Bendy Flexible Plywood

[Henry BuckeldeeParticipant @henrybuckeldee88769]

I am reupholstering a vintage car.

I am remaking curved boxes going over the wheel arches, ready to place carpet on top. The original boxes (Italian car) used a 3mm plywood over the curved sections of the box. I assume this was not heated to bend. I have bought some standard 3.6mm plywood, but there is no way this will bend over an approx 6 inch (150mm) radius.

Looking online there seems to a few different names for flexible bendy plywood, mainly targeted at modellers. Liteply is one name. The thickness that suits me would be 3mm, although a 2mm is also offered by some in the sheet size I want.

Does anyone have experience of this. Is this plywood suitable for an approx 6 inch radius.

Trimmers use what is called mill board, basically compressed paper. But I feel I want something a bit stronger than that. Preferably wood. So tacks can be used to secure carpet.

Any one know sources of supply. I need no more than 1/4 of a sheet. Of course this bendy ply bends perpendicular  to the veneer grain so need to check that out.

 

[JasonBModerator @jasonb]

You should be able to bend thin birch “skinply” or”aeroply” to that sort of radius. I’ve used it for lamination with a 200mm radius with no problem and it will bend a lot tighter than that. If you use two sheets with glue between then they will “set” to the curve once dry. Usually comes in 5ft square sheets.

Although I get most of my panel products from the link above this one tends to be more suitable for the public who just want a small amount an dwill roll a sheet up and send it to you

Several layers being laminated for this table I made

[BazyleParticipant @bazyle]

Liteply is just using balsa as the inner layer to reduce weight. Over ten years ago I made a lampshade from ply – so thin it is see-through as well as bending into a 10 in tube. However I don’t have any details from that long ago.

[parovozParticipant @parovoz]

Original probably steamed …..  Similar to hood hoops etc.

[bernard towersParticipant @bernardtowers37738]

Why not use two thicknesses of 1.5mm and glue together. I have done this in the past and it works well and dont forget that 3ply bends easily one way but not the other. Best of luck.

[Colin BishopModerator @colinbishop34627]

Liteply would be much too fragile. Jason’s suggestions are good, laminate for thickness as necessary.

Colin

[Michael GilliganParticipant @michaelgilligan61133]

Yes it exists [unidirectional plies]

https://materialsmarket.com/building-materials/sheet-materials/plywood-sheets/flexible-plywood

MichaelG.

[howardbParticipant @howardb]

“A newer method is kerf cutting, where grooves are cut into plywood, allowing it to curve smoothly. Kerf cutting involves making cuts along the back of the plywood sheet spaced closely together. These cuts, or ‘kerfs’, should not go all the way through; rather, they partially penetrate the plywood thickness, keeping the front intact. This partial cutting provides flexibility, enabling the plywood to bend around a curved form.

The number and depth of the kerfs depend on the desired curve’s tightness and the plywood’s thickness. Typically, the thicker the plywood, the wider and deeper the kerfs need to be. After bending the kerfed plywood to the shape needed, wood glue is usually applied within the grooves to secure the curve shape upon drying.

Clamping the bent plywood against a bending form ensures the desired curved surface is obtained. This is where bar clamps come into play, holding the plywood in position until the glue sets”

How to Bend Plywood – 2024 Guide

You could then use a thicker plywood than the 3.6mm plywood, say 5mm.

[duncan webster 1Participant @duncanwebster1]

Or you could make your own plywood by gluing layers of veneer with the grain alternating over a former. Sounds like a lot of effort, but it might work

[Stuart Smith 5Participant @stuartsmith5]

As stated earlier, just glue 2 sheets of 1.5mm together.

[Mark EasingwoodParticipant @markeasingwood33578]

The “Bendy Ply” I have used is always a three ply construct with a thin & stiff centre layer, (1mm or less), which has its grain at 90 deg to the 2 outer layers. The outer layers are a a very soft straight grained timber. The grain on the concave side compresses whilst that on the convex side opens out slightly, the “spine allowing it to bend without snapping.

Two pieces will keep their shape if glued together. It bends very easily, but not compound curves of course.

It is available in, “Long Grain” or “Cross Grain”, depending on whether you want an 8ft high tube or a 4ft high tube!

