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experiments with household goods casting

 Post subject: Re: experiments with household goods casting
PostPosted: Wed Aug 15, 2012 9:13 am 
Swarm Tyrant
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Likewise. There are not so many threads where I look forward to reading five pages of posts. :spin

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 Post subject: Re: experiments with household goods casting
PostPosted: Thu Aug 23, 2012 2:12 pm 
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Comrades, I am sad for three reasons:


1 ) a Milliput push mould + WD40 + Milliput = a small blob of snot coloured epoxy plastic and not an elephants foot (the part I was trying to replicate).
For whatever reason, I had zero success using WD40 as a release agent between millputs. So I thought I saw the blob in half and see what I could see.

2) Although I can now purchase such wonderful toys as milliput and dremels easily, my dremel appears to be left handed. That is, when you hold the tool in your right hand and the part in your left, the cutting disc will be flicking things towards your eyes. not such a huge issue unless...

3) I can happily report the addition of a water stream makes the dremel cut through hard materials like butter. Really energy intensive butter. I sliced through 90% of the cm2 area of milliput and steel wire within a few seconds. And then the battery ran ran out.

4) the spray of water + milliput dust coming off the cutting disc is best kept inside the sink, and not aimed at the clean crockery that's been stacked up to dry. It doesn't taste very nice either. (It's still probably better then filling the small room with a cloud of epoxy dust though). I might make a small stand + spray shield to use outside in future.

5) when getting up in the morning, and pouring a boiling hot kettle into a cafetiere, do try to get the water in and not on your hand. Currently regrowing half the skin on my left hand. Everyone needs a hobby.

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 Post subject: Re: experiments with household goods casting
PostPosted: Wed Dec 19, 2012 1:34 pm 
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Hmmm. apparently silicon caulk can be thinned to pourable consistency by mixing with paint thinner.

http://blog.makezine.com/2010/11/04/rea ... g-silicon/

That's easy...

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 Post subject: Re: experiments with household goods casting
PostPosted: Fri Jan 18, 2013 2:42 pm 
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So let's try something completely different:

Cheap eraser heated over a candle and used to make a push mould for some 28mm scale squat backpacks:
Eraser cracked slightly under the pressure (although the surface was very hot and soft, the back and sides were still too stiff to accommodate the change without cracking)

http://farm9.staticflickr.com/8053/8392 ... 009a_b.jpg

A better quality (purer and softer) rubber would probably work better.

Finished mould was liberally coated in KY-jelly and soft milliput pushed in, then model pushed on and mould peeled off (hence relatively soft lines).

A quick and dirty technique, but the rubber does appear to be stiffer and tougher then silicone caulk is. Better for pressure moulding, useless for high temp work.

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 Post subject: Re: experiments with household goods casting
PostPosted: Fri Jan 18, 2013 2:52 pm 
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Interesting. Any reason aside from curiosity to use rubber rather than just more milliput for the push mould?

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 Post subject: Re: experiments with household goods casting
PostPosted: Fri Jan 18, 2013 8:07 pm 
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I've not had a milliput-milliput mould-cast set work yet.

It's also a lot easier when the mould is a bit flexible, and I was in a hurry.

mostly the last point, slightly the other two.

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 Post subject: Re: experiments with household goods casting
PostPosted: Sat Jan 19, 2013 4:48 pm 
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Love this thread.

Have you tried out that Silicone caulk + paint thinner mold yet?


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 Post subject: Re: experiments with household goods casting
PostPosted: Wed Feb 06, 2013 6:45 pm 
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http://multimedia.3m.com/mws/mediawebse ... %20Web.pdf

This is an intresting article about the use of hollow glass spheres as a lightweight dimensionally stable filler in injection molding.
Why am I looking them up?

Becuase they are also the principle component of the big tub of filler. (Seriously, the stuff is incredibly low density).
This means I can cast big thick models, parts or buildings, without the shrinkage and weight issues associated with hot plastic.

the two items on the right- I'm sure you know what they're for. Now I just have to wait for this cold snap to pass...

Image

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 Post subject: Re: experiments with household goods casting
PostPosted: Fri Feb 08, 2013 1:53 pm 
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tips and tricks discovered so far.

Did you think silicon stank? Try a silicon and white spirit mix. It's as evil as hell and gets you as high as heaven.

This leads me to point 2 - do this outdoors, or in an open garage or something. Kitchen is not advised. Pot WILL have to sit somewhere well ventilated as it sets to avoid aphysixation, loss of brain cells or explosion. (White spirit fumes go BANG!). Mine has been relocated to the well ventilated shed

White spirit does seem to dissolve the caulk quite well - I stirred vigorously and got the consistency of lumpy tapioca, but after a minute the consistency was, well, consistent. Mix ratio currently 1/3 silicone to 2/3 white spirit. Final thickness was like a soup. Thick, but very pourable. We shall see how bad shrinkage is.

Since the consistency is much thinner, you cannot 'float' a piece on the surface anymore.

Having white spirit about really helps the cleanup process.

If you're using a plastic container as the mould bucket, then when you first pour the white spirit in, have it sitting in an old tuna can. This is just in case you accidentally dissolve your pot and will save you much grief if that does occur.

Disposable chopsticks are great for stirring, moving things about in the silicone and being disposed of afterwards.

Bit of construction site advice - rags or tissues with a lot of solvent on are best disposed of by burning. Better it happens under controlled conditions then in your rubbish bin.

I'm off to regrow my nose hair.
----

Also tried a quicky with the bubble filler.

