Callipers & Dividers - How big?

All,
In another recent post of mine, I was asked if I had a pair of dividers or callipers. I don't.


So, thinking that these would be handy to have around I started looking around and quickly realised that whilst I knew what I wanted had to look like, I didn't know what the sizes quoted related to. For example, whats the difference between a 2.5" and a 12" calliper? Is it the physical size of the thing, the maximum diameter or maximum radius that the thing can be used to mark out / measure? It is apparent that I could buy a 2.5", 3", 4", 5", 6", 7" etc all the way upto about 12" or so.

Im thinking that the largest diameter I could see myself marking out regularly would be downwards of say 6". Would I want a 7", 6", a 3" (or some other size) divider?


Thx
J

May be you should be asking what basic hand tools you might require for machining.

From what I recall it generally refers to the length/opening of the caliper.

I would also suggest that you buy a known brand ( Moore and Wright,Eclipse,Starrett etc) as most of the cheaper range/Chinese are very flimsy,ebay or similar are a good source for either new or second hand.

I would suggest looking for a couple of pair of dividers 3"-4" and 6".

A set of 4" or 6" inside calipers,similar for outside calipers.

A good quallity stainless 6"/150mm rule and 12"/300mm rule.

A few sets of thread gauges ( mm/bsw/unc/unf).

A good quality centre punch and light hammer for marking out.

Reasonable quallity measuring tools that you may already have.

Thanks Pipeclay. Much appreciated, as ever!

I was actually looking at the Moore & Wright and Starrett ones, so i'll keep going down that track.

Centre punches, stainless rule, square, scribe, mic, metric thread gauge etc are already in the shed... Clearly there are a few other basics Im in need of though.

I'll take your advice re a couple of pairs... and start building up the collection!


Thx
J

Having calipers from a previous life as a boilermaker/ welder, my selection selection is of 4",6" and 8" range .

For turning related layout purposes most of the applications required calipers smaller than my smallest pair ,4"

Laying out a sub 1/2" radii with the spring pivot engineering calipers is way too inaccurate and cumbersome to swing a very small radius.

A set of old fashioned tech drawing compasses fitted with the scriber pins fills the bill very nicely for my needs.

On occasions where more rigidity is required square legged dividers can be picked up in second hand tool sales.

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Grahame