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How do I bend 3mm plywood around a 6" radius?

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Forum topic by HuntleyBill posted 12-19-2017 11:15 PM 4445 views 0 times favorited 34 replies Add to Favorites Watch
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HuntleyBill

114 posts in 3288 days


12-19-2017 11:15 PM

I am trying to bend a 3mm piece of plywood around a radius. (see pictures) I have soaked the wood in with water, clamped it up and let it dry over night. When I take the clamps off, the plywood springs back A LOT!!

Is there a way to get this wood to wrap around this radius and stay there better than it does? If it even stays close the the bend needed, I can make that work.

I’m thinking steam but wonder if there is another way so I don’t have to buy more equipment. (not that it would be devastating to buy more tools)!!! Your ideas are always welcome.

Thank you for your help.

[URL=http://s494.photobucket.com/user/HuntleyBill/media/20171217110411zpswa73t0cr.jpg.html][IMG]http://i494.photobucket.com/albums/rr303/HuntleyBill/20171217_110411_zpswa73t0cr.jpg[/IMG][/URL]

[URL=http://s494.photobucket.com/user/HuntleyBill/media/20171217111017zpshuz5pjen.jpg.html][IMG]http://i494.photobucket.com/albums/rr303/HuntleyBill/20171217_111017_zpshuz5pjen.jpg[/IMG][/URL]

-- If you think you can, or think you can't...your right!


34 replies so far

View kaerlighedsbamsen's profile

kaerlighedsbamsen

1251 posts in 1911 days


#1 posted 12-19-2017 11:25 PM

Have had success bending thin sheets of wood around the pipe for my woodstove when hot. it is about 7cm in radius and i can see exactly when it is bent enough. There is only a small amount of movement after that.
See here for more info: https://en.wikipedia.org/wiki/Heat_bending_of_wood
Any metal pipe and a suiatable heat gun/blow torch/clothing iron/molten lava should do for a small number of piezes

Good luck!

-- "Do or Do not. There is no try." - Yoda

View Ocelot's profile

Ocelot

2113 posts in 2836 days


#2 posted 12-19-2017 11:26 PM

Saw slots in the wood at intervals – probably 1.5mm deep (half thickness) about 25mm apart. A standard or thin kerf blade will do. The slots, of course, go in the inside of the bend. You may have to experiment some to determine how close together and how deep they have to be.

View John Smith's profile

John Smith

1481 posts in 360 days


#3 posted 12-19-2017 11:28 PM

Bill – I can’t see your photos (thanks to the PhotoBucket Ransom).

how big is the piece that you want to bend ?
are you bending with or against the grain ?

-- I started out with nothing in life ~ and still have most of it left.

View HuntleyBill's profile

HuntleyBill

114 posts in 3288 days


#4 posted 12-19-2017 11:33 PM

Hi John. The piece is 34” x 18”. With plywood, I didn’t know there was a grain. Each layer goes a different direction…right?

I was thinking about using a steam iron but did not know if it would penetrate all the layers. I DO have a heat gun tho.

-- If you think you can, or think you can't...your right!

View Loren's profile

Loren

10477 posts in 3845 days


#5 posted 12-19-2017 11:42 PM

The kerfing method may sort of work if
you cut through all or most of the glue
lines so you’re only bending the face
veneer and perhaps a little material adjacent
to it. It’s the stiff glue lines that cause
the spring back. With kerfing though there’s
little structural strength and the bent
part will flop around if it isn’t fastened
down. You can bend it to the shape you
want and pack the kerfs with glue I suppose.
Messy though.

If you want a consistent, smoothly curved
part you’re going to need to introduce another
layer and a glue line to fix the shape. To
get the two layers clamped together tightly
you’ll also need cauls for the top.

This part can be made using single part
form and a vacuum bag to press the top
layer tight enough to make a good glue line.

If this all sounds like a pain in the butt, it’s
because it is. Curved work is always a hassle.

1/8” Italian bending poplar has all the plies
going the same direction and I suppose the
glue may be less stiff too. It still won’t hold
a shape unless it’s glued to another layer
of otherwise fastened down.

