Measuring

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

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

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

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

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

DEA machine?

Tony

Dead Easy Accuracy

I found the cut out in the tail piece ( or stinger ) is usefull for digging out swarf from chuck scrolls .

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

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

.

Very useful paper, John. Thanks for the link.

MichaelG.

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

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

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

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

Granite wears out after the first billion or two years.

Neil

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