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stretching sprue
edoardo
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Milano, Italy
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Posted: Sunday, October 11, 2009 - 11:11 PM UTC
Hi everybody!
Last night I was trying to strech some sprue and what I ended up with was just burnt fingers.
What I really need is a "stectching sprue for dummies" tutorial, is there something of the kind?
Would anyone mastering the process, ever think of writing one?
Thank you

Edo
alpha_tango
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Posted: Sunday, October 11, 2009 - 11:32 PM UTC
Hi Edo

Hmm, i do not see a problem. The best way is trial and error to figure out your best way. but here are my 2 €ct

Snip a piece of straight sprue from the IM frame of your kit (it is best without corners and part attachment points, but it really does not matter that much). I usually take about 5cm lenght. I use a candle because you can hold the part on both ends this way.

Hold it over the flame and slightly roll it between your fingers to get it evenly soft. it will get glossy when it softens. You can also feel that it is soft (here comes the trial and error part, because nobody can tell you exactly when to take it away --- you have to know)

At the right point just take it away from the flame. Depending on how thin you want to have it, you will have to way a second or more and then just pull the ends away --- again trial and error when and how fast you have to do it .. but honestly most modellers have a sufficient sprue stack to test for some decades.

You cannot reheat it and you will not always have 5m staight sprue of the right size. So you just have to practice it and even then you will need a few tries for you specific modelling task.

HTH

good luck!

Steffen
slodder
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Posted: Monday, October 12, 2009 - 12:38 AM UTC
I've found that different 'brands' of sprue stretch differently. Some are better than others, Tamiya's is pretty nice, ICM stinks, Revell is ok.

As I twirl the sprue I watch for a slight expansion to form. Then it's close, I test it by bending is very slightly. If it feels soft enough I then move off the heat and in one easy constant motion I pull.
One more thing - once you have the length and thickness - Hold it for a few seconds to let the plastic cool and set. It will stay straighter doing this.
Other than that Steffen covers it.
edoardo
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Posted: Monday, October 12, 2009 - 01:28 AM UTC
Thank you guys!
quite helpful!

But I have a question for you: when I heat the sprue eithr I end up with just a small portion of it soft enought to strech or if I move a little I end up with a blobby sprue...
What I am doing wrong?
alpha_tango
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Posted: Monday, October 12, 2009 - 01:43 AM UTC
Hmm, I am having problems to understand your approach. Do you heat one end? You have to do it in the middle of your sprue .. how would you pull a plastic string from a hot blob of plastic?
edoardo
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Posted: Monday, October 12, 2009 - 02:58 AM UTC
Ah! Ah! Ah! Steffen, this one makes me laught!!

No, I am with you: I heat it in the middle, but or I heat a too small an area and I brak the sprue, or, if I move right or left to heat a bigger area, I end up with an unheaven pattern.
Usually (starting from my left hand): hard (holder), soft stretched sprue, hard bit, soft stretched sprue, hard (holder on the right end side)...

I'm still laughting !!!
alpha_tango
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Posted: Monday, October 12, 2009 - 03:09 AM UTC
Well, Edo, I still do not get your problem ...

Heat the plastic (at one point, but all around) til it is soft and then pull in one move to get a constant thickness. re-read Scott's and my posts above and try again .. really there is nothing special about it and no magic. As written above reheating does not work as it mostly destroys the plastic because you changed the structure by the first heating and pulling process. ..

Say you want very thin stuff, you have to heat it very thouroughly (see Scotts remarks for the right point) and then almost immediately pull it pretty fast but constantly and you have to have quite an arm spread to get stuff thinner than hairs.

if you want thicker stuff let it cool for a moment and pull slow but constant. Scotts remark to let it cool for a moment before you give it free when you are done also helps to get straight results.

I have no idea what else to tell you as I just do not see any problem in that whole thing ...

all the best

Steffen
P.S: I am glad that i could at least brighten your day even if I could not help you
thegirl
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Posted: Monday, October 12, 2009 - 03:37 AM UTC
Setffen and Scott have covered every thing there is here , I don't even understand what you are asking about to your question .

My question to is , are you rotating the spruse around in a cicrle montion over the flame ?

How close are you to the flame ? To far you have poor results , to close and the plastic heats up to fast melting before you can do the pulling .

