Resin Viscosity

[pinkizhip]

Hello, I'm working on making some custom keycaps and can't seem to get my entire mold to fill. I'm using crystal clear 202 which probably just cures way to fast. Looking at the Viscosity of the crystal clear and it is 600 cps vs some other resins which are 80 cps. Seems a large difference. What kind of resin do you use for your keys? I went with the crystal clear 202 because of its strength ability in such a thin cast. For my next pour I'll try filling the bottom of the mold before putting the top half on. Then try to fill the remainder through the spruce. This may solve my problems but I still feel I'm using the wrong resin. Any thoughts?

Thanks!

[Findecanor]

Have you tried tapping the mould a few times after filling it?
I don't cast keycaps but I have been thinking of getting some kind of vibrating platform to help get rid of bubbles in my casts.

[0100010]

Why not use something like a Hitachi Magic Wand?  Remove the normal "head", and drill a hole in the platform (of the correct size to fit the drive shaft off the motor) you are using to hold the mold - turn on the wand when pouring?



Or just keep it as is, and hold it near the mold when pouring the resin?

[captsis]

Why not use something like a Hitachi Magic Wand?  Remove the normal "head", and drill a hole in the platform (of the correct size to fit the drive shaft off the motor) you are using to hold the mold - turn on the wand when pouring?

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Or just keep it as is, and hold it near the mold when pouring the resin?

why do you own one... :)) :))

[0100010]

Ha, yes.  But it is not mine, the wife maintains control of it...  You could go for a larger version, like one use for pouring concrete:

[captsis]

Ha, yes.  But it is not mine, the wife maintains control of it...  You could go for a larger version, like one use for pouring concrete:

Show Image

 ^-^
 :thumb:

[sinusoid]

There's a nice vibe to this thread 

I didn't work with Crystal Clear yet, but worked with some hi-viscosity stuff from Huntsmann with a 10 minute lifetime.

What's your entire process? How do you degass it, pour it? Do you pressurize it afterwards?

I used to fill the mold from the bottom with a syringe. Mold was prepared with a vent and resin lead on top, the amount of resin administered was enough to fill the lead. Then vac it all at 29mmHg, then pressurized it at 4 bars. You shouldn't run into any bubble issues (though you might get dimension distortions from pressure).

For low-pressure casting I chop a 1.2mm hypodermic needle in half, and use this on a syringe to administer resin to difficult parts of the mold, then press the two mold parts together so the excess of resin flows out. You end up with bleeds you have to file off, but it fills up the mold pretty well. Watch how you close it not to get bubbles in. You may want to run the open mold halves through vacuum before closing them together, too.
Personally, before closing the mold halves, I wait just below the resin lifetime, till it gets a bit more viscosity, but doesn't become springy, then close the mold, squeezing excess resin out in the process.

[pinkizhip]

Hey thanks the pointers.

After measuring and mixing the two parts of crystal clear for instructed time, the resin is vacuum degassed. After degassing, the resin was poured through 2 centre spruces into the two part silicone keycap mold. There is also a 3rd spruce for air to escape. I kind of squished the sides of the mold to help some air out. One mold was briefly vacuumed again and another was just left to set.  The mold that was placed in the vacuum seems to have come out better. The cap is complete, there are still some bubbles in the resin but they didn't dramatically alter the form. The other key wasn't filled enough.
Another problem with the crystal clear is tackiness. I'm not sure if it is poor mix ratio because of the small amount we are using, temperature or just too quick demolding time.  Our double vacuumed demolded pretty tacky still after almost 24 hrs. strangely enough the second key did not come out sticky but was removed at a similar time. Slightly baffling.

Anyways after doing more searching I have decided to try a few different products. A different silicone and a non clear resin, which are apparently easier to work with, and some syringes. Also likely invest in the pressure pot.

Now if only my PBT Caps would show up in the mail I could do some sculpting!

[dgneo]

Hey thanks the pointers.

