Technical
Castable resin casting problems: why 3D printed jewellery patterns fail, and how to fix them
When a casting from a 3D printed pattern fails, check five things before blaming the printer: that the resin is direct castable, that the print was washed and fully cured, that the burnout ramped slowly at the start, that the final hold was long enough for the load, and that the oven really reached its set temperature.
· 7 min read · By Dhyey Mehta
A 3D printer can draw a pattern finer than any hand carver, and it is all wasted if the casting comes out pitted, cracked or full of black specks. When that happens, the printer usually gets the blame. More often the cause is how the resin pattern was washed, cured or burned out. This guide lists the common castable resin casting problems, what causes each one, and how to fix it.
It is written for jewellery workshops casting gold or silver from printed patterns. Where we quote a burnout figure, it is one resin maker's published example, not a schedule for every resin.
First check: is it castable resin at all?
Jewellery printing resins come in two families, and only one belongs in a flask:
| Family | What it is for | Our resins |
|---|---|---|
| Direct castable (DC) | Burns out in the investment like a wax, so the print goes straight into the flask | DC Black, DC Yellow, DC Green |
| Non castable (NC) | Fit checks, client approvals and master models that will be moulded in rubber. Never burned out | NC Red, NC Red CWR |
Casting a non-castable pattern ruins the flask, and usually the investment and the shift with it. If your problem started after a change of resin or supplier, check this first. Details are on our resin range page.
Casting problems, causes and fixes
| What you see | Likely cause | What to do |
|---|---|---|
| Rough, pitted or orange-peel surface | Resin not fully burned out, or the pattern was under-cured, so the mould surface broke down | Wash and fully post-cure before investing; lengthen the final hold |
| Fins or flashing on the casting | Investment cracked: the pattern expanded before it burned away, or the early ramp was too fast | Slow the first stage of the burnout; follow the resin maker's schedule |
| Black specks or inclusions | Residue left in the mould after an incomplete burnout | Check the real oven temperature; extend the hold for full or heavy loads |
| Whole flask ruined | A non-castable pattern was burned out | Keep NC resin for fit models and moulding only |
| Problems only on thick or chunky pieces | The hold was long enough for thin parts but not thick ones | Lengthen the hold for thicker parts and fuller ovens |
Why resin burns out differently from wax
Wax melts and runs out of the mould. Printing resins do not behave like that: Formlabs, for example, describes its original Castable Resin as passing directly from solid to gas. That is why a wax burnout schedule can fail with resin patterns.
Dr Ian McKeer's 2007 Santa Fe Symposium paper describes the two problems that follow. Resin patterns are hard to burn out fully, which leaves a poor surface finish. And some resins expand before they melt, which cracks the investment and puts flashing on the casting.
Step by step: getting a clean casting from a resin pattern
1. Wash the print properly
Uncured resin left on the surface does not belong in the mould. Formlabs, for example, tells users to wash castable prints in two baths of isopropyl alcohol and dry them fully. Follow your resin maker's washing instructions.
2. Cure it until it is hard
A 2016 Santa Fe Symposium paper on acrylic photopolymers found that fully hardening the pattern before investing reduces investment breakdown during burnout and improves the casting surface. An under-cured pattern looks fine on the bench, which makes it an easy cause to miss.
3. Use the investment the resin was tested with
Resin burnout schedules are written for particular investments. If you change investment, use that investment maker's instructions for resin patterns as well.
4. Ramp slowly at the start
The early stage is where the pattern starts to break down and can crack the mould. As one published example, the Formlabs schedule for its original Castable Resin starts in a cold oven and ramps at 1 °C per minute to a hold at 177 °C, which it says "reduces the chance of cracking in the investment."
5. Hold long enough at the top
The same schedule holds at 732 °C for three hours and notes that the hold depends on the size and number of flasks and the thickness and volume of resin: thicker parts need longer. A full oven needs more time than a single flask.
6. Check the oven, not the display
An oven's set temperature is not always its real temperature. Check it with an independent probe or thermocouple, especially if problems appear only on some flasks or some shelves.
The printer still matters
A clean burnout cannot add detail the printer never drew. Choose the printer for the work, then the resin for the printer:
- DLP printers such as the S3D-125 (49 µm XY, 10–100 µm layers) suit the most detailed work. DC Yellow and DC Green are catalogue-specified for DLP at 405 nm.
- LCD printers such as the FOTO 6K (100 g of patterns a day) suit batch printing.
- MJM wax printing on the WaxJet-510 (300 g a day) prints in wax, so patterns burn out like conventional wax.
Our jewellery 3D printer buying guide compares all six printers. For the casting side, see the induction melting capacity guide.
What we publish, and what we do not
Our catalogue lists the properties of each DC and NC resin, but it does not publish a burnout schedule for them. Ask us for the schedule for your resin, investment and oven in writing, rather than copying one written for another maker's resin.
Questions about resins, printers or burnout on your floor? Send an enquiry or call +91 98216 12340.
Answers
Related questions
Why do castings from 3D printed resin patterns come out rough or pitted?
Two common causes are resin that did not burn out completely and a pattern that was not fully cured before investing. Resin that is left behind attacks the mould surface. Wash the print, post-cure it until it is hard, follow the resin maker's burnout schedule, and make sure the final hold is long enough for the size and number of flasks.
Why does the investment crack when burning out castable resin?
Some resins expand before they burn away, and a fast early ramp makes it worse. The expanding pattern cracks the mould, and the metal fills the crack as a fin or flash. Resin burnout schedules usually ramp slowly at the start for this reason. One maker's schedule ramps at 1 °C per minute to a hold at 177 °C to reduce cracking.
Can I cast a non-castable resin print?
No. Non-castable resin is for fit checks, client approvals and master models that will be moulded in rubber. It is not made to burn out, and casting it ruins the flask. Only direct-castable resin goes into the flask.
What burnout temperature does castable resin need?
It depends on the resin and the investment, so use the schedule from the maker of both. As one published example, Formlabs' schedule for its original Castable Resin holds at 732 °C for three hours, and says thicker parts and more flasks need a longer hold. For Semsons Tech DC resins, ask us for the schedule in writing.
What causes black spots or inclusions in castings from resin patterns?
Usually resin or residue that did not burn out completely. Check that your oven actually reaches its set temperature with an independent probe or thermocouple, extend the final hold for heavy flasks or full loads, and make sure the pattern was washed and fully cured.