In order for some one to help you with the trouble you are having , can you be more clearer on what you are asking about . We would like to help but need more info !
jaypee
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Posted: Monday, October 12, 2009 - 04:31 AM UTC
it's just one of those things like whistling through your fingers.
Once you've done it you wonder what all the fuss was about.
Tamiya sprue is what I used the first time I "got it". Who knows
why?

You can try this too. Heat one end stab it into corrugated cardboard and pull it back.
But really heating the middle is easier.
amegan
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Posted: Monday, October 12, 2009 - 09:21 AM UTC
I have most success using a hot air gun, seems to give a nice broad area of heat
mrockhill
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Posted: Monday, October 12, 2009 - 10:55 AM UTC
I'll just toss my thoughts in the heap. I haven't tried them all, but I really like Tamiya plastic for stretching sprue, I have used it forever and get consistent results. I snip off a small length. I am not worried about corners or attaching points, as long as there is a straight portion in the the middle to heat. I hold the sprue by one end keeping a straight portion over the flame. I roll the sprue in my fingers over the flame so it melts evenly. I prefer to hold it further than closer to the flame I find allowing it to heat slower yields better results (usually 2-3 inches above). When it is heated enough the center will be shiny and the sprue will start to bend. I let it flop over so that the 2 ends are at a right angle. I lift the sprue away and grab the other end with my free hand and stretch. If you want a thicker length wait a second or 2 before slowly stretching the piece a couple inches. To make really thin stuff begin stretching as soon as you remove it from the flame. Stretch it quickly (not fast just quick) and evenly, as far as you can, but again how far you stretch determines how thick it will be. I can get strands as small as .002" by stretching as far as both my extended arms. I usually take a couple minutes every so often and stretch a bunch of sprue to various lengths and put them in a box or hang from pegboard. So I usually already have what I need on hand. Personal experiment and good plastic are the keys.
JimMrr
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Posted: Monday, October 12, 2009 - 11:29 AM UTC
spin the sprue slowly in your fingers over the flame to ensure even "cooking" over a section of the sprue...dont move the flame side to side ..just spin the sprue over the flame . .then pull your sprue in an even motion about 3 feet of material....I let mine hang for about 4 seconds ( it may not help ...its just tradition with me..) then I take it up onto my cutting board and cut it into 6" or so lengths and select out what I need/what looks good...scrap the rest..
AussieReg
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Posted: Monday, October 12, 2009 - 11:32 AM UTC
Thanks for this post Edoardo, and many thanks to all the teachers. I have never tried this before either, but 15 mins thismorning playing around has shown me the way.

Grumpyoldman
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Posted: Monday, October 12, 2009 - 04:39 PM UTC
Age old top secret technique.

When stretching sprue: Stretch vertically, NOT horizontally ---- your sprue will remain straighter, and not develop any curve (sag) as it cools.
edoardo
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Posted: Monday, October 12, 2009 - 08:46 PM UTC
Thank you all!
Lots of info here!

My idea was to have a bigger area to stretch and so I moved side to side, which it turnes out, as Jim wrote, to be a mistake

I'll test some more and be back with the results.
pigsty
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Posted: Monday, October 12, 2009 - 09:37 PM UTC

Quoted Text

I'll just toss my thoughts in the heap. I haven't tried them all, but I really like Tamiya plastic for stretching sprue, I have used it forever and get consistent results. I snip off a small length. I am not worried about corners or attaching points, as long as there is a straight portion in the the middle to heat. I hold the sprue by one end keeping a straight portion over the flame. I roll the sprue in my fingers over the flame so it melts evenly. I prefer to hold it further than closer to the flame I find allowing it to heat slower yields better results (usually 2-3 inches above). When it is heated enough the center will be shiny and the sprue will start to bend. I let it flop over so that the 2 ends are at a right angle. I lift the sprue away and grab the other end with my free hand and stretch. If you want a thicker length wait a second or 2 before slowly stretching the piece a couple inches. To make really thin stuff begin stretching as soon as you remove it from the flame. Stretch it quickly (not fast just quick) and evenly, as far as you can, but again how far you stretch determines how thick it will be. I can get strands as small as .002" by stretching as far as both my extended arms. I usually take a couple minutes every so often and stretch a bunch of sprue to various lengths and put them in a box or hang from pegboard. So I usually already have what I need on hand. Personal experiment and good plastic are the keys.



