Re: Pressing BP rockets question

In article <1133825757.907949.147850@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, Jared
says...
>
>I too have been pressing dry powder rockets of various fuel
>compositions for some time and would also be interested if anyone has
>any info regarding the amount of pressure to apply. Also can anyone
>reccomend a good way to monitor it as my hydraulic press has no gauge.
>
>Cheers
>


You can govern maximum pressure without a gauge by pressing against a 'dead
load.' The platform on which your work sits is on one end of a lever, and at the
end on other side of the fulcrum is a weight. Press until you lift the weight.
You can vary the pressure exerted either 1) by adding to the weight or 2) by
changing the length of the lever arm carrying the weight, or 3) by placing the
weight at different points along the lever arm, as on a steelyard balance.

Another expedient might be to place a bathroom scale or other heavily sprung
scale on the bed of your press, and set your work on top of it. You would have
to do some calculation to figure out what pressure you were actually exerting,
but this is often not as important as having a means of pressing to a uniform
standard. In other words, if you establish by trial and error that you achieve
the best observed result when the dial of the scale reads (say) 150 lb. - that
less doesn't press as completely, and more bursts the case - you have a useful
(if arbitrary) measurement to guide your future work.

This may seem rather strange, but in the graphic arts we routinely use
densitometers, which give a similarly arbitrary measuring scale. The results
given by one densitometer are not reliably equivalent to those given by another.
Nonetheless a densitometer is, if regularly calibrated, capable of giving
consistent measurements relative to itself, and these are quite useful. It is
rather like marking off the length of your foot on a wooden slat, and dividing
it into inches and fractions. You won't be able to compare your results with
your neighbor, whose ruler is the length of HIS foot, but you can compare the
lengths of different objects measured with YOUR ruler in a consistent manner. As
long as this enables you do do reproducible work, it is a useful tool. Just so
with the suggested method of measuring pressures.

.

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