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Posted by Al Patrick on April 10, 2008, 6:16 am
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nick hull wrote:
>
>> The sand will have a lot of unwanted thermal mass - it will suck up
>> a lot of the heat from the inside of the plastic, and as the outer
>> layers of the pipe come up to bending temperature the inner layers
>> will be chilled as the sand sucks up the heat. And by the time the
>> inside (and the sand) is finally warm enough and ready to bend, the
>> outside is either soupy and losing it's basic shape, or on fire.
>
> Heat the sand before you put it in ;)
>
> Free men own guns - www(dot)geocities(dot)com/CapitolHill/5357/
It also seems that some of that sand could become embedded in the molten
pvc and serve to scratch up whatever is pulled through it. Even if it
is only a drain it could help to cause clogs, unless it is re-smoothed.
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Posted by Ned Simmons on April 10, 2008, 11:56 am
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>It also seems that some of that sand could become embedded in the molten
>pvc and serve to scratch up whatever is pulled through it. Even if it
>is only a drain it could help to cause clogs, unless it is re-smoothed.
A more serious problem is that filling the pipe with sand will prevent
the OP from doing what he wanted in the first place: squashing the
pipe into an oval. The volume of the sand is fixed and the
circumference of the pipe is fixed. Squashing the tube decreases the
volume of the pipe, but the sand won't compress. Which is why packing
a tube with sand in order to bend it helps prevent distortion of its
cross section.
--
Ned Simmons
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Posted by nick hull on April 11, 2008, 7:11 am
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>
> >It also seems that some of that sand could become embedded in the molten
> >pvc and serve to scratch up whatever is pulled through it. Even if it
> >is only a drain it could help to cause clogs, unless it is re-smoothed.
>
> A more serious problem is that filling the pipe with sand will prevent
> the OP from doing what he wanted in the first place: squashing the
> pipe into an oval. The volume of the sand is fixed and the
> circumference of the pipe is fixed. Squashing the tube decreases the
> volume of the pipe, but the sand won't compress. Which is why packing
> a tube with sand in order to bend it helps prevent distortion of its
> cross section.
So put in enough sand to fill the PVC pipe AFTER it is squashed. This
could be done by putting in a wood rod and then hot sand and removing
the rod before squashing.
Free men own guns - www(dot)geocities(dot)com/CapitolHill/5357/
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Posted by lostfrom68jay@googlemail.com on April 9, 2008, 6:04 pm
Please log in for more thread options Cool!!!
Thanks for the tips! I hadn't thought about the inversion/figure 8
problem. I really don't have the tools to make a form, but could I
buffer the clamping boards with some foam rubber to soften this
effect? Or perhaps blow some heat to the exposed sides and not just
through the inside, so that the area that I want to bend the most gets
more heat? I'll report bach after I've experimented.
Robobass
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Posted by newshound on April 9, 2008, 6:23 pm
Please log in for more thread options I originally thought hot air gun, but to limit the temperature and keep the
heating much more even, how about passing steam through it, e.g. from a
wallpaper stripper if you have one, otherwise fix a hose to a kettle? Board
plus weight sounds fine, but to prevent the figure of eight problem you need
to have "stops" of the right height each side (bits of wood, or something
else the right size) to stop the board from flattening it too far.
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