How do you stretch a sprue???

Hi guys,

Thanks very much for taking the time to reply, it's really appreciated. I'll have a go tonight and hopefully post pics of that sea cobra soon. Thanks again.

Rich

The only thing I would add to the great replies above is that the key is to pull a little as you rotate over the flame. You have to recognize when the sprue is soft enough and remove it from the frame. The only way to do that is to practice a few times. Not too difficult, just needs practice.

Stretching sprue can sometimes seem almost a "black art" - Plastics from different manufacturers aren't necessarily consistent. You might need to experiment a little, but fortunately, sprue is cheap.

A small candle should be fine for a heat source.

• Hold your sprue above the tip of the candle flame - you want to melt it, not burn it. If it blackens or bubbles, you're holding it too close to the flame.
• Holding both ends, rotate it until it gets soft - you need to rotate it so that it is evenly heated throughout the whole thickness
• When it is sufficiently soft, take it well away from the flame and slowly stretch it - don't pull too hard or too fast. IMPORTANT - don't stretch it over the flame and don't rotate it while stretching.
• You will find that the thickness of the "stretched" sprue depends on two things - how hot it is and how far you stretch it - this is where the experimenting comes in.
• When you have achieved the thickness you want, stop stretching and hold it at that length until it cools, otherwise it will bend or curl.

Good luck

Sounds like you are holding it over the flame too long. Hold the piece of sprue about 2 inches over the candle flame and rotate it continuously. Just spin it back and forth between  your fingers. When the surface of the plastic starts to look shiny, remove from heat and pull slowly. The plastic will stretch very easily, and it takes practice to pull with the right force and speed.

It helps to use a piece of sprue at least 4 inches long.

Tricky business it is...

I held mine over a stove (larger heat source), at the edge of a jet.
With pliers on both ends I slowly twisted in opposite directions (say from 10 o'clock to 2 o'clock) once the plastic became pliable enough.
I had to move the sprue around the heat source constantly as some spots would start to get thin compared to other areas.
It took a few pieces and a few tries but the technique finally worked and I ended up with my spagetti thin sprue.