Mouse Posted January 31, 2014 Share Posted January 31, 2014 Hi there I am hoping to build the dawn flyer as my first ever build and decided to build parts of the wing to give me an idea of how to do this and try to see how they fitted together seeing how the plans are quite poor on this point. I brought a sheet of Sundela hobbyboard on the advice of my local hobby shop and glued a 20 in X 12 in piece to some 3/4 inch flooring grade chipboard as recommended by the shop using industrial grade pva and then weighted it down for a good 10 days, the result was a perfectly flat surface on which to build. However after doing just one wing section over three weeks I have noticed the entire board is now bowed across it's length to a depth of just over 4mm in the centre, it is not that the building board has pulled away from the chipboard but it looks like the Sundela has pulled up the ends of the chipboard, is this likely ???. The rest of the Sundela sheet has also warped and I have even had two of my truck wheel and tyres on it for two weeks but as soon as I take them of it just bows again. Is there any way I can get round this as I do not want to throw the board away because of the cost and it seems to grip the pins quite firmly which is something I like. Thank you. Mouse. Quote Link to comment Share on other sites More sharing options...
Martin Whybrow Posted January 31, 2014 Share Posted January 31, 2014 I would suggest gluing some battens to the back of the chipboard, narrow edge to the board to get the best stiffness and running lengthways. Make sure the whole lot is flat as the glue dries! Quote Link to comment Share on other sites More sharing options...
Dai Fledermaus Posted January 31, 2014 Share Posted January 31, 2014 You could try screwing a couple of hefty battens to the chipboard to pull out the warp, but is probably cheaper to bin it and buy a sheet of 4 x 2 plasterboard. Edited By Colin Ashman on 31/01/2014 18:08:14 Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted January 31, 2014 Share Posted January 31, 2014 Mouse I think the reason this has happened is the use of PVA - its made the Sundella damp and so its expanded on the bottom face - result it bows and takes the chipboard with it. You would have been better using a contact adhesive. But that's for next time. TBH I doubt you can make it straight. You could try the battens - but there must be a hell of pull to bend chipboard which is very stiff. Also I'm not sure that chipboard would hold the screws well enough for the sort of counter pull you're going to need. I suppose you could glue the battens and then weight it again? But another problem is that, looking at the quality of wood in my local timber yard recently, really straight battens aren't that easy to find either! I too think you'd be better ditching it - I know it hurts financially, but you must be confident that your building board is truly flat. BEB Quote Link to comment Share on other sites More sharing options...
WolstonFlyer Posted January 31, 2014 Share Posted January 31, 2014 The Sundela has shrunk because of the PVA. An solvent based impact adhesive would have been better My building board is two thicknesses of 12mm MDF glued and screwed together and then two thicknesses of self adhesive cork tiles from Wickes. The board is 300mm by 1200mm, very heavy and has stayed very flat. It cost about 20 pounds to make. Quote Link to comment Share on other sites More sharing options...
Levanter Posted January 31, 2014 Share Posted January 31, 2014 You have found one of the problems concerning laminates. If you bond two boards (laminates) together it is incredible how one can affect the other and it won't necessarily seem logical. ie a relatively week material can cause a stronger material to bow. When I was involved in specifying and building laminated panels for a number of different applications we took great pains to ensure the laminate was "balanced". The easiest way to do this is with three laminates (Skin - core - Skin) where the skins are the same material. You can have unequal skins to produce the same effect but this is a bit more complicated and probably not practical. The ideas above could work but with timber, you will always be the victim of changes of temperature and humidity. My own solution has been to buy a cheap Ikea table 1000 x 600 and I have faced it with cork using very thin industrial type double sided tape. This will be easier to deal with than glue when I have to re-surface it. The table actually had about 6mm dishing lengthways but predictably flat on the short dimension. I bought two lengths of hollow steel squared section 20 x 20. (Very stiff and not too heavy) Drilled and countersunk it for long screws, painted white to match the table top and screw to the underside close to the edge where the solid material is. Because even with the steel there was, and will be a very slight deflection, I put some thin plastic shims under the middle of the steel sections and now these strong-backs are adjustable. I set the tension on one end screw to get the board totally flat and six months later it is still perfect. Quote Link to comment Share on other sites More sharing options...
Glyn R Posted January 31, 2014 Share Posted January 31, 2014 This is my building board still straight after some years. The bed is 1/2" ply with 2x1 stiffeners. The actual top is a piece of 13mm plasterboard which is resting on under its own weight. It will take pins etc. It can be thrown away at £4 a go from B&Q. It is designed to rest on a workmate, which will clamp it in place without adding any stress, Overall size is 1200X600mm. Edited By Glyn R on 31/01/2014 18:46:48 Quote Link to comment Share on other sites More sharing options...
