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Old 08-07-2009, 10:20 AM
Dave Krueger Dave Krueger is offline
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On sprue strecthing...

Looking through the vBench stuff, I see that stretched sprue is used as a basis to simulate welds (at least by James Tainton and presumably others). I understand the slicing and melting it with liquid glue, but how do yuo manage to get the spue stretched in a way that results in such a uniform thickness. I haven't tried it yet, since I don't have a need at the moment, but I suspect I will wind up with a piece of plastic that will go from the original sprue thickness down to the diameter of a hair without any appreciable length having a uniform thickness. What do you use as a heat source? A stove? Heat gun? Is there some secret to doing it? Do I need to sign up for sprue stretching school?
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Old 08-07-2009, 11:06 AM
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Coops Coops is offline
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Hi Dave,
You can use sprue for all sorts of things like filling gaps, sink holes and ejector pin marks and not just weld beads.
The trick is the heat used. It can be anything really [even boiling water] but a naked flame is quick and easy [a butane light is my first choice].
The correct heat will be determent by how thick you want the rod to be. A quick turn across the flame will give you a very short working time but if you wait for the sprue to "bend" under the heat you can pull it out as thin as hair [you'll need long arms if you get it dead right]. A bit more heat and it will just pull in two as it will be almost molten.
As it's the same material as your kit you can use it to do a lot of filling like unwanted location holes or mistaken trim work. Give it a go you will be surprised how good it is for odd jobs (melt it down with glue and it drys just like the kits plastic).
regards Steve


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Old 08-07-2009, 11:32 AM
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alanmac alanmac is offline
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Hi
Stretching Sprue

Cut your section of sprue to allow enough room to hold the plastic either side of the naked flame you'll be using, without getting your fingers burnt. About 4"/100mm is fine.

Use a Candle or nightlight to melt the spruce in the centre of your piece. Take your section of sprue suspend it above the flame, not to close. Roll it over so the heat is playing all the way round the piece. You'll feel it start to go soft and maybe the outer "skin" will go liquid shiny. Its just a case of holding it with both hands, the cool section not over the flame and gently pulling. The more you pull the thinner the piece gets.

Practise will determine the time over the flame required, how slowly you pull the spruce etc. Keep it taught whilst it cools or it will have a bend in it which may not be desirable.

Been doing it this way since I was a kid, although now I don't have to wait till Mum goes out

As kids we use to purposely set fire to sprue, outside, then use the thick sooty black smoke coming off to create "exhaust stains" on tanks and aircraft bodies by suspending it over the smoke. Rub excess off to leave a sooty black stain.

Alan

Last edited by alanmac; 08-07-2009 at 11:35 AM. Reason: Spelling
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Old 08-07-2009, 11:49 AM
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Last edited by armor fiend; 08-07-2009 at 11:54 AM.
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Old 08-08-2009, 08:53 AM
Dave Krueger Dave Krueger is offline
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Quote:
Originally Posted by Coops View Post
Hi Dave,

The trick is the heat used. It can be anything really [even boiling water] but a naked flame is quick and easy [a butane light is my first choice].
regards Steve

Thanks for the pix, Steve. Very nice work. I noticed that most people iuse a different color plastic when doing welds. My guess is that it's probably easier to see and control the shaping if the weld stands out from the model a bit.
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Old 08-08-2009, 08:56 AM
Dave Krueger Dave Krueger is offline
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Quote:
Originally Posted by alanmac View Post
Use a Candle or nightlight to melt the spruce in the centre of your piece. Take your section of sprue suspend it above the flame, not to close. Roll it over so the heat is playing all the way round the piece. You'll feel it start to go soft and maybe the outer "skin" will go liquid shiny. Its just a case of holding it with both hands, the cool section not over the flame and gently pulling. The more you pull the thinner the piece gets.
Alan
Thanks, Alan. I will experiment this weekend and see how hard it is. I'll probably use a candle since that's about the only thing I have that generates an open flame.

Last edited by Dave Krueger; 08-08-2009 at 09:00 AM.
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Old 08-08-2009, 08:59 AM
Dave Krueger Dave Krueger is offline
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Thanks for the videos, Armor Fiend. I never thought to look on youtube, although I've scouted them for other how-to stuff. That guy in the first one sure makes it look easy. I was thinking you had to heat up a fairly long section of the sprue before pulling it. I would probably have turned it into a much bigger ordeal than it had to be.
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Old 08-09-2009, 02:38 AM
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Quote:
Originally Posted by Dave Krueger View Post
Thanks for the pix, Steve. Very nice work. I noticed that most people iuse a different color plastic when doing welds. My guess is that it's probably easier to see and control the shaping if the weld stands out from the model a bit.
You are spot on about the color of the plastic. It makes it so much easier to check your work as you are going along.
Regards Steve
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Old 01-16-2012, 01:58 AM
DRAGONWAGON DRAGONWAGON is offline
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If you're looking for a bigger weldseam, for instance those on the upper hull of the earlier Sherman kits, one can also use 0.5mm Evergreen rod. Works with the same technique as discribed here....

John.
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Old 01-16-2012, 09:58 PM
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alexwencho alexwencho is offline
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Quote:
Originally Posted by DRAGONWAGON View Post
If you're looking for a bigger weldseam, for instance those on the upper hull of the earlier Sherman kits, one can also use 0.5mm Evergreen rod. Works with the same technique as discribed here....

John.
Tis sounds like good technique.

Thank you.

AWD
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