7 min read
What is castable resin?
Castable resin is a photopolymer formulated to behave like jewelry wax during burnout. It is printed on an MSLA or DLP resin printer, then placed in a flask, surrounded by investment plaster and heated in a kiln until it burns away. Molten gold or silver fills the cavity it leaves behind. This is the same lost-wax method goldsmiths have used for centuries, with a printed pattern replacing the hand-carved one.
Step 1: Prepare the design
Good casting results begin in CAD. Before you slice the model:
- Keep walls at least 0.6 to 0.8 mm thick so metal flows through the whole piece.
- Hollow large pieces and add drain holes to save metal and reduce weight.
- Allow for metal shrinkage, which is usually small but noticeable on tight ring sizes.
- Export a watertight STL with enough triangles that curves stay smooth.
Step 2: Orientation and supports
Tilt rings about 30 to 45 degrees so each layer has a small cross-section and suction forces stay low. Place supports on the inside of the shank or on surfaces that will be polished, never on stone seats or engraved faces. Use light supports: castable resins are softer than standard resins and heavy supports leave marks.
Step 3: Print settings
Use the exposure settings published by the resin maker for your printer as a starting point, then run a calibration print. Castable resins are sensitive to temperature, so keep the room and the resin warm, ideally above 20°C. In winter in Amman, an unheated workshop can cause failed prints that look like a settings problem.
Step 4: Wash and cure carefully
Wash the pattern in clean isopropyl alcohol for the time the resin maker recommends. Over-washing can soften castable resin, so do not leave it soaking. Dry it fully, then post-cure. Proper curing matters: an under-cured pattern can expand in the flask and crack the investment.
Step 5: Investment and burnout
Attach the patterns to a wax sprue tree, then invest with a plaster designed for resin patterns if possible. Resin investments are formulated to resist cracking as the pattern expands. Follow the burnout schedule supplied with your castable resin exactly: it normally includes slow ramps and holds at intermediate temperatures before the final high-temperature hold that removes all residue.
If your castings show rough surfaces or inclusions, the most common causes are under-curing, a burnout that was too short, or investment mixed with the wrong water ratio.
Step 6: Cast and finish
Cast as you normally would, by vacuum or centrifugal casting. After devesting, the surface of a well-printed pattern needs only light polishing, which saves both time and metal loss at the finishing bench.
Get the right materials in Jordan
Jordan Automation stocks resin printers, jewelry resins and wash and cure equipment in Amman. Tell us which printer and casting setup you use and we will recommend a resin and starting settings.
Frequently asked questions
Why did my casting crack or show fins?
Fins usually mean the investment cracked, often because the resin pattern expanded during burnout. Make sure the pattern is fully cured, use a resin-compatible investment and follow a slow burnout ramp.
Can I use standard resin for casting?
Standard resin usually leaves ash and can crack investment. Use it for samples and mold masters, and use a resin labeled castable for patterns that go into the flask.
How should I store castable resin?
Keep bottles sealed, out of sunlight and at a stable room temperature. Shake or stir well before each print, because some castable resins contain fillers that settle.