I have been approached by an artisan hardware mfg. to design cabinet knobs. I have zero experience with sand casting which is how they cast the knobs. I use lost wax method for all of my castings. I am looking for advice! How much detail is lost with sand casting? How much shrinkage should I anticipate? What material is best to provide as a master for the pattern? Thank you.
Talk with the mfr. as to what they want or do not want in the way of design for THEIR sand casting process. There are a number of “sand casting” processes, some allowing more and others less “original design requirements” and some processes are more capable of detail than others. IF the company is a “traditional” sand caster, the “drawability” of the master (overall shape, how the design is developed on the piece, etc.) all come into play. The mgr. should be able to give you some parameters as to their requirements and limitation in masters they are able to use. If they already are in production with knobs of other artists, look at them for design “requirements” and if no knobs are currently being made by them, look at other items they make to get an idea of detail, undercuts (an often/usually a BIG problem for sand casting but not always), detail, etc.
Just some thoughts……………
I will definitely speak with them just trying to gain some knowledge so that I ask the right questions! They have mfg. many knobs and they have quite a bit of detail but would describe most of that detail as “soft” and sort of rounded. Treading carefully so as not to find myself in a difficult position.
Sand casting can reproduce fairly fine detail (using Petrobond, which is commonly used in the US), although the patterns have to have at least 2 degrees of draft to pull out of the sand, so undercuts aren’t possible. Shrinkage will be from the metal, not from the molding process, so you just need to look up the shrinkage factor for whatever metal you’re using. Metal masters should work fine; they will typically be remolded to produce a pattern board in aluminum, that will cast ten or more knobs at a time and last through many pressings. The most important thing to consider is how the mold will part. It’s easiest to use a 2-part mold with a straight parting line, so either the whole face of the knob will be cast in one section and the base in the other, or it will split down the middle of the knob and the left side will be in one section (called the “cope”) and the right in the other (the “drag”.)
Thank you so much Andrew, this is very helpful. Since I will still be making my designs using wax I will cast them in a non precious metal and figure out the double shrinkage from metal to metal. Sounds to me like it would be best to cast the base as the parting line. Onward!