David P Williams Posted January 31, 2014 Share Posted January 31, 2014 I think if you check on the Sundeala website you are supposed to 'condition' it before use, by brushing water into the back of the sheet at a certain litres/square metre rate. I've used it in the past and done this, but I just let it rest on an already flat bench surface rather than glueing. Just use plasterboard now - MUCH cheaper and just as good. David Quote Link to comment Share on other sites More sharing options...
Plummet Posted January 31, 2014 Share Posted January 31, 2014 I think I was told that to keep things flat you should do the same thing to both sides of the board. If this is true you could try gluing something to the back of the board with PVA and then letting it dry under pressure to see if this will stress relieve it. Plummet Quote Link to comment Share on other sites More sharing options...
Andrew767 Posted January 31, 2014 Share Posted January 31, 2014 Hi Mouse......I think the issue is the substrate rather than the sundeala. Chipboard or mdf are not realy suitable. Use battens as others have suggested or better still use a kitchen worktop off cut. My boards are made this way and have lasted for years. Sadly as Beb says,it's time to start again. With sundeala ,also remember to to use'K' grade, not 'A' grade as this is easier to push pins into ( should look light brown rather than light grey). Andrew Quote Link to comment Share on other sites More sharing options...
FWAL Posted January 31, 2014 Share Posted January 31, 2014 Hi Mouse I'm moving house in a couple of weeks so having a big bonfire! You are more than welcome to my Sundella backed half of a solid fire door building board. It's free, true and heavy. Collection only from Mumbles, Swansea. Mk Quote Link to comment Share on other sites More sharing options...
kenking-King Design Posted January 31, 2014 Share Posted January 31, 2014 Mouse, if you're unable to take advantage of FWAL's generous offer I would suggest the following. Go to any building supplies company (even B&Q) which sells worktops, the heavy 30mm thick stuff. Ask if they are shipped in clamped between unclad blanks and if so could you please have a blank, saving them the cost of disposal. There may be some small edge dings from shipping damage.(that's what they're for) but that won't matter to you. Glue and screw lengthwise battens to the underside if you like, 2" x 1.5" or more will be good. You can screw through the blank into the timber, countersinking the screw heads. Battens can be rough sawn timber as long as it's dry and seasoned, but plane the mating edge flat and true. Otherwise use slightly more expensive ready-planed section. Add a sheet of plasterboard as your working surface, it's own weight will hold it, and do a lot of building before needing to change it (after you've turned it over and done a lot more building, of course). I'm sorry but I fear your laminated board must be written off against experience, Though a future use for it may materialise in due course (rabbit hutch etc.). I can't help feeling that your model shop should have offered similar advice, at the cost of a sale of Sundela board, but with the advantage of gaining a grateful, happy and contented regular customer. Quote Link to comment Share on other sites More sharing options...
IanR Posted February 1, 2014 Share Posted February 1, 2014 kenking, I like the way you add to your instructions "...plane the mating edge flat and true..." Easier said than done, mate! Ian Quote Link to comment Share on other sites More sharing options...
kenking-King Design Posted February 1, 2014 Share Posted February 1, 2014 IanR, yes of course you are right, much easier said than done, and not everyone has a decent woodworking plane, but in fairness I did suggest an alternative. Just trying to keep the cost down, and I did add 'if you like' too. If you can get 30mm worktop chipboard free, or at least very cheaply, then screw two pieces together back-to-back without glue. it's very dense, heavy stuff that won't move and battens definitely not needed.. Quote Link to comment Share on other sites More sharing options...
Mouse Posted February 3, 2014 Author Share Posted February 3, 2014 Hi and thank you for replying, especially Glyn for the photos and FWAL for his kind offer. I still have some of the Sundela left and would like to use this as I am limited for space and not able to have a large board, I am looking at about 30 inch by 12 inch. Do you all think that two thicknesses of 12mm ply glued together would be o.k as I have quite a bit of this laying about or should I look to one of the other suggestions. Thank you Mouse. Quote Link to comment Share on other sites More sharing options...
Former Member Posted February 3, 2014 Share Posted February 3, 2014 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
iqon Posted February 3, 2014 Share Posted February 3, 2014 I dont do a lot of building, but when i do its a plasterboard offcut for me Quote Link to comment Share on other sites More sharing options...
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