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Making a Flexible Mold and Mother Mold

September 17, 2013

Mold Making : Brush-On Rubber Mold of a Bust using Smooth-On Urethane Rubber (Brush-On 40)

http://www.youtube.com/watch?v=sOyBawt1-Ec

 

PART I

1. Apply Universal Release to all surfaces including base

PART II

4. Mix Urethane Rubber: Brush-On 40 –  Measure A and B in equal amounts

5. Mix urethane rubber: you’ll add colored pigment to layers 2 and 4

6. APPLYING URETHANE RUBBER

First layer is the “detail coat”; apply thinly; push urethane rubber into detail

Mix and apply more materials as needed

7. Allow urethane rubber to gel till tacky 30-40 mins at 72 degrees.  Should be TACKY: sticky to touch but doesn’t come off model

8. Mix and apply second layer… no color

9. Allow urethane rubber to gel till tacky 30-40 mins at 72 degrees ~ can thicken with shredded black tire rubber

Add shredded black tire rubber to thicken urethane rubber to make parting “shims”; paint it from top back of head down to bottom of model and to outer rim of base; paint a line around the model’s base about 1 ½” from the model. This is a Registration Key.

Use this thickened urethane rubber in undercuts and indentations

Use this thickened rubber to create Registration Keys along base

11. Mix and apply third layer of urethane rubber (color added)

12. Allow rubber to gel till tacky 30-40 mins at 72 degrees.

13. Build up parting shims and undercuts using one more batch of urethane rubber

14. Apply fourth coat (no color)

15. Let all layers cure overnight at room temp

PART III

16. Applying the support shell = “Mother Mold”

Draw parting lines : divide model into 3 sections

Use modeling clay to make support for parting shims

Apply clay supports to other side

Fill in open spaces and smooth clay pieces together

Complete clay shim around model

Apply clay supports all around to back of shims

Carve registration keys into clay

Apply wax over shims, model, base

Apply Universal Mold release over shims, model, base

Mix Plaster FGR

Apply a ½” layer evenly to mold rubber including base

Remove shims

Use this clay to make the 2nd parting shim : defines 2nd and 3rd          shell segments

Apply clay supports to other side

Fill in open spaces and smooth clay pieces together

Carve registration keys into clay

Apply wax over shims, model, base

Apply Universal Mold release over shims, model, base

Mix Plaster FGR

Apply a ½” layer evenly to mold rubber including base

Remove shims… no shims are necessary for the third section

Apply wax over model, base

Apply Universal Mold release over model, base

Mix Plaster FGR

Apply a ½” layer evenly to mold rubber including base

PART IV

17. Demolding: remove shell segments

Can use chisel or screw drivers or wood shims to open up shell

Use X-acto knife to cut mold from bottom up along thickened seam in rear of head

Get another pair of hands to help with this

Gently pull mold away from model

PART V

18. To Cast

Apply Universal Release to all surfaces

Seat mold in shell; make sure seam is aligned

Secure mold with stretchy inner tubes

Mix and pour ingredients of your choice into mold cavity, being    conscientious about its properties:

viscosity, drying time, safety,    measuring

Rotational cast or solid cast material

Let it cure for required amount of time

PART VI

19. Demolding:

Remove straps, mother mold, have a look

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