After measuring and mixing the two parts of crystal clear for instructed time, the resin is vacuum degassed. After degassing, the resin was poured through 2 centre spruces into the two part silicone keycap mold. There is also a 3rd spruce for air to escape. I kind of squished the sides of the mold to help some air out. One mold was briefly vacuumed again and another was just left to set.  The mold that was placed in the vacuum seems to have come out better. The cap is complete, there are still some bubbles in the resin but they didn't dramatically alter the form. The other key wasn't filled enough.
Another problem with the crystal clear is tackiness. I'm not sure if it is poor mix ratio because of the small amount we are using, temperature or just too quick demolding time.  Our double vacuumed demolded pretty tacky still after almost 24 hrs. strangely enough the second key did not come out sticky but was removed at a similar time. Slightly baffling.

Anyways after doing more searching I have decided to try a few different products. A different silicone and a non clear resin, which are apparently easier to work with, and some syringes. Also likely invest in the pressure pot.

Now if only my PBT Caps would show up in the mail I could do some sculpting!

How are you measuring the 2 parts of the resins? What sort of environment are you casting in? Temperature and humidity, as well as mix ratios, will definitely affect the finished product.

[pinkizhip]

"How are you measuring the 2 parts of the resins? What sort of environment are you casting in? Temperature and humidity, as well as mix ratios, will definitely affect the finished product."

Followed the mix ratio of 100A to 90B. Using small cups and measured on a gram scale. I'd like to try mixing a larger portion to see if it would turn out differently. Used a dehumidifier to dry the room before casting and kept it and another fan going during the first part of the cure. Its is possible that the room was not 23C which the instructions state it should be. I also did not heat the mold at all before casting which is something I am going to look into further.

[sinusoid]

Using small cups and measured on a gram scale.

You might get a 15-20% drift at such weights, if not more. Tried that, didn't work, unless you have a very precise and expensive lab weight. I tested the hell out of this with both resins and silicones. Now I just calculate the volume ratios, and go by syringe scale. Use same syringe sizes for both parts though, you want the scales to be uniform.

Room temps are relative, you don't have to keep them tight. Epoxy resins (crystal clear is one afair) usually like to jump into the oven for a 12 hour 60°C post-cure or such. OK, autoclave, but us plebs usually use ovens 
I like casting in the winter or low temps in general, you get low humidity, no condensation, long setting times, less shrink, less bubbles. Works wonders for preparing silicone molds, though you have to wait a few days for it to set if you don't increase temp mid-way.


re:bubbles, did you measure the vacuum you're getting?

If the mold doesn't get filled well, vacuuming it might not give you a success - resin (especially highly viscuous) can withstand some pressure, and keep the air pocketed inside the mold. The expanding air needs to defeat that pressure to escape, and as it expands, the pressure inside the bubble drops.
Pressurizing it afterwards makes the bubble present, but microscopically small. It works, but IMVHO, that's an ugly method. Also, beware - if a pressure pot goes off at 4 bars, it can strip you off a vital organ or two. I try to avoid pressure casting, personally.

My guess is you should pre-pour the problematic parts before closing the mold, or rethink the way the mold is made.


Oh, and yea, good luck with the syringes! They make everything easier. Just... USE THEM ONCE XD
You're gonna start doing that anyway, when you dip the resin syringe into the catalyst, or the other way around, or your resin sets in 1/3 of the time because you introduced resin crystals from the previous batch with a dirty syringe

re: tacky, not tacky - in what order did you cast them? Did the first one came out tacky, or the second one?
The crystallization might get inhibited by a mold separator, silicone catalyst, or residue present in the silicone mold that got there when you made a cast from your master model. In this case, the first mold would suck these up, end up tacky, and leave the mold relatively clean for the second non-tacky one.
If the second pour was the tacky one, one of the resin's components might have gotten stuck in the silicone's chemical chains, and reacted with your pour. Silicone will readily take small particles of aromatic solvents into its structures, so it's a thing to watch out for. In such case, leave the mold in vacuum for a few hours.
Wash the silicone mold with a detergent, and use a compatible mold separator/barrier. PVA or wax in solvent are used professionally.