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Old Nov 16, 2007, 05:36 PM
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motorhead's Avatar
Kansas, USA
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Fuse layup over white painted mold

I am wanting to layup my fuses prepainted with white paint. Here is my problem. It is hard to see bubbles under the glass against the white back ground. I am considering bagging two layers into the mold and then trimming them flush. Then laying up a third layer and using it to join the halves.
The stinky part is it will now take me 48 hours to get a fuse and about twice the time to on the part overall.
I have thought of other options but am not totally convinced.
I tried using a balloon but it bunched up the glass.
I could make a custom rubber balloon but am afraid of the same problem. Plus if any air is there then it would be trapped.
There are other options but I cannot decide. I definately cannot afford to spend double the time on them and do not know if it is worth it over just finishing and painting outside of the mold.
Ideas???
Mike
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Old Nov 16, 2007, 05:51 PM
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Falcon, Colorado
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Laying up over white is different, but you can still see the bubbles. Do the normal cabosilled epoxy on the sharp edges, then pure epoxy everywhere else. Lay in a light layer of glass (.75-1.7oz), wet it out with a brush, then rough trim it with straight scissors to about 1" oversize. If you have any really sharp bends, you can cut the excess glass vertically down to the mold flange. This will help. I would let this green up, if you have a hotbox or a space heater, this will help if you are impatient like me. I run old #11 exacto blades down the mold flange after this greens up to trim the excess glass. It is easy once you figure out the technique. After this, lay up whatever you are going to place into the mold, trim if you have to, and wet seam them. Bagging fuses is overrated. You may save .25oz on a two meter fuse. I finish fuses that are either 5 layers of 5oz kevlar or 5 layers of 5.7 carbon in about an hour, including painting. Total time including drying/curing is around 3-4 hours until I pop them out of the mold. Good luck with it!
Jim
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Old Nov 16, 2007, 05:52 PM
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One more thing.. It is WAY worth it to finish in the mold. You do get a seamline, but the paint will stick through ANYTHING!
Jim
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Old Nov 16, 2007, 06:31 PM
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Kansas, USA
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What kind of epoxy are you using and what cure speed? I bought some white gel coat but it ends up too thick for my inner nose cone to work. The gel coat is epoxy based so I am thinking of using it in the corners. I will give this a shot on my next one.
Next question, anyone interested in molding my fuses for me?
Mike
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Old Nov 16, 2007, 07:06 PM
RC LIFER
santa rosa California
Joined Aug 2005
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I paint RC car bodies. When i need to back white so dark colors behind it are not visible, I use silver. It's metal content blocks light and it's light enough to not need a lot of white for coverage.

So, on the molds, I'd do white, the back that with a light coat of silver, then go for the layup. You won't see anything but white.
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Old Nov 16, 2007, 07:31 PM
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It may be too far into the game for you now, but you might want to consider a silicone plug for each side. You don't need any thickened epoxy anywhere. plus it is soooo easy to wet out the glass--you don't even have to be very careful about how much epoxy you use, since the excess will get squeezed out by the plug. There is the cost of the silicone--but if I was going to make even a few molded fuses I would do it . You do need to join in a second operation, though.
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Old Nov 16, 2007, 08:05 PM
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Quote:
Originally Posted by Ward Hagaman
It may be too far into the game for you now, but you might want to consider a silicone plug for each side. You don't need any thickened epoxy anywhere. plus it is soooo easy to wet out the glass--you don't even have to be very careful about how much epoxy you use, since the excess will get squeezed out by the plug. There is the cost of the silicone--but if I was going to make even a few molded fuses I would do it . You do need to join in a second operation, though.
I have really been thinking about this. Silicone seems like a great way to do fuses. The only issue I have is trimming. I like the outer layer, i.e. light glass, to be trimmed flush, as it keeps you from having a large seam line. If you used silicone plugs, I would think that you would get a bead of epoxy right at the flange line, which would suck to trim with an exacto. They gum up already, which is why I use old blades. Sure would be a lot easier then going on "bubble patrol" after you layup though.. May save a few minutes. As for paint, I have been using straight Krylon for the fuses. As long as you pull the part and hang it for an hour or so, it dries pretty hard. I have used car enamels, and they work well also, but I am lazy and the Krylon dries in 12 minutes or less (says that on the can!)

Ward.. Can you enlighten me on the trimming process when using silicone? It seems like a really good idea, but do you have to wait for the epoxy to cure completely before pulling the silicone out? I would like to do each fuse half completely seperate, flush with the partline, but I need to have about a 1/2" overlap on the top of my fuse that is 3 layers of 5.7oz carbon that is done in a wetseam. Is this possible with silicone???
Jim
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Old Nov 16, 2007, 08:41 PM
working to the closest cm
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brisbane australia
Joined Nov 2002
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Hi Mike- dealing with these issues myself. I have usually done things the way Jim has suggested - letting a gelcoat tack off before proceeding.

I have just got myself a set of moulds that came with European instructions..
http://www.rcgroups.com/forums/showthread.php?t=765337

The fuz is vacuum bagged in much the procedure you have outlined. Coat of epoxy - flox into the tight areas, light glass and then heavy layers - leaving out the final 45-45 layer used for wet seam joining.

