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  • He Who Shall Not Be Named
    replied
    Originally posted by Davidh
    Hi David,

    As well as elaborating further on why you don't use latex I was wondering if you could also elaborate some further details on the BJB TC-5040 silicon that you use. My nearest supplier of all things composite is an hours drive and there's not much variety. I have looked over the MSDS for 5040 and was thinking that if I could not get that brand which I don't think I can at least what specification should I be looking at? I noticed on the MSDS that the viscosity was 65,ooo whatever that is. Should I be looking for a certain value or number that would indicate that the tin I was looking at on the shelf would contain silicon that would do a similar job.
    What specs should I look for?

    Thanks
    David h

    Why yes. Yes I can. Latex BAD. Silicon GOOD.

    My every post need not exceed the length of War and Peace.

    A mother-mold backed rubber tool eliminates the concern on how 'hard' the glove-mold is.

    Either take my advice (and it's advice, not a pronouncement from God), or don't.

    M

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  • Davidh
    replied
    Should I look at the shore hardness?

    Dave.

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  • Davidh
    replied
    Hi David,

    As well as elaborating further on why you don't use latex I was wondering if you could also elaborate some further details on the BJB TC-5040 silicon that you use. My nearest supplier of all things composite is an hours drive and there's not much variety. I have looked over the MSDS for 5040 and was thinking that if I could not get that brand which I don't think I can at least what specification should I be looking at? I noticed on the MSDS that the viscosity was 65,ooo whatever that is. Should I be looking for a certain value or number that would indicate that the tin I was looking at on the shelf would contain silicon that would do a similar job.
    What specs should I look for?

    Thanks
    David h

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  • Davidh
    replied
    Thankyou David,

    Can you elaborate?

    Dave h

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  • He Who Shall Not Be Named
    replied
    Latex bad. Silicon good.

    M

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  • Davidh
    replied
    Hello all.

    I was hoping to have some feedback on the questions that I posed about latex. Maybe I've scared HWSNBN off my threads. I haven't been berated about using Timber for my mike project yet either so Either David is too busy or ill or I don't know what else...

    As can be seen from the previous pictures I'm pretty chuffed about the way in which these clear mould pieces for my Gotland class came out of the moulds. This silicon stuff is the bomb. The sprue and vent system has worked well for me and these are only initial pieces. I have taken to filling up the cavity and then using a paper clip inserted down into the sprue and stirred a little just to stir up any bubbles.

    Moving along and intrigued by the glove and hardback set up for flexible moulds of larger pieces that require layup I have decided that I will utilise the big tub of latex I bought a couple of months ago when what I really wanted was silicon but was rather annoyed at the cost. I bought the latex anyway and eventually coughed up for the silicon. Silicon is great but I may as well give the latex a go..

    David mentioned the TC -5040 silicon. I have been looking up Australian suppliers to try and find it or something like it , There is little on offer here. Most suppliers have maybe one or two silicons and I'll simply have to look around further for a wall clinging one.

    So I pulled out the sail master of the Resolution class that I have just completed earlier this year. I would like to make and sell a couple of hulls of this boat. (don't laugh). A complete set of tooling for just one boat is a huge task. I've completed most of the tooling already in the form of the silicon moulds for appendages and surfaces. However the sail being a layup I didn't want to use a huge amount of silicon if I could avoid it hence latex.

    I have cleaned up the sail of the Resolution. Re-etched the plates and cleaned up some of the detail. Scribing and etching has never been a strong point for me. The first photos show an adequate effort.
    With latex you can only put down thin layers at a time one after the other after the previous has dried. You need about 20 layers. The next picture looks like I coughed up half a lung. but this is the dried latex. Comes out white and looks like phlegm when hard!
    I was concerned because half way through the lay up at around layer 10 I noticed that around the edges where the master meets the moulding board the latex was separating. Pressing down around the edge of the mould the latex would pop back up, surely not good
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ID:	108977 . Is this common? I was wondering if my use of a heat gun may have caused the drying layers to contract or pull and thus separate the latex from around the edges of the master and board. Any illumination on this? Is this a common problem. I could just see this playing havoc with the overall accuracy of the finished glove.

