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Thread: help needed


  1. #1

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    help needed

    Hello,
    I know this subject been beat to deat but there are so many different opinions out there I tought someone might give me some help.
    I am in the process of making an fiberglass cawl for my patern plane. I have made a 2 part plug painted and ready. I also have a parting board with smooth surface. but i am little lost on the next step
    what wax/PVA should I use on the plug.
    what is the first step to making a mold/what is the first layer of material used.
    Then i build it up with some thick glass.
    please help.
    thank you

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    RE: help needed

    ALmost any paste wax will work if you have finished the plug to a really smooth, painted finish. Apply several very thin coats of paste wax, buffing it out in between coats of wax.
    I have used PVA (polyvinyl alcohol) after the wax, but I consider it optional. If the wax is done right you don't need the PVA.
    Use a light fiberglass for the first layer of the mold - e.g. 2 oz per square yard. then whatever thickness to build up some rigidity. I use several layers of 6 oz cloth.
    If you have a two part plug, I don't think you will need a parting board. Parting board is mostly used when you need to make a two part mold from a one part plug.

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    RE: help needed

    In my opinion the use of PVA isdependenton the paint. Wax provides slip but is unable to block reactivity. If your paint is chemically reactive with your resin, it will stick with just wax. PVA is able to block this reactivity. Unless you do some testing with your paint and the resin you can't know the outcome. The safest bet is to use PVA. It's best to use a wax that is designed to work with PVA. Nearly any wax will work, but some can cause the PVA to fish-eye on the surface (can be worked around by using light coats). Part-all Paste #2 and Part-all Film #10 play nice together. If you want to retain the finish of your plug you can use a semi-permanent like Frekote. The downside to Frekote is that you need to use a 2 part catalyzed paint on the plug. The solvents in the Frekote will etch single component paints and cause a stick-up.
    I would start the molding process by brushing on a surface coat. It can be made by adding 30% West Systems 404 and 7% graphite powder by weight to a batch of laminating resin. The purpose of the surface coat is to insure, if properly applied, that the mold surface will be void free. The graphite powder will make the surface black and increase it's slip. Once the surface coat tacks up (tacky to the touch but won't transfer to your glove) I start by adding 3 pieces of resin saturated 12K carbon tow to the corners. This creates a fillet to strengthen the corners and help prevent the fabric from bridging the corner. I usually start laminating with 2 layers of 1 ounce, then a few layers of 2 ounce, then a few layer of tight weave (56x56) 4 ounce, then some 6 oz. You want to alter the orientation of your layers to maximize the stability of the mold. If the fabric all runs the same direction the mold will be more prone to warping. The thickness of the layup is really dependent on it's size and the part processing. Molds that have large opening like a cowl mold need some good thickness to hold their shape. I consider a 60 ounce lay-up to be the minimum.

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    RE: help needed

    thank you for all your help.
    Ordered some griphite powder for the first coat.
    I have several more questions.
    What kind of PVA will work if I use it.
    Will fiberglass resin (home depot) kind work for the moldmaking or only epoxy(West systems), I konw the resin gets hot and may damage the plug?
    Will the first coat run or will it stay put.
    Thank you again

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    RE: help needed

    The graphite powder alone will make a pretty runny consistency. The concoction I posted in my first post (#3) will not run. You need to brush it on paying special attention to tight corners.

    Here is a little video that I did a few years ago on making and applying a surface with epoxy: Surface Coat. In the video I used a black pigment instead of graphite powder.

    Part-all Film #10 (PVA) works well with Part-all Paste #2 (wax).

    Polyester resin (fiberglass resin) generates more heat while curing than epoxy. On thick layups you often have to go in stages to reduce the total mass that is curing. Large masses generate more heat than small ones. Going in layers can help. Laminating epoxy cures slower and generates less potential heat. Typically you can do the whole layup with epoxy in one go.

    Epoxy will make a more stable mold than polyester resin. Personally, I only build my molds from epoxy. Epoxy also has a much lower oder level, contains no VOCs, shrinks less, and creates mold edges that are less brittle.

    I build a lot of my production molds fromUSC 635 Epoxyand the medium hardener.

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    RE: help needed

    thank you wyowindworks
    cool video very informative, do you have any other links to videos.
    I have lots of microbaloons, will that be ok to use instead of the 404 or should I order the 404.
    thank you again I always wanted to know how it was done and now I am getting better idea.

