Direct female molding

Discussion in 'Fiberglass and Composite Boat Building' started by groper, Feb 3, 2012.

  1. CatBuilder

    CatBuilder Previous Member

    Groper, you can do that easily by skipping the melamine and just thermoforming the foam around the bilge curve and screwing it right to the longitudinal battens.

    Alternatively, for really tight curves, make very long planks of foam (6 meters?) to run fore and aft in a tight curve - strip planking.

    These two techniques are all I used on my entire boat. Here are some pictures...

    1) Thermoforming the foam onto a tight bilge radius by directly screwing into place with temporary holders seen on foam

    2) End result of thermoforming - how fair is that? Also, off the the right in this picture, see the strip planking in the very tight radius from hull to deck.

    3) Strip planking the very tight hull/deck radius curve

    BTW: This is 25mm 100KG foam. Really stiff Core Cell. That thin foam you are using should be very easy to bend comparatively.
     

    Attached Files:

  2. groper
    Joined: Jun 2011
    Posts: 2,483
    Likes: 144, Points: 73, Legacy Rep: 693
    Location: australia

    groper Senior Member

    yep, thermoformed vertical strip farrier style is the method ill be using... except i wont be doing a half hull, ill be doing a full shoe, flip it over and glass the otherside... assembling the frame and batten mold today :)
     
  3. CatBuilder

    CatBuilder Previous Member

    Yeah, I saw your other thread. That shoe method looks great!!

    Much faster, I think, especially if you are doing the interior at the same time. Good thinking.

    (I am doing my interior after the launch)
     
  4. tunnels

    tunnels Previous Member

    Its a breeze !!

    We were making racing boats for the Korean first ever international boat show so the boats were in the public eye so to speak the finish was and had to be spot on and shiney and fair and nice . Contured foam just would not do what we wanted and it has this habit of showing every individual block specially with thin skins and nothing looks worse than foam marks joins and the like . All our cores were bagged into just a double skin of 450csmagainst the gelcoat and a single 600 gram 0/90 glass then another wet 450csm to bed the core ! Scary stuff ! so what alternatives do you have to get 18mm high density foam round a 80mm radius right in the bow section running back in a cone shape to a much larger radius as it progressed aft !,so as luck would have it i found amongst all the tools in a store room a small dia saw blade with very fine teeth and quite thin . the blade fitted into a angle grinder so a guard was manufactured with a deepth adjustment and set to cut the 18mm thick foam sheets !! The cuts only went 13mm deep and in the first part of the sheet the cuts were just a few mm apart but as the curve got bigger so the cuts were further apart . took about 20 minutes to work out the number of cuts required and with the 5 mm of uncut foam to the outside against the skin there was never at anytime any print though to the shiney surface . NO HEAT REQUIRED !!During the bagging of the core the resin filled all the saw cuts completely so no filling required when the bag and peel ply were removed !! Once the first boat was done and all was sorted the next 7 boat lots ,port and stb were all precut numbered and stored away . The thing was the heat was never going to work with 18mm high density foam and we broke many pieces and cooked lots a samples trying . 80MM RADIUS is tight !! and with hard foam the designer was sceptical that we could even get close to the very bow with the core !!
    One little trick we also stumbled on was to cut blocks of the foam out of the sheet and Hot glue then to the skin to hold the sheets perfectly in possition during the fitting of the other topside sheets and also when wetting the glass under the core and laying in place covering with peel ply, scrimm and the bag as we went aft !,bothsides and half the length of the boat in one bag all at the same time . It took a little thinking about at first but by boat 3 was a breeze . :D
    So cut the foam dont heat the closer the cuts the tighter the radius you can go round leave 5mm of uncut foam to go against the skin then you wont get any print through of any sort at any time !
    its simple!
    its works !
    and dont need to be a genious to work it out . :)

    Did ya like that ??:p
     

    Attached Files:

  5. groper
    Joined: Jun 2011
    Posts: 2,483
    Likes: 144, Points: 73, Legacy Rep: 693
    Location: australia

    groper Senior Member

    i actually considered this exact same idea! my hull shape is almost identical! its a half cone bilge in the bow section and then a tight U shape aft...

    However i still decided against this because i didnt think i would be able to get all 35ft of the hull core installed and then bagged down within the working time of the bedding resin... so then there is infusion, but i didnt know how this would go with all the grooves and predictable resin flow... for a 1 off build, the potential for mistakes was too great... so then perhaps i could vacuum bag sections at a time to a skin coat on the mold, but then the whole process is getting more and more time consuming so i figured it woulnt save me anything over a traditional method.

    id like to try all these things, but im only building a 1 off boat and the economics didnt seem worth it, and the discovery time id be spending - i could be building my boat...

    Good to know that it works for your boats, any chance of giving us a little more detail? So you are bagging a core onto a completed skin laminate in the mold, then are you doing the inside skin with the core in a 1 step vacuum bagging process? If so, how do you get it all in there within the working time of the resin and stop everything from moving out of position? i could see a way with a very long open time vinylester and many hands, but im using epoxy and the longest gel time i can reasonably use (without a serious post cure) is about 1 hour...

    the only way i can see of adapting this method with epoxy would be with infusion... and still how do you hold the layup secure whilst your applying the top layers and resin lines etc before you can get the vac on and the bag finally holds it all down?
     
