Another mystery object

Hi,

1 : 1.078 corresponds with the typical shrinkage factor for Aluminium castings so it is quite possible that this caliper is made for someone producing small patterns for aluminium castings, perhaps even 1" to the Foot scale models. Patternmakers rulers certainly exist, with different shrinkage ratios for each different material that they are associated with but it is an inexact science due to the effect of different cooling rates, depending on the cast section and also influenced by the alloying of different melts. Additional allowances are also made to leave metal for fettling in some applications but this is very much a matter of whether "as cast" or machined finishes are specified.

Bob D

If I was making a casting pattern from a finished object that vernier could be quite handy, adding as it does about 8% to the actual dimension.

Eug

Sorry, posted at much the same time as Bob

Eug

Bob,

Maybe a silly question ... have you checked the actual size of the "millimetres"

The reason for asking is that 27.38mm [i.e. your "inch"] converts nicely to 1 5/64"

... It might be a pattern-maker's calliper, corrected for shrinkage.

MichaelG.

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Edit: Sorry, took a telephone call before posting

... Looks like we all got the answer.

Edited By Michael Gilligan on 05/09/2014 20:41:51

> Looks like we all got the answer.....

We now await the size of the 'centimetres' with bated breath!

Neil

Ah well, 1 Cm on the calliper = 1Cm on my modern rule. Over the 10 Cm of the Calliper it measures 99.8 Mm, but I think this may be wear and tear and general abuse of the instrument.

I think that this still leaves us somewhere near Neil's first post, but not quite ! However I do like the patternmakers idea. But why would an 'inch' be divided into twelfths ?

Bob H

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Not that uncommon ... Old style school rulers had a twelfths scale too.

• 1" to the foot is a useful scale for drawings & models [e.g. Doll's House]
• Twelfths allows access to thirds, which are not available on decimal or binary divisions.

MichaelG.

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Edit: Very interesting notes about using twelfths, here.

Edited By Michael Gilligan on 06/09/2014 07:31:03

Bob,

Is the scale engraved with the word "Inches" [or whatever], or was that just your reasonable assumption?

MichaelG.

Hi All

I remembered that type was based on numbers that divide into 12 so did a little web searching.....
The calliper might have been used to measure type?

**LINK**

**LINK**

Regards
john

You didn't read the link I gave properly! 12 lignes make up one pouce!

Neil

Neil,

The ligne was [and still is] commonly used by watchmakers.

... unfortunately, none of this explains the scale factor on Bob's calliper.

MichaelG.

French cabinet makers used to use 'French Inches', maybe they still do?

Bert

We think the clue was "Found in South West France". looking on the web **LINK**

It talks about the 'Toise' and then the Pied de Rois (or foot of the King). This being 32.66 Cm which divided by 12 becomes 2.7216 recurring. Not quite 27.38 mm, however there were regional difference and as SW France is some way from Paris, we think this may be the explanation. But always open to opinion.

BobH

the later Pied defined by law in 1799 is closer at 27.07

Neil

(Angels and pins?)