Don't want to mess up a mold plug

Discussion in 'Fiberglass and Composite Boat Building' started by aaronhl, Oct 1, 2013.

  1. aaronhl
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    aaronhl Senior Member

    This is what it's going on to cover the engine:

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  2. SamSam
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    SamSam Senior Member

    That's quite a strange shape. As far as I can see, a one piece mold would work except for the area on the upper part where it is lighter colored.

    Yes, the part would be one piece. A two (or more) part mold bolts together, you lay up the part and then when it's cured you take the mold apart to release the part.

    Google this " two part fiberglass molds " and you will get a good idea on how it's done.

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  3. aaronhl
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    aaronhl Senior Member

    Maybe I should consider redesigning that area. Do you think if it was redesigned a one piece would work? I would love to do it in one piece after looking at some two piece mold youtube videos
     
  4. SamSam
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    SamSam Senior Member

    It looks like it has positive draft except in that one area, which is the vertical area that has the light colored filler on it. If that part is included in the mold, it will need to be two pieces. It will still be a sort of difficult part to laminate as you won't be able to see or get at it very well.

    If you wrap the mold down onto that base that it's built on, that has to have positive draft also.

    It's hard to tell from the photos so you'll have to imagine how the mold will pull off the plug and figure out if it will.
     
  5. aaronhl
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    aaronhl Senior Member

    I am going to redesign that area and post pictures. I've been trying to imagine the removal for a while now.

    For the base- Are you saying the bottom should be the widest part and taper narrower to the top?

    I think the mold will flex a little bit. The part I need to make will be stiff but very flexible (couple fiberglass layers), so I don't plan on making the mold too thick
     
  6. SamSam
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    SamSam Senior Member

    No matter how flimsy you make the part, the mold has to be stiff enough to hold the shape you want. But they can flex a little.

    I imagine the mold and plug/part coming apart by the mold going forward and the p/p going aft, so the draft I was talking about on the base plate was in that direction, not bottom to top.

    Sometimes parts can be rotated out of a mold and can then tolerate some negative draft, but probably not on your project.
     
  7. SukiSolo
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    SukiSolo Senior Member

    Thanks SamSam for confirming my suspicions about the shape and a one piece mould!.

    My experience in making moulds and making carbon fibre acoustic guitar backs in 1mm cloth confirm that you can get away with a local 0° draft area, as long as the rest of the mould has 2° draft taper. I use 0° for the neck area. Also the deeper the draw the more problems you will have on release, hence my suggestion of a small hole at the bottom to get air/water in to blow or float it off.

    I think I can see how to split it but you will need to work out what is best for you. On my moulds I have tended to use gelcoat, tissue, CSM until plenty stiff and even then often glassed a small frame on to stiffen it locally. For your splitting purposes the 'frame' part can be a flange that you use to join to the other part of the mould. If you have no undercuts it should come out.

    I've made quite a few other moulds too and these have been both one and two piece and other silicone and vinyl ones for solid cast objects.
     
  8. aaronhl
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    aaronhl Senior Member

    Great info once again. I am going to work on the plug in a little bit and will report back!
     
  9. aaronhl
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    aaronhl Senior Member

    Here is an update on the design change. The more I sand and stare at the piece I understand mold draft and can picture the mold coming off. I feel confident the mold will come off easily and my next plug will be even better now knowing what mold draft is. Let me know what you think?? Still have a lot of sanding to do in the crevasses

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  10. SamSam
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    SamSam Senior Member

    Yes, that's looking kosher. As long as you understand draft is what counts as it is hard to tell exactly from pictures.

    Is the paint you're using some kind of easy sand, hi build primer?

    If your plug is made from styrofoam, polyester resin will want to dissolve it, so, what is it made of ?
     
  11. aaronhl
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    aaronhl Senior Member

    Yes the plug is foam insulation, the big sheets of 2" thick by 8 foot long from Home Depot- then there is a coat of body filler over it. I used a spray paint can of wet sandable car primer.

    I plan on using gelcoat then epoxy and fiberglass to make the mold
     
  12. lohring
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    lohring Junior Member

    Lots of information here. Epoxy is more expensive, of course, but I found it easier to work with than polyester. You might consider making your cowl so the bottom of the carb cover is in the hull. That's how some similar gas rigger cowls are made.

    Lohring Miller
     

    Attached Files:

    Last edited: Nov 7, 2013
  13. aaronhl
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    aaronhl Senior Member

    Nice link and info, small world I see you on the boat dock too...

    I am changing the design again so will post back soon
     
  14. aaronhl
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    aaronhl Senior Member

    OK Finally have a big update, took a while to get the right draft shape and wetsand. Used automotive wet sandable primer and SC Johnson paste wax for release. You can see some of the bondo and paint broke off the plug, but it was really easy to remove- all I had to do with hit it a few times with the hammer.

    Only used one layer of tooling gel. On second thought should have used 2. Not too bad for the first time using tooling gel. Will have to patch the big chip in the middle with gel and wax paper. And then continue 1500 wet sanding...

    I'd make my next mold a lot differently. I need a foam that is easier to work with. And then coat it a few times with epoxy. I don't want to use the automotive primer or body filler. Seems like the surface isn't too durable..

    I have learned a lot from the help of everyone on the board. It's actually very easy to make a mold, just a little time consuming..Looking forward to starting the next project since understanding MOLD DRAFT is very important for a successful mold

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  15. SamSam
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    SamSam Senior Member

    That looks pretty good.

    It's not a good idea to be hitting the mold with a hammer as the gelcoat is brittle, especially tooling gel. You should pry the mold off, they have plastic wedges and things for doing it, or you can use things you have. Wooden wedges or door shims work.

    You might have had trouble with sticking because of the dull finish on the plug. Using epoxy might have had something to do with sticking also, since it is more adhesive than polyester.

    You shouldn't have to do much with a new mold besides a light buffing or polishing with no sanding at all. Yours looks to need a little more than that, though. The same way parts come out and don't need buffing or polishing, is the same with a mold off of a plug. I never used much besides auto paint products- bondo, hi build primer, sprayed enamel. Multiple wax coats and PVA. The PVA is a good thing to use.

    It is much easier to work on a positive, convex object like the plug, and get that all shiny and swell looking, rather than a negative, concave one like the mold.

    Next time, you might try getting the foam to shape and then putting a layer or two of glass on it and then start with the bondo and primer and paint (or whatever). That gives a surface that is easier to work with compared to bare foam. But maybe that is what you did.

    You might take the mold to an auto paint supply place, like NAPA, and tell them what you want to do. They have buffing pads like this ($10) that go on a regular drill and they'll have liquid buffing and polishing compounds also.

    [​IMG]

    I think you did pretty good for a first time and I'm sure you learned a lot and got a little used to using the materials. Don't throw the plug away until you've gotten a few parts from the mold, sometimes things happen and you need the plug to make another mold.
     
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