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    RE: help needed


    ORIGINAL: haikt

    thank you wyowindworks
    cool video very informative, do you have any other links to videos.
    I have lots of microbaloons, will that be ok to use instead of the 404 or should I order the 404.
    thank you again I always wanted to know how it was done and now I am getting better idea.
    Microballons have a lower compression strength than the WS 404. I've tried a lot of fillers and have settled on WS 404. Another filler that works is pure Portland cement...no aggregate.

    You can access my other videos on the right hand side of the page that I previously link to. You can click the little "see all".

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    RE: help needed

    I watched your builds on rcgroups very cool items.
    I have a cnc cutter at home so if you need anything cut let me know.
    I have couple more questions before I go into making the mold.
    1. when you paint the tooling coat and wait until tacky i assume you mix new batch for the next coats or heating the epoxy make it setup faster maybe?
    2.when you say spray flowing coat of PVA what is this mean and how many coats do you spray.
    thank you

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    RE: help needed


    ORIGINAL: haikt

    I watched your builds on rcgroups very cool items.
    I have a cnc cutter at home so if you need anything cut let me know.
    I have couple more questions before I go into making the mold.
    1. when you paint the tooling coat and wait until tacky i assume you mix new batch for the next coats or heating the epoxy make it setup faster maybe?
    2.when you say spray flowing coat of PVA what is this mean and how many coats do you spray.
    thank you
    Each coat of surface coat is a new batch. I often use a fast hardener for the surface coats.

    A flowing coat of PVA is one in which all the atomized droplets come together and form a smooth, flat, glossy finish. When a flowing coat first gets sprayed on it will look milky. As it sits, the little air bubbles will escape and it will look clear. Typically an airbrush does a pour job of spraying a nice smooth finish because the nozzle is too small to let enough product out of the gun. I like to spray with a 1.4 mm tip.



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    RE: help needed


    ORIGINAL: wyowindworks
    Each coat of surface coat is a new batch. *I often use a fast hardener for the surface coats.

    A flowing coat of PVA is one in which all the atomized droplets come together and form a smooth, flat, glossy finish. *When a flowing coat first gets sprayed on it will look milky. *As it sits, the little air bubbles will escape and it will look clear. *Typically an airbrush does a pour job of spraying a nice smooth finish because the nozzle is too small to let enough product out of the gun. *I like to spray with a 1.4 mm tip.


    The website said that the USC 635 thin with medium hardener blushes. How much of a problem is that with that particular system? Have you laminated parts using the same epoxy system?

    How hard and strong does the USC epoxy cure? Any relative comparison with West Systems or Pro Set? Also with JGreer epoxy?

    Thanks

    Regards,
    MattK
    (Rcmaster199@aol.com)

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    RE: help needed

    ORIGINAL: MTK

    The website said that the USC 635 thin with medium hardener blushes. How much of a problem is that with that particular system? Have you laminated parts using the same epoxy system?

    How hard and strong does the USC epoxy cure? Any relative comparison with West Systems or Pro Set? Also with JGreer epoxy?
    Blushing is only a problem if the surface is directly exposes to air (carbon dioxide & moisture). If the part is made in a mold the exterior surface isn't exposed to the atomosphere. If the part is fabricated using some kind of assistance (vacuum bag, bladder, press) then the inside won't blush either. When making a mold, the only surface that is exposed to carbon dioxide and humidity is the back of the mold. If you're doing laminating over open structures then the blushing could be an issue if your environement very humid.

    I haven't used West Systems for the last 10 years and have never used JGreer so I can't comment on those. I don't use WS because of it's rather low HDT (Head Deflections Temp) and Tg (Glass Transition Temp). The HDT of USC 635 is better than WS but isn't quite as good as Proset. When is comes to the physical properties, USC is very good compared to other budget resins. I use MGS for all my part fabrication which is a very premium resin that is suitable for full sized aircraft construction. Here is a link of my comparison of US Composites, Resin Research, MAS against MGS: Epoxy Comparison. You can jump to this page for the final room temp cure after 7 days. HERE are the results after a 125*F post-cure (done after the 7 day room temp cure). The downside to USC is that it's a little more difficult to use than some premium resins due to its higher viscosity.




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    RE: help needed

    if mixed with acetone to reduce viscosity do you know if it will dissolve the pva and wax layers?

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    RE: help needed


    ORIGINAL: haikt

    if mixed with acetone to reduce viscosity do you know if it will dissolve the pva and wax layers?
    You shouldn't mix in any solvents when creating composite structures. The solvent ends up acting like a flexiblizer. It creates space between the polymers and inhibits cross linking. The end result is a decrease in strength, hardness, and HDT. Adding 5% solvent can reduce the strength by 40%. See this link as an example. Adding solvent to a resin also increases the shrinkage. Shrinkage reduces the stability and surface finish of the composite.


