Casting Design Basics
As with all casting methods, uniform walls work best. Heavy sections must be at
the part perimeter to allow direct gating or must be connected to the perimeter with
heavy feeding ribs.
Milling operations can be eliminated through the use of flat surfaces parallel to
the parting plane. Drilled clearance holes or tap drill sizes are replaced with
cored holes.
The following guidelines should be considered:
- Sizes: Up to 12″ x 14″ x 5″Up to 20″ if narrow
- Radii parallel to parting line: 0.030″ minimumRadii normal to parting line: 0.063″ minimum
- Walls: Must be of uniform thickness from .125″ to .25″.
Avoid heavy sections. - Draft: 2° nominal on all surfaces perpendicular to parting plane
(See Draft Requirements.) - Gates/Risers: Allow for heavy gates (60% to 80% of prevailing thickness)
on perimeter of part at parting line. - Lettering: Raised lettering or artwork can be accommodated.
- Avoid:Applications over 300°F; multiple side pulls (slides)
Tolerances
- General Dimensions: First inch ± .005″; Additional inches ± .002″
- Critical Dimensions: First inch ± .003″;Additional inches ± .001″ per inch
- Across parting line: Add ± .005″ to above
- From side core: Add ± .005″ to above
Draft Requirements
To protect the graphite mold, adequate draft is required on all surfaces
perpendicular to the face (parting plane) of the mold. Normally, 2° of draft per
side is adequate, but thin sections may require 3° to 4°. On part drawings,
plus or minus draft should be specified for all dimensions affected by draft,
not indicated by angled lines.
“Plus” draft indicates that draft increases the size of the feature
described.
“Minus” draft indicates that draft decreases the size of the feature
(see drawing below).