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Measuring

Snap Gauge

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John McNamara28/07/2011 15:16:17
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1341 forum posts
127 photos
Hi All
I mentioned a “snap gage” in the Epoxy worden post.
I know this description can also mean thread go no-go gauges.

Across the pond and in Australia it also refers to spring loaded bore gauges.

This video provides a good description of their use.
 
He should have used a micrometer not a caliper!
 
Cheers
John
DerryUK28/07/2011 15:43:03
125 forum posts
Why hold the handle 5 deg below the centreline? Is this because when you lift the handle up the points will read the smallest diameter and stay there?
 
Derry.
John McNamara28/07/2011 15:51:23
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1341 forum posts
127 photos
Hi Derry Hincks

The Man in the video referred to “snugging” the lock screw; meaning not tight.
By holding a few degrees below centre the measuring tips are not parallel to the bore, they are wider. Then by rotating through the centre point the tips are compressed inwards as they pass “Top dead centre” at 90 degrees to the bore axis.

It a matter of feel; enough tension on the lock screw to hold the tips firmly but not so hard that the tool will be strained.

Cheers
John
Richard Parsons28/07/2011 17:42:47
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645 forum posts
33 photos

Humph! Ever since about 1950 I have called them ‘telescope gauges’. They go down to about ½” (12mm). Below this down to about 0.2” (5mm there are the Open cup ball gauges. I can get down to about 3mm with a Moore and Wright ball gauge (2 off 0.4mm balls in a tube pushed apart by a needle). Below that I made a series of 3 steps on a single pin. One step is 0.05 mm too large one is just right and 1 is 0.05mm too thin. I make there in my 5mm Lorch as needed. The actual size of each part is made to size and the extra metal removed with a pivot file so I have three narrow rings of the sizes needed.
rgds

Dick

Edited By Richard Parsons on 28/07/2011 17:43:28

NJH28/07/2011 17:59:46
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2314 forum posts
139 photos
Or more usually "Telescopic Bore Gauges" ? Sound like a good idea - and do work well after a bit of practice! Available very cheaply from the usual sources but may need a little "fettling" as they can stick. I've seen a note somewhere of how they can be improved but can't recall where. I do have a Mitutoyo version in a small size and that doesn't stick --but I dread to think what price it may be today!
 
Norman

Edited By NJH on 28/07/2011 18:00:18

Boiler Bri23/09/2013 01:14:19
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842 forum posts
199 photos

I have: a 0-25mm micrometer which i trust, i also have a 0=1" micrometer which i trust. I have a few verniers which i distrust including a very good make! In the case below i can not use a mic as i can not get at both sides to take reading. So using the vernier as a depth gauge i get different results at the same position!!

So why do i make this assumption. I am making a 4" Durham traction engine and have decided that instead of making an angle section guide bar for the cross head to follow, i would make a solid section (a bit like a loco). In doing so i reduced a 16mm x 20 mm bar to 16mm square in my milling machine over 8-75inch. I know that reducing said bar will stress relieve it and cause a bow when i loosen it from the table, that i can live with as i have a power press at work to put it straight.

Why do i get different readings on my vernier every time i take a reading, what changes? it's so frustrating and confusing. Would a digital readout improve things?

I asked this question at the club yesterday but the guys there all said 'it's model engineering and we make things to fit each other' well that's ok but when two things do not match its frustrating to think that i can not match two items!!!!

Bri

Bazyle23/09/2013 08:49:40
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6390 forum posts
224 photos

Bri, are you using the 'spike' out the back end of a vernier caliper vertically down as a depth gauge? I find this is very variable because itis so easy not to be vertical. Even a slight twitch as you withdraw it might move it and getting even pressure on body and tip is awkward. Perhaps holding up agianst a 123 block could help.

For small holes I have some of the type with a fat foot that is split and the halves moved apart by pulling a cone up the middle using a knurled knob.

Edited By Bazyle on 23/09/2013 08:51:06

jason udall23/09/2013 09:05:00
2031 forum posts
41 photos
Caliper in depth mode.
1 is tail/pin parallel to bore? Two different ways for that to go wrong..maybe a guide to fill most of bore..helps keep tail vertical
2 are you seeing the radius at the bottom of the hole?.
Thats what the nibble out of the end of tail is for...
3 is the tail bending?
Sorry thats just technique. .

