Advice for parting line in my first 2 piece mold

Discussion in 'Boatbuilding' started by 717innovations, Sep 13, 2013.

  1. 717innovations
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    717innovations Junior Member

    I am getting ready to make my first 2 piece mold with a parting line due to the draft angles it will require to be done this way to release it from the mold. I will post pics of the plug shortly it is for a sprint car hood.
    From what I have read I pretty much understand how to construct the parting line and lay up procedures. However just curious if anyone has any tips to help out.
    My parting line flange will be made of 1/8 alumnium with keys and cut to fit snug against the surface. After attached I will then fill the voids with clay unless anyone has any other reccomedations other than clay. After parting line is perfect I will wax then pva and build my mold as I normally would. After half is done remove the parting flange and do the other side.
    Am I on the right track? And does anyone have any other tips that are welcome and very much appreciated
    Thanks in advance
     
  2. SamSam
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    SamSam Senior Member

    That sounds OK.

    When you tool the clay, try and get the sharpest 90 degree corner you can. Any cove or fillet shape will be re-produced in the second half of the mold, leaving a knife edge which will chip and become ragged.

    After the tooling gelcoat, when glassing the mold, that corner needs glass in it. Some use a resin, milled fiber fillet. I always used mat with a sharp cut edge on the body of the mold and worked that edge up to the flange. Then the same on the flange working it up to the body. Then repeat. Lastly a few strands pulled from woven roving would be layed in that corner the length of the flange. That would leave it strongly reinforced with no air lines trapped or weak, resin rich lines. The rest of the mold laminations can then be applied in one piece, as the corner will be filled and filleted enough so the glass will easily lay in the corner.

    Don't forget to make some 'impressions' or a 'bumps' in the first mold flange so the second half will be keyed into it.

    Before you separate the mold from the plug, drill the holes for the bolts that will hold the two halves together. It's best if just the shank of a bolt is in the holes, it fits more snugly as compared to threads. Threads will also tend to enlarge the hole over time.

    Put a 3-4" flange around the outside if you ever plan on infusing or vacuum bagging.

    When molding, put a thicker layer of gelcoat along the mold parting line (if you use gelcoat). That will help prevent sanding and buffing through the gel when you clean up the line in the finished part.

    If you search for 'molds' or 'moldmaking' on the 'Fiberglass and Composite Boat Building' forum here, you will find a lot of information.
     
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  3. 717innovations
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    717innovations Junior Member

    Thankyou. Is clay my best choice for filling the voids or would I be better off using 100% silicone caulk?
     
  4. SamSam
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    SamSam Senior Member

    No, don't get silicone on the mold, it can cause big problems. Silicone causes problems with mold release agents and thence mold release. It will transfer to parts and then screw up painting etc.

    Clay can give the sharp corner you need plus you can get the extra off the plug, whereas with silicone caulk you just end up smearing it and spreading it thinner and thinner. There are also tooling waxes available that probably work better, but I never used them as they weren't easily or quickly available at the time. Modeling clay was available at the local toy store.
     
  5. wet feet
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    wet feet Senior Member

    Please post some pics.It will be much easier to make relevant suggestions.
     
  6. 717innovations
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    717innovations Junior Member

    Sorry it took so long for the pics. The first couple will show my orignal design I made the plug out of alumnium then molded. I then used and actuall part put of the mold and am currently making the changes I want. I have a little ways to go. However I know this will need a parting line to release and want to know what direction to go before I get there
    http://s944.photobucket.com/user/71...00000BA842FDE_zpsf0e17709.jpg.html?sort=3&o=7
    http://s944.photobucket.com/user/71...0000121843116_zps42781998.jpg.html?sort=3&o=1
    Making the changes
    http://s944.photobucket.com/user/71...0000125466FCB_zpse6f02087.jpg.html?sort=3&o=0
    http://s944.photobucket.com/user/71...00000C50CBCFC_zps57d1713a.jpg.html?sort=3&o=3
    http://s944.photobucket.com/user/71...00000BEC26343_zpsde5f9a1b.jpg.html?sort=3&o=5
    http://s944.photobucket.com/user/71...00000C25D9076_zps4247291a.jpg.html?sort=3&o=4
    My apologies the pics are in links it's the only way I could post them from my phone
    Thanks in advance
     
  7. SamSam
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    SamSam Senior Member

    I guess you know about "draft", rounded edges, sharp corners and all. With those louver shapes you might have some difficult areas to reach or get to when making parts. Sometimes you have to work 'blind' or with mirrors, but it's best to avoid that.
     
  8. 717innovations
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    717innovations Junior Member

    Yea I have thought of the blind areas. It seem the most difficult part will be spraying the gelcoat to get good coverage in the blind spots
     
  9. wet feet
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    wet feet Senior Member

    The simple answer is that the nature of the part would seem to alow splitting the mould on the centreline.The bad news is that there is no worse place to have a finishing project if there is any shrinkage or even a slight mismatch of the mould faces.I would look at locating the flange at the point where the top surface is tangential to the top of the corner radius and then from the centre of the new addition to the middle of the front edge.You would have an assymetric mould with no great challenge in the finishing.
    As has been mentioned,you will have quite a challenge trying to produce a void free laminate between the upper edge of the louvres and the top surface even if you do find a way to spray gel in there.
    What do you propose to do about flanges around the periphery of the mould?
     
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  10. 717innovations
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    717innovations Junior Member

    Due to how big the part is and being able to get inside from the front and back I think laying the glass won't cause too much of a problem. I worrie more about getting gel on it. So your suggesting I build the flange in the middle of the radius on the upper part? Once I finish the shaping I will add a flange around the plug before I mold this is mainly for support not for bagging because these parts are a simple 1.5oz mat and 6oz cloth in the weak areas. On a positive note most send their parts off to get painted so even tho the finish time will take away from the profit I can always offer them in primer. Thanks for the replys
     
  11. wet feet
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    wet feet Senior Member

    Not in the middle of the radius,at the edge of the radius where it is tangential to the top surface.Then at the nose of the new piece I would go along the centre.
     
  12. 717innovations
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    717innovations Junior Member

    Thankyou. I will be working at getting the plug finished and ready for the parting line. I will post up pics as I go along.
     
  13. 717innovations
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    717innovations Junior Member

    The plug is just about finished. I will be building the parting line this week also
    [​IMG]
     
  14. 717innovations
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    717innovations Junior Member

    I did some playing around and got a parting line cut and fit out of plexiglass. I also ran a strip of clay and set it in it too see how things would go with trimming the excess and what finish I would have. I'm very satisfied with the results of my first time. I plan to take it down and pull the clay off and do it again taking my time making it 100%. My last question I hope is should I wax the entire plug before putting the parting line on? Or should I put the parting line on and wax up too it? I fear the wax will not allow the clay to stick to the surface as well as it is now giving a sturdy Flange. I do intend on building supports on the back side of the flange as well once it is up
     

  15. SamSam
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    SamSam Senior Member

    I would wax it all and then install the parting form. The clay gets mashed in between the plexiglass and the mold and doesn't really have to stick much. It should kind of stick anyways and being waxed will help you clean it up before laminating the second half of the mold. Do a test and see if it will work on a waxed surface.

    You have to support the flange somehow, with tape, big blobs of clay, or you can screw in supports and then patch before doing the second half. You can screw pieces of wood or brackets to the plexiglass and then tape that to the plug with a bunch of that blue painters tape that won't damage the plug. The clay just fills the gap. Once it's installed and the clay mashed in and tooled off to get a sharp 90 degree corner, then you have to wax the whole mold and the flange and clay too, a number of times. I would use pva also.
     
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