2.2_semacode door knob [milling+making the molds]

[SHOPBOT-CNC SETUP]

Pink foam 9″ x 9″ x 2″.
Roughing pass 1/4″ end-mill (flat)
Finishing pass 1/8″ end-mill (flat)
Speed = 9000 rpm
Feed rate = 4.5″/s
Stepover = 50%

15 minutes each milling time for each mold.
Total time setting up, trouble shooting and running job = 1.5 hours.

Problems:
1. Collet will hit foam as the spindle goes down to carve out the pixels.
2. Pixel’s edges would be filleted around.

Solution:
We tried doing undercuts (models flipped upside down and bank for spindle movement was created). This way, the pixels square shape should be preserved as well.

The top-half of the mold passes.

The bottom-half of the mold passes.

[CNC-MILLING]

Starting with the top-half roughing pass, the roughing process did not take long at all (approximately 7 minutes) but we had to change from 1/4″ to 1/8″ for the finishing pass (which takes 9 minutes) and encounter glitches along the way.

Top-half foam milling. A significant problem here was that of the plastic protector attached around the collect as it damaged the milled foam as the arm went deeper.

Bottom-half foam milling with deeper step down carving distance. At one point the 1/8″ bit went too deep that the collet started to chip the foam out so we paused and brought the spindle 1.25″ out (max allowance before it flies out loosely).

[FOAM MOLDS REFINEMENT]

Using knife (scalpel) and high-grade sandpaper, the foam leftover were cleaned up before the walls for the casting process were built.

Air compressor cleaning up process.

Building up the walls for pouring Smooth-On mold into.

[SMOOTH-ON POURING PROCESS]

Before executing the pour, the foams’ porous surfaces were sealed using Gesso. Two coats of Gesso (1-2 hours drying time each) were applied to close porous surface and smoothen shapes. You can most likely do it with one coat but I highly recommend doing the two coating as one might still leave uneven gaps throughout the area applied. The Gesso also shut the gaps between plywood wall and the foam.

Molds covered thoroughly with Gesso.

I applied one thin layer of corn oil to prevent the later mold stuck onto the Gesso layer. You can also use hand soap or any oily material for this purpose.

Smooth-On Star Mold 15 is a platinum quality silicon rubber with 50 min pot time and 4 hours cure time. It’s suitable for a good quality rubber mold with strong bond to use for casting many more times.

HMIS (Hazardous Material Identification System):
Health = 1 (generally safe to work with at room temperature with sufficient air flow)
Fire = 1
Reactivity = 0

Gloves and safety glasses must be worn when working with this material.

1:1 Part A and Part B ration. Wall too far away from object resulting in excessive use of the silicon rubber.

Taking out the dry silicon out of the foam-work.

Top -half of the silicon rubber mold.

Bottom-half of the silicon rubber mold.