How Can I flatten a Warped Plywood Bulkhead?

[Kelp]

Any suggestions on how to flatten this warped plywood bulkhead?

 

Thank you,

Don

 

 

 

 

Any suggestions on how I can flatten this warped plywood bulkhead?

 

Thanks,

Don

[druxey]

You might try to briefly soak the piece in warm water, then clamp it between wood boards for 24 hours or weight it flat using layers of paper to wick away the moisture.

[hamilton]

This may not be entirely adequate, but you might be able to correct for this in the installation process. I'll try to describe what I'm thinking of as clearly as I can.

 

1. On the centre keel piece, trace vertical lines from each bulkhead slot on the face running down to the bottom edge - this will show you where a straight vertical run of the bulkhead should be

2. Dry-fit the bulkheads as they are and see where they drift off the vertical you've marked on the keel

3. Add bracing pieces - 3/16" or 1/4" square stock can work - between the bulkheads - cut them so that they push the bulkheads roughly into position - or exactly if you can be very precise.

4. Brush PVA into the seams between the bulkheads and centre keel to fix them in place and glue on the braces

 

Here's a picture from my build of HMS Bellona that shows a small (1/8" square) batten installed to square off two bulkheads that did not sit evenly on the framework - I hope this is a decent illustration of the idea.

 

When everything sets, the warp should be corrected. Admittedly, I've never seen a warp quite like this on a bulkhead piece before, but I have used the above strategies to correct for asymmetries in frameworks before. More experienced modellers might not agree with the above approach - and I would follow their advice first. But I think the above method should work ok.

hamilton

Edited September 20, 2022 by hamilton

[Jaager]

28 minutes ago, Kelp said:

Any suggestions on how to flatten this warped plywood bulkhead?

The warped piece of plywood is telling you what shape it "wants" to take to be in equilibrium.  It can be flattened but it will be recidivant.

 

1. -Punt.

Replace it.   Quick check  Home Depot has  1/4" x 2' x2'  Poplar faced or Maple faced for $9.  A fret saw will allow you to free the new mold by hand.   Doing this will demonstrate that you are more independent from the kit maker than you realize.

 

2.   scab it with straight supports on either side.   something like 1/4" x 1/4".   two parallel rows  -  PVA - and using bamboo skewers as dowels.

The tricky part is cutting the openings in the central spine for the supports and then gluing it all.  What with the dowel insertion  and the clamping, the repaired mold will have to be applied to the spine before the two or so molds on either side of it.

[vaddoc]

Perhaps take two pieces of plywood half the thickness minus 1 mm and laminate them with thickened epoxy (hence the 1mm). Let it cure with lots of books on top. You ll get perfectly flat plywood and you can cut a new bulkhead.

[allanyed]

MIght it be easier to buy a small sheet of birchwood ply, trace the errant bulkhead onto the sheet and saw out a new bulkhead with a scroll saw or even a hand coping saw?
Allan

[Snug Harbor Johnny]

  One old boss of mine used to say. 'We don't have problems - we have opportunities."   Another old boss said (after doing a work-around on something), "It's good enough for a dog."  Wood is a 'natural product' and subject to change over time and seasonal movements.  I wouldn't bother trying to get a 'replacement', but forge ahead with a work-around like any modeler will have to do from time to time (or even on a constant basis).

 

  The above suggestions all can work so you can take your pick.  Now I'll throw in another 'solution' to consider.  Since the errant bulkhead has moved to 'where it wants to be', you could cut it in half vertically in the center using an XActo and multiple light cuts so that no material is removed (sawing will do that when it makes a kerf, which would require a bit of veneer to apply to make up for the loss and maintain the width of the notch that engages the keel) ... since that seems to be where the piece has warped.   Lay the pieces flat on a piece of waxed paper (on a firm, flat surface) so that whichever side has a small 'gap'  faces up - and glue them together again with Titebond (excess glue will fill the tiny gap).  Lay another piece of waxed paper on top and then a book or paperweight to keep everything flat.

 

  Then once the glue has cured (I'd wait a few hours), then add some thin plywood pieces to both side (plus glue, of course) to make a 'sandwich' which you clamp together overnight.  Then you will have a strong bulkhead with correct positioning.  Now I like the idea of ALSO adding 'spacer wood' between most (if not all) of the bulkheads before fairing the hull.  This will make them all mutually supportive, and the chances of further warpage of any member will be almost eliminated.  It will also make fairing the hull (a key step) easier, as fore-and-aft abrasion with water tool you are using tends to move the free ends of unsupported bulkheads back-and-forth.

 

  Some use basswood (or even balsa) to fill in the space between the foremost and rearmost bulkheads entirely, since that is where there is the greatest bend when planking.  Solid filler between bulkheads there also makes fairing easier and provides a good solid surface for planking against.  Heck, I'd be tempted to use filler on the entire hull (except where there must be gun ports -if applicable), but the filler only needs to be on the outer portions of the bulkheads.  Hmmmm, 'reminds me of the old days when many ship kits had solid hulls ... but you can plank those too!

 

  So don't fret, mate ... maybe you can think of something else on your own.                   Johnny

 

 

[Kelp]

Thanks for all of the good suggestions.  I’ll be putting a couple of these ideas to use.

 

Don

[Dr PR]

An adaptation of Johnny's idea would be to saw a groove vertically above the slot for the keel on the face of the part on the inside of the curve. Don't cut all the way through the bulkhead. Just cut about half way through the part or enough to allow you to bend the part around the groove. It looks like t is three layer plywood so cut down through two layers.

 

Then bend the part flat. Be careful - if it is an old kit the wood will be brittle and might break (but that would be easy to repair).

 

Now lay it flat with the cut side up and weights on the outer edges to hold them down.

 

Glue a wide wood patch over the cut from just above the keel notch to just below the deck.

 

This should give you a bulkhead of the proper dimensions with no significant curvature.

Edited September 21, 2022 by Dr PR

[Roger Pellett]

A well equipped shop needs inventory; a stock of commonly used raw materials.  Ready access to these allows the modeler to solve problems like the warped bulkhead without having to visit the local hardware/ hobby shop.  Otherwise there is always the temptation to muddle through with poor results.  An essential material that I keep in stock is thin craft plywood.  This is available in several fractional sizes from 1/64 to 1/4in.  I use this material for patterns,  mockups, repairs, reinforcing joints, etc.

 

If you don’t want to fabricate a new bulkhead, I would cut it in half as posted above and laminate it to two pieces of thin craft plywood; one on each side.

 

 

Roger

[Landlubber Mike]

I haven't been very successful in trying to remove the warp in plywood keels.  My guess is taking the warp out of a smaller part might be even harder.  I'd cut a new one out - shouldn't be too hard.  The time you spend now will save issues down the road should you try to use a bulkhead that is not perfectly flat.

[Kelp]

Hi Spyglass,

 

This is an old Sergal HMS Victory kit.  Back from the days before laser cutting.  I still have to cut more bulkheads on the scroll saw this weekend, but can then do a dry fit.  I think the lower decks may help the correct the warping.  If not, I’ll trace this bulkhead and cut another one.

Thanks,

Don