    The next photo shows my response to how to fix this. Once 20 layers are on I then laid up a GRP hardback. Polyester resin and cloth. I then clamped down 3 small strips of wood around the edges of the master to clamp down the latex. It also helped pull down the GRP cloth , two birds..... Once the hardback had dried I pulled the whole assembly off and was pleased to see that the fidelity in the latex was fantastic. Every little detail was there. However I am concerned that when I lay up my first GRP piece that the flexibility in the latex is going to cause problems. Even with the hardback in place does it really support accurately the shape of the glove mould?

    I would really appreciate some answers / suggestions to these questions.

    David H

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  • Davidh
    replied
    Thankyou Trout for the advice.

    Every time I have made another mould I have tries to do something differently. After the first half baked attempt I then increased the number of vent holes around near the top of the mould. Doing them either side of the metal shaft insert. I found that pouring the resin into the mould requires a fair amount of steadiness that I'm guessing could be assisted by moulding a funnel shaped entrance to the sprue. I have moulded a funnel shaped section into my latest mould design to see if this would help.

    As you can see the mould set up features aluminium tubes. These create the mould for the sprue. The black lines are the intended vents that will be cut into one side once both moulds have been made, just making sure they are not going to go through a register bump. To create funnel I simply placed some modelling clay around the end of the tube where it meets the wall. after the first attempt made with grey pigmented polyester resin I decided to use a clear resin. I wanted to be able to see the air bubbles and where they form but also I have a theory that may or may not be bedded in truth, that pigment slows down curing. As you can see form the third photo of the clear pieces still in the mould, this is the best attempt so far. There were virtually no air bubbles. There was a fair amount of resin loss along the joint of the two moulds in the form of flashing but so what. You loose some in the sprue. you can see the funnel shape at the top of the sprue. The funnel idea does make it easier to pour and the attribute the zero bubble to increased air ventage.

    More later.

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  • trout
    replied
    David,
    Your write up is like gold. With this new system, can we post in the style like you did with the rubber glove over the mold?
    Davidh, Yes practice helps. Yes you are on the right track on cutting a vent. I like having vents, but look closely at David's pictures he also uses a short sprue that leads nowhere and its sole purpose is to give the trapped air a place to go. I think you are doing great!
    Last edited by trout; 07-05-2015, 01:42 PM.

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  • Davidh
    replied
    So I have made a couple of silicon moulds as I wish to produce some planes and components for HMS Resolution that I have just built. This thread has been very interesting and useful.
    I have been a little fastidious with the tooling production. I like to make a box out of MDF and have the moulds created with a flat surface, using minimal clay around edges.
    As you can see from these pics it has been a learning curve. The initial mould is for the vertical rudders top and bottom of the Resolution. These are the largest silicon moulds I have made to date and the layer of silicon is possibly a bit thin? I have not poured resin into these yet. Since then I have made silicon mould parts, thicker. I don't know what the optimum thickness is yet. Maybe David or others can guide on this. But as mentioned earlier at $65 a litre these mould are a little pricey, but I can see the tremendous advantages in them.

    Most of my moulds so far have been of parts where the top edge of the part is exposed at the top of the mould. This allows a large area to pour the resin and allow air to escape. However the last series of photos show my first attempt at producing a sprue and air vent type mould design. I made the two parts of the mould using an aluminium tube as the sprue and simply cut a small air channel after the two parts were made.

    Being my first attempt at producing parts using this method went a little pear shaped however I can really see the potential. The last photo shows the messy result of the sprue and air vent set up. The mould tried really hard. There is an air pocket at the top of one of the pieces, I'm guessing I should cut another air channel at the top? I know that with practice the art will get better and pieces will start looking the business. It's just a time thing however any advice would be appreciated.

