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Shrinking a model


#1

Hi everyone, We have a model of a piece and we need to make another
version that is around 2/3 the size. Is there a way we can vulcanize
the peice and have it shrink more than the normal shrinkage… and
if so how or what would we need to be able to do it.

Any help you guy’s can give would be greatly appreciated.

Thanks in advance,
Russell McColough , Sydney Australia.


#2

Hi Russell, Rio Grande in the US has a model reduction product called
Reduc-It, however, it claims to reduce the model size by 50%, so it
may not work for you. I once had to incrementally shrink a design to
accomodate several sizes, and I did this using a latex mold
material. By speeding up the cure time I was able to achieve
something like a 10 to 15% reduction with each generation, so you
could achieve a 2/3 size model in 2 to 3 molds. The only downside
was some distortion of the model and the molds were only good for a
few waxs. Rio Grande’s website is at www.metamorphosisdesign.com .
I hope this helps!

Best,
John


#3

Try Pink House Studios. They have a mold making material called
reducit. They can be reached at 802-524-7191 or through their
website www.pinkhouse.com. Good luck, Dolores


#4
    Hi everyone, We have a model of a piece and we need to make
another version that is around 2/3 the size. Is there a way we can
vulcanize the peice and have it shrink more than the normal
shrinkage.... and if so how or what would we need to be able to do
it. 

Rio Grande (and others?) sells a high shrinkage mold compound for
doing what you’re talking about. I haven’t tried it, but it seems to
be the stuff to use. Works the same as RTV, you pour a bit in your
master mold, and it shrinks down as it cures, then you have a
positive from which to make a second mold that’s up to 50% smaller
than the original. Kind of a 2 step approach, but I’ve been thinking
about this also, and it’s what I’ve come up with. Good luck -Doug
Harroun


#5
       Hi everyone, We have a model of a piece and we need to make
another version that is around 2/3 the size. Is there a way we can
vulcanize the peice and have it shrink more than the normal
shrinkage.... and if so how or what would we need to be able to do
it.  Any help you guy's can give would be greatly appreciated. 

If the model is relatively simple, without large undercuts or
complexity, you can get a dental molding compound called Jeltrate in
one brand name. Generically the stuff is called Alginate. Dental
supply houses carry it. It’s sold as a powder, which you mix with
water to form a goopy mix which sets up to a soft rubbery state within
a few minutes. Great for molding various body parts that need a mold
material to set up reasonably quickly (use your imagination).
Usually, it’s then used as an open pour mold for wax, usually for
just one or two parts. However, if you let that mold just dry out
for a couple days, it shrinks quite a bit on drying, and you can still
pour wax into it, though usually only once, as the mold then breaks
when you remove the wax. But it’s an easy way to reduce the size of
a model.

Hope that helps.

Peter Rowe


#6

If you want to shrink a model effectively without too much loss of
detail, the best way to do so is to use heat cured red silicone from
the Contenti Co. ( 800-343-3364) What you do is set your vulcanizer
for 375 oF and vulcanize for 15 minutes per 1/4 inch of thickness.

At this temp , you should achieve about a 10 to 12% shrinkage per
mold made… if you include casting the first shrinkage and cleaning
it up a bit, you will be very close to 30 % … and the final mold
will work well in production… this same rubber is normally used at
325 oF for normal standard molds… Quenching the hot mold frame and
mold into cold water will help to increase the shrinkage slightly.
Contenti’s moldex rubber is the least expensive heat cured silicone
based rubber on the market .

I have used the Reduce it compounds and have found that much work
will be needed on the model afterwards and have not had much use for
the material . I could usually carve a better model by hand faster
than using this material and then going through all the clean up
work !

Hope this helps. Daniel Grandi

We do casting, finishing , mold making , cnc model work and a whole
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