[Random note]Memorandum of making silicon molds for small parts and casting them (Patreon)

Parts for garage kits are usually basically what is included in the kit, but the quality of cast reproduction depends on the situation.

Even if a vendor casting, it does not necessarily mean that there are no air bubbles or mold deviations. (This is something that can't be helped by the difficulty of casting, busy season, or the life of the silicon molds...)

The syringe that HOKKE-san's nightingale is holding in his hand, which we are currently working on, was so distorted and misshapen that no amount of filing could make it worthwhile.

Then why don't you just make it yourself? But if you can't come up with a concrete procedure, you won't give it a try.

So I was thinking of making 12 of them by processing plastic rods by myself at first, but that would not be enough to get the same quality.

I thought about making one and casting it, but I had only done casting using Oyumaru, so I didn't know what to do... (I had silicone and resin on hand, just in case.)

I had my head in the sand like that, but Otaken-san (He is the one of the professional painter) gave me some advice and I decided to give it a try, so I cast the parts.

In conclusion, it took a long time but I was able to cast it myself in a nice way and it was very helpful. Thank you so much...!　

...So, in the preface, I would like to write about the prototype making and cast of syringes as a reminder.

┃Small casting seems surprisingly doable once you get the hang of it

First, the original syringe looked like this.

I don't think it is a part to be looked at carefully, but it is impossible to make a beautiful cylindrical shape by filing. Therefore, I gave up on using this part as a prototype and made it myself first.

■Make a prototype of a syringe with a plastic rod

First, make a prototype of a syringe using a plastic rod. It is not versatile, but maybe you can learn it as an idea?

It use 2mm, 3.2mm, and 5mm plastic rods.

2mm is for the nozzle, 3.2mm for the syringe body, and 5mm for the lid portion.

God Hand's Amazing Cutter Middle is useful for cutting plastic rods.

I like the fact that the cut edge is not distorted so much that it can be smoothed out just by filing it down a little. Also, it is easy to cut plastic rods.

It is easy to cut the body and nozzle parts around the area shown in the photo and adjust the length after processing.

It would be nice to have a mini lathe for machining cylindrical objects like this, but unfortunately, I don't have such a thing! So, an electric drill is used (But I'm not recommended because of shaft shake).

Machining can be done by applying a Godhand's Riegel needle or spin blade to the area to be machined while turning the drill like this.

I think a drill without shaft shake would be able to engrave striations more neatly.

For the nozzle, use Altima AT as a lathe. This one has no shaft shake, so it is possible to process quite cleanly.

I like it because it can do tapering and streak carving quite nicely. The process itself is quite fun, so I hope people will feel free to try it.

It looks good.

All that remains is to connect the processed parts together.

This completes the prototype of the syringe.

■Cast work with bump-off molding

Surfacer should be painted to check for scratches for the parts.

This time, I made a pressure type mold that does not create an air vent and cast it.（In Japanese, it is called a "裂き型" silicon mold, but I don't know what to call it in English. If anyone knows, please let me know.）

It's super easy because you don't have to use a vacuum de-aerator or mold release agent, but the life of the mold is short: after about 10 pulls, the mold will warp and the silicone will fall apart, but I think it's enough for less than 5 or so duplicates.

Normally, I think of the pressure type as making a gate leading to an air hole to create a two-sided mold, but the fact that I didn't have to do that also encouraged me to try it out.

After the surfacer is dry, glue the prototype to the pla plate.

And then, glued to the bottom of the paper cup.

The reason for gluing is to prevent the prototype from floating when the silicone is poured.

Then, draw a line on the paper cup part with a magic marker. This will be transferred to the silicone and will be used as a guide for the cut. (The cut edge is not straight, but cut in a wavy shape to prevent the mold from shifting.)

Well, to be honest, with this prototype, it is the same no matter where you cut it from, so you don't need to guide it...but just in case.

Once this is done, the silicone is poured.

This cup uses about 70 grams, but you can reduce the amount of silicon used by using a smaller paper cup.

Wait for 3 to 4 hours for the silicone to harden.

Once cured, remove the silicone from the paper cup and use a knife to make a corrugated cut, and then break off the parts that the knife blade cannot reach by hand.

The point is to stop tearing until halfway through. If you make a two-sided mold, there will be two dividing lines, and one of the advantages of the tearing type will disappear...

Once the mold is made, mix and pour the two-component white resin.

The trick to duplicate small parts is as follows

• Mix gently and quickly with a spatula or other metal rod (about 30 seconds).
• Remove air by pulling or tapping a metal rod or bamboo skewer with a rounded tip into or out of the hole.
• When moisture mixes with the AB liquid, microbubbles form, so after each duplication, remove it from the can into a paper cup or silicone cup (never leave it out in a paper cup, etc. & never put the remaining liquid back into the can).
• Paper cups and disposable chopsticks easily retain moisture, so replace them every few times when duplicating multiple times.
• If the amount of resin solution mixed is too little, it tends to fail to cure, so mix a little more than usual, even for small parts. Allow for the loss, or prepare another mold and use that one.

My biggest mistake was transferring the resin solution from the can to a paper cup and leaving it out so that I could mix it immediately.

This may have caused the resin solution to become moist, and many times I ended up with casts that were full of microbubbles... Also, even with small parts, I had to mix a certain amount of resin to get the resin to harden properly, resulting in translucent or speckled patterns.

Once we know the cause of these problems, we know how to counter them. So I decided to increase the number of molds to four and replicate them with fresh resin each time while reducing the amount of excess resin.

Incidentally, if the mold is broken, it can be cut into squares with a cutter knife and reused as a bulking agent.

Just pour the silicone here.

I have seen many times on Twitter that prototype makers are cutting silicone, but I never thought I would have to do this myself... As with the first time, the silicone will cure in about 3 hours. I think you can avoid air bubbles around the prototype by enclosing the thickener around the prototype so that it does not touch the prototype. (I'm not sure how this will work in practice, I'm just imagining)

It took two full days to duplicate about 25 beautiful syringe parts like this. I was able to duplicate them beautifully without losing the shape because I only had to pull them out 6 times with one mold.

And a paper cup full of leftover resin solution and failed parts. This is easy for me, because success is always accompanied by failure.

So I made a prototype of a simple part by myself and duplicated it. I had thought that replicating parts would be somewhat difficult, but once I figured out how to do it and the tricks of the trade, I felt that I could make a silicon mold without any fear in the future.

By the way, the silicone I used is Wave silicone rubber and Creos Mr. White Cast 2.

I also have a scale and mold release agent, but this was not enough to use in either process. If you ever need to duplicate these small parts yourself, I recommend you give it a try, even if it seems like a lot of work.