Short answer: for small and medium decorative brass parts, we treat a finished wall of about 0.08 in (2 mm) with 1.5° draft as a practical minimum for sand casting. The part is cast slightly heavier and polished down to that thickness. Thinner walls are possible only on very small features and should be reviewed part by part.
A real example from a lighting project
A US designer lighting brand asked us how thin a brass part could be if it was sand cast. Their designer had originally drawn it as 0.04 in (1 mm) brass sheet, laser-cut and bent. For the look of the finished fixture, they wanted the softer edges and solid feel of a casting, with the wall as thin and the draft as small as possible.
Their product engineer sent two versions of the part, both with 1.5° draft: one at 0.0625 in (1.6 mm) and one at 0.125 in (3.2 mm). A second, deeper part in the same family used 3° draft on its walls and 1.5° on a lower lip.
Our recommendation was a finished wall of 0.08 in (about 2 mm) with 1.5° draft, delivered as polished parts rather than raw castings. The customer confirmed the change, and we quoted the part family on that basis.
Why sand castings cannot be as thin as sheet metal
In sand casting, molten brass or bronze has to run through the whole mould cavity before it starts to freeze. A long, thin section cools quickly, so the metal may not fill it completely. Thicker walls give the metal more time to flow and feed the part.
A sand mould also leaves a slightly rough surface. Decorative parts are normally ground and polished afterwards, so the casting needs a little extra metal to polish away. That is why we talk about finished thickness, not cast thickness.
Finally, the pattern has to come out of the sand without breaking the mould. That is the job of the draft angle.
What draft angle to use
On the lighting parts above, 1.5° was acceptable on shallow faces and lips, and 3° was used on deeper walls. Smaller draft looks crisper but makes moulding harder. If the design depends on a very small draft for appearance, tell us at the RFQ stage so we can review which faces really need it.
When another process is a better fit
- Die casting: for parts that will be reordered in steady volumes, die casting can hold thinner walls and tighter dimensions. It needs a steel die, so it rarely pays off for a one-time run. The project above was 75 pieces with no planned reorder, so sand casting was the sensible choice.
- Lost-wax (investment) casting: worth reviewing for small parts with fine ornament or thin details, where sand cannot reproduce the detail well.
- Sheet metal: if the design truly needs 1 mm walls over a large area, fabricated brass sheet may still be the right answer.
How to design a thin-wall brass sand casting
- State whether dimensions are for the raw casting or the finished (polished or machined) part.
- Keep wall thickness as even as possible; sudden changes cause shrinkage and distortion.
- Add draft to every face that leaves the mould, typically 1.5° to 3°.
- Send a 3D model (STEP) as well as a 2D drawing, so weight and metal flow can be checked.
- Tell us the order quantity and whether you expect repeat orders; it decides between sand, lost-wax and die casting.
Frequently Asked Questions
What is the minimum wall thickness for a brass sand casting?
For small and medium decorative parts we use about 0.08 in (2 mm) finished wall with 1.5° draft as a practical minimum. Larger parts or long, thin sections need thicker walls. We confirm the number for each part after reviewing the 3D model.
Can a brass part be sand cast at 1/16 in (1.6 mm)?
Usually not as a general wall thickness. When a lighting customer asked for 0.0625 in, we recommended 0.08 in finished thickness so the metal fills the mould reliably and there is enough material to polish.
Is the wall thickness measured before or after polishing?
We specify finished thickness, after grinding and polishing. The raw casting is poured slightly heavier.
What draft angle do brass sand castings need?
Typically 1.5° to 3°. Shallow faces can work at 1.5°; deeper walls are safer at 3°.
When should I choose die casting instead of sand casting?
When the part will be reordered in steady volumes and needs thinner walls or tighter dimensions. For one-time or low-volume runs, the cost of a steel die is rarely justified.
Written by the Gaton Brass team, Zhongshan, Guangdong, China. Published 2026-10-07. Customer names and drawings are withheld at the customer's request.