Bending Plywood

[John3528]

Woodworm have completely demolished the plywood rear seat back in my recently acquired AH Tourer.  The seat back has been re-upholstered at some point and the leathercloth is still in excellent condition and my plan is to try and replace the plywood and re-use the upholstery which, of course, matches the rest of the car.

Whilst most of the plywood is flat, the 'wings' on either side curve gently forward to some degree.

My question is how best to introduce these curves into the new plywood?  Steaming is one obvious way but the seat back is a not a small item and would require me to concoct a large steaming cabinet.  It seems that one can also place towels repeatedly soaked in hot water along the bend line over a period of days.  It seems too that one needs a former over which to gradually tension the plywood into the desired shape.  This is completely new territory for me but an interesting challenge and a change from mechanics.

I should be most grateful for any advice on how best to tackle this problem.  It would be interesting to know too if one type of ply bends more easily than another or is better suited to the job, marine ply maybe.  Whatever the final result, it is going to be soused in Rentokill woodworm fluid!!

Many thanks,

John.

[jonblob33]

Hi, have you thought about using 3 sheets of 2 mm ply glued together clamped to a former?
Kevin.

[Howard Wright]

Hi John

As Kevin says thin ply glued together works well.  I’ve bent 4mm ply to a quite tight radius.  I spray the ply with water then use a heat gun.  

Cheers

Howard

[Chris KC]

I have never yet tried to steam bend wood and succeeded, but lamination works very well indeed.
Multiple thin layers of course much easier than few and thick.
Think carefully about what adhesive to use as it may get wet / damp and you don't want it de-laminating later.

[Jays]

When I worked for Morgan we laminated a lot of the ply used for cockpit backs, centre consoles etc on the Aeros. We did use vacuum bagging to hold the laminations to a former but clamping works nearly as well. Thin layers of birch ply and a glue the type of I now can’t remember apart from the fact it need a bit of moisture....similar to Gorilla wood glue!

[Douglas Alderson]

John it is not to difficult to bend plywood for the seats, have a look at the link below.

http://www.da7c.co.uk/technical_torque_a..._shap.html

["Slack Alice" Simon]

One of my favourite materials is 1.5mm birch ply.

Horribly expensive but just perfect for something like a seat back.

Bends more easily one way than the other.

I think it comes in odd sizes: 5' x 5' as I recall

[Pearls not a Singer]

The tricky part is getting the width right after bending so its fits in the body, possibly slightly easier in a tourer.

I would check out what Martin Prior has available and then re-fit your upholstery to a back you know will fit both the car and the upholstery.

[Derek Sheldon]

    Don’t know what part of the country you are in but Toton timber, just up the road from Beaulieu have 0.8 mm birch ply. I have used it successfully on my Rosengart. As suggested earlier multiple layers can build strength

[DavidL]

I know it as "skin ply". Here's a link:

https://sheetmaterialswholesale.co.uk/sh...e-plywood/

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If wanting to get an exact curve you need to allow for a bit of "spring back" - that means bending it a bit tighter on the former as it will relax a bit when released. If its only two laminations that will be more than with many thinner bits. Do tests with thin strips to get the idea and a feel for it before going for it with full panels.

As its going to be covered you could screw it to the former. Ratchet straps work well as does a "spanish windlass" (loop of rope, put a stick in and twist it tight).

Titebond do PVA type glue that is waterproof. Maybe screwfix do a waterproof one now. Titebond also do one that sets slower so you've more time to butter up and get everything clamped tight. The conservative approach is to add a layer at a time.

"If it was me" I'd try and get away with just do two layers for a seat back, three is plenty. PVA glue is in theory not good enough and is said to creep over time but stuff I made 15 years ago with PVA is still 100pct fine. Gorilla glue is great, used to use it, but I react to it with a rash and asma type breathing difficulties so avoid it. Epoxy brilliant if building a space ship but PVA is fine... Used gorilla on a boat for the deck and to laminate a rubbing strip but with gloves and in the open air and not doing too much at once.

These YouTubes gives a guide.

https://www.youtube.com/watch?v=avdmm0TRlSg

Can see how strong it is at the end of this one https://www.youtube.com/watch?v=g0ikg9NdUvM

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You don't need the flexi ply / skin ply. Birch ply is brilliant for this as well.

Something else to consider if wanting to steam is just steam the little curved bits at the ends then glue them on to the flat section in the middle.