Vac bagged in hot box - watching a sample of the layuo to test for green time - trimmed and joining layer to complete the job. Back into hot box. I think the use of fast epoxy and hot box can reduce the 48hr turnaround.


I have recently had some voids occurring with HLG pods under vacuum that cured by using the suggested regular peel ply. No effort made in these to search for bubbles as the cloth is laid in with the peel ply in place as a big wet sandwich. Vacuum took care of all the pressing and getting rid of voids.
http://www.rcgroups.com/forums/showt...68#post8538068

Given all of this I am more probably with Jim and his methods (no Bagging) however when you bag you don't have to watch the lay up (weight build-up due to epoxy) so much and it allows me to wet the cloth before placing into the mold. Bagging a dlg pod can save 2-3gm on a 8gm pod half --11gm vs 8gm (not sure if it matters?)

cheers jeff
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Old Nov 16, 2007, 08:57 PM
working to the closest cm
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Using silicon

Quote:
Originally Posted by threcixty
I have really been thinking about this. Silicone seems like a great way to do fuses. ..snip..
Jim
Hi Jim I have been on the silicon merry-go-round.

This is experience only based on DLG pods. First SG11 pods with silicon plugs worked well. However the placement of carbon reinforcements required a second operation couldn't really master getting it all done in one go without the pressing in of the plug upsetting th position of reinforcement layers.

After some hiccups with getting processes sorted I now prefer vac bagging mainly due to the ease of positioning fabrics - true it is more fiddly than using plugs but it is more economical and suited to low volume work.

With your need to keep a ledge of carbon above the join line (for wet seam) vac bagging wont do this - the ledge is added after green trimming the main laminate or joggle gaskets are used (another fiddle!!).. In the european forums i have seen strips of 45-45 carbon added to the seam line for joining after the vac bag and trimming.

cheers Jeff
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Old Nov 17, 2007, 12:44 AM
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The thing I have found with the molded parts is this... Resin control leads to weaker parts. Before I get flamed on that, this is why:
I built 2 wings, one using peelply (woven nylon) and one without for the bagging operations. The one with peelply is noticeably softer and also dings much easier on the wonderful rocks we have here in vegas. The finish also does not look as good as the one that was built "heavy". The difference in weight on the two wings is around 1oz. 1oz on a 50oz sloper means nothing. I have tried the same methods on DLG planes, and the ones that I used resin control, from paper towels to blot up the wing skins, and peelply on the fuses, compared with not blotting and no peelply was also a small percentage, perhaps a half an ounce. Without bagging, my fuse pods were around .4-.5oz and were made from 1 layer 1.4oz glass, 1 layer 1.7oz kev, and a piece of 50k tow pulled in half, one on the bottom of the saddle and one near the bottom partline.

Moral of the story is that for the extra 5-10% of weight, the durabillity of the part goes up a lot. Makes it easier to build as well.

I used to vac the fuse molds, but once ya get the hang of it, you can build almost as light, even without much cabosil. Other then the first layer, you can do it in one step and it goes really smoothly.
FWIW...
Jim
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Old Nov 17, 2007, 10:23 AM
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San Diego
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This should help. Or, use Silicone at least.

http://www.rcgroups.com/forums/showt...ight=have+mold

Sean
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Old Nov 18, 2007, 03:25 AM
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Thanks, Sporter. I like how you do that. I'm doing a pauper's variation on that. I layed up the pod cowl/sheath and then ironed on some solite. Then, I applied PVA. My mold has 4 pieces, 2 front halves and 2 back halves. When the fronts and backs are bolted together, I'll do the layup for the main pod. The fit should be pretty good, but using tape would have been easier.
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Old Nov 18, 2007, 11:48 AM
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Well I decided to try and go with Blue for the fuse. We will see how it turns out. I can already see some pinholes in the paint. I might have to brush paint on these areas.
I will post a picture when done.
Mike
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Old Nov 18, 2007, 12:16 PM
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Quote:
Ward.. Can you enlighten me on the trimming process when using silicone? It seems like a really good idea, but do you have to wait for the epoxy to cure completely before pulling the silicone out?
My pod mold uses a joggle gasket, so I let it cure fully before trimming, but I think that it would be an easy thing to pull the silicone and trim while green. It may even be possible at that point to trim above parting line and do a wet seam joint.
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Old Nov 18, 2007, 01:50 PM
chetosmachine's Avatar
Madrid, Spain
Joined Sep 2004
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I do fuses with wet seaming, no vacuum, no silicone plug. I paint the molds, then do the parts. On corners, epoxy+microballons+cotton flocks or cutted fiberglass(3mm).
I have great succes using this technique, it's just a matter of learning the right timming for each thing. i spend around 2 hours per fuse, then wait 24 hours until i remove it from the mold.
I use 20 minutes gel time resin, but i wish i had a faster one...
On my thread about my F3B glider(F3X forum), i explain how i do it, and the layup.
Chets
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