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Stretching Sprue
retiredyank
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Arkansas, United States
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Posted: Tuesday, October 01, 2013 - 12:44 PM UTC
So, I stretch sprue using a candle. However, I burn through 3/4s of my stock to obtain a few pieces. I've heard you can use hot, but not boiling water. This does not work, for me. I have a blow dryer, but have not tested it yet. In your opinion, what is the easiest way to stretch sprue? TIA
FAUST
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Posted: Tuesday, October 01, 2013 - 12:52 PM UTC
Ola Matt.

I have always used a simple lighter for making stretched sprue. Simply heat the piece of sprue till it starts to bend on it's own accord. Lay the lighter down. And slowly stretch it. And keep it stretched untill it's cooled down. Always worked fine for me. I have not even heard of people doing it with boiled water or with a hairdryer. All seems too elaborate or timeconsuming for such a simple thing. But I might be wrong there.
retiredyank
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Posted: Tuesday, October 01, 2013 - 01:16 PM UTC
I don't remove it from the heat soon enough. I feel stupid, now. Lesson learned.
meowmonster
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Posted: Tuesday, October 01, 2013 - 01:36 PM UTC
"Dear, you're on fire."

"Nah, it's just the plastic."

"No, YOU'RE on fire. Put yourself out."

Real conversation. Happened three times so far. I feel your pain.
retiredyank
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Posted: Tuesday, October 01, 2013 - 01:40 PM UTC

Quoted Text

"Dear, you're on fire."

"Nah, it's just the plastic."

"No, YOU'RE on fire. Put yourself out."

Real conversation. Happened three times so far. I feel your pain.


chumpo
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Posted: Wednesday, October 02, 2013 - 08:26 AM UTC

Quoted Text

Ola Matt.

I have always used a simple lighter for making stretched sprue. Simply heat the piece of sprue till it starts to bend on it's own accord. Lay the lighter down. And slowly stretch it. And keep it stretched untill it's cooled down. Always worked fine for me. I have not even heard of people doing it with boiled water or with a hairdryer. All seems too elaborate or timeconsuming for such a simple thing. But I might be wrong there.

. You could substitute a candle for the lighter so both hands will be free to manipulate the spruce .
Sandy
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Posted: Wednesday, October 02, 2013 - 07:52 PM UTC
Hi all , a few pointers , use a tea light , the small candle in a aluminium cup as heat sourse . Hold the sprue over the flame till plastic just starts to melt , then remove and at the same time pull apart and turn your hands vertical . This gives the straightest stretched spue ever .
It all depends on the plastic some will never stretch , I find that the darker the colour the less chance of it stretching , hope this helps cheers ian ian
spacewolfdad
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Posted: Thursday, October 03, 2013 - 12:32 AM UTC
Hi,

I do the same as Ian, use a tea light. It is reasonably safe, well as safe as any naked flame can be. Just heat the sprue, turning it gently and once it becomes pliable take away from flame and pull gently. If you hold it until it cools you get dead straight pieces, also the bit at the end is useful for conical items such as horns or flash deflectors on guns - never waste anything that can be useful .

All the best,

Paul
retiredyank
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Posted: Thursday, October 03, 2013 - 04:55 AM UTC
I'm using tea lights.

I'm not sure how I could free up a hand, with a lighter as I use a candle and have two free.
exer
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Posted: Thursday, October 03, 2013 - 10:19 AM UTC
Stretching sprue takes trial and error but once you've mastered it you never forget it. I just took a look at youtube and there are lots of demos of sprue strtching some of which are just plain boring