1) 30min to the skin to harden, not for the entire thing to go solid.
2) use a mold release. this is a very important lesson I keep forgetting.

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 Post subject: Re: experiments with household goods casting
PostPosted: Wed Feb 13, 2013 3:59 pm 
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So, first pass with the white spirit / silicone caulk mix.

After a weekend curing in a very cold shed, I popped the piece in question out of the mold, winced at the amount of white spirit still evaporating and put the mold back in the shed for a few days.

In retrospect, I removed the metal original far too early. The inside of the mold was still very soft, and a lot of detail was destroyed. On the bottom of the mold (where it was touching the yoghurt pot and could harden), the spirit/silicone mix had extremely good retention of detail – far better then pure silicone caulk. After a few more days in the cold shed, I decided to test the results.

The final silicone is pretty soft – much less stiff then pure caulk., almost to the consistency of jelly. It retains a decent tension strength, and will stretch a long way without damage. This made getting the parts of the mold enjoyably easy.

Minimal shrinkage was observed.

Temperature checks were mixed – heating the mold on a low electric hob caused several bubbles to expand and distort the surface of the mold. It seems over the curing time, air bubbles also filled up with a dense (possibly close to liquid) mix of air and white spirit diffusing out of the silicone matrix. This makes it much much more sensitive to heat then a conventional air bubble, and even normal air bubbles can destroy molds. The silicone itself seemed stable..

Clearly, avoiding large voids in the first place is key. The mold was tapped for a few seconds but clearly longer is needed (until air bubbles are no longer visible, not just moved off the cast object). It might be worth testing the results of a conventional household vacuum cleaner…

The first cast done in this mold was wax (it was handy, sets fast and is pretty safe). Alas, I forgot that white spirit is effectively light kerosene and wax is effectively heavy kerosene. In other words, the edges of my not yet-stable-mold dissolved into the warm wax, and visa versa. Drat. You can see this loss of detail in the photo.


Conclusion – leave longer, in a warm, well-ventilated place before demolding.

Possibly the mixing of a large quantity of flour throughout will help the excess white spirit to escape. At least some of it seems to be bound up permanently in the mold, either reacting with the caulk or simply being encased by it.
Experiments will continue, but my god i should stop doing this to my braincells.


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 Post subject: Re: experiments with household goods casting
PostPosted: Wed Feb 13, 2013 8:03 pm 
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I really love reading this thread. I also love that you're risking your brain cells, and allowing us to profit from it. :)


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 Post subject: Re: experiments with household goods casting
PostPosted: Wed Feb 27, 2013 12:23 pm 
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So, after a week on the cold side of the window, the silicone/spirit (need a better name) mix has stabilized a wee bit.
You can actually put it to you nose, sniff deeply and neither cough nor dilate your pupils. This is a pleasant change.

I popped the 2 parts back inside a yoghurt pot so you can see the extent of shrinkage. I'd estimate it as about 15% vol change.

Interestingly, while the pure silicone is quite fire resistant and self extinguishing, mixing little pores of white spirit through the matrix leads to something that's quite burnable, even from the low heat of a candle flame*
It dosen't self extinguish either. I recommend anyone silly enough to replicate this particular experiment dosen't absent mindededly do it when the wife is watching telly. She's been very suspicious since that Barbie's head incident.

*when I say low, it's about 1000 deg C over a very small area. Remember kids, wax play is fun, 3rd degree burns are not.


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 Post subject: Re: experiments with household goods casting
PostPosted: Mon Mar 11, 2013 9:46 am 
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just tried casting up some pieces for my squats, placed wet mould on outside window sill to set (smell).

Closed window (cold)

Opened window a day later to find I'd crushed the mould by closing the window on it. Pieces now soaking in white spirit hoping that will clean the silicone off.

UPDATE:

Hmm. turns out white spirit will slightly dissolve plastic...
The originals i was trying to clean silicone off have turned to goop.
This also suggests mold making this way would end up with a big lump of goopy plastic/silicone. drat and double drat.

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 Post subject: Re: experiments with household goods casting
PostPosted: Mon Apr 08, 2013 2:29 pm 
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Concrete.

It's great stuff, tough, heavy, cheap. Very fine, with good detail retention and small shrinkage making it easy to remove from the mould

But it's brittle and takes at least three days to harden off.

This was a quicky experiment for a new lamp base. The top layer had 3 days to harden, the lower layer only 1 (and had less cement in the mixture). You can see where the outside just disintegrated on demoulding.

It's a great material, but I'm not sure I can be bothered making enough moulds to allow casting at a decent speed. 3 days feels like a long time to wait.


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 Post subject: Re: experiments with household goods casting
PostPosted: Fri May 03, 2013 9:20 am 
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madd0ct0r wrote:
Hmmm. apparently silicon caulk can be thinned to pourable consistency by mixing with paint thinner.

http://blog.makezine.com/2010/11/04/rea ... g-silicon/

That's easy...

Any more tests with this? I tried a mix of ~ 10g silicone & ~ 5g white spirit last night for a small test ended up adding a whole load of food colouring and when I was ready to pour into a mold added cornflour to act as a hardener. Had to spoon out into the container and pushed test model in for the night.

Checking this morning before leaving for work it appears that I have a good half inprint in my dried mold. The one problem I have is that the top finish of the rest of the mold is all over the place at it was too thick to self level. Any thoughts on getting it to be self levelling other than the obvious use more white spirit (increasing setting time and possible shrinkage)?

I'm wondering if it might just be something that I accept and using something like the old GW terraine cutter I can give myself a flat surface to cast the other side of the mold up against. Or even a big sharp knife?


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