I first learned this technique on glass - turning test tubes into pipettes. Amazingly, it works for that too! - although it's crucial that you hold the glass vertically.

Another tip from the same source: to cut sprue for this, don't muck about with razor saws or side-cutters. Simply nick the sprue with your knife and bend it; it will usually break at that point.
drabslab
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Posted: Monday, October 12, 2009 - 09:38 PM UTC
Holding the sprue to close to the flame makes that the piece of sprue closest to the flame heats up and melts very fast and the heat is not "distributed" in the material.

better start from a bit further, giving the sprue the chance to heat up over a wider area and then move it a bit closer
tornado64
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Posted: Monday, October 12, 2009 - 10:16 PM UTC
a video saves a thousand words !!


http://www.youtube.com/watch?v=pFGuyWVNmgE
modelnutz
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Posted: Saturday, October 17, 2009 - 07:55 PM UTC
Another "nifty" trick....once you master the technique, try this...

using a sharp blade, change the cross section of the sprue ( rectangle,hex,oval etc. )
I use a scraping technique.... works fast.

Then, being careful to heat the sprue slowly, proceed to pull as described above.

If done carefully, you will end up with the same cross section.... only much smaller.

This is a great way to make very small bolt heads
stonar
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Posted: Sunday, October 18, 2009 - 12:37 AM UTC

Quoted Text

Age old top secret technique.

When stretching sprue: Stretch vertically, NOT horizontally ---- your sprue will remain straighter, and not develop any curve (sag) as it cools.



I'm glad I read the whole thread before jumping in! I was,as they say, about to say that.
Steve
Merlin
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Posted: Sunday, October 18, 2009 - 12:48 AM UTC

Quoted Text

Another "nifty" trick....once you master the technique, try this...

using a sharp blade, change the cross section of the sprue ( rectangle,hex,oval etc. )
I use a scraping technique.... works fast.

Then, being careful to heat the sprue slowly, proceed to pull as described above.

If done carefully, you will end up with the same cross section.... only much smaller.

This is a great way to make very small bolt heads



Hi there

And just to add to that, you can also stretch tubes. Plastic cotton bud sticks are often hollow and work well.

All the best

Rowan
thegirl
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Posted: Sunday, October 18, 2009 - 02:20 AM UTC
The Q-tips work great for doing turnbuckles in 72 and 48 scale . I also use it for making spark plugs on WW1 engines. For glass rod you can use the sprues from that the same way, great for navagation lights !
zhengwei4226
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Posted: Monday, January 24, 2011 - 10:35 PM UTC
To stretch sprue you should hold a length of sprue with both hands over a candle flame (any small flame will do) in the middle and hold it there until it is soft enough to stretch. Then pull both sides gently until you get th desired length of stretched sprue. Hold it still to let it cool and harden for about ten seconds and there you have it: stretched sprue!
Athlen
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Posted: Wednesday, April 11, 2012 - 12:23 AM UTC

Quoted Text

I first learned this technique on glass - turning test tubes into pipettes. Amazingly, it works for that too! - although it's crucial that you hold the glass vertically.

Another tip from the same source: to cut sprue for this, don't muck about with razor saws or side-cutters. Simply nick the sprue with your knife and bend it; it will usually break at that point.



That must have been a while ago , I buy pipettes as they are very cheap, but I make capillaries. I never thought of pulling vertically!

As far as nicking the sprue and bending it, does it still help if you put a dab of saliva/water on the scratch, like it does with glass?

This is one of those things that has to be practiced, really. My first time with glass I made one and broke 20, but now I never break it. It's mostly about knowing precisely when to pull and how fast and hard to do it. I've not done this on plastic for some time, but with glass there are visual cues to knowing when to pull...

More on topic -- you ought to be able to pull polystyrene *tubing* into very thin capillaries, too. It's much more expensive than sprue but you could use it for a cannon or pitot tube if metal tubing wasn't available.
chris1
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Posted: Monday, May 19, 2014 - 08:00 AM UTC
Hey Edo
I make sure to do any sprue stretching near the kitchen sink.
Just in case I need to cool my fingers if they get a little to close to the flame.

Chris