Hey everyone,
at present I'm building some (5) marine Abrams' and therefore have to cast all the additional parts I scratched before...
Basically everything is going pretty well but I'm somehow having problems getting the air bubbles out of my smoke grenades, which causes me some headache, since I have to cast about 80 of these pieces to outfit all of my builds... thank god i already managed to cast four without any bubbles

Well, to solve that problem I thought of making a new mould with some more air vents to get rid of any air bubbles, I'm just not quite shure what's the best way to build the vents and where to locate them to eventually get rid of those bubbles...
here are the "prototypes":


and here's the problem and my thought of where I should locate the new air vents:


Does somebody maybe have an idea of what would be the best way to attach the air vents or maybe some other ways how to get rid of air bubbles?

Cheers Max

For some of my more problematic castings I use a home made centrifuge. Really just a plastic bowl tied to a length of rope. Center the mold, hold it in place with clay, pour the resin, and swing it around for a minute or so. Molds that you use for this just need a bit of reservoir on top for extra resin. The bowl keeps any spillage from flying around the room, that's about all there is to it!

Pressure casting or Vacuum casting are the way to go. Pressure casting is cheaper as it uses a paint tank and your compressor. Vac casting needs a vac. pump and thay can be expensive.

The quick solution would be to "paint" some of the resin in the mold before pouring or trying the centrifugal method mentioned above.

G'day Max,
Forget centrifuge, vacuum and pressure for this job (sorry guys).

See below.
The only high tech tool you will need is a old paint brush handle with the paint removed from the handle.
As you can see all you will need to do is cut the mould. The use a small amount of talcum power to coat the inside of the mould. Mix up the resin as per manufactures spec's and fill the reservoir. Then take the paint brush handle and gently push it into the centre of the cut.
Then, slowly press the tip of the tool into all of the corners and under cuts ect. And then slowly run the tip up the sides into the reservoir. This will draw out most of the air. As you do this some resin will spill out of the mould. Just top it back up and start on the next cut. Once all of the pouring has been done, gently squezze the mould side to close up the cut and to minimise the amount of flash. For a pour like this, (after a bit of practice) it should take about 15 seconds to do.

Good luck and remember to use eye protection.

Cheers Jason

Thanks for the ideas....What I have been doing with about a one half success rate is to cut a small vent......inject the resin with a hypodermic syringe with the needle removed and then vibrate the bubbles out by holding it a minute gently next to my electric toothbrush. It works great when it works but I gotta say I do throw out quite a few that end up with bubbles. Usually the bubbles are on the chin or on the nose. It's enough to really piss you off sometimes..........Al

Hey everyone,
first of all thanks for your great replies, I guess I'm going to combine the centrifuge with the cutting method
@Matt, propably the most approved solution, but due to a limited budget and as long as pressure casting doesn't work with a tupperware box instead of an expensive paint tank, it's out of reach for me...
@Alfred, glad to hear I'm not the only one playing around with toothbrushes when casting, but well, as for the smoke grenades it's not too practical... as I mentioned above, it only worked with four pieces (out of about ten casts )
@Jason: sounds good, but is that the way you cast the mouse house/arms corps kits???
One question though, do I have to sharpen the brush's tip and can I use a toothpick instead?
cheers Max

One other thing you can do is to heat the mold up a little. Put it in the oven (on a low temp) for a few minutes, just to get it nice and warm.

Jesse

Hey,
@jason, just cut my molds and poured in some resin, erased some airbubbles with a toothpick right now the resin cures, I'll post some pictures of the finished pour.
@Jesse, I'll give it a try, do you know whether it will work with non-heat-resistant silicone as well?

Cheers Max

Yep, thats how I have been doing it for the last 2 years. I'm now going vaccume.
The stick should NOT be sharp. It should be rounded as a sharp edge will damage the mould.
Warming the mould will help a little bit but it will also make the resin exothrem faster giving you a shorter pot life. The best way to warn the mould (especilly if it is not desgined to be heated to much) is to use a desk lamp with a 60-75 watt bulb.

Cheers Jason

Hi everyone,
again thanks for the kind help, I used the "brush method" and it worked fine...
took me some 20 casts with a new mold for eight pieces to finally get two sets of each 16 pieces done. not very "cast-effective" but as long as it works.
I actually wanted to post this earlier, but my camera was on strike...






oh, and some more scratch building from the same build



Regards Max