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Jun 19, 2019, 01:45 PM
Parkcityflier
parkcityskier's Avatar
J, now I see what you are doing. I hadn't thought about making the mold right on top of the bottom of the wing by building the dam right there. That makes it a lot easier than how I thought I was going to have to do it. This kind of stuff is all very new to me. Thanks.

Jim
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Jun 19, 2019, 03:27 PM
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J Morgan's Avatar
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Easiest way I know Jim.
On the big doors I cut a tight fitting block and then drew a line on it around the perimeter. That is the outline of the doors. They needed 5/8" rise at the
rear for the wheel. That's plenty of rise but I only wanted to do this once. Then measured out the strut/wheel area and marked it. Just cut/carve/sand to shape.
Needs a little more sanding to smooth and then I'll slap some sideboards on it, pour it full of Ultracal and I'll have the big gear doors. But just for one side, I'll have to do another for the other because of course I have them fractionally different in size.
Pics shows it in the well but didn't want to push it all the way in and get it stuck.

J
Latest blog entry: A2D Skyshark at 1/8th scale
Jun 19, 2019, 06:14 PM
Parkcityflier
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I was really going to do it a much harder way and I didn't have much confidence of success. Just seeing your first picture turned the light on in my head and I've got it now. You're a great guy to follow in new territory for me. Looking forward to doing it now.

The tail feathers are about done on my A-1 except for the rudder. I'll probably frame it up and then put it aside and start making the doors.

Jim
Jun 19, 2019, 07:38 PM
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J Morgan's Avatar
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Glad that the pics helped out Jim. Once you get into it, not much to it really. The Ultracal molds usually require some sanding because I don't waste time making perfect plugs. It sands so easily that in just a few minutes it's as smooth as you need.
I glued sides around the main door plug and poured it before I quit for the day. It will be ready to remove, clean up( wash off the PAM) and then sand to final finish. The PAM isn't really necessary since Ultracal doesn't stick to foam but it does make difficult plugs easy to remove and washes off easily. Just a little insurance I suppose.
You can do FG molds the same way, just lay up some real heavy cloth or multiple layers to get a thick mold.
And while I was sitting around thinking about it, I thought I should probably be able to use the same plug for the other side. Just add material where it is short or subtract where it is too long. Have to do a little measuring in the morning but don't see why it wouldn't work.

J
Latest blog entry: A2D Skyshark at 1/8th scale
Jun 19, 2019, 09:40 PM
Parkcityflier
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My thoughts on the size, for the A-1. I intend to make it a bit oversize on the edges and then just trim the doors to fit. My plan is make the whole three doors as one piece and then cut them apart. By making the whole piece a little oversize it allows for the material that I lose with the cuts. My thoughts for making the whole thing in one piece is also so that the three doors should be more likely to meet pretty perfectly upon retraction with just small cracks where the pieces meet but we'll see how it all comes out. Just so I'm on the same page with you, when I pull the plug out of the hardened Ultracal what I have is a female mold. I will then make the doors by laying cloth and resin into the mold after I have liberally coated the mold with a release agent. None of the contours of the doors are very deep so it doesn't sound too difficult to do, just being sure to use a good release agent, of course.

Jim
Jun 20, 2019, 05:29 AM
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J Morgan's Avatar
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Jim,
Yes, it is a female mold. You want to wax and use a release agent too. Try to use a wax( several coats) that doesn't have silicone in it. I like Partall products, wax and PVA release agent, but there are others but some products wax isn't compatible with others release agents and vice versa. so I stick with what works for me, Partall products. Also, if you don't have the PVA then good old cheap hair spray works as a release agent too. It stinks to high heaven, but it works. Spray and let dry several coats.
So here is what I will do for the layup:
1. Wash molds with soap and water to remove PAM
2. Sand the molds smooth as I prefer
3. Wax at least 3 coats of Partall wax, probably more
4. Spray or brush on 3 thin coats of PVA release agent
5. When PVA is dry, brush on a surface coat of epoxy and let cure until it gets tacky, about 1-2 hours. You can test it by touching the excess epoxy on the sides, not on the surface itself because you don't want to leave a fingerprint in it. This surface coat is your final finish and prevents weave showing through. I also mix a little graphite powder in my surface coat so it turns black and I can see the coverage better than the clearer epoxy. But it's not necessary.
6. When it's ready you can brush on a thin coat of epoxy and start your layup. I will give these doors 3 or 4 layers of 3 oz, or a layer of 1.5 oz and then a couple of layers of 5 oz. Want to get a total layup weight of cloth in the neighborhood of 10-12 oz total. I will also lay an add'l strip where the hinges go to stiffen it more.
7. After the layup has cured several hours and is getting hard but still "green", I will use a snap off blade knife to trim the edges. Much easier to do then before it sets up hard.
8. Let cure at least overnight or maybe 24 hours before removing from the molds. And don't let the temp drop below 70F. I sometimes add a heat lamp to speed up the process and it does make the parts harder with add'l heat too. Epoxy loves heat.
9. Once cured I use a piece of plastic shaped like a handle with rounded end to slip between the part and the glass to help release it. Or blow air between the mold and part, there are several methods to try to release it. Just work carefully when removing.

