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Old 06-05-2008, 10:52 AM
  #47  
Slow Low
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Default RE: All Composite 1/7th P-40E Mould Build

You bet Steve; blend after it's hard, but pull the tape a well before that. For blending I use a small block maybe 1"X3/4"X3/8". Don't know what I can say about blending technique accept practice makes perfect, and a good place to get some experience would be some bodywork on an old fender. lol I could say this - sand very lightly, and just enough to remove the scratch marks from the previous grit of sandpaper. For standard seams along a fuse or wing I thin the epoxy out pretty good so there isn't alot to take down - this will help the blending. In terms of grit, I might start with 180 and then move to 220, 320, 400, 600. That's usually enough, but you may want to take it up to 1000 or 1200 if you're feeling crazy. I use a nylon masking tape and I don't have a mic here at the moment, but I held it up to a standard sheet of paper which if memory serves, is about .004" - it's a little less .0035" maybe. (good eyes eh? calibrated them this morning!) Don't know about the fairing compound because I've never had the pleasure. I use the finishing resin thinned to about the consistency of milk, but here's the crazy part - I also add microballoons. Sounds funny I know to thin it with methyl hydrate and also use microballoons, but the balloons will gravitate toward the tape as it sets and it will still be very thin towards the centre of the panel. For butt seams I will finish the edge on one panel, and then apply the tape over it and brush on the epoxy mixture onto the adjacent panel so that they end up level. You will still see the seam, it's just that both panels come up to meet each other.
PVA - yes I know - the whole thing puts me between a rock and a hard place because I hesitate to promote subjecting other peoples hard work to risk, and yet I've never had a problem. Fear can be paralyzing. Let me say this - even while building the mould in this thread I took a few risks and tried a few different approaches to several problems. The idea is that no matter what the outcome, I will know what works best as time moves forward, and I have enough confidence to know that if I did it once, I can do it twice - probably better the second time. The only problem I have now, is that there are a couple of things that I would like to go back and improve where the new method I tried worked better than the original method that I knew yeilded acceptable results.
Here's what I know
- I don't try to mould a plug that has questionable surface finish
- 100% carnauba paste wax is the only wax that I have ever used (I did alot of research to end up there)
- I wax in small circles at eye level and I am absolutely anal about getting every microscopic nook and cranny
- I lay down no fewer than 5 or 6 coats of wax buffing like I apply
- I spend the money for a good high temp abrasion resitant tooling epoxy

I guess that all that fear I had the first time I ran out of PVA turned into a healthy respect for preparation, and that's about all I can say on that; the rest is up to you. No I'll say one more thing - if I was running a business and trying to get things done quickly I would be using PVA.

IMHO The other thing to remember is that even if you have to scrape part of your plug off of the mould tool with an old popsicle stick, the tool underneath will be good and you can make parts; parts with all of the detail of the original.

Good luck with panel lines. I'm looking forward to seeing the results.
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