10mm 'D' impulse
This is a combination of
James Yawn's cast-nozzle micro motors
Chuck Knight's quikcrete/washer molded-in-place-nozzle PVC motors
and hopefully, eventually
Sugar Shot to Space's 2-phase sugar-burning maths blaster.
1) get tube. i went to the tip and retrieved a TV aerial, with 10mm rolled/pressed/welded aluminium tubular prongs
2) cut it to a suitable, sensible length, tidy up the ends and clean out the crumbs
3) find a suitable washer [or washers if it needs extra toughness]
4) make some nozzle formers out of alfoil or whatever, as long as they're non-stick, smooth and symmetrical
5) mount the tube securely and verticaly and mix up some PVA putty
6) put a glob of PVA putty in the tube and squash it down against the convergent former or plug or whatever you have stopped up the section of tube with, and also mush it against the sides of the tube so it sticks. insert the other nozzle former with PVA putty packed around it and wiggle it down so the washer is sandwiched in the correct position, and the PVA putty has settled completely into the space [NO GAPS ALLOWED]
7) leave it alone for half and hour or so, then when its definitely not sticky or spongey, pop out the formers. the inside one will drop out if you drill the throat [use a smaller bit than the washer hole!]. inspect and tidy up any rough bits, then leave it at least a day to dry out.
8) now is a good time to clean up the PVA putty, rather than later. the other end is self-explanatory, make sure the epoxy is WELL SET before drilling or it'll get all ripped up.
For my next trick i will draw a diagramme:
i formed my convergent cone with the end of a phillips screwdriver after casting the nozzle directly against a flat tissue paper plug. this works fine as long as the putty is still a bit damp, but its totally hopeless after that. the touch hole is important, it should be not less than 2mm in diameter and the epoxy needs to be about 2mm thick - less and it'll burn through, more and the charge might not light, either way you lose. the putty erodes quite a lot but doesnt disintergrate or let go of the washer. to re-use the tube, just soak the nozzle in water and gouge it out with something sharp. epoxy is a bit more awkward but can be scalpeled/heated/wiped/abraded out too. the washer might even be re-useable! hurrah!
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