Casting Beginner Questions

[Anvils Hammer]

*uses wooden sticks for mixing anyway*

Though up till recently I used bit of garden wire cut and bent into a spiral.

And yes, I use pressure AND pour under vacuum, So I could probably fill my molds with a crumbled up Aero bar and still get bubble free parts

AH

[Zhatan]

I have just completed my first cast in my first mold and I must say I'm very impressed with both the silicone and the resin.

The mold came out perfect, I'm guessing it's because it degasses itself, and any air bubbled up to the surface before it set.

The casting went well too considering it's my first try and I just made a mold with one pour hole and no place to let air out. I made it just to try it and the cast only had one single bubble and that is easily mended with greenstuff.

For my next mold I will try it with a separate pour channel and a air vent.

[mangozac]

Make sure you try repeatedly squeezing the mould after you've poured in the resin - that helps agitate the bubbles out of the mould. Also, dusting the mould with talc helps prevent bubbles from sticking to the surface.

I can't imagine the tiny amount of moisture in a wooden stick having that much effect. I'm currently using fibreglass strips broken off production circuit boards from work (they would otherwise be binned and make good mixing sticks).

[Zhatan]

[mangozac]

The Pinkysil I use is only Shore 20. When you say deform do you mean permanently deform - the silicone or just the cast? The silicone should spring back to shape no problem. This is different to tapping the mould though. The point of tapping is to loosen the tiny bubbles. The aim of squeezing is to force out the larger bubbles and air pockets that get trapped.

Baby powder should be ok instead of talc. There is a small chance of complications due to the perfumes in it, but if it's worked so far then it's probably fine

The wood thing is indeed just a precaution. I'm pretty sure here in sub-tropical latitudes of Australia the resin sucks up more moisture from the air than it ever will from a mixing stick.

On a related note, are they called paddle-pop sticks anywhere else?

[Deadmeat30]

I use wooden waxing spatulas, seem to work a treat.

[blind pig]

[Zhatan]

[mangozac]

Oh yeah I forgot about the resin overflowing - I have a "reservoir" built into the top of all of my moulds for this (required because I use a vacuum + pressure casting technique). However if you so the squeezing while you're still pouring the resin you should be able to control it well enough to not overflow.

Temporarily deforming the mould shouldn't be an issue - it will spring back immediately and won't deform the cast. Yes you do have to worry about upsetting the mould alignment though, but so long as you are squeezing the right way (and without any sideways force) it's unlikely

[Zhatan]

Back again with another question.

How do you clean a oil based clay from a silicone mold after you use it to hold the original part? I have no problem getting the clay off the original with a small brush and water but there is some left on the mold itself I am unable to clean off.

I use Chavant NSP Soft Clay if that helps

[Anvils Hammer]

anything that cant be scraped off with your finger nail is no problem at all, just pour the second half as normal.

Most of my molds have traces of blue clay on them even after several dozen pulls!

AH

[paulson games]

I use hot tap water on the mold it melts any of the left over clay and I give it a quick go over witha toothbrush and it comes out nice and clean.

You might get a few small streaks of clay on the modl left over but as long as it's not up near any of the parts it shouldn't be a problem. If you've used hot water and a brush anything that's left should be really minor.

[Zhatan]

Yeah I get most of it off with hot water and a brush as you say... the small amount left just annoys me.

On another note I tried casting again and it was a massive failure. I think the resin thickened to quickly and got stuck in the pour channel leaving half the mold unfilled. Could something like this happen if I got the wrong ratios when mixing the resin?

The problem I have with my resin is that it is 1A:1B by volume but 10A:9B: by weight. It makes it very hard when you only need resin for small molds as it's close to impossible to pour those small amounts by volume and my scales are only accurate to the gram. Add to that the weird ratio when weighing it's a real hassle.

[Deadmeat30]

Grab some cheap scales that give you decimal place in grams. Plenty on Ebay . Best way to get good ratios.

[mangozac]