If you use a digital caliper then measure .zero ..home..read ..a technique that helps with fiddly measurements....
Nobby23/09/2013 13:36:24
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587 forum posts
113 photos

I always make a rule always measure with a Micrometer if you can . Not unlles you have a DEA machine
Nobby

Tony Pratt 123/09/2013 17:15:25
2035 forum posts
12 photos

DEA machine?

Tony

Rik Shaw23/09/2013 18:16:30
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1484 forum posts
398 photos

Dead Easy Accuracy face 20

jason udall23/09/2013 21:09:49
2031 forum posts
41 photos
Well .I have tried laser mic 's...tenth micron quoted accuracy and resolution.
But try measuring the diameter of a plug gauge only to be told ahh you have to hold it right... (you end up measuring the major/minor "diameter" of an elipse...)...
Never heard of dea...cmm was the term in use last year
I.M. OUTAHERE24/09/2013 05:23:07
1468 forum posts
3 photos
Posted by jason udall on 23/09/2013 09:05:00:
Caliper in depth mode.
1 is tail/pin parallel to bore? Two different ways for that to go wrong..maybe a guide to fill most of bore..helps keep tail vertical
2 are you seeing the radius at the bottom of the hole?.
Thats what the nibble out of the end of tail is for...
3 is the tail bending?
Sorry thats just technique. .

If you use a digital caliper then measure .zero ..home..read ..a technique that helps with fiddly measurements....
 
 
 
 
 
 
 
 
 
 
 
 
I found the cut out in the tail piece ( or stinger ) is usefull for digging out swarf from chuck scrolls devil ... Shift+R improves the quality of this image. CTRL+F5 reloads the whole page..
 
May also be usefull to pry the lid off a coffee tin also !
 
Other than that i got nothing .

 

Edited By SLOTDRILLER on 24/09/2013 05:23:57

John McNamara24/09/2013 05:32:33
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1341 forum posts
127 photos

Hi All

This is worth a read......

Abbe's Principle

**LINK**

 

Images of examples:

https://www.google.com/search?q=abbe+principle&sa=X&tbm=isch&tbo=u&source=univ&ei=ARZBUv6dGpOgiQfto4GQDA&ved=0CD8QsAQ&biw=1255&bih=694&dpr=1

 

Regards
John

Edited By John McNamara on 24/09/2013 05:34:16

Edited By John McNamara on 24/09/2013 05:35:54

Michael Gilligan24/09/2013 07:10:15
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20289 forum posts
1064 photos
Posted by John McNamara on 24/09/2013 05:32:33:

Hi All

This is worth a read......

Abbe's Principle

**LINK**

Regards
John.

.

Very useful paper, John. Thanks for the link.

MichaelG.

Edited By Michael Gilligan on 24/09/2013 07:11:48

Nobby24/09/2013 17:56:15
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587 forum posts
113 photos

Hi Tony & Guys
A DEA is a co-ordinate measuring machine . Have a look on U Tube .
Nobby

Edited By Nobby on 24/09/2013 17:57:26

jonathan heppel27/09/2013 15:01:50
99 forum posts

Snap gauges and telescope gauges are called what they always have been - google them. I suspect someone had a brainstorm and the misnomer has gone viral in the hobbyist community.

This sort of mistake makes all of us look ignorant.

How about using a foot on the caliper? You can buy them but they are easy enough to make, though mics are better.

A

Steve Withnell27/09/2013 16:45:42
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848 forum posts
215 photos

Co-ordinate Measuring Machines. I remember going to see the manufacturer of a CMM range many years (25?) ago (With a view to converting to CNC...). Anyway the machine base was a piece of polished granite about 2m x 1m x 1m. The sales guy related how he had just offered another customer a deal based on a new machine but with a refurbished base. The customer turned down the special offer insisting on new granite...

Steve

Stub Mandrel27/09/2013 19:26:47
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4315 forum posts
291 photos
1 articles

Granite wears out after the first billion or two years.

Neil

Nobby27/09/2013 20:53:01
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587 forum posts
113 photos

Hi
The one I used was mounted on a granite surface plate . it was good for checking bores etc
By placing the probe in 3 or more postions to see readout or you could also print out the result to show the customer
Nobby

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