Things that don't turn up every day, these are patternmakers rules for making sandcasting patterns. The shrinkage factor of the cooling metal is calibrated into these rules, 2-3% for steel (5/16" per foot) and 4-5% for brass, so the pattern will be made to the correct larger size to compensate.
The L.S.S. Co. Athol, Mass rule is a Starrett, J. Rabone is an English manufacturer, love the homemade-looking font on the Rabone rule below.
I hadn't thought about patternmakers scales in ages.
ReplyDeleteActually most of the shrinkage takes place during the solidification process, which is why a poorly designed casting can have porosity in regions where still-liquid metal can't flow as needed to produce complete solidity. Designing for "directional solidification" addresses this.
Don in Oregon