Andy's email got me looking around a little bit. I didn't find much
that was inspirational.
Along the lines of what we were discussing
Look at the diagram under "Antenna Leads Severance Guillotines"
The picture Andy found
Looks nice and simple, but i don't understand the mechanism.
Similar to our discussion
Note the use of a cartridge squib, and O-ring.
I browsed the patent database a bit
I'm sure i missed something significant, but i did see a trend developing.
Most everyone uses a hollow tube with two side-holes for passage of
the line as the main cutter body. Most use a pyrotechnically actuated
piston sharpened to a wedge shape at one end, which drives the line
against an anvil thus shearing the line.
A couple patents i found mention the difficulty of shearing fine
threads in a slack line, and the tendency of the threads to bind
between the cutter and the tube. The most insightful solution to this
problem i found is to insert a plastic sleeve into the side-holes of
the cutter body and pass the line through the plastic.
Patent# 3,452,631 April 17, 1967.
The other one i liked was 3,885,484 May 27, 1975. They use a thin disk
forced into the hollow of the cutter body and propelled by a
cylindrical piston, to do the cutting. The idea here is that
the very close fit and spring tension of the disk doesn't allow for
any threads to get into the gap between the disk and the body. (And,
hey, they claimed it worked ;)
I updated the wiki with the old design info
At the bottom of this page are some thoughts about where to go with
the new design. It might be simply adding a plastic confinement ring,
similar to the '67 patent, to the old design would solve most of our
> I also found a couple links to commercial line cutters aka "reefing line
> Here is a system that is used by skydivers that has an altitude computer.
> We might be able to use a couple of their line cutters (found under the
> products/accessories section.) I would hope that these have some measure of
> reliability. :-)
> Finally,here is an illustration of the Apollo line cutters with information
> in the follow up link:
psas-airframe mailing list