Sink form building

We have gone through several options while building the forms. One sink was supposed to be a curvilinear surface with only a small off-center depression for the sink bowl. The other sink for the master bathroom was meant to be more aggressive sharp-edged faceted form.

It turned out to be very difficult the get the right results while building the sinuous form using a sheet of thick acrylic and a heat gun. We had to use extra weight to push the surface down, but since we did not have access to vacuum forming tools, this method was very hard to control.
I have used 4 or 5 acrylic sheets and never achieved the desired smooth curvature I liked.
After this I tried sculpting the form out of rigid insulation foam. It could have been done with a CNC milling machine, but why bother if you can do it by hand? :)


Later I planned to cast gypsum into this form and then smooth and paint it to get the final negative top surface of the sink. But after wasting a bag of gypsum that cured in seconds in the mixing bucket I finally came to conclusion that it is time to simplify.
I have changed the design of the guest bathroom sink to a simple slab with a shallow rectangular depression. The only curvilinear element left was how the surface gradually sinks in from one side. I used the acrylic again but in a lot simpler manner.

The only complication was creating the negative forms to create cavities underneath so the it is not entirely solid. That reduced the weight by about 30%.


The faceted sink for the master bathroom was a little more straightforward. All of the geometry consists of planes. The difficulty was in connecting the planes at different angles.
We have built a 3D model of the sink surface and of the form that was to be made out of laminated particle board you can buy in any Home-Depot-style store.
Using a 3d model is not necessary but it was the best reference for measuring all of the angles. Each seam was mitered at a different angle that required adjusting for every single cut. I had to use both a compound miter saw pictured below as well as a table saw with a custom jig for nearly each cut.
Then what was left was assembling the top and bottom of the forms. Each had a distinct shape and angles to maintain a minimum thickness of the concrete slab and accommodating the drain that has its own minimum thickness to be installed properly.