  6. tunnels

    tunnels Previous Member

    The locating of fitted sheets is simple !! CUT AND FiT one row of sheets where they need to go and use a hole saw about 50mm dia and drill a hole in the core in from each end!, the plug gets hot glued to the skin and acts as a anchor /locator . Infusion or bagging the plug is surrounded and soaked in resin and never a problem .
    Fitting the sheets and getting everything tighly in place had always been a hassle and used loads of sticky tape in the past but the plugs with a hot glue is magic !! Can simply use a knife and cut blocks if you dont have a holes saw !! 30mm X 30mm is a good size and when stuck can hold a lot of pressure so do all the bottom panels first and then work up the topsides and plug and glue as you go even had guys that used to Dovetail some of the joins or use a Bow tie shape the joins !!,seemed a waste of time and effort but what ever system you use it becomes familiar and simpler as time goes by .
    Important to fit everything in place , cut and fit the peel ply and the scrim and have all you pipes fitter and lightly taped in position first including making and attaching the bag to one long straight side then rolling it over off the job out of the way . The boats we were doing were 36 foot long and we could do 75% of the hull in one hit !! Just left the small 25% patch to work inside the mould !.When it was gelled just lifted the bag and rattached the small bag with the last 25% area and was all done in a mater of hours . We used Standard Vinylester resin hand mixed with a 450csm as a bonding layer under th e core always had plenty of time to get it down sealled and checked vac pressure etc and then every one left and kept away just one person stayed and constantly monotered the job till it was gelled and hard . !!.
    Race tracking through the grooves could be a problem if you were infusing but its important to use a narrow blade when doing your cuts and more of them !!
    Make youself a small sample and see how it works !! remember the saw cuts are inside and close up as the sheet is laid down onto the curved surface ,Only need 5 mm of uncut foam so theres little chance of any kind of print through showing up latter .
    If you are Bagging ! how much vac pressure will you need ?? Now think about that !!
     
  7. groper
    Joined: Jun 2011
    Posts: 2,483
    Likes: 144, Points: 73, Legacy Rep: 693
    Location: australia

    groper Senior Member

    Im still not clear on this, you hot glue the plug to the skin? - What is the plug? - ive always thought this to mean the temporary model of the part which you use to take a female mold from?

    Do you have a 2 part mold, male and female?

    What is the hole saw or 30mm x 30mm blocks for?

    Im sorry, i feel really stupid but i just cant understand any of it? :confused:
     
  8. tunnels

    tunnels Previous Member

    This is planet earth we are both on isnt it ?? How long you been glassing for ??
    When you use a hole saw you cut a circle out of the foam sheet that is called a plug !! sorry the plug or circle will be inside the hole saw and you have to take it out of the hole saw so you can use it ( plug of foam core ) to glue to the skin !! or you can cut a square 30mm x30mm out of the sheet and stick that to the skin to hold the sheets firmly in place so they dont move about while you are fitting the next sheet to it !can do it with all the sheets to locate and hold them in place :eek::)
     
  9. waikikin
    Joined: Jan 2006
    Posts: 2,440
    Likes: 179, Points: 73, Legacy Rep: 871
    Location: Australia

    waikikin Senior Member

    The "plug" in this case is the "biscuit" from the hole cut by the hole saw, you use this as an indexing nodule for positioning a sheet of foam
     
    Last edited: Feb 7, 2012
  10. tunnels

    tunnels Previous Member

    Oh i say youve got it old chap ,well done !!:):D:p
    :idea::DJust have to convince groper we are all on the same planet !! :p
     
  11. waikikin
    Joined: Jan 2006
    Posts: 2,440
    Likes: 179, Points: 73, Legacy Rep: 871
    Location: Australia

    waikikin Senior Member

    Tally Ho, Is there a prize? Onwards & Forward..............
     
  12. tunnels

    tunnels Previous Member

    Jolly good old chap !!on ward and upward tally ho !!!
    Thank you for getting the meaning first time . !
     
  13. groper
    Joined: Jun 2011
    Posts: 2,483
    Likes: 144, Points: 73, Legacy Rep: 693
    Location: australia

    groper Senior Member

    :) sorry.... ok i get that part... but still, that wasnt what i had concern with... what i meant was, doesnt the core want to spring off the mold when pushing it into a severe convex shape? - or does the surface tension (tackyness) of the bog/resin on the mold and in the foam grooves hold it down sufficiently until you can get the bag over it all and vacuum on?

    i was envisaging the first few peices springing off the mold when i was half way thru it and ending up with a complete mess - which is why i gave up on it before i ever tried it...
     
  14. gonzo
    Joined: Aug 2002
    Posts: 16,790
    Likes: 1,714, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    If the bedding compound won't hold it in place, you have several options. One is to vacuum bag the foam to the skin. Another is to use scored foam.
     

  15. tunnels

    tunnels Previous Member

    Groper how old are you ?? what is your problem ?? if you cut your foam sheets like i showed you there is very little tension and the hot glued blocks hold everything in place before you even think about bags and sticky stuff every where . . If it wont sit dry it deffinitly wont sit if its covered in sticky stuff and sliping and slding every where !bagging you have to make ,fit and put everything in place dri 100% fitted and marked and coded including the peel ply scrim and bag etc etc all in place ! Its as simple as paint by numbers !!:eek:if theres convex do the same with the glued plugs and use a 3 mm thick ply strap with a screw to hold the foam in place !! Dry fit everything!! Including run the vac pump :(
     
Loading...
Similar Threads
  1. Felix Gruter
    Replies:
    15
    Views:
    5,995
  2. fallguy
    Replies:
    30
    Views:
    4,701
  3. Roy Berntsen
    Replies:
    37
    Views:
    9,074
  4. benglish300
    Replies:
    31
    Views:
    7,687
  5. CatBuilder
    Replies:
    33
    Views:
    9,527
  6. tunnels
    Replies:
    4
    Views:
    3,151
  7. Joe0157
    Replies:
    24
    Views:
    938
  8. fallguy
    Replies:
    11
    Views:
    837
  9. pironiero
    Replies:
    34
    Views:
    4,419
  10. jangr
    Replies:
    34
    Views:
    3,929
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.