mold casting question

J

jdmchaos

New member
i have been casting my own sculpted bits and bases.ive been using smooth on products.
i would like to start casting in metal because it seems to be cheeper.
my question is does anybody know what the best rtv would be temp wise.
i noticed every brand has a different temp level they can take.
i also saw that there is a two part hand mix type that expands as it hardens.anybody use
this before?any help would be great.
 
Einion

Einion

New member
I don't think there's a best here, partly because of the different melting points of the casting metals and partly because there might be a tradeoff with toughness/resilience and detail capture for the RTV.

I'd just pick a good one which is listed to withstand a temp higher than the melting point of the white metal you're intending to use and see how things go (what the detail is like, how easy it is to demould, how long the mould lasts before the surface breaks down).

Einion
 
J

jdmchaos

New member
i got you but when surfing around the net i see most have a 350-400 meltdown point,and finally i found and talked to a guy who said the stuff he uses is as hard as a truck tire.
the problem is he was being quite on how he made it and wanted me to pay him to make the molds.i guess he heats the mold up and said whatever i wanted casted would have to
be able to withstand a temp of 200.
i dont know what he's using but he said i would get 1000 or more cast out of it.
 
Shawn R. L.

Shawn R. L.

New member
While I haven't done the casting itself, I have had a lot of things cast and talked with the casters many times. They tell me that 350 F degrees is how hot it has to be able to withstand and about 1000 pounds of pressure during the mold making process.
 
Einion

Einion

New member
jdmchaos said:
...finally i found and talked to a guy who said the stuff he uses is as hard as a truck tire.
Click to expand...
It sounds like he's making vulcanised moulds, not using RTV. That's a Shore A hardness of about 60 or 70, most RTVs are lower (some a lot lower) so they're more flexible.

In addition to the masters needing to be heat resistant they also have to be able to withstand quite a bit of pressure.

Einion
 
G

Gryphin

New member
The thing is, the material may seem cheaper via buying pewter to melt and cast vs. buying resin, but you'll end up spending twice what you save in making vulcanized molds and casting equipment to cast the metals vs. room temp curing resin with RTV silicon molds.

unless you're scaling up to be a genuine miniature company moving several hundred copies of multiple miniatures, stick with the RTV silicon+Resin for your casts for personal/hobby-selling.
 
Einion

Einion

New member
Gryphin said:
The thing is, the material may seem cheaper via buying pewter to melt and cast vs. buying resin, but you'll end up spending twice what you save in making vulcanized molds...
Click to expand...
Yep, but you can cast white metal in RTV for limited numbers. That surely works out cheaper than polyurethane resin because all the sprues/gates can be recycled.

Einion
 
J

jdmchaos

New member
anouther thing I was told is with metal no air bubbles.i some times have to throw away stuff due to that with resin.what do you guys say the problem is and is there no bubbles with metal?
 
Einion

Einion

New member
Spacemunkie said:
Don't even bother with drop-casting metal. Complete waste of time - you'll only be disappointed.
Click to expand...
Well gee, the dollhouse and shipbuilding fraternities are going to be gutted to hear that!

People have been successfully drop-casting for years, it's certainly not a complete waste of time. You just have to design the mould properly, use lubricants as necessary and choose an appropriate alloy for best results.


jdmchaos said:
anouther thing I was told is with metal no air bubbles.i some times have to throw away stuff due to that with resin.what do you guys say the problem is and is there no bubbles with metal?
Click to expand...
That's correct, you don't get bubbles (of the type that resin can have) with white metal/pewter. But that doesn't mean you can't get voids in castings, for various reasons. Improperly cast items can be remelted, essentially indefinitely, so there's the metal doesn't go to waste.

To prevent bubbles when resin casting you should degass the mixed resin or pressurise the mould and the poured resin, or both. In the absence of additional equipment it's possible to pour resin to minimise the problem of air bubbles (in a long, skinny stream).

Einion
 
L

Legacy Account

Active member
Einion said:
Well gee, the dollhouse and shipbuilding fraternities are going to be gutted to hear that!

People have been successfully drop-casting for years, it's certainly not a complete waste of time. You just have to design the mould properly, use lubricants as necessary and choose an appropriate alloy for best results.
Click to expand...

Compared to using resin it's an utter pain in the arse and yields lower quality results if you're after reproduction of fine detail. In my experience.
 
J

jdmchaos

New member
well im convinced,ill stick with resin.im not top notch with my resin skills yet,and to try and jump to something that from what i here is a little more work would not be the right thing to do.
my next question is i use smooth cast 300 resin from smooth on.i m not to happy with (a) the color(b)the way it seems to not flow good enough when it comes to making a spru of parts and small parts.
have any of you used it,and can you tell me witch one you have used or have found to be the best.thanks ahead of time for all the help and comments guys.this is why i love this site,so many great people here.
 
J

jdmchaos

New member
still trying to get some feedback from you who have casting skills.
my question in short is what kind of resin do you use,and witch do you think is the best.
i use smooth cast 300 but it seems to be unreliable at times.im looking for feed back on
what you think is best for smaller parts such as armpads swords sculpts 28 mm heads
stuff like that.
 
L

Legacy Account

Active member
It's not really the resin that's the problem - you could try as many different makes as you wanted and they'd all likely suffer a similar problem. You need to vac-cast to accurately reproduce very fine details with any sort of consistency. Bottom-filling your moulds can help as can decent venting and a bit of agitation, but it's still hit and miss with very fine details without a vac chamber to force air from the mould. You need to degas your resin before filling your moulds if you intend to vac-cast as well. No easy solutions unfortunately.
 
mickc22

mickc22

Granddad!
nor any cheap ones either, if you want the quality you've either got to pay for the equipment or pay someone who has the equipment
 
J

jdmchaos

New member
the only problem with vaccum cylinder is tou have to use a certain resin.
most resin by the time you get it in the container will have started to harden.
now i herd that tapplastic has a brand that flowes like water.that is the one
i want to know about.the one i use is kinda thick in a way witch tells me that the
bubbles have a hard time getting out.
i do have some idea,s on a vaccum unit thou.they say that 30 p.s.i is enouph
to do the job.
 
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