Any tips on releasing a long mold from the plug?

Discussion in 'Fiberglass and Composite Boat Building' started by mrdebian, Nov 30, 2022.

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  1. mrdebian
    Joined: Apr 2021
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    mrdebian Junior Member

    Hi all,

    Do you have any tips on releasing a plug from the mold?
    It is a kayak mold, 5.3 meters long and 56 cm wide at is middle section; front and rear very narrow just to get an idea about its size.

    Usually is very easy to release the flanges and front/rear but more difficult in the middle sections. Any tips to help the release to avoid breaking the plug?

    What tools are you using for releasing relative large molds?

    Thanks
     
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    An air fitting helps. Introducing air pressure between the hull and mold will release it.
     
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  3. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    As long as air can't escape between the mold and the hull, it can be the solution. Sometimes water is used because it can be given a lot of pressure by simply putting a sufficiently high column of water (no need for an air compressor).
     
  4. rxcomposite
    Joined: Jan 2005
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    rxcomposite Senior Member

    A nylon plastic wedge about 2 1/2" x 6". Insert between the mold flange and plug. Tap lightly with a plastic mallet moving around the perimeter. Be patient. Usually you hear a crack indicating that particular area has released.

    If it won't, you will have to destroy the plug flange and hammer harder on the mold flange. Sometimes a slight persuasion with a rubber mallet on the mold itself helps. That is the last recourse.
     
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  5. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    Lots of slim hardwood wedges and patience.Sufficient draft on the plug is assumed.Don't try and release from one spot -keep moving around-and don't use rubber hammers.
     
  6. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    On any of my too difficult table releases, I used a combination of wedges and air. Once the wedges were in; I would shoot the air 120-150psi; wedge again, etc
     
  7. KD8NPB
    Joined: Mar 2018
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    Location: South Carolina

    KD8NPB Senior Member

    small wedges
     
  8. mrdebian
    Joined: Apr 2021
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    mrdebian Junior Member

    The problem with the wedges is that they can't follow the relatively vertical part of the hull after the flanges.
     
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  9. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    Are you quite certain there was good draft on the "relatively" vertical surfaces?If there was,a couple of millimetres of movement at the inboard edge of the flange will be enough to achieve separation.Occasionally,it may help to slide a thin batten along-not across-the flange to ensure that the whole surface is free because a flexible flange can lift along the outer edges when wedges are inserted.If you believe some amount of the surface has released and are willing to take a risk you can invert the whole job and very carefully drill a hole to apply the compressed air trick listed above and I would recommend a pressure of less than 5 bar initially.

    If,on the other hand,the draft was insufficient or there were grooves worn by poor fairing technique then things are altogether more serious.
     
  10. KD8NPB
    Joined: Mar 2018
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    KD8NPB Senior Member

    As the part slides vertically on the mold, the draft angle should allow the part to come free. The part should be able to be lifted off with no excess friction in less than 3mm of upward travel.

    the biggest problem most people experience is binding. They insert wedges asymmetrically, causing the part to bind and drag against the mold.

    for a kayak or canoe, we use 6 wedges and slowly insert them about 6mm at a time.

    the wedges we use are medium density plastic, 50mm wide by 150mm long, about 2mm at the edge and 20mm at the thickest.
     
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  11. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Even pressure all around, see if you can find a way to shoot air in on the vertical..custom fitting with a pitot tube?
     
  12. gonzo
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    gonzo Senior Member

    Some molds have an air fitting to connect an air hose to and help release the part.
     
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  13. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I wonder if @ondarvr would have any wisdom.

    Did it release yet?
     
  14. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    In desperate times, suspend the mold upside down, with a soft surface for the hull to drop onto. This gets gravity working for you.

    Drill small holes all over, through the mold, not deep enough to damage the Hull, but enough to let water in. You might have to use a fine grinding tool do the last few mm's and not damage the hull. This helps break any vacuum locks.
    Hot glue 2 metre 30mm diameter PVC pipe lengths vertically over the holes, to form watertight columns, and fill them all with water. Add detergent to the water, to help dissolve the waxy mold wax.

    You can even put a hose connector on a few, and connect a garden hose. You may need to reinforce the joint between the PVC and Mold for these high pressure points.

    Trying to force the hull out with wedges can be destructive on lightweight layups.
     
    Last edited: Dec 4, 2022
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  15. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    I agree that holes for the admission of water or air can help,but with the project inverted,I would drill through the plug.A dimple in the mould surface is less damaging than a hole right through.The other step that can be taken when things look serious is to attach sturdy cross beams to the framing and use blocks and wedges (or jacks) to apply a constant force while trying all the other techniques.

    What we haven't been told is the type of finish on the plug,the amount and type of release agent applied and the means by which the correct amount of draft was determined and then verified as being present.If things get really grim,which I hope doesn't happen,a decision has to be made about destroying the plug or destroying the mould.Either is likely to cause an amount of damage.I've only witnessed this once and it was when an unwise individual thought he had devised a fast way to apply a release agent to a plug,in spite of never proving the process.The plug came out of the mould in bucket fulls and it took a team of finishers seven weeks to make good the damage.I was really pleased not to have been involved in that one.
     
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