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monkeytennis

Cold Casting

8 posts in this topic

I've been thinking about this for a while so I thought I'd do a small test to see how easy it would be to cold cast a NSD; mixing metal powder into clear gelcoat and standard polyester resin.

This hemisphere is cast using brass powder. It has a slight green tinge to it in person (I know the lighting is not great). I think the actual colour used on the NSDs is a slightly warmer, more yellow colour.

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I made a small panel from fibreglass and bronze powder. I think the bronze is not a bad match for the NSD bronze, considering. I haven't tried sanding this panel yet so I don't know how much brighter it will look.

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Here is a pretty good reference photo for the NSD colouring.

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I have some aluminium powder. I might see if it is possible to mix some combination of the three to get something approaching the correct hemisphere colour. It's also worth mentioning that I only used a roughly 1:1 ratio of resin to powder. A higher proportion of powder would make for a more metallic finish.

Metal powders are expensive, but as a long term project they could be used to make a NSD that wouldn't need to be painted and would have a good resilience to scratches.

Edited by monkeytennis
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Would you believe I have already done some tests for this? I have a Cybusman suit that's all cold cast aluminium, so am pretty familiar with working with it.

The trouble is you need to have it relatively thick (a few mm) all over and have it quite dense in order to keep a solid look when you buff it up. It means the parts tend to get quite heavy, and you end up being quite thick in surface area where you would rather not be. Particularly around the cowl (it needs to join to the dome) and the edge of the dome, it starts to get thick enough to start hitting the struts.

The big thing holding me back from doing a whole Dalek in that style, is the neck cage, you would have to do moulded neck struts and neck rings to keep the look consistent.

The mix you want is ideally around 70/ 30 or so, and I believe you would be looking at around 8-10kg of metal powder for a whole NSD minus hemispheres (probably bringing it to the 10-11kg material mark. When you're cleaning it up, work you way from 00 steel wool to 00000 steel wool going over the surface evenly, then go over it with a buffing compound to seal the look over.

It does require a LOT of buffing and does tend to dull over time. Because the material is thick applying it over large flat areas can be a pain in the bottom without getting air pockets, and then they have to be drilled out and filled, and the newly mixed material never quite sits at the same shade.

But it's a good idea, but it would be an expensive, heavy build and you would have to overcome the moulded neck ring problem and be prepared to use a LOT of steel wool.

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We're the original NSD hemis cold cast?

That a method I never thought of. You could do an entire Dalek in either bronze or aluminium.

Now that would be interesting.

Edited by Dalek Supreme
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No, they were plain fibreglass.

The new series "Cybus" Cybermen were, and look rather lovely as a result.

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I had a quick go at trying to cast a dome with a 1:1 ratio of aluminium powder, which unfortunately failed.

 

I tried making the gelcoat quite thick but I suspect I either over-catalysed it or made the gel coat too thick as I could feel the mould was getting quite warm.  On de-moulding I could see the dome had quite a few lumps and had even cracked around the back.  I might try again by adding multiple thin layers of gelcoat to try and prevent too much temperature build up.  I gave the dome a quick sand with a bit of sand paper I had lying around.  It looks like it could have looked good had the layup not failed.

 

I'll try again in a week or two...

 

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Edited by monkeytennis
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Did you add the catalyst before or after the powder? I've read about problems with catalyst distribution when powders are added. The recommendation is that you add in the catalyst first, so that it gets mixed properly into the resin. Doing it the other way around can cause hot spots where too much catalyst is concentrated and spots that remain tacky due to catalyst starvation.

 

I think I've got some aluminium powder kicking around somewhere, so I might give this a try, so we can compare results. :)

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I weighed out the gelcoat and powder in two separate pots, catalysed and mixed the gelcoat and then slowly folded in the powder and mixed up.

 

I think I'll give it another go.  I reckon it could give good results if I can get the technique right.  I'd be interested in seeing any results you come up with. :)

 

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I tend to add the catalyst at the same time as mixing the powder and the resin, and mix all three pretty well together. I don't know how I missed this post.


Oh- you can use regular polyester resin rather than mixing it in with gelcoat, the powder will thicken the resin up massively anyway.

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