Monday, June 20, 2011

Shrink rule

Contraction Rule

Odd-ball tools fascinate me and so I couldn't resist this one. It came to me at the weekend while digging through a box of second hand tools for sale. I'd already acquired a spoke-shave,  for no better reason than I don't own one already, and was looking at a pile of steel rules when Dave shouted at me "You don't want to use those Phil."

Enquiring why, it was explained that they were pattern makers contraction rulers, sometimes called "shrink rules". These are used when producing anything that will be cast in a material, such as whitemetal, that shrinks when it is moulded. So the markings are slightly bigger than they should be. Each scale is marked by the amount of contraction so on the scale above we have scales for 1/40 and 1/30 contraction.

The only material I use that shrinks is polyester resin, and even that is negligible. Thus, this tool isn't actually of any practical use. Maybe I could make models with it that are slightly bigger than they are supposed to be. Never mind, it's another interesting addition to the toolbox.

Anyone else bought an odd-ball tool that they have never used ?

1 comment:

Pat Brown said...

Ah yes. My wife was a patternmaker for many years and I was caught out early in our marriage when I couldn't find my own steel rule and so borrowed hers without knowing about such things. I wondered why nothing fitted........

As for my own oddball tool purchases, I did buy a government surplus geiger counter from an autojumble stall once, mainly because I was so taken aback to find it amongst the grubby bits of Triumph Herald that I was trawling through at the time.