18 replies to this topic

[munter]

I've been casting some small bits lately....failure rate is quite high but I'm still pleased.

[Mobbzee]

looking pretty good munter
i'm sure the failure rate will drop the more you do

[manimmal]

Awesome space robot 2nd from the right on the top row
On a serious note, that's got to save some searching and some coin, was it difficult and smelly?

[Stubbo]

Are you using a pressure pot or chamber?

They look nice and crisp.

[munter]

Still learning a few basic rules....no pressure pot.

[dangermouse]

Me to John, maybe we should share some tips and castings. I am impressed by your wire wheels.

Aside from silicone moulds I have played around with some small castings using plasticene for a mould. I want to try some of this next to make some impression moulds
http://www.barnes.co...0pk-p-3003.html
video here
!

Here are some of my projects

cheers
David

Edited by dangermouse, 23 July 2012 - 09:07 PM.

[Ember]

John, I'm very much looking forward to the time when you feel confident enough to cast that Revellogram (?) 300SL of yours.

I was really surprised at the detail picked up in those Scaley 300SLR shells. I was dumbstruck to see the impression of the 722 tampo. Just seems a matter of getting the bubbles out. But that's bound to be over simplifying things.

Embs

[kalbfellp]

John try using a syringe to fill the moulds, one about 10cc should be big enough, just put it in some water after and you can use it again.
This should reduce the failure as you have no pressure pot.

[munter]

Thanks for the tip Phil. I will definitely try that.

mmm getting the bubbles out can be done by standing on my head and if I hold my tongue in a certain position then.....
I think I have that nailed as well but as I said some basic lessons have to be learned first.

As Van Gogh or some one said a while back.." I am always doing what I cannot do yet in order to learn how to do it."

[dangermouse]

Pressure pots

hmm I need to learn some more about them, any info or links to share Phil

cheers
David

[grt]

<sub>Hi John,

I use Barnes 5ml syringes for the small casts, they are plenty big enough. I find the biggest trick tio getting bubble free casts is to get your bleed holes in the right place. I use a small hole punch, and position them at the highest point(s) of the mould, or in corners where air can get trapped. It does mean you have excess resin strings to cut off, but the trick to that is to mould the part upside down, so all the excess resin from bleed holes and the like is on the "back" of the cast.

And, of course, even if you still end up with bubbles (as you invariably do every now and then, no matter how good your moulds and injection skills are, you can always fill the bubbles in with excess resin when you cast your next batch up.You just need to open up the bubble (on a hidden side if you can), and drip the resin in slowly to fill in the hole.

Its fun though isn't it? Creating your own parts, restoring old wrecks to their former glory, spending time in the "man-cave". (We need a "Tim the Toolman" smiley here - ugh, ugh,. ugh)</sub>

[grt]

John,

One other thing I just remembered. Barnes sell a product thats perfect for maikng permanent impression moulds. I've used clay and plasticene before for making temporary one off moulds, but you destroy the mould when you pull the cast out, and invariably, I have found I nearly always need to make another one. I think its called Sil-Pression? I'll dig out the stuff later this week and get the correct name.

[Garry J]

For anything that has a flat side (wheel inserts, etc) I use an open, one piece mould and pour the resin from one side until the mould is full. I use a toothpick to pick out any air bubbles, if needed, and get very few failures. For anything requiring a 2 piece mould I use pieces of plasticene to form filler and evacuation tubes. Complicated items can require several evacuation tubes to eliminate air pockets.

I have a vacuum pump and made a small chamber with some 150mm PVC pipe and a couple of flanges with 12mm polycarbonate end plates and rubber seals. I only use the vacuum to make the moulds, it's amazing how much air is in what appears to be bubble free liquid silicon.

Edited by Garry J, 24 July 2012 - 01:18 PM.

[Ember]

So it's vacuum to remove bubbles from the silicon for moulding? And positive pressure to remove bubbles from the resin casting?

Would be interested to try one day. Only casting I've done has been in glass, bronze or silver. But there's just way too many things on the 'want to try' list.

[FLY in the wall]

BTW. I am sure you all know but just in case that an old fridge compressor will pull a vacuum. They are cheap if you can find one. As casting is not a continuous service application they will work fine.

[Garry J]

Plenty of examples of home made vacuum pump setups on the net.

Here are a couple -

http://www.dream-mod...vacuumpump.html

http://www.seabreeze...50_1293413.aspx

[munter]

It is fun grt....no air bubbles in this....I expect the trimmed weight to be about 22 or 23 grams..... interior tray to come.
There are a few bogeys here and there but nothing an average modeller couldn't deal to.

Edited by munter, 24 July 2012 - 07:11 PM.

[Ember]

Now that's looking good!

Who is a smarty pants then?

[Rob]

The other thing that can influence how the resin flows is the actual viscosity it self, you could try heating it prior to mixing to help flow. We use to run our resins at approximately 40 deg c which allowed for prep, mix and pour time. One side note heating the resin will reduce the pot life of the resin.