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    RE: help needed

    thank you for the list, some cool info and looks like you got this stuff down to science.
    what filler do you use for painted surfaces, i used bondo on Rastolium pain after 2 day cure and it ate a hole in all layers of the pain, primer and all.[&o]

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    RE: help needed


    ORIGINAL: haikt
    what filler do you use for painted surfaces, i used bondo on Rastolium pain after 2 day cure and it ate a hole in all layers of the pain, primer and all.[&o]
    Are you refering to the filler used to seal the plug in a parting board?


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    RE: help needed

    no pin holes ans such.

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    RE: help needed


    ORIGINAL: haikt

    no pin holes ans such.
    I do all my filling while doing the primer. I do major work with bondo before priming/painting. If I know there is going to be a lot of pin holes I mix microspheres with my primer to make a filler. I shoot a light coat of primer on the plug to reveal any pinholes. Then I'll fill them with the home made filler with my finger in a glove while the primer is wet. Then I'll shoot another coat and look again for pinholes and blems. If filling is required I'll fill them right away. I then usually give it one more coat of primer. The final surface will not very smooth due to the filling. I'll then stick the plug in a low temp oven to do an accelerated cure of the catalyzed primer. I can usually sand within 1 hour. I'll then sand everything smooth and shoot it with one last coat of primer (before the primer cures in the gun). I can usually go ahead and paint in another 1 or 2 hours.

    Bondo can wreak havoc on event 2 component paints. Back in my rattle can days I used to use DAP light weight filler (like wall patch) for doing quick work.


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    RE: help needed

    here are some pics of my plugs and the plane that they are for.
    I am ok with the wood but when it comes to paint and glass work i get stuck.
    Been sending all evening, there is one spot on the plug that paint does not cure so i had to get it off again and sprayed a light coat
    it has been cold here so i dont know if that may have something to do with it
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  19. #19

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    RE: help needed

    one more in paint
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    RE: help needed

    i got the molds done and got some parts done I will post some pictures soon,
    the tooling layer came out great and the whole thing is good only I had little issue with releasing the plugs. damaged the plugs to get them out.
    how do you wax and pva the plug?
    I put on 3-4 layers of wax ( one min dry time and buff on each layer)
    after 4 coats i let dry for 30 min and spray pva. Let the pva dry for 1 hour and start layup

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    RE: help needed


    ORIGINAL: haikt

    i got the molds done and got some parts done I will post some pictures soon,
    the tooling layer came out great and the whole thing is good only I had little issue with releasing the plugs. damaged the plugs to get them out.
    how do you wax and pva the plug?
    I put on 3-4 layers of wax ( one min dry time and buff on each layer)
    after 4 coats i let dry for 30 min and spray pva. Let the pva dry for 1 hour and start layup
    Depends on the wax. PartAll will separate easily after 4 coats.

    Other mold release waxes need more build up
    Regards,
    MattK
    (Rcmaster199@aol.com)

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    RE: help needed

    i am using partall #2

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    RE: help needed

    There are several things that can cause stickups when making molds:
    There are several things that can cause plugs to stick in molds:

    1) The surface of the plug is rough. This creates friction, binding and in the worst case a mechanical bond. Orange peel can make plugs with vertical surfaces (to the parting plane) difficult to remove even if the paint is very glossy. Not only should the surface of the plug be glossy but it should also be very flat/smooth.

    2) The heat generated by the curing mold exceeds the operating temperature of the release system. If the temps of a curing mold exceed 125*F you can have problems with many waxes unless they are high temp waxes.

    3) The geometry of the plug can causes it to get locked into the mold. Larger vertical (to the parting plane) surfaces can cause the plug to have to be extracted at very precise angles. The parts/plug coming out of the mold in the pictures below have to come straight out. The part cannot be tipped out in any fashion. I use two levers against blocks to slide the part straight out.

    4) The surface of the plug is reactive with the resin. WAX IS UNABLE TO BLOCK REACTIVITY. You can put 1,000 coats on and still get a stickup if the surface is reactive. PVA, in combination with wax, will block reactivity IF THE COVERAGE IS ADEQUATE. If the PVA goes on too thin/sparse you can have issues. The PVA coat should completely cover the surface with one continuous film.

    5) The release system softens the plug surfacing agent. Some waxes and release systems can soften some paints.

    6) The paint on the plug is not allowed to adequately cure.

    I typically use 4 to 6 applications of Part-all Paste #2 followed by PVA. On molds that will produce painted in the mold (PITM - see photo below) parts I use Frekote FMS sealer and Frekote 770-nc release to make the mold.

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