One other thing, sometimes I will spray primer over the PVA when it is dry. Then you layup as you would on top the primer. This gives you a finished primed part when it comes out of the mold. Just depends on my mood while I'm doing it if I prime the molds or not.

I should be laying up some parts in the next couple of days and will document each step if that will help you. I want to get enough parts ( wings, stabs, etc) ready for glass so that I don't waste any epoxy.

If you have any questions at all, just ask.

I will add that you can pour these female molds full to form a male plug. That could be used for vac forming too. Just another strategy in case you need it.
Also, if you don't use Ultracal, you can just make your mold the old fashioned way by laying up multiple layers of glass to get a thick heavy/stiff layup.


J
Last edited by J Morgan; Jun 20, 2019 at 05:41 AM.
Jun 20, 2019, 07:42 AM
Parkcityflier
parkcityskier's Avatar
J, thanks for all that and taking the time to lay it all out for me. It may help others, too. It really does give me the confidence to try it and I already have the Ultracal so I will be using it the way that you describe.

Jim
Jun 20, 2019, 08:26 AM
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J Morgan's Avatar
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Quote:
Originally Posted by parkcityskier
J, thanks for all that and taking the time to lay it all out for me. It may help others, too. It really does give me the confidence to try it and I already have the Ultracal so I will be using it the way that you describe.

Jim
Great Jim, you can follow right along and hopefully not make the mistakes I do.
Which is my lead-in for this post. Came in the shop expecting the door mold to pop right out. Wrong. It was stuck. And I mean STUCK!
And then it hit me. I was lazy sanding it smooth, thinking I could just do the work to the mold and sand it smooth. This mold has some depressions and curves to it and I didn't take the time to address those crevice areas( like corners) well enough while sanding. Took a shortcut( as I usually do) and just smoothed them with some light weight spackle. I've done this before but just in a few little places and had noticed that the Ultracal didn't react normally with it. The spackle would sort of stick to it and have to be rubbed or sanded off the finished mold. I used quite a bit on this and it was firmly entrenched on the foam. I actually had to cut the foam apart in smallish pieces just to get it off the mold. But I got it off and sanded the mold clean and smooth. Had a small problem at the back, no material on the far end of the mold so I glued some balsa to it and them patched with bondo. This will be sanded smooth before the layup and shouldn't be a problem.
The problem with the spackle and Utracal? I'm thinking that spackle must have something compatible with the Ultracal, maybe a little lime in it, that makes them stick together so well. Anyway, lesson finally learned, don't use spackle with it unless you cover with a barrier of some sort. Plus I skipped the PAM and that didn't help either.
Also checked and I can use this same mold for the other side after I add just a little bit to the front.

J
Latest blog entry: A2D Skyshark at 1/8th scale
Jun 20, 2019, 10:45 AM
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Thought I would go ahead and layup some doors. That way Jim can follow along. Not saying this is the best or only way to do it but it's what I like to do.
Gave the molds 6 coats of wax( Ultracal is basically just portland cement and very porous) and then three thin coats of PVA. I'll give them a surface coat
and while it is tacking up, get the stab, elevators, outer wing panels , flaps and ailerons ready to glass. Still have some cosmetic work to do to the middle section before glassing. It will take a couple of days to finish this glassing session so I'll move back to the fuse for some of its work left to do.

