Info on molded parts requested

http://www.tapplastics.com/info/plasticsinfo.php ?
The above site keyed my interest in making copies of cowls and such. Years
ago I made a female mold for a Chipmunk cowl out of fiber glass (loose fibers) and polyurethane resin. This was a VERY messy and labor intensive effort. I then used the mold to make a cowl by laying (too much) fiberglass cloth on the inside of the mold. I did not use a vacuum bag and, as a result, the raw part needed lots of work. The whole effort was somewhat consuming.
Looking at the web site suggests that new materials may reduce the required effort (I did notice they have a nice vacuum -- for $695 -- and found a cheaper one for $310 -- both a bit beyond my means!).
Any recommendations for male vs. female molds, methods and a good source for a hobby vacuum?
TIA
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Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:

You can make your own vacuum former using a vacuum cleaner, although a shop vac tends to have more power.
Do a Google on vacuum formers or go to RC Universe and do a search there on vacuum forming. You will come up with a variety of plans.
Using my shop vac for power, I built my vacuum former for around $10 plus some scrap wood I already had.
For your plugs, you can carve one yourself from pine or basswood. I do not suggest balsa as the balsa tends to compress with the forming frequently causing a lop sided piece.
The other way is if you already have a part, put a THIN coat of vasoline on the inside of the part, then fill it with plaster of paris and let it harden up. Remove the plug from the part and let dry for about 2 - 3 weeks OR put in a 175 degree oven for 3 - 4 hours to completely dry it.
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On Fri, 06 Mar 2009 18:46:48 -0500, Ted Campanelli wrote:

Ted -- you're talking about vacuum forming ABS plastic, not laminating fiberglass or carbon fiber, right?
--
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Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:

Correct. This is for vacuum forming parts. I have had my best results using PETG for the parts. US Plastic has some excellent prices on 2'x4' sheets and they have no problems with a 1 or 2 sheet order. The name they use is "Vivak" for their PETG.
http://www.usplastic.com/catalog/category.asp?catalog%5Fname=USPlastic&category%5Fnameb&Page=1&utm_source=google&gclid=CPydyfvMm40CFRNyZQodAEf_6g&cookie%5Ftest=1
For fiberglass parts I use the "Lost Foam Method". You carve a piece of foam to the shape you want, cover it with some low temp film, then apply strips of fiberglass cloth (I usually use 2 oz cloth) over the plug using resin and let dry. Depending on the size of the item, I may use 2 or 3 layers.
After the resin has dried, sand the outside to get off any minor imperfections (fill any low spots with spot putty). Then make an X in the covering on the back side and put some gasoline in the foam. The gasoline disolves the foam.
Remove the "sludge" and film, then wash with soap and water.
The part is going to be soft and pliable at this point. Do any final shaping and put aside for 3 or 4 days. The part will harden right up.
Now you can cut any holes you need for the engine, muffler, etc. and prime and paint.
The lost foam is somewhat messy, but for a single cowl it is much stronger than plastic.
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On Fri, 06 Mar 2009 19:44:04 +0000, Lee B. wrote:

I've never vacuum bagged, but I've got extensive experience with manufacturing car parts out of fiberglass, so I think I can speak to this. Just keep in mind that much of what I say below is just me regurgitating things that I've read:
If you bag, you can get a much better finish on the non-mold side of the part -- so you can use a positive mold that's just a bit undersized. This positive mold then can be built out of any material or combination of materials that will stand up to the pressure of the bagging and will accept some form of mold release. So your plug can be plaster, wood, bondo, fired porcelain (i.e. coffee cups), whatever.
Remember that you don't care about the quality and workmanship of the plug _except_ for the part of the plug that touches your desired part, and the parts of the plug that keeps it from collapsing when you apply vacuum. It can be the Ugliest Thing In The World (and I'm always suspicious of nice-looking plugs). So just build the damn thing, already.
Also if you bag, it is much easier to get a good resin to fiber ratio. With hand layup (which is what I'm used to), the best you can do is use just barely enough resin to prevent air bubbles from spontaneously forming on your top layers of laminate. It is very tempting to use too much, and even when you use just enough it's more than you can get away with if you bag. It's also very tempting to use too little, which gives you a dry finish on the outside; if you were using a plug to form a cowl, this would lead to lots of sanding, filling, and cussing.
I have seen articles that suggest that for small items like cowls, you can "pressure bag" -- instead of putting your part in a vacuum, you press a balloon over the part (on a positive plug). You still have a pressure differential, it's just between a cheap balloon and the air, instead of between the air and a vacuum.
Also, I have seen pages on vacuum bagging sailplane wings that call out a hand vacuum pump from an auto parts store to generate the vacuum. If you do a good job of sealing the bag this is (supposedly) a good way to go. If that doesn't float your boat, I have also read that a refrigerator compressor can be easily re-purposed to act as a vacuum pump that'll pull way more vacuum than you'll _ever_ want for bagging. If you ask on rec.crafts.metalworking you'll get in touch with folks who have actually done it.
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