Shrinkage scaler
Scale a 2D DXF drawing or a 3D STL model by an exact percentage. Built for casting: oversize the pattern so aluminium, iron or steel shrinks to the size you want — or just use it as a precise resizer.
How casting shrinkage works
When molten metal cools and solidifies it contracts, so a mould made to the finished size would produce an undersized casting. Pattern-makers fix this by making the pattern slightly larger — the standard linear contraction allowances (about 1.3% for aluminium, 1.0% for grey cast iron, 2.0% for cast steel) are added to the pattern, i.e. the model is scaled by 1 + shrinkage%. This tool applies that factor uniformly to every point of your DXF or STL and shows the before/after dimensions so you can check them. It only scales the geometry — nothing is re-meshed or distorted — and everything runs in your browser.
Which factor does it use — 1 + s or 1/(1 − s)?
It uses the standard pattern-maker's rule, scaling by 1 + s/100, because published casting-shrink percentages are already the linear pattern oversize. For small percentages the difference from 1/(1 − s) is negligible (a few thousandths of a percent); if you need that exact form instead, switch to “Scale to a percentage” and enter it directly.
Does it keep my units and exact geometry?
Yes. STL and DXF are unitless, so a 100 mm feature simply becomes 101.3 mm at 1.3% — the numbers scale, the units are whatever your CAD uses. The geometry is only multiplied, never re-triangulated, so there's no loss of accuracy or detail.
Origin or centre — which should I pick?
For a cast pattern it usually doesn't matter, because only the size matters, not the position — Origin (scaling about 0,0) is the simplest and keeps the model anchored there. Choose Centre if you want the model to grow outward from its own middle and stay roughly in place.
