We have just completed casting and machining 8” diameter knobs for the entry doors to an upscale Connecticut residence.
Although The handle design was minimalist the knobs were cast in steel and hand polished to create a subtle but beautiful contrast to the dark doors where they will be mounted in the center panel. In the picture below, we have created a mock-up of what the entry sets will look like.
Step by Step account:
Designing, pattern and mold making;
We began the process by discussing with Fletcher Development the function and style of handle and determined that there would be 2 knob sets, one that would operate and release the custom mortise lock made by Accurate Lock with second set being fixed as through bolted dummies. We chose to cast these in 316 stainless steel which is a corrosion resistant very durable alloy.
We then created 2 wooden patterns one for the rose or escutcheon and one for the knob itself both of which were turned by hand on a manual lathe. The patterns were coated with primer to fill in the wood grain and flexible rubber molds encased in rigid plaster were made. The pattern and mold making process could have been eliminated had we opted to make quick cast stereolithographic prints for all the knob sections.
Custom backset
Once cast, the operative set had to be machined to function with a custom mortise lock made by Accurate Lock for a door that would have a 14 7/8” backset. The backset is measured from the edge of the door to the center of the door knob. The knob was machined and fitted with a custom spindle that was designed to slot into the mortise and thereby throw and retract the latch when the knob is turned. The escutcheon plates for the knobs were machined so that connecting bolts could be attached to the exterior knob, pass through the lock body and connect to the interior knob. While the escutcheon plates could have been surface mounted this would not have provided a firm support for our 8lb knobs. As the mortise body was 7/8” thick and the door was 2 ¼” deep , surface screws, had they been used would have been insubstantial at ¾” in length. The body of the lock was customized by Accurate’ s experts to accommodate our though bolts and we bench tested it with our castings to ensure all the moving parts were aligned.
