Casting Experiment: Elliptical Horn Flare

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Point being,untouched sprayed sealant,varnish,has smoothest surface.

Not even close actually. Wet sand with 2000 grit paper and polish with polishing compound and you are getting there.

Have to agree with John on this one. I've never seen a smooth sprayed surface. Not unless you put it on so heavy, that gravity overcomes the substance's orange peel surface tension, and flattens it out. But at that point I'd think you'd be dealing with runs and pooling within the mold.
 
Hi John

Great thread and very admirable job your pulling off.

I've done a bit of this myself over the years. And although you have a firm grasp on all the principles it's the little points that always bite you in the butt.

I stumbled upon thinned out vaseline or petroleum jelly as a good mold release. Thin it out with mineral spirits.

Why the bonding of the mold to the casting? If I remember correctly that product heats up as it cures? That is what happened to me. I was doing molds for cast aluminum driver baskets.

One technique I ended up doing to save on the silicone that you seem to be migrating to was to create a rough form that would take up most of the void area. Pour in your silicone and then you use a lot less.

One last tip. I know you are ingenious enough. In a pinch you can use the inlet side of a air compressor to draw a vacuum. You do not need a total vacuum to draw out the air bubbles in the silicone you just need a combination of vacuum and curing time.
As for vacuum tank. If you have a paint pot or even an old pressure tank that you can cut open on one side and apply a sealing tape to and a flat top. Remember even a total vacuum is only 14.5 PSI on the atmospheric side. So a well made MDF box will do the trick in a pinch.

Always looking on. And applauding your ingenuity. You'll beat this.

Mark
 
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Thanks for the compliments and tips :)

I used the "bombs away" method of de-gasing the silicone for the mold shown in post 78. It works very well - I didn't have any air bubble defects in the mold.

The silicone is expensive so I will use a styrofoam "core" for the majority of the mold.
 
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Almost there, still need to do a little more filling and sanding:

NPX_312.JPG

Looking not bad now, huh?

Hey, it's a long process and takes some time but it keeps me outa the bars and away from the loose women ;)
 
Almost there, still need to do a little more filling and sanding:

Looking not bad now, huh?
Looking very nice John :) You might finish the job off with some proprietary metal polish such as Brasso, i'm not sure what it'd be called where you are but the stuff does a most excellent job of removing scratches fron CDs & DVDs ;) Luckily i haven't had to use it on any secondhand blu rays yet :D

T-Cut, paint polish might do the same trick. I doubt you'll need to go too mad though not unless you want it to look the business.

Just something i learned & remembered during working on plastics at school...
 
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My heart rate has just come down after such an exciting game...:)

Hi Mark,
As seen in the pic is as smooth as I need to make it right now to see any defects. The previous heavy sanding exposed some air bubbles that were under the surface. These need to be filled with spot putty and then I'll sand the whole thing with 1000 grit then 2000 grit paper to get rid of most of the scratches. I'll then use automotive polishing compound to gloss it up. The gloss may be the final step before molding (again!) but can reveals defects that are not visible on a matte surface.
I'm bearing down to make this perfect. Nothing else will do at this point.
 
I'm bearing down to make this perfect. Nothing else will do at this point.

Damn skippy.... :D

I feel your pain... I've got about 2hrs worth of brainstorming, and 1.5hrs of mill time into the enclosure for your jig, and I'm not even at 25%. Diminishing returns on effort is definately exponential, but for our breed ;) it gets to a point where it's all or nothing...

Looking forward to seeing the end result.
 
~~~~~Snip~~~~~~~~~~~~

Hey, it's a long process and takes some time but it keeps me outa the bars and away from the loose women ;)

John,

That's the real value of projects like yours.

Everyone needs to take a break from their true calling. After you're done with this one, you'll be able to return to the bars and loose women totally refreshed, with that fine honed "edge" that you've always displayed.
:D

I've been following this thread from the start, great work!

Best Regards,
TerryO
 
Or possibly the inner mold in plaster with a better mold release?

If you practice with a funnel or such and mix the mold release I mentioned you will find a good match. The only difficulty is getting a smooth consistency when using petroleum jelly as a release. The right amount of thinner is the trick to it. As is temperature. I tried a couple of tricks on that account and thinned it enough to brush it with difficulty and then ran a hot air gun over it to smooth it out. Then poured the plaster. The stuff I was using was for industrial porcelain molds. It had chopped fiberglass in it already. But for John's application what he was describing sounds tough enough.

I went in cannons blazing to and made four molds that I had to burn. The only revenge a cabinet maker has. Muhahhaha

Especially when he is masquerading as a machinist/artist. Heck what the plaster doesn't know won't hurt you!

Mark
 
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I've been following this thread from the start, great work!

Thanks :)

I doubt that a silicone mold will be stable enough, at this size

Silicone will be fine as long as it is supported. I'll take some pics of the process (again!).

Or possibly the inner mold in plaster with a better mold release?

If you practice with a funnel or such and mix the mold release I mentioned you will find a good match.

I actually used vasoline straight (not thinned). This on top of 3 coats of wax. In the thickest part of the resin casting (around the throat) it completely stuck. I believe the act of pouring the resin in "washed" off most of the vasoline in that area.
I should have used PVA release agent with some layers of wax on top of that.
It's in the breeze now though, the silicone will do the trick without any of that shite.
 
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