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Stretching Sprue


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Just found out I'm lousy at it.

Using a candle, I hold the sprue at each end while passing the mid portion though and above the flame. I slowly pull tension on the ends while lifting higher above the flame. At some point, the piece just breaks in half with very little stretch. Every time.

I've done this with different thickness sprues down to 1/16 inch. Same result. I need to get sprue down to the .040 range for hole filling. I've seen whole ship and air models with hair-thin sprue rigging and marvel at them.

Any advice appreciated.

 

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Maybe your letting it get too hot or too cool yet..?  Usually if your careful after heating it up so it can be stretched while gently pulling the plastic blow on it and you can learn to control the shape.  I have used sprue for years to make my own fine tipped detailing paint tools and other things.

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I've been doing it for years with pretty good and consistent results.  I have found that some plastics work better than others, and I've come across a few that do what the OP describes no matter the heating process.

I'd suggest experimenting with different brands and colors of sprue.  I generally have better luck with black, white and silver, red can be a little finicky.  FWIW, Tamiya plastic works very well and is very consistent.

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This is a technique I've tried and failed at many times. It just requires too much control for the minimal results. Plastic rod is available down to at least .02" and I would rarely need anything smaller, so I don't get why anyone would go through this for something that has a constant taper to it and is readily available .. unless the taper is needed. I am amazed at some results from people who have mastered this.

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I use stretched sprue for a million different things.

It's very easy. Don't over think it. 

I've found that some times we tend to over think simple things making them more difficult.

As long as the sprue is styrene, it should make no difference where it came from.

It really need not be styrene either. you can stretch almost anything, although they may act a little differently.

Just hold your sprue over a flame, ( I just use a Bic lighter) rotating it a little to heat it all around until the piece begins to sag on the end you're not holding.

Then just grab both ends & slowly stretch.

If you stretch it quickly while it's still the hottest, it will be longer & thinner, if you stretch very slowly, stopping occasionally to let it cool a bit you'll get shorter thicker pieces.

You should be able to get pretty much any thickness you want with a little patience.

Make sure you keep it stretched to the size you want until the plastic cools, ( 20 seconds or so) & you'll have a nice straight piece.

I make everything from carb linkage to antennas with stretched sprue.

I even use stretched clear sprue for some items. I've used it to make early 60s Mopar & Pontiac transparent steering wheels & recently used it to make backup lights for my '61 Ford build.

 

Steve

 

 photo DSCN2776_zpsgk3l2ik6.jpg photo DSCN3479_zps2rmatmk7.jpg

 

 

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OK Cato, I have not seen anyone else post this method.  Disclaimer:  I have only done this once or twice, and that was a LONG time ago.  The details are a little foggy.  You may find better instructions on some of the military modeling sites as that is where I read it.  As I remember, you heat one end of the sprue until it actually runs.  (I think I actually caught mine on fire.  I'm not talking forest fire here, more like an incense stick or match stick fire. ^_^  If it does catch on fire blow it out).

Anywhoooo, you basically stick the melted end to your workbench and pull.  I was able to get hair fine strands every time.  Once the sprue cools it pops right off the bench.

I hope I explained this well enough.  If you can handle a match stick flame, you can handle the sprue flame.  I personally had more control with this method than I have with the holding the sprue over a flame method.

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The method John describes above does work, but I hate burning styrene fumes.  (Plus it's not the best for our health.)  I'd suggest practice with different sprues first.

Also the comment by Steve about letting it cool fully is important. 

I prefer a candle instead of a lighter for better control.   I have a "sprue stretching candle" for a consistent flame.

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Well that;s varied advice but all obviously work for you guys. Steve that's amazing curved sections of clear in the steering wheels. I feel so lame...

Mike, i didn't realize rod was available in .020. Smallest I have on hand is .0625 and I didn't want to wait for a delivery. So I tried stretching and started with the .0625 - instant breakage.

Will try all the methods and several different plastics. It pisses me that I can build a project of this complexity but can't make a straight, skinny piece of plastic........:angry:

Thanks all.

 

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I prefer a candle instead of a lighter for better control.   I have a "sprue stretching candle" for a consistent flame.

Yep, me too. Also, the hotter the plastic, the easier the draw to smaller diameters. For thicker sections, I heat a wider area, then draw as is starts to get really soft, but not yet melted. The candle also allows two hands free to handle the sprue.

Well that;s varied advice but all obviously work for you guys. Steve that's amazing curved sections of clear in the steering wheels. I feel so lame...

Mike, i didn't realize rod was available in .020. Smallest I have on hand is .0625 and I didn't want to wait for a delivery. So I tried stretching and started with the .0625 - instant breakage.

Will try all the methods and several different plastics. It pisses me that I can build a project of this complexity but can't make a straight, skinny piece of plastic........:angry:

Thanks all.

If you're going styrene, I'd highly recommend Plastruct over Evergreen, as the Evergreen (below a certain diameter) is not actually round in cross section, but egg shaped. Plastruct also has it as small as .010 diameter, and it's perfectly round.

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Well that;s varied advice but all obviously work for you guys. Steve that's amazing curved sections of clear in the steering wheels. I feel so lame...

Mike, i didn't realize rod was available in .020. Smallest I have on hand is .0625 and I didn't want to wait for a delivery. So I tried stretching and started with the .0625 - instant breakage.

Will try all the methods and several different plastics. It pisses me that I can build a project of this complexity but can't make a straight, skinny piece of plastic........:angry:

Thanks all.

 

Those curved pieces are a little more tricky than just stretching.

You have to stretch it & then form it over a mold while it's still warm enough to take the shape.

It's really not difficult, you just have to work quickly, & practice.

It's not a big deal to throw away mistakes. It's just sprue.

Take your time & practice a little Cato. You'll get the hang of it.

 

Steve

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