Okay. I'm not a complete dunce, but I spent about a half hour today trying to figure out how to properly stretch sprue that I needed for a radio antenna. I had a small candle and lots 'o sprue, but I could only get one piece to stretch out like I needed. I kept the sprue a proper distance away from the flame (after torching a few!) and I thought I had a fairly good grasp on the concept. I'd like to be able to do this "on command" so to speak. Is that possible or is a hit or miss type thing? What's the secret?
--daredevil

The secret, besides a lot of practice, is to stretch the sprue in a vertical fashion rather than pulling it horizontally. This prevents the molten sprue from sagging.

Hi there,

Also, Heat a large area, like 2-3 inches with the candle. That should soften the area and make it more willing to stretch and not bust. Practice does make perfect.

Certainly not that I'm an expert but one thing I found recently that has helped is taking it off the flame and waiting a moment or two before streching. I got decent results by streching it when i was almost cool.

Hi daredevil,

Given the fact that I use stretched sprue for a lot of things, I'd say it's just a matter of practice before you can maetsr it. It's not rocket science anyway!

Here are some of my uses for sprue:
1. Wiring for cockpit interiors.
2. Making oxygen hoses by wrapping it around a copper center.
3. Wheel well ribbing, after flattening with a broad, straight block of stone/hard wood.
4. Wiring for undercarriage details.
5. Aircraft antenna wire.

Some of my tips for making sprue:
1. Practice, practice, practice!!!
2. Try to use sprue pieces of minimum length of 1-2 inches. Helps to get a better grip.
3. Heat the center part till it begins to sag. Don't hold the piece too tightly, or you won't see this sagging effect. As soon as you see it sag, pull away from the flame and start stretching..
4. Roll the piece in your fingers as you heat. This will ensure uniform heating, and it starts to sag faster.
5. Try to keep a minium distance of 1 cm from tip of flame to sprue. Any lower, and it'll either blacken or melt!
6. Don't pull apart over the flame. Take it away from the flame, and then stretch.
7. Once stretched to reqd diameter, blow over sprue for it to cool quickly.
8. I always use CA glue and not plastic glue for attaching sprue.
9. Don't throw away unused sprue. Keep it in a separate box for future use.

Hope these tips help!!

Cheers,
BP.

Practice is definitely the only answer.

Make sure you are heating the sprue evenly, - rotate it and move it sideways while heating to get a spread of heat. You will see the surface of the plastic become shiny as it reaches the right temp.

I find the Tamiya tip of only holding one end of the sprue during initial heating also helps. As the sprue gets to the right heat the unsupported end droops.

Sit down with a big heap of sprue and stretch away. I have a sprue stretching session from time to time and keep a jam jar full of various colour and diameters of stretched sprue so I dont have to make on demand.

Regards Dave

Pretty much what everyone said. I stretch mine horizontally without problems. The big thing is even pressure as you stretch to keep a nice even sprue. I'll occasionally attach a weighted alligator clamp to one end to insure a straight sprue. Pull slowly to get a thicker piece of stretched sprue and faster for a thiner piece. Once you get the rhythm, you'll be limited only by the span of your arms.
Do you kknow anyone who already knows how to do this? It took a demonstration at a club meeting some 20 years ago to learn this, and I've passed that arcane knowledge on to others as well.

hi test each type of plastic , some are better than others for stretching , and some of the silver grey are superb , i can get it down to the thickness of a human hair and a full arm span every time , as prev posters have said it is all down to practice . cheers ian

Hi Daredevil

One obvious point... you are taking the sprue away from the candle before trying to stretch aren't you?

Other than that... and sorry if this is getting monotonous but... practice, practice, practice...

Once you get it right, you'll wonder how you ever messed up!

I rotate the sprue to heat it evenly and can tell by the "feel" when it's ready to stretch (sorry... it's practice!!).

I also stretch horizontally - no problem - just maintain even pressure. Depending how fast you pull, you can vary thickness.

I keep a range of different colours and cross-sections handy.

Hope this helps... good luck, and don't give up!

Rowan

Test each 'type' of plastic. Each batch of plastic may have a slightly different melting point, stretching consistency. I notice it most from manufacturer to manufacturer.
You'll have to test each and get a feel for how soft it is. The softer the plastic the deeper the heating has to be before you stretch. And the slower the pull has to be.
Whatever the plastic is a nice steady even pull is part of what I focus on. Not to fast that the plastic breaks, not to slow that it hardens to fast. I go in with about six pieces of sprue for one antenna.

One thing I see every one else missed. after it streches out, hold it in place (keep the same tension) for a bit till it cools. I usually stick it in my mouth and wet it as I move the streched piece btwn my fingers. this helps tokeep what I streched from breaking and curling. And no it is not gross, I never get any bits and pieces in my mouth.

wow--who would have guessed that something as seemingly innocuous as stretching sprue could have so many approaches! Thanks to all for the wonderful tips-- I now have quite a nice stash of strectched sprue at hand.
I also discovered one tip that NOBODY mentioned though--the fumes from melting plastic. I used my vapor mask while "practicing" since I figured that the fumes must be quite toxic.
Thanks again to all that replied!
--daredevil

ok...my turn at this. Found it difficult myself untill about a month ago, i accidentally grabbed the wrong plastic and ...."watson, come here i need you" moment. What i had picked up by mistake was the nozzel tube for a can of air. you know, the straw thingy that you place in the nozzel to concentrate the air to a point?...well to my surprise it worked better than anything i've yet to try. This type of finished stretched plastic has a great use for artifically replecating tubing from here to there. sprue plastic kinda gets alittle hard a brittle to bend...practice, type of plastic, distance from flame (perhaps no flame but a heat source instead?), blaster is right about holding it taught untill it hardens, and lifting your right foot while holding your tounge just right.

okay....practice

kglack

I see a lot of variations but I have to add this.

Instead of a candle you can use a hot air gun. Advantage, stable temperature, no risk of setting fire to the sprue.

If you don't know what I'm talking about take a look a this site http://www.steinel.de/englisch/produkte/heimwerker/heissluft/index.html

Strangely enough I couldn't find any on the sites of American tool suppliers that I know of (Dewalt: no, Skil: no, while Skil sells one in Europe).

Kris

When stretching sprue I've always use the candle. It's just matter of practicing a bit and, as other people said, to identify the spre that best fits your needs. Personally I gave up using stretched sprue for antennas what I use instead are guitar strings. This way iven if you by accident hit them they will remain in place and will keep their shape too...
Ciao

Flossing and modeling at the same time! A true multitasking expert! #:-)

I think you are getting the plastic too close to the flame. In all the years I've been doing this, I've never gotten any noticeable fumes.

Burning plastic can release Dioxine a very dreadful agent, but not when you just heat it up for stretching it...
Ciao

"i love the smell of burnt styrere in the morning"

smells like ...victory