So just to make sure I have the concept right, just layer fiberglass and resin on each side so that it sets up hard, making sure to line up to the very edge of each side, and then once cured I would essentially tape it together with resin along the edge and a thin strip of glass? I suppose my question if that is the case is, when sanding it down smooth, because I understand Fiberglass to be a bit rough to start, how do I smooth that edge without destroying the link?
Sorry its kind of hard to explain without pictures, I'll try my best though, also you'll have to bare with me on some of the names for things, it appears you guys over the pond have slightly different terms for things) I work in the film industry and this is how I've always done it, I'll see if I can find pictures I'm allowed to put up for you as reference. But anyway, with your two part silicone mould, (which I'm assuming you're comfortable in preparing)
paint in a thin layer of gel coat into each half (basically a nice fibreglass resin (without any matting)) going literally just up to the edge of the recess left from your original piece, and no more, if you feel the need you can add aluminium powder to this gel coat so you get a nice metal looking sword at the end, this only needs to be one coat thick
then once the gel coat layer is tacky (cured enough to keep its form but soft enough to leave finger prints) paste in your fibreglass matting with the fibreglass resin, again do this is neatly as possible, (remember though this stuff can be trimmed back quite nicely, if it really needs to be) you should build up a few even layers of matting (as many as you can get in up to about 4 max without going over the halfway point of the mould) again do this to both halves
once this his has gone tacky mix up some more fibreglass resin, before applying it chop a load of matting up into the mix, literally tiny bits, no more than 6/7mm in length this will give you a gungy mess with a ton of glass mixed in, take this goop and apply it to the edges, being quite liberal with the amounts but applying it as neatly as possible ( I recommend applying this by hand tbh, but obviously wear gloves, coz that **** is nasty) this stage has to be done pretty quickly but only 'really' needs to be done to one half
optional, use additional squish mix all down the center of the piece and insert a pre made steel armature right into the middle of it (again not necessary but doesn't hurt if you feel like doing it)
whilst the squish mix is still wet pop the second half of the mould ontop making sure all keys match up and everything is well aligned. (Depending on your two part mould you may need to add additional weight or boards/strapping)
leave for a few hours or overnight, and when you open it you should find you have minimal flashing ( I don't know if you guys call it flashing, but the excess **** that splays out of the sides) and because you used chopped strand to do the squish, as opposed to normal matting you should find that it's easy to remove without issue, generally with a nice mould it can be removed with normal sandpaper and you shouldn't even need to use a file or dremel. If you've done everything accurately you should also find you have no bulging in your cast at all and should have a really tough piece.
some people may have issues with this technique, there are some variations you may like to use instead, but this is the basic tried and tested way of doing it. If you have any more question feel free to ask, I'm pretty sure I can answer them all.
