don’t thank me… thank claudio and dick… those are the ones who i learned the trick from… pretty nifty… 
here is my project for today…16.7 lbs of dry aged rib roast…
LOL mine was a 15lb turkey that my wife was giving out about cos it was too big for the oven :rolleyes:
well started working on the keel…
took a symmetrical heli blade and cut it down the middle and added in a wedge shaped spacer of bass wood. and than have been adding and removing drywall mud to shape and smooth.
between th eblue lines it is 347mm upper(left) blue line, where it meets the hull is 110mm bottom blue line(right) is 74mm and it will be 17mm deep in the bulb. I have not figured out my keel trunk shape yet…
the area right of the blue line will be my rudder
so I am going to use these pieces to make a mold…so I can make some carbon fins…
So, I guess I gotta get some gelcoat and once I have my shape set, i need to paint and add copious amounts of wax… so I can make a two piece mold…
do i really need the gelcoat??? I guess I could go with the packing tape method but then I have tape lines to sand out…
You probably need gel coat for the first MOLD layer. It will give you something to wetsand and polish if needed, without hitting any glass. You can go with a clear coat of epoxy on the fin layup, and then CF layer once it has thickened up. This will also give you ag molded layer that you can wetsand and polish once out of the mold.
Hew, I have been using the west system 105 with 205/206 how long until it tacks up enough so the CF or glass doesn’t push through…???
working time on the 205 is 60 minutes on a thin film and 90-100 on the 206
Just curious as to your experience…on time frame…
I learned long ago not to rush things when making molds I use the slow hardener and wait several hours. soft enough that a thumbnail will dent it, but hard enough that no fingerprint or stickyness is there.
Hi Marc! I have just started my first scratch IOM hull. I am very curious of the technique that you used to fiberglass this plug. I think I see that you have strips laid out at an angle and overlapping?
And from the prior posts that you used different weights of glass, 6,4,2 ounce glass. Is this technique documented anywhere? If not, can you share some of your thoughts on how to best layout the fiberglass?
Thanks,
Glenn
Glenn
actually is 6, 2, 1 the 1 ounce is almost silk like in nature…and makes for a nice top coat which is easy to sand…
the strips you see, is just the packing tape overlaps showing through the wet glass.
I extrapolated the fiberglass weights from one of claudio posts. Claudio and dick and a few others have used the packing tape method for a while. the packing tape acts like a release agent and keeps the epoxy from bonding to the hull…
having to sand the hull to remove the fiberglass pattern is probably ly the worst aspect of using a “male plug” method of making a hull…
I will be working on my first female mold for the keel/rudder.
I did make a female mold of a keel bulb for an RG 65… I’ll take some pics and most later in my albacore post. while not perfect, it needs to be sanded and shaped…
cut and machined the deck attachments and did a trial fit… also been painting and sanding the keel and rudder plugs… and playing with the milling machine…
now I’m bummed out…
all the time spent on the keel fin and rudder… while not totaly lost… I have a set back…
got the tooling gel coat got the parts all waxed up nice and smooth and preped it all of half of the mold…
did this saturday afternoon and attempted to remove everthing today…
smoothed on a coat of the tooling gelcoat (black stuff) let it set and get tacky… and then started the glass layup over he course of several hours. did several layers of chopped strand and some wood for support…
was frustratingly difficult to get everything separated… and in the process of getting everything separated. the rudder and keel and were damaged…not irreparable. but, just more work to do…
the parts of the the entire gel coat surface is dull so a fair amount of waxing is going to need to occur to even get the current halves remotely close to being able to accept a layup of carbon and epoxy… and I still have the second half to go…
sad to say but I think I could have gotten a better result using the packing tape as my “mold release” agent… have a couple small spots were the gel coat never hardened… again though I had mixed it plenty well…
Oh well, time to sand and prep the fin and rudder all over again… next time, going to use packing tape I think… at least its a sure thing…
read that post… already… as well as several others.