The two best I've seen are this one by Santa Rosa IPMS and this one by Matt H -Skip to 1.25 for the sprue stretching
Railspltr
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Posted: Thursday, October 03, 2013 - 02:59 PM UTC
Just my two cents (or pence). Used the small candle, in an aluminum cup that I have always used again but turned hands up vertically while stretching the sprue and came up with some of my best antennae candidate parts to date. Thanks guys.
retiredyank
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Posted: Thursday, October 03, 2013 - 04:41 PM UTC
I'm slowly getting it down to a science. I have ordered various diameters of styrene rod. I'm trying to stretch it to .005mm diameter. I think I can get it done, with .010mm.
fitzgibbon505
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Posted: Friday, October 04, 2013 - 05:56 AM UTC
.005" shouldn't be a problem, even with kit sprue. Trying getting an area about 1/2" long heated until it is shiny and sagging on its own and stretch away. You can control thickness by have fast you stretch. Twisting slightly will help keep it straight. Our club used to hold an annual sprue stretching contest, and it wasn't uncommon to exceed 50' with a two-person team. BTW, if you want to eliminate mounting holes on a kit, simply use the tapered ends from you sprue-stretching efforts. Insert from the outside, apply some solvent glue, let it soften a bit, then give it a little tug from the inside. Let dry, then clip off the ends and sand the visible end smooth. Since you are using the same plastic the kit is made from, you can easily get invisible results.
russamotto
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Posted: Friday, October 04, 2013 - 06:01 AM UTC
I agree on the tea lights. Don't tip over, no wax spilling around on the desk, easy to work with. I have found that Tamiya sprue works best, with Academy a close second. Dragon plastic varies and doesn't always stretch very well. Pull slowly and keep tension on the plastic as it cools so it won't curl up. Don't stare at the flame of course.
Hohenstaufen
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Posted: Friday, October 04, 2013 - 06:18 AM UTC
Jim, great idea for hole filling - why didn't I think about that myself!
Russ, I think you're bang on about the different plastic qualities. In the good old days Tamiya always got you to form the antenna from stretched sprue - it never seemed to be a problem getting the length and thickness about right, and of course a slight taper. DML sprue, not so consistent. Good job I've got loads of Tammy bits lying around....
Hohenstaufen
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Posted: Friday, October 04, 2013 - 06:19 AM UTC
What did you say, don't stare at the flame? Mmmmm - Fyaaahhh!
retiredyank
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Posted: Friday, October 04, 2013 - 10:58 PM UTC
Actual sprue is 100x better than styrene rod. The rod kept separating. This only happened once, with sprue. Oh, should have been "trying to make .0050mm diameter rod".
KoSprueOne
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Myanmar
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Posted: Monday, October 07, 2013 - 03:40 PM UTC
Oh... heat it up first.
I've been pulling on this stuff for years thinking that maybe this time...
Nope, just sore finger tips.
One time I lost grip and back handed the whole model right off the bench










just kidding.

Yes, I use the candle (or Tea Candle) method as well. I still have about 1/2 to 1/3 production success rate.

Straight parts are makable. I also have successfully pulled it down over forms for grab handles




ropeynz
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Posted: Tuesday, December 10, 2013 - 10:47 AM UTC
It is useful property that the stretched sprue generally keeps the shape of the original. This can be bad if you want a round rod and the original is slightly oval, but you can also use it to advantage. Shape the sprue as a hexagon before stretching and you can make thinner hexagonal sprue that can then be sliced for nuts and bolts.
retiredyank
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Posted: Tuesday, December 10, 2013 - 10:55 AM UTC
P Rowe: I hadn't thought about that. I'll have to give it a try. Unfortunately, this means I will have to buy another Tamiya kit as I have run out of stretchable lengths. Yeah, right. "Unfortunately" lol
easyco69
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Posted: Friday, December 13, 2013 - 01:24 AM UTC
I use a lighter, rotate the sprue . Till it sags, then stretch slowly, then blow on it when correct length & width are achieved.
tankmodeler
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Posted: Saturday, December 28, 2013 - 04:40 AM UTC

Quoted Text

"trying to make .0050mm diameter rod".



Matt, You're getting your conversions wrong!

.0050mm diameter is .00002 inches, or roughtly 1/10 the diameter of a human hair.

I think you mean .005" or 5 one thousandths of an inch, no?


And, to actually contribute to the discussion, I find that one of the best ways to fill small pin holes in resin parts is to put a small dab of gel CA glue on the end of a small piece of stretched sprue and then jam it onto the pinhole. Once it dries, you trim flush and it's like the hole was never there and you don't get shrinkage in the filler as you tend to with other fillers. You are also sure to get the filler in the hole which can be really difficult and tedious with fillers you spread or trowel into the smallest pin holes.

Paul