Hi guys.
I have come across some “funny” rulers in my garage that I acquired a few years ago. I would be grateful if someone could tell me what they are used for. They are mostly 24″ long, some in metric and some in metric and imperial. Some have markings ” double contraction cast metal 1/48 ” along one half of the length. The other half is ” contraction cast metal 1/96. The other side of rule is in metric and says ” contraction 1/50 and 1/100 “. Some of the rules are marked aluminium or brass. There is about 17 of them and I think all are different. They look quite old and need some cleaning. It would be worth it but do they have any use in today’s world? Many thanks for any feedback.
The reason I have posted on this forum is someone suggested they could be for making scale drawings possibly for aircraft?
By: cornovii - 30th November 2015 at 13:33
Dev one
Thank you for your reply. I’m guessing that this sort of work is done on computer now. I guess they might come in useful as a straight edge!
Ken
By: Dev One - 29th November 2015 at 19:24
IIRC these rules are used by the pattern maker, not the draughtsman. The draughtsman draws the final product size. (I’m old enough to be pre computer age, but have difficulty remembering some things!)
Keith
By: cornovii - 29th November 2015 at 19:14
trekbuster
Many thanks for your reply. Would they be used today or would this sort of work be done on a computer now?
By: trekbuster - 29th November 2015 at 18:46
Rules for determining scale drawings for casting patterns?
Metal contracts as it solidifies, so if you want the part to be a given final size, you have to make the pattern/mould that percentage bigger to allow for the contraction.
This is mostly for sand and investment casting, I believe most die castings have a compacting stage that reduces this effect.
For example, if the metal contracts 1 part in 96 then the rule could be used to draw an engineering drawing for a pattern for a part cast in that metal.
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November 29, 2015 at 6:39 pm