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How much does FBR expand when heated?


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#1 s0lidace

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Posted 22 August 2012 - 03:02 AM

Hi everyone. I've checked around to find an answer to my dilemma but I have had no luck. That's what this topic's for, I guess.
So i've come to a problem. In my country backing rod is sold in mm. I am stumped. I could either buy the 12mm diameter, which is close to 1/2" if I remember correctly, or I could buy the 10mm. I have no idea how much FBR expands when heated. Basically what I'm trying to say is that I'm scared 12mm will expand too much. Unfortunately its not as simple as "find out yourself" because well..

I'm poor.
Yup.

I apologize for my noobness. D:

Edited by s0lidace, 22 August 2012 - 03:04 AM.

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#2 Daniel Beaver

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Posted 22 August 2012 - 07:54 AM

You might find the answer disappointing you:
The amount it expands depends on too many factors to reliably predict. Trial and error is the only way to figure it out. And unfortunately, that means you need to actually go buy some foam and start playing around with various heating times and methods.

You might want to ask this question on Oz Nerf as well. Very few of us have access to metric piping (though I suspect your FBR comes from the same sources and is the same size as ours). One thing you can do is go to the hardware store, grab a bag of FBR, tear it open a bit, and start sticking it into pipes in the plumbing section to test fit them.
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#3 DX-Robert

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Posted 22 August 2012 - 09:46 AM

In general, less dense foam expands more when heated. Some very dense foam varieties barely expand if at all. If you can identify the manufacturers for the FBR options you have, it would be easier to figure out. But, there are also variables beyond the material itself, such as how you heat it and for how long. Individual batches can vary, as can batches between different stores and countries. As Beaver said, there really isn't a set answer for this.
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#4 roboman

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Posted 22 August 2012 - 11:24 PM

12mm foam is probably your best bet. If anything, just heat it in increments, and test the blanks between each heating cycle. I think you'll have a pretty hard time getting that foam to expand more than .7mm, as that's actually quite a bit.
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