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Author Topic: Flattening / Straightening Lite Ply Sheets  (Read 2688 times)

wally

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Flattening / Straightening Lite Ply Sheets
« on: January 26, 2013, 05:17:38 PM »

Well i've got the sheet materials together for my swordsman build which I shall be documenting over the coming weeks.

Unfortunately the suppliers shop is in a barn and although the sheets of lite ply were laid flat they are slightly warped.

Being a perfectionist I'd like to try flattening the sheets out prior to cutting. Is it just a case of acclimatising them inside or do I need to add some heat/moisture to the equation?

Thanks in advance.
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derekwarner

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Re: Flattening / Straightening Lite Ply Sheets
« Reply #1 on: January 26, 2013, 09:34:41 PM »

Wally.......try Mr GOOGLE. :-)) ..he seems to have many suggestions on the subject.......Derek
 
http://www.finehomebuilding.com/how-to/tips/flattening-warped-plywood.aspx
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Popeye

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Re: Flattening / Straightening Lite Ply Sheets
« Reply #2 on: January 26, 2013, 11:10:21 PM »

Well i've got the sheet materials together for my swordsman build which I shall be documenting over the coming weeks.

Unfortunately the suppliers shop is in a barn and although the sheets of lite ply were laid flat they are slightly warped.

Being a perfectionist I'd like to try flattening the sheets out prior to cutting. Is it just a case of acclimatising them inside or do I need to add some heat/moisture to the equation?

Thanks in advance.


I personally found lite-ply to be a bl..dy nuisance coz it would invariably develop a warp, took oodles of sealer and patience to get  its' surface to an acceptable standard for finishing and would still quickly deteriorate once exposed to the wet stuff >>:-( [size=78%]. [/size]


So if you're a perfectionist discard the lite-ply and revert to good quality ply (or plasticard) for all external fabrications O0 [size=78%].  Limit the former to internal uses which are  moisture/dampness free.[/size]


Apologies for the sermon :-)) [size=78%]. [/size]
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wally

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Re: Flattening / Straightening Lite Ply Sheets
« Reply #3 on: January 26, 2013, 11:30:05 PM »

Thanks for your replies thus far. The lite ply is intended just for framework and will be getting a liberal coating of resin to protect from any unfortunate capsizing!

It is my intention to double skin the hull overlapping sheets to avoid the need to glass cloth it and probably skin the deck with hardwood planking.

I'm pretty sure the warped lite ply will be fine as I shall be squaring everything as i go.

Wish me luck!
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inertia

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Re: Flattening / Straightening Lite Ply Sheets
« Reply #4 on: January 27, 2013, 09:09:03 AM »

Watch the weight! WBP birch ply weighs about twice as much as liteply.
There is an article on here somewhere about finishing the Swordsman (built with liteply) with cellulose sanding sealer and tissue.. It's not complicated and does result in a smart and durable finish if done with patience.
I didn't find it necessary to glass-cloth either inside or outside my Swordsman hull. Three coats of thinned polyurethane varnish is more than enough inside to waterproof the thing - it soaks into the porous ply and sets up very hard.
DM
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Circlip

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Re: Flattening / Straightening Lite Ply Sheets
« Reply #5 on: January 27, 2013, 09:49:37 AM »

Quote
The lite ply is intended just for framework
Beware of cutting out the centre of the bulkheads if using liteply for them. You originally said you wanted to scale up an existing design so they might not stand "Lightening"
  Regards  Ian.
 
Re: Obtaining a good finish on ply and balsa hulls with simple materials.« Reply #8 on: December 13, 2007, 11:15:37 PM »

[/color]OK - on the basis that anyone who reads this should take it as A method and not THE method (like I said before), let's have another try, shall we?

Extract from article describing Fairey Swordsman finishing method – Original plan and article published in “Model Boats” May 1999. Reproduced by kind permission of The Editor.