View John Smith's profile

John Smith

1481 posts in 360 days


#6 posted 12-19-2017 11:52 PM

when you look at a 4×8 sheet of plywood, with the 4ft side up, the grain will be horizontal.
the weakest part will be between the two 4ft edges – which would be easier to bend.
Question: what is the thickest material you can get away with ?

a thin sheet, such as 2×3ft will be easier to bend with the grain vs across the grain.
but 6 inches is still pretty tight. My suggestion would be to get thinner veneer and laminate
them over your form. then it will keep its shape forever.
or like Ocelet suggested: cut saw curfs on the inside, slather it with glue or epoxy and form it that way.
sharing more about your project will help with more accurate feedback.

-- I started out with nothing in life ~ and still have most of it left.

View MrUnix's profile

MrUnix

7038 posts in 2396 days


#7 posted 12-20-2017 12:14 AM

For the photobucket impaired:

And the above is correct… cut relief cuts in the back side of the board.

Cheers,
Brad

PS: To the OP, please refrain from using photosuckt – upload directly here instead.

-- Brad in FL - In Dog I trust... everything else is questionable

View HuntleyBill's profile

HuntleyBill

114 posts in 3288 days


#8 posted 12-20-2017 12:33 AM

Thank you all. it is hard to cut relief cuts in less than 1/8” thickness wood. I can get it to bend, I just can’t get it to stay there! Maybe I need to soak it longer in water.

Just out of curiosity, would steaming the plywood work for this application?

I agree Brad… it would be nice to be able to load pictures here directly but when I tried to do that, it said I needed to use a third party such as photobucket. It’s a pain!

-- If you think you can, or think you can't...your right!

View HuntleyBill's profile

HuntleyBill

114 posts in 3288 days


#9 posted 12-20-2017 12:35 AM

Oh…wait….I just figured out how to put pictures in without PB!
silly me! I was clicking on the “pictures and video friendly” link.

-- If you think you can, or think you can't...your right!

View MrUnix's profile

MrUnix

7038 posts in 2396 days


#10 posted 12-20-2017 12:52 AM

Thank you all. it is hard to cut relief cuts in less than 1/8” thickness wood.
- HuntleyBill

Got a table saw? How about a circular saw and a long 2×4?

I doubt you will get it to stay exactly where you want it without some kind of support/fasteners. What exactly are you trying to do?

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

View HuntleyBill's profile

HuntleyBill

114 posts in 3288 days


#11 posted 12-20-2017 01:19 AM

I am building a steamer type trunk for the back of an old car. The piece in question is the skin covering for the lid of the trunk. It will fit around a framing of the lid but I am concerned that the lack of bend might put unnecessary strain of the framing.

-- If you think you can, or think you can't...your right!

View John Smith's profile

John Smith

1481 posts in 360 days


#12 posted 12-20-2017 01:43 AM

Bill – I restored a 1930 Buick sedan several years ago and wanted to include
the trunk in the package. I never found one that was period correct before I sold it.
do you have the bones of an original trunk or are you working with a reproduction ?
now that I have an idea of what you are trying to do, there aren’t too many options on the table.
if I were doing it for authenticity, I would build a plywood frame and order several sheets of poplar
veneer and laminate it all together for the lid – trim to fit after it has cured for a couple of days.
all the veneer layers should have the grain run longways – from left to right – not up and down.
once a half dozen or more veneer sheets are laminated together – it will retain the shape permanently.
sounds like a fun project !!!!!!!!!! more photos would be awesome.

you mean something like this ??

-- I started out with nothing in life ~ and still have most of it left.

View HuntleyBill's profile

HuntleyBill

114 posts in 3288 days


#13 posted 12-20-2017 01:53 AM

This one is for a 1930 Model A. Not sure how period correct it is, but it fits the trunk rack I have for the car.

This is VERY close to what I am doing: https://www.brattons.com/trunk-straight-back-black-vinyl.html

Hope this helps answer some questions.

-- If you think you can, or think you can't...your right!

View Loren's profile

Loren

10477 posts in 3845 days


#14 posted 12-20-2017 02:03 AM

Italian bending poplar.

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TungOil

1055 posts in 692 days


#15 posted 12-20-2017 03:13 AM

+1 on the Italian Bending Poplar. Easy to work with and holds its shape exactly provided you glue up 2 or more layers as Loren pointed out. I used it for the cores of the sleigh bed in my projects section.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

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