RE: [DSII] Genre - and details about casting/moulding

About a year ago, I remember seeing something about "precious metal
clay".
It was a clay like substance that contained some form of silver or gold.
The clay could be shaped to what ever the sculptor wanted and then baked
in
an oven for a short period.  The sculpture would shrink a certain
percent,
but would then be solid silver or gold (I'm not sure what purity,
though).

It would be really nice to have a steel, aluminum, or pewter equivalent
of
this.  Has anyone else heard of anything like this?

Thanks,
Nathan

> -----Original Message-----
> From: Adrian Johnson [SMTP:ajohnson@idirect.com]
> Sent: Tuesday, February 23, 1999 3:35 PM
> To:	gzg-l@CSUA.Berkeley.EDU
> Subject:	Re: [DSII] Genre  -  and details about casting/moulding
> 
> >On Mon, 22 Feb 1999, Nyrath the nearly wise wrote:
> >
> >> Michael Llaneza wrote:
> >> > 
> >> > IMHO the best thing GW ever did
> >> > was the plastic Epic-scale infantry. Plastic is expensive to set
up a
> >> > production run for, but dirt cheap over a long production run. 
> >> 
> >>	I was always curious about that.
> >>	An uninformed layman would think that metal miniatures
> >>	would be more expensive to produce than plastic ones.
> >> 
> >>	I guess plastic is less forgiving a medium to work with.
> >
> >i understand that the expense is in the moulds; since lead melts at
quite
> >a low temperature, you can use a vulcanised rubber mould, and you can
> make
> >that yourself with comparatively little effort or expense. however,
the
> >lead is expensive. now, the plastic used in minis is a thermoset, so
you
> >have to heat it to a high temperature to get it to fuse. thus, you
need
> >steel moulds, which are very pricey. however, the plastic is cheap.
> 
> 
> That's almost right.	As several others have pointed out, the
vulcanized
> rubber moulds are quite inexpensive (relative to metal moulds) - tho'
they
> don't last as long.  Yes the plastic used in injection moulding is a
> thermoset, but the high temperature is not needed to get it to fuse. 
The
> high temperatures are needed to get the plastic to "plasticize" ie
become
> "plastic" ie gooey/runny.  To get the plastic into all the tiny detail
> crevices in a mould (look at a tank kit or a GW troop sprue - lots of
> small
> detail) requires enormous pressure - both to maintain plastic flow and
to
> expel all the trapped air in the mould.  The pressures are commonly
over a
> thousand PSI, hence the need for steel tooling (moulds).  These are
very
> expensive, 'cause it is difficult to cut steel accurately - well, not
so
> much difficult as really time consuming, and requiring specialized
metal
> working equipment.  For commercial injection moulded plastic parts
(say,
> the front face of a PC or the case of the monitor you are looking at),
the
> cutting tools are driven by 3D CAD data.  It takes a lot of time to
get
> the
> CAD data correct, and to then develop mould plans from that data.  For
> models like GW tanks - picture the Eldar Falcon Grav Tank which is all
> curvy - they do not create 3D CAD data - they produce a master model
about
> 3 times normal size and then use that as a guide for doing the mould
> cutting.  This is all very time consuming and costly.
> 
> As I said in an earlier post, injection mould tooling even for a small
and
> simple part will be in the tens of thousands of dollars - so you need
to
> produce a lot of parts to make it worth-while.  The cost of the
plastic is
> minimal - your average tank kit will use less than $1.00 worth of
> material.
>  The cost is in machine time (for the moulding equipment - which is
also
> expensive, by the way) and amortizing the tool cost over the
production
> run.	
> 
> Having said all that, I have a pretty good idea what it actually costs
GW
> to produce one of their big tank models - say the "Leman Russ
Demolisher",
> with a full GWscale tank and a blister pack of pewter detail bits.  I
> figure it costs them about $1.50 to $2.00 for the plastic parts, maybe
> $1.00 to $3.00 for the metal parts, and maybe $4.00 to $5.00 for the
> packaging.  And they sell the kit for over $50.00 here in Canada -
they
> make a HUGE profit margin, even accounting for shipping and
distribution
> costs.  (These costs may be high, too...)
> 
> 
> >
> >thus, you use plastic in steel moulds for your large-volume,
> low-diversity
> >stuff, like basic tanks and troops, and lead for the more exotic and
> >diverse stuff.
> 
> 
> yep.
> 
> 
> 
> >
> >of course, everything GZG makes is exotic and diverse, so they only
use
> >lead :-). well, except for the resins. i assume that resin is cheaper
> than
> >lead, but that for some reason it's no good for small minis. can
anyone
> >explain this?
> 
> 
> Resin casting is a "low tech" process, as far as these things go.  It
does
> not require a large overhead investment in complex machinery, the
power to
> run that machinery, specialized factory space with reinforced
flooring,
> etc
> etc etc.  Moulds can be rubber, which is inexpensive.  It is very
suitable
> for small industries who do not do large production runs - like gaming
> miniature producers.	In the end, on a per-piece basis you spend a lot
> more
> on material than you would with an injection moulded tank kit, but you
> save
> in initial investments.  As I said above, the cost in injection
moulding
> is
> the equipment and tool costs, not material.  With resin casting, it's
the
> resin that's one of the two expensive parts - the other is the low
> production rate (you get a lot of injection moulded parts in the time
it
> takes to do one cast part).  In the end, the only way you could do the
> kind
> of things people like GZG, GeoHex, Armorcast, etc. do is to use a
process
> like resin casting.
> 
> Oh, resin is a less expensive than lead by weight, and a lot lighter
> too...
>  And yes, it isn't much good for small minis.  You get a high reject
rate
> with small figures because they require small moulds.  Small moulds
have
> tight air passeges (ie the arm or leg of a foot trooper in 25mm), and
> there
> is an extremely high likelyhood that you will trap air in the mould,
> causing a rejected part.  With spin casting, air is forced out of the
> mould
> by centrifugal (centripidal?? I always forget which is which) force as
the
> mould spins and the molten metal is forced into the mould cavities. 
In
> injection moulding, it is the injection pressure that forces out the
air.
> With resin casting, you just have gravity working for you - the weight
of
> the resin pushing against the air.  Also, it is difficult/impossible
to
> have proper air venting in a cast resin mould to allow trapped air out
-
> the material takes so long to set that you might have problems with it
> draining through an air vent (or plugging it up after one or two
casts).
> With spin casting, the material sets almost immediately, and with
> injection
> moulding there is cooling liquid passing through the moulds to cool
the
> plastic very quickly.  Injection moulding typically has a cycle time
> measured in seconds (except for really big stuff).  Spin casting in
> minutes, and casting in hours.
> 
> Incedentally, the reason why most cast resin parts are flat and
blocky, or
> have smooth curves (I'm thinking of the GZG vehicles and the Armorcast
GW
> 40k scale models) is that these are less prone to trapping air bubbles
> under comples detail AND they are much easier to demould.  Complex
detail
> on cast parts would result in more abuse on the mould each time you
pull a
> part out.
> 
> 
> Hope this is informative - I wouldn't have rambled on so much, but
people
> do seem genuinely interested.
> 
> Adrian