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Old 30th January 2010, 07:39 PM   #11
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Originally Posted by MJL21193 View Post
I'll let this set overnight and reveal my masterpiece tomorrow.
Again i have to spout the "ingenious" bit

If there is one thing i have learn't it's that virtually anything can be done! It's just a question of working out how to do it simply & cheaply without compromise.

By the way, i voted that your enclosure will work I have no doubt it will, all now rests on fitting it together & on that note i wish you the best of luck. I doubt luck will come into it though as i'm sure you'll have thought it all out & know you can do it.

Nice one, great work & ideas
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Old 30th January 2010, 09:15 PM   #12
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Good looking work on the horn casting! Look forward to seeing how that comes out
Thanks

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Very nice indeed John.
Thank you

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This is a great tutorial Keep it coming!

By the way, what did you use for making those rendered images / drawings of the waveguide?
Thanks but a tutorial indicates a tutor, as in someone who knows what he is doing. I'm learning as I go.
I'm using Sketchup for the drawings.

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Again i have to spout the "ingenious" bit

Nice one, great work & ideas
Thanks again,
Waiting game now while the plaster cures. It is very hard already but I'd rather not take the chance of breaking it un-molding the plug.
Tomorrow is another day.
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Old 30th January 2010, 09:59 PM   #13
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Oh go on, warm up the oven and shove 'er in. Done before 8 this evening
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Old 30th January 2010, 10:25 PM   #14
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Oh go on, warm up the oven and shove 'er in. Done before 8 this evening
Pizza in one oven, apple pie in the other

You should know you can't rush perfection!

Ok, I couldn't wait either - I took it out:

NPX_136.JPG

It slipped out easily - release agent was 3 coats of car wax and a light coating of vasoline. Nice to see that there were no bubbles and that the shape appears to be virtually flawless. I've even impressed myself!

NPX_139.JPG

Kinda looks like a bathtub.
I don't want it to crack so I put it in a sealed up plastic bag for tonight.
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Old 30th January 2010, 10:32 PM   #15
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That looks mighty impressive if I do say so myself.
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Old 30th January 2010, 10:37 PM   #16
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That's came out very well! Nice work
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Old 31st January 2010, 12:40 AM   #17
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Thanks men!
Mission for tomorrow is to immaculately smooth out the new casting with fine sandpaper and get a form ready for the new positive casting. Depending on how dry the new casting is and if I can properly seal it, I may cast the new positive also.
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Old 31st January 2010, 01:05 AM   #18
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Ok, I couldn't wait either - I took it out:
Those look great. So that's what else you can do with vaseline eh?

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I don't want it to crack so I put it in a sealed up plastic bag for tonight.
Excellent idea. Maybe put them in the fridge too.
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Old 31st January 2010, 01:20 AM   #19
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Thanks men!
Mission for tomorrow is to immaculately smooth out the new casting with fine sandpaper and get a form ready for the new positive casting. Depending on how dry the new casting is and if I can properly seal it, I may cast the new positive also.
Casting the positive would require heating it right?

I'd guess you'd want all the moisture out of the mould if it's to get quite hot. Could that potentially crack the thing, if the water turns to steam? I suppose it wasn't that hard to make in the first place, so you can always make another if it breaks.

I know thick plaster can take weeks, sometimes months till all the moisture is out.

It seems the water combines with the powder in a chemical reaction that causes the plaster to set. A reverse of the process that made the powder in the first place. So any spare water, not integrated into the structure could indeed perhaps crack it. That is if it were to build up any significant pressure somewhere inside.

Maybe gently heating the thing to speed up the drying process would be a good idea. It will obviously be fully cured, but you need to get the water out somehow.
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Old 31st January 2010, 03:23 AM   #20
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Excellent idea. Maybe put them in the fridge too.
No room - too much beer in there.

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Casting the positive would require heating it right?
My main concern is to have it dry enough to effectively seal the surface in order to ensure it will release the positive casting. On the plug I used solvent based polyurethane over the cardboard because I wanted superior protection for the water in the plaster casting (I didn't want the cardboard to get soggy).
With the plaster negative, I'll use water based polyurethane to seal it so it should be ok if the plaster is still a bit damp.
Casting the positive will make it slightly warm so no real amount of heat involved.
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