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Old Nov 03, 2012, 06:07 PM
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AvB
Wind, hill, ... I'm keen ...
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Australia, QLD, Woody Point
Joined Nov 2006
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Hey Adam, I'll watch those videos when I'm in a better frame of mind. Your video of the bladder technique was inspirational for me and it's my main method. No digressions into latex, balloons or whatever ... I still do mine with the thin plastic welded as per your method and have great results. Recently I made a new nose cone mould (yes, one of the moulds that had one side stuck up ... the inception of this thread!) and made it with a completely open end. A friend told me it wasn't worth mucking around with inflation bladders for a simple nose cone and just to roll the seam. I did the first one that way and wasn't happy with the seam being more bulgey than before and needing sanding etc to fit onto the fuse. Probably because originally, the fuse was made a close fit to a cone made with a bladder. So I made an "end plate" that screws onto the open end of the mould, has a foam seal and a spigot hole in the centre and converted it to an inflation mould! I used it a few days ago and it was the best nose cone I've ever made!!! The bladder does such a good job of squishing everything together and squeezing out excess epoxy.

But I'm (again, sigh ...) despondent about frequent failures after so much work. I am having so many disappointments and (seriously) I get to the point of deciding I'm just not cut out for this stuff ... there's something missing from my DNA, or I'm just thick and clumsy.

I could fill up a page ... but the latest downer is this. When the paint stuck to the Scratcho tail and stab moulds (as reported above) I cleaned them up and repaired various old chips and blemishes. Carefully wet sanded them flush with 800, 1200, 2000 grit (using shaped blocks) and then with G3 and then finish polish. I had some other stuff to polish (post-painted wings) so I borrowed a friend's electric rotary foam pad polisher and used it to buff out the polish pastes. They turned out excellent, so in a way I was glad that the stickup had got me to fix up the moulds properly.

Then as mentioned above I did the FMS sealer and Frekote routine. Two-pack paint, and was this time more careful to splooge the edges because I regularly get bubbling. Vac cured the skins, trimmed, then laid partial blue foam cores inside, and Sicomin PB170 foaming epoxy to fill the gaps. I'm playing with the PB170 because it's less dense than the Ampreg F230, and so far I'm really happy with it.

When I popped out the parts, they were the best result yet. A few paint masking blems (the mould release was so good I couldn't even get my good masking tape to stick!) but the edges are all solid, and best finish yet thanks to the mould polishing. But I had a double-take when I looked at the trailing edges of both fin and stab. Instead of tapering to a nice fine point as before, they were really thick. So thick that the skins weren't touching and you can see an epoxy foam sandwich between them.

At first I thought darn, I've trapped something in the moulds and they didn't close properly. I sandwiched blobs of putty in there and shut the mould, and the thickness of the blobs showed that it wasn't a closure problem ... the taper has been removed from the trailing edges! I'm not sure if it was from sanding or from the polisher or both.

Not sure whether it can be fixed. Maybe I can sand back the TE areas, smear some gelcoat on and press the plugs back in. I wonder if the gelcoat I'm using for moulds is too soft? It's Rengel SW10 and it seems to sand pretty easily.

(EDIT: I just measured the thickness of the finished parts ... they are 0.4 to 0.8mm thicker than the previous ones! So it's not just the TE area. I thought the polishing would take back a microscopic amount of the surface but in fact it's all been cut back considerably. Disaster!)

It's a bummer. As I said I feel like giving up again. Too many problems.
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Last edited by AvB; Nov 03, 2012 at 06:46 PM.
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