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  #1  
Old 08-09-2017, 07:38 PM
Bart Bart is offline
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Default Body part copying

Hi guys
Need a bit of advice on copying a sill/door jamb. It’s approximately 2 feet long section X 3.5 inches wide.
Issue is the car is in a different location from my workshop. Quite a few miles.
So basically I was thinking of getting a “3D print” of this section but not an electronic print more like using modelling clay. Not sure on how much shrinkage will come from modelling clay when dry though.
Bondo would be better with little or no shrinkage but means I would have to put some release agent on the part and more costly.
Any advice would be great!
Thanks
Bart

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Old 08-09-2017, 08:47 PM
steve.murphy steve.murphy is online now
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Hi Bart,
Just thinking out loud here, but maybe you could use a plaster or fiberglass cast like used for broken bones? Lay it up on your part andremove it after it has cured.
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Old 08-09-2017, 09:03 PM
CaptonZap CaptonZap is offline
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If you do use a plaster cast, a thin film of Vaseline will provide the mold release.
Plaster of Paris and cheese cloth does a pretty good job of mold making. Burlap is a bit harder to saturate, but builds bulk quickly.
A supply house that supplies the brick and concrete trade should have Plaster of Paris at reasonable rates.

CZ
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Old 08-09-2017, 10:10 PM
cliffrod cliffrod is offline
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Understand that plaster or any comparable gypsum product will generate heat and express water vapor as it catalyzes, creating & trapping condensation between the cured gypsum and the positive being copied. Then, when it's iron/steel being copied, it's about rust... Really a drag to pull your plaster mold only to see a sea of new rust that is now prone to keep bleeding through porous paint.

Burlap can be saturated just fine. It doesn't happen instantly, but that's all I use for my plaster mothers. I never use gauze. I rarely use plain plaster, unless I want a weak product for a waste mold.

I bought 150lbs of hydrocal -much stronger than plain molding plaster but still not as strong as something like dental stone- this afternoon for the current projects in studio. Hydrocal is not much different in price than plain plaster. Either can be purchased at better contractor supply houses. Dental stone needs to be mail ordered, but is well worth the cost and effort.

Plain paste wax- car wax, Johnsons floor wax, whatever- works well. So does Vaseline, soap (naphtha laundry soap, scraped/shaved & dissolved in water is one of my favorites. So is joy dish detergent) and some other products are effective release agents. What I use varies on the positive media. Wax helps seal paint better.

Just plan your mold properly. Any draft, not just obvious overhang & undercuts, will cause that mold to lock onto your positive original part. Even if you get it off, a cast made in that drafted mold may not come out in one piece if not made strong enough. it may be necessary to produce a multi-piece mold.

Not sure if you're thinking of casting a complete part to use as a sort of hammerform or simply to use it as a buck to check your progress. Dental stone is immensely more durable than any other gypsum product.

Concrete products are another durable option, just like bondo, plasti paste, etc.. You may be able to make simple template patterns from chipboard, sheet metal or plastic to use to make a regular station buck that should be easily reversed to make a complementing piece for the other side.

There are many options , all with their good points and bad points.
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Old 08-10-2017, 07:33 AM
hot rivet hot rivet is offline
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Don't know what it's like getting medical supplies where you are but the pre impregnated cloth(glass?) that they use to set broken legs usually has a use by date and can be sourced quite cheap once past it...doesn't have the problems associated with conventional plaster. I have seen people use it as a form for carbonfibre work.
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Old 08-10-2017, 07:37 AM
hot rivet hot rivet is offline
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This is what i'm thinking https://www.amazon.com/gp/product/B0...KZ44CJMXVBT2FS
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Old 08-10-2017, 09:17 AM
billfunk29 billfunk29 is offline
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Default Smooth-on casting materials

I have had a lot of success using the many casting supplies from Smooth-on.

https://www.smooth-on.com/tutorials/
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Old 08-10-2017, 11:42 AM
norson norson is offline
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I have the fiber glass casting cloth that I bought with a similar project in mind. I found that it proved to be too flexible after it dried. I have several boxes if anyone needs some (you pay the freight). My vote would be for the dental stone.
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Old 08-10-2017, 01:18 PM
cliffrod cliffrod is offline
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The only caveat with dental stone, which is my favorite product without exception, is that you cannot sand a hardened positive/negative without having to fill the infinite number of bubble holes that are formed immediately beneath the surface. Cleaning off witness lines is really tough. Make sure that you have a great surface at the beginning.

Otherwise, you'll need to very carefully skim coat it and try not to break through any good undisturbed surface or it becomes a perpetual problem to try to solve. In my experience, it's less work to produce another positive or negative than to try to salvage an imperfect dental stone job.

Dental stone also seems to last much longer in proper storage. Big plus for me.

By comparison, there are hardly any holes revealed by sanding in regular molding plaster or even hydrocal. So I use hydrocal for rough(er) work and dental stone for anal/accurate results.

Don't forget- PatMan recently did some classes using concrete products for the same general purpose. thought there were some pics posted in recent events?

Smooth On products are great, just not always as inexpensive as some of the other comparable products.
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Old 08-10-2017, 03:31 PM
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Z5Roadster Z5Roadster is offline
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There was a thread here a while back discussing Polymorph, I've tried it on on reverse hammer forms and I intend to use it on planisher tooling for thin stainless moldings. found the link for you. http://allmetalshaping.com/showthrea...ight=polymorph
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