“After final sanding with 180 and 320 Finishing Paper, give the whole model one coat of sanding sealer*, thinned at least 50/50. It should be almost as thin as water i.e. if you can see brush-strokes in it then it's still too thick. Rub down with 320 grit Finishing Paper*. Cover the hull sides, bottom panels and transom with lightweight tissue* as separate panels. Cut the tissue slightly over-sized then lay it onto the model and brush thinned sanding sealer through it. Immediately smooth down the tissue with a folded piece of kitchen roll, mopping up any excess sealer in the process. Allow to dry, then feather off the edges with 320 paper. Apply a further three coats of thinned sealer, allowing to dry between coats. Rub down to a satin finish with 320 Finishing Paper. Don’t cover around the inside corners between the hull sides and the spray rails and rubbing strips, as the sealer has a shrinking action and will result in voids under the tissue; cut the tissue hard up into these corners with a sharp blade instead. The cabin sides and roof are tissue-covered in the same way as the hull. The wood veneer is not covered in tissue but has three coats of thinned sealer.
Mask off the wooden decks and rubbing strip. I personally use and recommend Tamiya masking tapes; they aren’t cheap but give a superb edge and can be bent around quite sharp curves. Also never use newspaper as masking; the ink usually comes off onto the model. I purchased a pad of A1-sized Flip Chart paper some time ago for about a fiver; so far it has served over a dozen models and will probably last me until I retire! Now apply two spray coats of Halfords White Primer (or equivalent car paint); allow to dry for 24 hours, then rub down with 600 grit Wet or Dry* paper, used wet. Rinse off any paint dust; allow to dry naturally; dust off then apply three thin coats of Appliance Gloss White, leaving each coat to dry for about 20 minutes before applying the next coat. Remove the masking as soon as this is touch-dry, but leave it at least 24 hours before proceeding. Re-mask the decks and mask the areas to remain white, then spray the hull below the paint line, the sides of the cabin and the face of frame 25 with Renault Midnight Blue (mine took four thin coats). Finally apply two slightly thinned coats of Ronseal Satin Wood Finish to the deck, cockpit floor and rubbing strip”.

*Further notes:
Finishing paper (which is also sometimes called Production Paper) is a pale grey colour. It’s manufactured from aluminium oxide and can be obtained in the UK from Wickes Do-It-All under their own brand, or from other DIY stores under the 3M or Scotch brand names. Grades vary from 60 grit, which is far too coarse for all but the crudest shaping, to 320. I use a selection of 120, 180, 240 and 320 for finishing wooden models.
Sanding Sealer is a mixture of clear cellulose dope and a filler powder. Humbrol is probably the best-known brand but I also have acquired assorted tins from H Marcel-Guest and J Perkins. If you can’t obtain any then you can make your own by adding talcum powder to clear dope. It should not be used “thick” – I thin down the commercial stuff 50/50 and apply it with a flat, soft brush. Ripmax used to do a fantastic little range of very soft dope brushes called “Flatties” – these are just the right tool for this job, but I don’t know if they’re still available. If not, a wide, flat squirrel-hair brush is nearly as good. Best advice is to visit an artists’ supply shop.
Modelling tissue is available from most model shops and is commonly used to cover the open rib-and-spar structures of small model aircraft.
Wet or Dry Paper is available from practically any shop which sells car paints – Halfords being the most obvious. I use several grades from 600 to 1200 for finishing paintwork; the former for flatting down primer and the finer grades for later coats. Wetting the paper helps it “stick” to the paint and eases removal of the paint surface, while rubbing wetted 1000 or 1200 paper onto a block of ordinary soap will give a very fine abrasive suitable for flatting down final gloss coats prior to lacquering, burnishing or polishing.

When sanding a timber hull smooth prior to painting, ALWAYS wrap the paper around a flat block – never use a fold of paper in the hand (you’ll just dig grooves in the surface where your fingers are). Sand with a circular motion and let the paper do the work; don’t press on too hard. Once the paper clogs, replace it.

Don’t just rely on a good blow to remove dust; use a clean paint-brush on uncoated wood to brush away the dust, then go over the whole thing with the domestic vacuum cleaner, using that little round dusting brush attachment. Wash down the sanded primer and gloss coats with clean water and allow to dry naturally.
Never spray in a cold or damp atmosphere; aim for a minimum 15 degrees C. Any colder and you risk the paint crazing at a later stage; ask me how I know….. 
Always wear a face-mask when spraying (Machine Mart do an excellent one with replaceable filters for about £15).

THE TWO BIGGEST ENEMIES OF A DECENT PAINT-JOB ARE DUST AND IMPATIENCE.

There is no agreed “best practice” here. This is just the way I did it – there are numerous variations on the same theme. Suit yourselves; works for me.

FLJ

  Found these ramblings that should have been made into a sticky. Author gone but not deseised  {-)
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wally

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Re: Flattening / Straightening Lite Ply Sheets
« Reply #6 on: January 27, 2013, 11:24:50 AM »

Thanks again for your reply. I've decided to stick with the original plan dimensions on this build as it's my first effort in a bid to keep things simple!

Beware of cutting out the centre of the bulkheads if using liteply for them. You originally said you wanted to scale up an existing design so they might not stand "Lightening"
  Regards  Ian.
 
Re: Obtaining a good finish on ply and balsa hulls with simple materials.« Reply #8 on: December 13, 2007, 11:15:37 PM »
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inertia

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Re: Flattening / Straightening Lite Ply Sheets
« Reply #7 on: January 27, 2013, 02:20:17 PM »

Thanks again for your reply. I've decided to stick with the original plan dimensions on this build as it's my first effort in a bid to keep things simple!
Then I strongly suggest you don't alter the construction either. Leave the experiments for the next model.
DM

"Deseised"??  No - just morphed a couple of times.............. 8)
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