How do you "stretch" sprue?

"A picture speaks a thousand words"

There are quite a few good sprue stretching videos on Youtube - it's far easier to watch the process than having it explained.

Take a piece of sprue; heat the center of it; pull on both ends....

I'll start on the You tube, but do you use open flame or is a heat gun required?  Styrene being a petroleum based product I figured it'd burn too easily to use open flame.

I think most people just use a candle and keep it a bit up away from the flame.

I'd say it's actually far easier to learn by doing than watching.

• Get a small candle - votive, tea candle, etc.
• Get a length of sprue.
• Hold sprue over candle until it starts to go "soft".
• Stretch sprue in smooth, even motion. How fast and far you stretch determines how thin you get.

There's definitely an art to how close to the flame you hold the sprue, at what point in the heating process you start to pull, how fast you pull, etc. I learned by getting two dozen or so lengths and just going for it. The first six or seven were absolute crap, broke in the middle, too thick, etc. But I did start to get a feel for it. 

Don't forget that once you glue the sprue to the model you can use a heat element (blown-out match, cigarette) to get it to contract and go taut. Again, it's a feel thing, and practice on something that's not your otherwise-finished build first!

Big_Dog

I think most people just use a candle and keep it a bit up away from the flame.

Yes. Don't put it in the fire.

Maybe Fermis will chime in---he is the master IMO when it comes to using stretched sprue...just sayin'...

Try this;

http://www.youtube.com/watch?v=cpCzL2GJ0b4

I prefer heating it with tea candles, but in a pinch, a butane lighter works quite well..  Anything with a flame..

Cut a piece at least three-four inches long.

Hold it over the heat source by each end, rolling it, rotissary-style..

When it gets glossy, it's ready to pull...

Here's where practice comes in..

The thickness (or thinness, rather) will all depend on how far and how fast you pull it..  By varying your speed and heat, you can stretch it to diameters less than a human hair, or simply make plastic rod... 

Another thing to keep in mind is that different manufacturers plastics behave a little differently, and color can matter too...  Some will heat faster than others, especially those kits that are made from "softer" styrene.. Clear sprue stretches easily but is quite brittle...

When you use it for biplane-rigging and aircraft antennas, you can leave it sag a little.. Applying heat to it will cause it "snap" taut, but that's another technique and I'll not go into that right now..

By making it varying thicknesses, it's easily used for the applications described, as well as for filler in gaps between parts...

Another thing... Stretching plastic Q-tips can also be done when you need small-diameter tubing, say for gun-muzzles in wings or blast-tubes... The tubing will remain hollow, even when heated and stretched...

Sprue will always be thicker at each end, and thinner in the middle, giving a taper that's really useful for whip antennas on AFVs and man-pack radios...  Then take some thin electrical wire, and wrap it around the bottom for the spring on the matching-unit..

Stretching sprue is the first step in scratch-building... Think I stretched my first one when I was about 11 (It was for the whip antenna on the Monogram Typhoon)...  

Personally, I cut down all the sprues from kits after I'm done with them, keeping the long, straight sections (the ones without the bumps and numbers) for stretching...

For a visual of one neat application of stretched, clear sprue, check out Von Manstein's "Death in the Courtyard" diorama in the Diorama Forum...  It makes great "streaming" water from a bullet-holed rain-barrel...

DoogsATX

Big_Dog:

I think most people just use a candle and keep it a bit up away from the flame.

 

Yes. Don't put it in the fire.

I love the smell of burnt melted sprue in the morning....

Depends on thickness required. For antanne you may not need to burn the sprue but must heat sprue  uniformly for consistent thickness. It is harder as different plastic/heat will have varied results.

If thiness is all that matters (rigging etc), I prefer burning the sprue mid section, let it catch fire in fact, for 2 seconds, then just pull - the center's already liquidified, it's the cooling that generates the line. Only issue with this is non-black plastic may be partially burnt so the plastic may have black spots that may need painting.

Looked for Manny's "Death in the Courtyard" thread but could not find it

It's probably a good idea to hold it away from the fire before pulling or the flame will break the line. Don't catch it on fire, the fumes are kinda tough.

/forums/t/100824.aspx?PageIndex=20

It appears, sadly,  that Manny removed all his pictures though...

Just an update, I tried it out tonight with a candle, and got some really good results!  I found it worked better if I waited until it was just about liquefied, then took it away from the fire for 3-4 second, and then pulled.  I made myself a nice little stockpile of various thicknesses for use at antennas.  Its great stuff, strong yet still flexible!