thought I had all the bases covered…
I’m going to repair the foils and try again, but using the packing tape as my “release agent” so I can make up a female mold.
if that does not work, then I will resort to asking my cad guy to see if he is willing to run some aluminum through his machine or do a layup like claudio has done here
http://www.rcsailing.net/forum1/showthread.php?4991-IACC120Cup/page13&highlight=ac120
Marc,
I learned something the hard way recently, and it may have been what caused your keel mold issues. It turns out that wax is insufficient as a release/barrier for mold making. Unless you use a catalyzed two-part paint, the odds are very high that the gel coat and/or resin will chemically interact with the paint and cause the issues you saw. There has to be a barrier to keep the paint completely separate from the gel coat. It turns out that is really what PVA is for. I always thought PVA was a release agent, and was a belt and suspenders move if you have a thoroughly waxed plug. Not so much! A complete, unbroken coat of PVA keeps the gel coat or epoxy from interacting with the paint. The wax is the parting agent. Once the mold and plug are separated, the PVA washes off as it is water soluble.
By the way, once you have a smooth mold that has been waxed, you can pull parts without PVA. This is great as PVA often leaves surface imperfections from slight sagging. You can polish these out of the mold, then forget the PVA going forward.
Cheers,
Eric
so instead of using the tape for my release the PVA would do the job…
what PVA do you use? does the pva leave any residue/impression in the mold? I don’t have spray equipment…
what about hair spray???
http://www.westsystem.com/ss/mold-release-pva-and-hairspray/
Craig keeps hassling me to justs buy a keel from you
My question is what do you use for applying a smooth and equal layer of PVA? I am redoing my deck at the moment and I put two layers of PVA. I was spreading them with the piece of cloth and the effect was satisfactory in terms of suface, but when it came to separating, I also pulled some chunks of paint. Thank you
Lukasz Koch
A wealth of molding info is contained within:
http://www.rcgroups.com/composites-fabrication-210/
You can search the threads with your particular problem. Look first under the sticky thread at the top of the list. Molding an airplane wing is just a large fin!
I have found using dense sponge to be the best for smooth layer application.
Added Note: If your using sponge application first time a few tips, soak the sponge in PVA, it absorbs quite a lot of PVA and then gentle glide the sponge over surface and it will leave nice thin film without sagging, pays to have lighting conditions where you can see the wetted surface (semi dark with backlite window light)
If you want to re-use the sponge again, after use squeeze as much PVA out of the sponge as possible by hand, otherwise when it dries the sponge becomes rock hard, I soak the sponge in warm water couple of times to rinse out the PVA and then store it in zip plastic bag to keep it moist until next time I need to use it.
thank alan,
just ordered a qt of partall PVA… and started working on repairing the keel and rudder
I also use Partall PVA when making molds, and it is applied with a small square of old t-shirt cloth. It generally takes two coats to get a uniform coverage. Don’t bother with bristle brushes, you will not be happy. Some foam brushes will work, as will a hard sponge that is softened in warm water then wrung out. It is also helpful to dilute the PVA by 10% with water. That slows the drying and thins it out, which is both good and bad. You will get a smoother skin on the dried PVA, but it will also be more likely to run. On a keel plug, thinning would be good. On a hull plug, it is a bother as sagging is a real possibility.
If you get a really even coat of PVA, then there will not be any impression in the mold. That is easier said than done. However, even if there are some small imperfections, they are probable less than .001" and easily polish out. Compared to the disaster of the gel coat reacting with the paint (wax does not protect against this), a small PVA blem is not worth worrying about.
I have not heard of the hairspray trick, but that sounds worth testing out. The spray would be easy to apply in light coats, so the finish should be better. I will make a test plug and give this a try.
Cheers,
Eric
gonna take a couple days to get the foils ready to go… again…
not sure what I’m pissed off about more…the damage to the foils, or the the expoxy, fiberglass and gel coat I wasted on the molds…