Plaster Mold after Complete Drying is Resistant to Heat! DIY One-off Rubber Parts Challenge [Part 2]

As far as the shape of the original master part is concerned, it seems to be possible to take out smoothly, so it might be best to challenge with "plaster mold". This time, I decided to make DIY parts. If you are planning to make a certain number of parts (e.g. 10 or 20 parts), it would be better to make a silicon mould. However, the shape of the cable protector is flat and simple, so if you are planning to make at least 2 pieces of the cable protector with plaster mold, plaster mold is definitely more common.

In the previous report, "The first half of the mold making process", I explained the pouring of the plaster liquid and the reinforcement of the mold using sisal.

Urethane rubber is hard to reduce against friction

I use a product called Adapt Color Urethane Rubber 80L to make products. This product becomes a product of moderate hardness by mixing the hardener at a setting of 60 to 100 of the main agent in weight ratio. Always use new paper cups when making a pouring mixture to avoid using the wrong ones. The ratio is by weight, so it is best to prepare a cooking scale.

Coloring urethane rubber with color toner

This product is easy to use because it comes with a color toner solution. It can be purchased at large model shops, specialty shops that deal with art and craft products, and web mail order. Urethane rubber gives the impression of becoming quite hard when completely dried, but if it is medium strength, it has moderate elasticity and does not give the impression of being too hard. Be careful not to put too much toner. Especially, the color penetration seems to be good because it is black this time. Put an appropriate amount of toner, not too little or too much, into the mixture of the main agent and hardener. After mixing, use chopsticks or something to mix them thoroughly. Since the mixed liquid does not harden immediately, you can work slowly and surely.

Stripping process using the same potash soap as the master mold

The dried plaster mold should feel lighter because it is completely free of moisture. The best way to dry this master mold is to do it slowly and slowly at room temperature. A household dehumidifier can also be used for this purpose. It is best to let it dry for more than a few days in all four seasons. It seems to be okay to work slowly enough to leave it until the next weekend. In terms of days, it is best to let it dry for a week to ten days. Apply an appropriate amount of potassium soap, which is a mold release agent, to the surface of the demolded master mold on a rag. Make sure to spread the potassium soap not only on the mold but also on the flat part molded by the acrylic plate and to further promote mold release!

I heard that it's good to use not only potassium soap as a release agent, but also "silicon mold release spray" sprayed firmly to promote mold release. Here is a reconfirmation. Before applying the mold release agent, be sure to clean off any remaining master correction nendo in the mold before practicing the mold release process.

When urethane rubber is poured, use a plaster mold.

Slowly pour in the urethane rubber liquid from upstream while tilting the plaster mold at an angle, then gradually eliminate the inclination and pour in the rubber while making it horizontal. Pour in the urethane rubber mixture thoroughly until you can see the surface tension. Place the plaster mold horizontally and pour in the urethane rubber mixture, making sure to check the surface tension. This surface tension = a certain amount of rubber, and it is possible to cope with the rubber pulling (subtle shrinkage) that occurs during curing. The plaster mold in a horizontal state is tapped with a fingertip to promote air release. To stabilize the mixture, three holes are drilled in the colored and easily recognizable amber acrylic sheet. As for the dimension and the curve of the hole, let's decide the hole position dimension with the front fender as a master.

Accelerating the hardening of rubber by using a high-temperature dryer

ADAPT color urethane rubber can be dried and cured in 24 hours at room temperature of 23℃. If you use a high-temperature dryer, the curing time is 4 hours at 60℃. It seems that too high a temperature is not good. Carvek CV Junior is overwhelmingly useful in this kind of work.

The result is like a dumpling with feather.

The urethane rubber of the surface tension part came out like "dumpling with a feather", and the remainder overflowed from the three holes. As a result, I cured it for about 5 hours at 60℃ using CV Junior. Because it was able to confirm that the urethane rubber which overflowed was cured, it took out. After peeling off the gummed tape slowly, I carefully peeled off the acrylic sheet from the plaster mold. The plaster mold can continue to be used until it breaks or loses its shape.

When installed on the motorcycle body, it looks like a genuine part.

A delicious feathered dumpling is ready! More attractive reprinted parts than dumplings! Now you have a completely one-off DIY cable protector! If you work carefully and don't break the plaster molds, you could probably make 5 or 10 of these! It might be possible to make 5 or 10, but in fact, I only made 2 and that was it. The cable protector looks more like a creepy crawly worm than a dumpling with wings. The burrs on the feathered part can be cut with scissors. After cutting, spray the surface with silicone spray, polish it well with a rag and you're done!

If you have good quality original parts left over and you can mold them, it's really quick! However, it is important to note that plaster molds are not as easy to reproduce as silicone molds when making one-off rubber parts. For this reason, we want to use the best possible condition for the model. This time the master part was completely hardened, but I was lucky to be able to remove it cleanly with a scraper.

On the other hand, if there is no master mold or no master mold at all, it is possible to create a similar shaped master from acrylic sheet material. In fact, after making the reprinted parts for the Kawasaki, I found a product that had a corrugated acrylic sheet, so I cut that corrugated acrylic sheet into a material, heated it up, and bent it into a shape (Kerbeck's CV Junior played an important role here). Then, it was possible to make a mold with obviously higher precision than using a genuine part that had been used for many years as a master mold, and when a product was poured using urethane rubber, this finished product was sharper than the original. When the completed parts were visually compared with each other, the master mold made from the acrylic corrugated plate clearly had a sharper edge, and a more satisfactory finish could be obtained.

Pouring rubber products after making plaster molds is not an easy task, as in this case. We need to remember that we need time to work on it slowly. In particular, in the first half of the plaster mold-making process, "the complete drying of the plaster mold is the decisive factor for success," so you must not rush to force dry the mold that is still drying, or make products before it is completely dry. The key to accelerating drying is to wrap the mold in dry newspaper and replace it with new newspaper when it feels damp. It is also a good idea to use a dehumidifier to keep the temperature from getting too high.

Photography cooperation: Model Create Maxi

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2021.01.08