Hi all.
Just a few observations, to prove I'm still alive, if not kicking too much !
On the subject of the diy approach.
We're all hard pressed for cash, so it seemed to me that having to acquire/build a huge vibrator for what may be a one-off mold pour needs to be avoided. The cost of the epoxy being a large enough component, it doesn't need to be doubled by adding in the capital cost of the equipment.
Consider a mold needing 10 jugs full of EG(note the new international unit of volume, where 1 jug = 10 cups).
Given a working time of say 60 mins for your own epoxy mix, and a mix/vibrate/pour time of say 6 mins per jug, then a vibrator that can do the business for 1 jug is fine. The last pour will go into the mold about the time the first one is starting to build up the exotherm reaction, and the whole mass will become a single solid.
This is obviously an improvement on needing a 10 jug vibrator, but it seems to me that there is no need to stop there. A 1 cup size should also work, and this leads me on to consider if it might be possible to design/build a system that continuously vibrated the mixture as it was being transferred from the mixing vessel to the mold.
This would have the added advantage of needing only a very short distance for the bubbles to escape from the mix.
Regarding air entrapment during the pour. This can be avoided by careful pouring and starting at the lowest corner of the mold, and only adding a steady stream of material to that already in the mold.
If the mix is so lumpy that it doesn't pour, then continuous ramming will be needed. This might be the "killer" to the whole idea, of course.
Another problem might be edges, where there will be a tendency for a lumpy mix to bridge over. I wondered if a separate mix, possible losing the largest aggregate component, might be placed along these difficult areas, without jeopardising the strength of the whole.
Of course, those who have followed my ramblings, know that my own preferred method of de-airing is to spin the whole lot, with all the danger to life and limb that might entail. Much more exciting.
This leads me to my other thoughts on reducing total weight.
Rather than casting a large single block, along with low density cores, why not consider building the frame up from small components - a space frame of EG girders.
They could be simple plain ended struts, with separately molded joints, or molded ends, only requiring epoxy adhesive to build up the frame.
Any variation on this approach would also have the advantage of drastically reducing the size of any equipment needed, both for weighing, vibrating, and handling in general.
Is there any fundamental disadvantage, ie from an engineering point of view, in this approach ? I acknowledge that the placement of insert/fixing points would now be a different ball game, but who said it would be easy.
For most diy-ers, the extra time in the build would be more than worth it for the reduction in equipment costs.
Regards
John
It's like doing jigsaw puzzles in the dark.
Enjoy today's problems, for tomorrow's may be worse.