J
Latest blog entry: A2D Skyshark at 1/8th scale
Jun 20, 2019, 11:03 AM
Skill Collector
rockyboy7's Avatar
Appreciate the step by step walk through on this - I've just started using Ultracal and didn't know about the wax step. I put about 5 coats of mold release on the Ultracal with my most recent cowling and things didn't look quite right, but I went ahead with the epoxy and fiberglass anyway. When it cured I had to bust the mold up with a hammer and use a chisel and sandpaper to get the Ultracal off from several quarter sized spots where the epoxy bonded to it very well.
Jun 20, 2019, 11:14 AM
Classic jets rule
AIR SALLY's Avatar
nice recovery and great tips ... "partall" is what I use ..there wax and pva .....have had issues when using different wax and pva that are not compatible just like you described...I use the purple colored pva.
Jun 20, 2019, 12:59 PM
Parkcityflier
parkcityskier's Avatar
I much appreciate you describing all the details on doing the mold, and the possible mistakes, too. Should make my efforts all the easier and successful too.

Jim
Jun 20, 2019, 03:31 PM
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J Morgan's Avatar
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Yeah Rocky, you really need a release agent. As I said before, you can use cheap hair spray, and it works good. Even West Systems mentions it on their website.

Thanks Rodger
I use Partall also, the green liquid and actually green wax too, Partall #2. I've run into the same problem, incompatibility of different brands. the PVA would just bead up on the wax instead of spreading out and covering.
Not realizing how little you use with thin coats, I bought a lifetime supply about 12 yrs ago. Still have about 60% of it left.

Jim,
Glad to be of assistance. Tomorrow we should see if we have doors or not. I mixed the surface coat. Forgot to mention that I also mix in some silica to thicken the mixture. Makes it stay put once you apply it, esp on vertical surfaces which I have a few of.
Then it was a full two hours before it got tacky enough. Don't rush this step. You want the surface coat to be touchable and tacky w/o leaving fingerprints on a light touch. If you don't have any graphite or silica powder, don't worry about it. Just give them a coat of unthinned epoxy as a surface coat.
Once the surface coat was ready I started glassing. Nice on these small parts that you can use scraps. I had a bunch of volan finish 3 oz cloth. The volan finish conforms to compound curves like butter. Used small pieces around the perimeter first and then started filling in the middle with larger pieces. My perimeter will have the hinges on the large doors and on the "strut tunnel" type structure it will have the flat perimeter that I can screw to the wing so it is removable to pull the gear if need be.
I actually lost count of the layers. I want the large doors to be strong and stiff enough to withstand the airstream. Wasn't worried about weight. The strut tunnel type structure will have the kneecap door cut out of it and that needs to be strong too. I laid quite a few layers on the key areas and finally threw a bit of carbon tow on each layup and then covered it with a layer of 1.5 oz just to clean up the inside a little.
I also got all the other surfaces glassed while I was waiting for the surface coat to tack up. So I've been pretty busy this afternoon.
Set both units out in the sun hoping that they would set up faster so I can trim before I quit for the day. But we have intermittent clouds so not sure if I have enough time. If not the Dremel will get a workout in the morning.

J
Latest blog entry: A2D Skyshark at 1/8th scale
Jun 21, 2019, 08:16 AM
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J Morgan's Avatar
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So PVA is water soluble. This morning I got a bucket of water and dropped the layups in it while I trimmed the surfaces I glassed yesterday.
Then when done, pulled them and the layups just popped right out of the molds.
I went a little crazy on the weight but they are stiff and shouldn't flap around in the wind. Each piece weighs 1 oz. But as Sparky says, weight on a model is like a bank account, it keeps adding up. The strut tunnel will be trimmed a bit shorter in front and then it needs that funky cap on it. The main wheel doors fit good, just a little sanding should provide the needed gap to operate. And yes, it will be split down the middle.
Tried it on the other side and all I have to do is add another 1/8" to the rear and it will work for it too.
One more layup and we're done. Then it's hinges and servos which are actually the whole PITA thing about gear doors.

J
Latest blog entry: A2D Skyshark at 1/8th scale
Jun 21, 2019, 01:32 PM
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CatManDu's Avatar
Neat work, J. outstanding craftsmanship.


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