Thread: Mystery Rule - Chesterman Sheffield No 19570 - Help please

Looks like a patternmakers contraction rule.

You learn something new every day, thank you for the link and info

Originally Posted by Chief Tiff

Looks like a patternmakers contraction rule.

Fantastic.
Many thanks
Tom

Here’s a few I have.
Double contraction for metal patterns for production stuff.
H.

Many thanks for these images. They are great.
I was thinking that there might be specific rules for each metal, and lo and behold here are some.
I wonder what double contraction is?
Tom

Known as a shrink rule in the U.S.

Originally Posted by Chief Tiff

Looks like a patternmakers contraction rule.

Oops - Requests for pics a miss hit.

Originally Posted by verawood

Oops - Requests for pics a miss hit.

Yep - me too. Was trying for "thanks for Pics" DOH!
Couldn't undo it.
Tom

The other interesting rule type that I have several examples of is the circumference rule, beloved of sheet metal workers* and those in similar trades. This one does the calculation for the circumference of a circle based on its diameter for you: no need to remember what the numbers in pi are (let's see, 3.15...shoot, can't remember). Lufkin, an American manufacturer of layout tools for the trades, even put some handy tables on the back of the rule, for figuring standard (at the time) dimensions for one-quart, one-gallon, etc. containers.

Sheet metal work is still a viable, but very small, trade here in the States; but these rules command a surprisingly high price on the auction sites, which puzzles me.
-----------
*Australian slang question from a colleague across the great big pond: if an electrician is a sparkie, what's a sheet metal worker? A tinnie? Here in the States, one of the common slang terms for this trade is "tin bender."

Originally Posted by clear out

Here’s a few I have.
Double contraction for metal patterns for production stuff.
H.

Double contraction?
Is this right?
It's for casting a part that will be a metal pattern to be cast from?

You make a wood pattern with a double contraction rule . Use that and the casting shrinks . Take that casting and use that as pattern and second casting shrinks and is now the right finished size?

Its so the pattern lasts years or for ever in use .

The wooden ones don't last.

We here in Australia call a Sheetmetal Worker a....."Sheety"
We have a Pop Singer who was popular during the 70s ....John Paul Young....he was a Sheety
Then we have some famous/infamous singers who came from the Plumbing Game
John Farnham
Joe Cocker (British Pop Singer) was a Gas fitter

Does it mean there is a chance of Stardom if you can start in a Metal Trade?

Singing Yesterday's hero for 45 years . Think Id be missing the workbench .

Originally Posted by auscab

Double contraction?
Is this right?
It's for casting a part that will be a metal pattern to be cast from?

You make a wood pattern with a double contraction rule . Use that and the casting shrinks . Take that casting and use that as pattern and second casting shrinks and is now the right finished size?

Its so the pattern lasts years or for ever in use .

The wooden ones don't last.

OK so use the double contraction first to make a metal casting master, then you don't need to use the single contraction at all - just go ahead and pour.
Single contraction only used for wooden masters.
Is that it?
Tom

Originally Posted by Scribbly Gum

OK so use the double contraction first to make a metal casting master, then you don't need to use the single contraction at all - just go ahead and pour.
Single contraction only used for wooden masters.
Is that it?
Tom

That's My guess at it Tom .
I started the post with a question about what Henry meant and the more I thought about it the closer I got to that .