Reproduction of molded parts
Repair material
The reproduction of molded parts is particularly interesting to complete
a series of buttons on a vintage radio while keeping its original appearance.
Products used
- RHODORSIL
- RTV2 Silicone
- Modeling clay or Plastiline
- Resin
- Polyester
- Vaseline
These products are on sale at:
ROUGIER & Plé Tel.: 01 64 54 70 00
Also provide various colorants such as ebonite powder or lampblack.
These can be found at building material suppliers for tinting concrete and
in drugstores. (Dugay, rue des rosiers. In Saint-Ouen).
Preparation of the part
This one will be perfectly clean and lightly coated with Vaseline. For a
button, it will be necessary to reinforce the threaded area by filling the
hollows with modeling clay. A threaded rod with a
diameter of 4mm and a sufficient length to pass through the mold will be prepared
and coated with Vaseline to avoid probable adhesion
of the RTV.
Making the mold
First part
The RTV2 resin allows making a flexible mold in two parts perfectly matching the shape of the model. The mold should have a thickness of one to two centimeters around the part to be reproduced. For a Philips button from the 30s for example, a yogurt pot will be used to contain the whole thing.- Put one to two centimeters of modeling clay in the bottom of the pot.
- Place the button on top, pressing lightly so that its imprint is marked and in such a way that the threaded rod touches the side of the pot.
- Make a few 2 mm hollows in the modeling clay to create alignment keys on the two parts of the mold.
- Prepare the RTV and pour it up to 1 or 2 cm above the part.
- Let it polymerize...
Second part
That's why you should take a commercial yogurt pot and not a
grandmother's jam jar:
Turn the pot upside down and cut out the bottom. Remove the whole thing from the mold by pushing on the bottom. Remove the modeling clay, coat the mold with Vaseline and put it back in the pot. We are ready to pour the second part of the mold, or almost.
Place an 8 mm diameter tube vertically on the part to make vent holes through which the air will escape when pouring the definitive part. The whole thing will come out when pouring the definitive part. The whole thing will be held vertically as best as possible with iron wires.
All that remains is to pour the other part of the mold.
Turn the pot upside down and cut out the bottom. Remove the whole thing from the mold by pushing on the bottom. Remove the modeling clay, coat the mold with Vaseline and put it back in the pot. We are ready to pour the second part of the mold, or almost.
Place an 8 mm diameter tube vertically on the part to make vent holes through which the air will escape when pouring the definitive part. The whole thing will come out when pouring the definitive part. The whole thing will be held vertically as best as possible with iron wires.
All that remains is to pour the other part of the mold.
Finishing the mold
The two parts of the mold may be stuck together. In this case, they will
separate quite easily with a thin cutter by pressing
the tool on the back of the button. A cut will have to be made
dissymmetrical which will serve as a marking for reassembly.
To remove the model, you will not be bothered by the threaded rod if you have taken the precaution to split it to allow access to a thin screwdriver. Remove the rods from the pouring and vent holes.
The material of the mold is flexible enough not to be hindered by undercuts.
To remove the model, you will not be bothered by the threaded rod if you have taken the precaution to split it to allow access to a thin screwdriver. Remove the rods from the pouring and vent holes.
The material of the mold is flexible enough not to be hindered by undercuts.
Making the part
Replace the threaded rod so that it reaches the central core of the
mold after coating it with Vaseline.
The yogurt pot will advantageously serve to align the two parts of the mold.
When preparing the resin, look for the right color with the colorants quite quickly but taking care not to create bubbles.
Pour the material, taking care not to trap too much air. If possible, the whole thing will be placed on a vibrating table made with an electromagnet. There is generally no cutting problem; cut the parts that have risen into the pouring and vent holes.
The yogurt pot will advantageously serve to align the two parts of the mold.
When preparing the resin, look for the right color with the colorants quite quickly but taking care not to create bubbles.
Pour the material, taking care not to trap too much air. If possible, the whole thing will be placed on a vibrating table made with an electromagnet. There is generally no cutting problem; cut the parts that have risen into the pouring and vent holes.