    Dave h

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  • Davidh
    replied
    Thankyou David,

    fantastic write up, when you get the chance I would love to see photos of the surface of the inner glass layup over the silicon. Do you get air bubbles forming underneath the glass resin if there's lots of dried silicon dribble of does a thick gel coat deal with that?

    I am very interested in the rubber glove/hard mother mould arrangement. Chasing down the precise silicon that would be ideal for not running down the side of a hull is a bit tricky here, not a lot of choice at the supplier. However I do have a big bottle of latex. I assume this would work just as well ,just lots of layers?

    thanks,

    dave h

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  • He Who Shall Not Be Named
    replied
    Originally posted by bwi 971
    I found the time to sit back and enjoy reading this topic......again many lessons learned and plenty stuff to put in practice.

    grtz,
    Bart
    Thanks, Bart. Just passing on what others taught me. You all have an obligation to do the same.

    Keep the ball rolling, guys. This Craft ain't dead .... yet!

    M

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  • bwi 971
    replied
    I found the time to sit back and enjoy reading this topic......again many lessons learned and plenty stuff to put in practice.

    grtz,
    Bart

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  • He Who Shall Not Be Named
    replied
    My pleasure, sir.

    M

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  • Davidh
    replied
    Hi David

    Thankyou for this incredibly detailed write up. I am currently in Canberra showing my kids the war memorial. It is a very extensive museum and took some good photos of the japanese midget submarine that attacked Sydney harbour. I also have some nice pics of a beautiful little model of AE1 Australia's first submarine. So I haven't had to time to read the write up but should in the next couple of days when i get back to the coast.

    David h

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  • He Who Shall Not Be Named
    replied
    MOTHER MOLD-GLOVE MOLD AND HULL LAY-UP

    Hard shell tools suffer from an inability to flex significantly. Therefore the hard shell tool looses utility when the job is to produce GRP parts possessing high relief surface detail (rivets, raised and engraved panel lines, high relief clinker strips and plate, weld beads, and other such surface depressions or projections) and/or significant draft. Unless provision is made to break down the hard shell tool into many sections, to reduce relative draft between tool and GRP part, the hard shell type tool is only suitable for producing hull and other parts that are as simple and smooth as a babies bottom. Attempting to capture high detail and deep draft forms with a hard shell tool usually results in tool damage after only a few lay-up cycles as the parts break away the high-draft, narrow tool projections.

    The cure to the problem presented by richly detailed hull and sail masters -- to capture them in the tool and have the tool survive production -- is to employ a rubber tool element to give form to the GRP part, and to contain the rubber tool within a strongback or GRP tool element to give rigidity to the assembly the rubber alone cannot provide. This hybrid is said to be made up of the mother-mold (the strongback) and glove-mold (rubber). The mother mold-glove mold tool not only captures the smallest detail of the master, but can even handle negative draft relief -- there is nearly no limit to the complexity of geometry a mother-glove mold can handle and to do so without damage to tool or deformation of GRP part.

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    After securing permission from the British guy (sorry, I can't find your name) who produced a small resin kit of the STINGRAY I went on to produce tooling from which I could render thin walled GRP parts for an r/c version of the model. I made this mother-glove tool for the models hull to accomplish the task. Pictured here is one-half of the two piece tool. The brown mother-mold is a GRP construct and holds the semi-clear glove-mold element. During part layup the assembled combination presents a rigid cavity that is prepared and used like a hard-shell GRP tool.

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    But, unlike the hard-shell GRP tool, the flexible glove of the assembly pops out of the mother-mold when the completed GRP hull piece is yanked out. It is then a simple task to 'peel' the glove-mold away from the model part as you see here.