You can also buy flexible MDF, basically a sheet of MDF with saw kerfs machined into it, it snaps easily, and like most kerfed timber it ends up being multi faceted, and needs sanding smooth if visible. “Bendy Ply” is much better in my experience.

If you want to make your own ply, then “constructional” veneer is available up to about 3mm thick, normal veneer is only 0.6mm. It might only be around 6 inches wide though.

Mark.

[MacolmParticipant @macolm]

Millboard is quite a strong material, but might not perform well if wet, the same as quite a lot if current plywood.

[Henry BuckeldeeParticipant @henrybuckeldee88769]

Many thanks for your replies.

I visited an auto trimmer. His first suggestion was millboard. A sample he had was quite strong, despite being only compressed paper. The intended use is on the interior. So I doubt it will suffer due to damp?

Then he managed to obtain from next door a sample of bendy or flexible plywood. This will undoubtably bend to the radius. It seems to consist of 3 layers, the inner one being very thin. I read some of these are waterproof, but the sample seems to be very soft material. I wonder if it could be varnished to give water proof properties.

Looking at the 3mm plywood I removed, it has 3 layers, the outer ones being at 90 degrees to the inner. So I do perhaps wonder now if it was bent under heat.

So things to consider.

 

[larry phelan 1Participant @larryphelan1]

Just wondering, Jason, who won, black or white ??

Lovely piece of work.

[Henry Buckeldee]

On Henry Buckeldee Said:

Many thanks for your replies.

I visited an auto trimmer. His first suggestion was millboard. A sample he had was quite strong, despite being only compressed paper. The intended use is on the interior. So I doubt it will suffer due to damp?

Then he managed to obtain from next door a sample of bendy or flexible plywood. This will undoubtably bend to the radius. It seems to consist of 3 layers, the inner one being very thin. I read some of these are waterproof, but the sample seems to be very soft material. I wonder if it could be varnished to give water proof properties.

Looking at the 3mm plywood I removed, it has 3 layers, the outer ones being at 90 degrees to the inner. So I do perhaps wonder now if it was bent under heat.

So things to consider.

 

All ply has an odd number of layers at 90deg to each other for balance,  so as above 3 ply will bend twice as easy in one direction than the other.

Whether it will steam is dependant on the glue, modelling birch ply was water proof last time I bought any. Most other ply is not unless bought from a very reliable source, some ‘marine’ ply is not very marine at all.

[Henry BuckeldeeParticipant @henrybuckeldee88769]

An interesting and obvious point David.

3 ply plywood will always bend easier in one direction than the other.

May explain how it was done. Many thanks.

[parovoz]

On parovoz Said:

Original probably steamed …..  Similar to hood hoops etc.

 

Think this would be the way to go, in a completely different application( false doorway arch) i found steaming ply worked pretty well,using just a humble kettle, sometimes multiple steaming applications were needed.

The ends did prove a little tricky, seemed more resistant to bending??

 

[DiogenesParticipant @diogenes]

Henry, is this just a flat bit that’s in an ‘arch’ shape, or does it curve smoothly in two directions at once? ..er, say, something like the ends of a plastic washing-up bowl?

 

 

[Henry BuckeldeeParticipant @henrybuckeldee88769]

Thanks Samuel, will keep this in reserve. I don’t have or want to make/purchase any expensive steaming equipment. But have a kettle. Need to experiment.

Diogenes – its bent in one plane. So basically an arch shape.

 

[bernard towersParticipant @bernardtowers37738]

Borrow a wallpaper stripper to do your steaming they work really well.

[JasonBModerator @jasonb]

Two layers of the 1.5 and you won’t even need to steam, just a bit of glue between then simple hand pressure will have it follow the 6″ radius. Job done.

[Henry BuckeldeeParticipant @henrybuckeldee88769]

Thanks Jason.

So I would glue, and then while its drying bend to the radius.

As opposed to letting it dry flat, then bend.

Just makes a difference to former I use.

[JasonBModerator @jasonb]

Thats it coat the mating faces with glue, bend to shape and leave to dry. The big advantage is that it should stay that shape when removed from the former though as you are only using two layers there may be a little spring back.

You want the grain of the central layer of each sheet running along the bend and the outer layers across the bend. That applies to both sheets. So in the end you will have 4 plys across the curve and two running with it.

[Henry BuckeldeeParticipant @henrybuckeldee88769]

Many thanks Jason.

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