0.1 protective slips, to prevent wear of the actual Gauge Blocks.

Howard

Oh dear Howard - I have two of these 0.1 slips and will admit I have never used them

I'll try to be better behaved in future though! Thanks for the reminder...

IanT

robjon4427/10/2019 08:51:52
111 forum posts

Hi all, just as an aside for those who don't like to touch down on gauge blocks, perhaps I should have mentioned gauging the approach to 'touch down' by that most legendary of really thin things, a cigarette paper.

Ps my good set of slip gauges are tungsten carbide.

Bob H

SillyOldDuffer27/10/2019 10:37:01
4844 forum posts
1018 photos
Posted by Mike Poole on 26/10/2019 21:51:36:

The passion for dimensioning drawings for models using fractions of an inch is I feel ridiculous, a sixtyfourth of an inch is 0.015625 so most people are going to call it 15 or 15 and a half thou and the rest is lost using practical tolerances and home workshop equipment. A set of gauge blocks is not able to accurately produce a size involving a sixtyfourth but for practical purposes it’s not going to matter but it’s going to bother anyone with CDO ( that’s OCD but with the letters in the right order).

Mike

Well, in the good old days you could buy a set of gauge blocks which included extra blocks (about 8 I think) covering common fraction sizes.

However, I wouldn't go so far as to describe fractional inch drawings as 'ridiculous'. Archaic is enough! Whilst there are good historical reasons for fractions in drawings, they've been pushed out by thou and mm.

Before about 1900 most people dealt with simple divisions. Ordinary life is full of them - sharing out food, booze, money, fuel, etc. Fractions deal with ordinary situations so effectively that decimal notation wasn't even taught to anyone receiving a basic Victorian education. Decimals were rarely needed in workshops.

Before precision engineering, workshop measurement was dominated by dividers. Dividers allow dimensions to be captured and transferred such that parts can be made without measuring at all. Dividers also divide: it's remarkable how accurately halving can be done by eye, hence the popularity of fractions in powers of 2. Dividing is one of the foundations of the imperial system, giving us 1/4" 1/8" and 1/16", all handy in carpentry, cobbling, tailoring and many other trades.

In metalwork 1/64" is about the best that can be done by eye, and this was the highest standard of professional accuracy up until about 1850. But then the fractional system began to break. As technology advanced it became ever more obvious that most problems aren't conveniently represented by fractions. One example is Letter and Number drill sizes, basically odd diameters needed to plug gaps in the 1/64" system. Although the axles of a locomotive can be spaced perfectly by applying simple fractions, the relationship between firebox size and boiler size, and boiler and cylinder volume, and cylinder volume and piston stroke are less obvious. And the design detail needed achieve speed, reliability and fuel economy is important. So mankind moved from craftsmanship and proportions based on individual experience to engineering. Engineering proportions are calculated by reference to scientific method.

Fractions deal extremely well with anything involving integer ratios, but they are awkward for everything else. Decimals don't run out of steam in the same way and have other advantages. For example, it's not obvious if 73/112 is larger or smaller than 74/113 : decimal representation makes it plain. And being more general means decimals simplify many calculations and measurements for instance by allowing people to use slide-rules and digital calipers.

Because of all this, fractions - though still important - have been largely displaced by decimals. As soon as micrometers became available, Imperial Engineering started shifting to thou. Later the advantages of working to tolerances became apparent and tenths became important. This wouldn't be possible were it not for ultra-precison gauge blocks because tool-rooms making jigs, fixtures, and inspection gauges need to be about 10 times more accurate than anything done on the shop floor.

I suspect most people faced with a fractional drawing convert most dimensions into thou? Does anyone produce new drawings with fractional dimensions?

Not that I care much - I prefer to work in metric!

Dave

Ian Johnson 127/10/2019 11:02:01
174 forum posts
50 photos
Posted by robjon44 on 27/10/2019 08:51:52:

Hi all, just as an aside for those who don't like to touch down on gauge blocks, perhaps I should have mentioned gauging the approach to 'touch down' by that most legendary of really thin things, a cigarette paper.

Ps my good set of slip gauges are tungsten carbide.

Bob H

Ahh the good old fag paper trick! I've got a pack of green rizal in the drawer, I can't remember which are thinner green or blue? Don't think I'd use a gauge block for touching off though, maybe use something of a known size like a piece of ground bar. Something softer than the cutting tool.

Ian

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