    Since the mother-mold was laid up over the glove-mold the two register perfectly. So, after peeling the glove off the model part, it's an easy matter to re-insert the glove-mold back into the mother-mold with perfect registration between the two, and everything ready for another GRP hull fabrication cycle.

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    Caswell-Merriman produces a 1/96 Type-212 GRP hull kit. The masters of which were roughed out by Steve Neill, super-detailed by Brian Starks, and that master used by me to make production tooling. Here are pictures of a completed kit.

    The exceptionally well done engraving Brian did on the master literally screamed out for use of the hybrid mother-glove type tooling. The keel, bilge-keels (actually sonar array projections), and very deep engraved lines would never work in a simple, two-piece hard-shell tool. In rubber? No sweat.

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    If your hull master is not split; if it's the entire unit, you need to 'hide' half of the hull within a mold-board constructed for the task, like what I've done here with the Type-212 master. Rose is holding one of the securing screws that runs up through holes in the mold board base and up into the hull to hold the model down on the mold board assembly.

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    The rubber glove-mold tool that will be poured over the half-model (capturing in negative the shape of the model) and mold board (that produces the flange running equatorially around the cavity) must not leak through any gaps between the two. You want as tight an interface between the two as possible; a no-leak transition between mold board and master. This is done by filling any gaps between mold board and master with modeling clay.

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    In this condition the master and mold board can either be used to give form to a hard-shell GRP tool, or a rubber tool. Which type tool you fabricate depends on the detailing and draft of the master. The Type-212 master demanded creation of the mother-glove type tool.

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    Building up the RTV silicon rubber tool that forms the glove-mold over the master is done with a special 'brushable' material. BJB's TC-5040 is what I use. You first pour it on and work it with a spatula (or old credit-card) to cover the entire model. What's magic about this form of silicon rubber is that it tends to stick to vertical surfaces without running down. It takes 3-5 layers of rubber to get the required nominal wall thickness.

    (sorry, didn't have a shot of this process as I worked up the 1/96 Type-212 tooling)

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    The glove-mold built up, its flange (those portions where the rubber adhered to the face of the mold-board) is cut back to be just a bit wider than the wall thickness of the rubber covering the master.

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    The rubber and mold board are waxed and the hard-shell tooling material is build up over both. This can be GRP or a specialty hard-shell material like the Freeman Repro two-part polyurethane resin. Note that I left plenty of 'runs' in the glove-mold rubber -- these key with the mother-mold, insuring that re-assembly of the two will occur with perfect registration.

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    Since I'm going to make hundreds of GRP parts off this tooling, I want it to sit in the shed season-after-season and not warp on me. So, I egg-crate the mother-mold to keep things in shape. Note that I use the same mother-mold forming material (which is glass shard re-enforced) to hold the wooden elements of the egg-crate brace together.

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    Once the egg-crate brace is permanently bonded to the back-side of the mother-mold the entire unit is inverted and the three screws securing the master to the mold board are removed and the mold board carefully pulled away from the hull master, glove-mold, and mother-mold with bonded egg-crate -- what you see in this photo. It's then an easy matter to pull the master and rubber glove-mold away from the mother-mold, and to strip off the glove-mold and put that master, and it's purpose build mold board, into safe storage. The glove is made up to the mother mold, part-release applied and GRP part production begins.

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    And GRP hull production begins -- the hull part glass lay-up process the same as that done for hard-shell GRP tools.

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    The virtue of the mother-glove tool becomes apparent when it comes time to separate the GRP part from the tooling: All the undercuts and deep draft items (those flank bilge keel looking things, for example) would have locked the GRP part forever within a hard-shell type tool. However, with the hybrid, you pop out the part still attached to the rubber glove-mold. Then, without the stiff backing of the mother-mold supporting and giving rigidity to the rubber glove-mold, it's an easy task to strip off, like a glove, the rubber mold from the GRP part.
    The rubber element is put back into the stiff element and another GRP hull production cycle can begin.

    M

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