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View HuntleyBill's profile

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

by HuntleyBill
posted 12-19-2017 11:15 PM


34 replies so far

View kaerlighedsbamsen's profile

kaerlighedsbamsen

1251 posts in 1885 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

2103 posts in 2810 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 (online now)

John Smith

1428 posts in 334 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 3262 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 3819 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 (online now)

John Smith

1428 posts in 334 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

7003 posts in 2370 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 3262 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 3262 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

7003 posts in 2370 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 3262 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 (online now)

John Smith

1428 posts in 334 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 3262 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 3819 days


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

Italian bending poplar.

View TungOil's profile

TungOil

1039 posts in 666 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"

View HuntleyBill's profile

HuntleyBill

114 posts in 3262 days


#16 posted 12-20-2017 03:33 AM

Ive never heard of Italian Bending Poplar.

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

View mtnwalton's profile

mtnwalton

37 posts in 1197 days


#17 posted 12-20-2017 05:07 AM

Bending plywood

View AlaskaGuy's profile (online now)

AlaskaGuy

4626 posts in 2481 days


#18 posted 12-20-2017 07:55 AM

For what it’s worth here’s a kerf calculator

https://www.blocklayer.com/kerf-spacingeng.aspx

I did a lot of kerf bending on this is project but I was using 3/4 stock.

-- Alaskan's for Global warming!

View AlaskaGuy's profile (online now)

AlaskaGuy

4626 posts in 2481 days


#19 posted 12-20-2017 08:07 AM

View mrg's profile

mrg

834 posts in 3171 days


#20 posted 12-20-2017 11:57 AM

Vacuum veneer it to the lid.

-- mrg

View robscastle's profile

robscastle

5381 posts in 2376 days


#21 posted 12-20-2017 12:24 PM

As mrg posted you can vacuum bag it.

You will need to have beny ply oriented with grain direction to suit your needs.

I have many sheets of it, Drop by and see if the stock I have is suitable

This is a 90mm pipe I did as an an experimental section

prepped for vacuum

In the bag

Some defects

A door I did no where near the radius you need but an example

-- Regards Rob

View rwe2156's profile

rwe2156

3134 posts in 1652 days


#22 posted 12-20-2017 02:20 PM

You can try steaming but keep in mind the glue us not waterproof.

You could also use a router and 1/8” straight bit. I you can slip the material under your TS fence you can move the fence in regular increments and use as a guide for the router.

Since the material is so thin, I’m thinking 3-4 layers and use plastic resin glue or epoxy to make it stiff.

-- Everything is a prototype thats why its one of a kind!!

View HuntleyBill's profile

HuntleyBill

114 posts in 3262 days


#23 posted 12-20-2017 02:41 PM

I live in Clinton WI. I looked up the Italian Bending Poplar but don’t seem to find a local vendor. I found one place that has it in 4’ x 8’ sheets for $29 but they don’t ship it. Kinda rules it out for me then.

hmmmm wonder if it can be ordered from Home Depot?!

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

View John Smith's profile (online now)

John Smith

1428 posts in 334 days


#24 posted 12-20-2017 03:51 PM

it seems as though all the recommendations for this particular project is Poplar Veneer.
whether it be in the form of Italian Bending Poplar – Wiggle Wood – Wacky Wood or Plain Veneer sheets.
some are available only in full sheets by the skid load, which is not an option.
once glued up, plain individual sheets of veneer become the plywood of your choice that will never loose its shape.
vacuum forming, steam bending, clamp pressure, are all good ideas for fabrication.
I have purchased mahogany veneer from https://www.certainlywood.com/index.php a few years ago and they
offer a good product with great customer service. and also, everybody’s favorite: https://www.woodcraft.com/
Please keep us in the loop as to your progress and techniques. I for one am very interested in your project.

Johnny

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

View TungOil's profile

TungOil

1039 posts in 666 days


#25 posted 12-20-2017 04:36 PM



I live in Clinton WI. I looked up the Italian Bending Poplar but don t seem to find a local vendor. I found one place that has it in 4 x 8 sheets for $29 but they don t ship it. Kinda rules it out for me then. hmmmm wonder if it can be ordered from Home Depot?!

- HuntleyBill


It may only be available from commercial plywood suppliers. That is where I bought mine (Fessenden Hall). HD might be able to special order it for you but I would recommend seeking out a local plywood distributor and beg them to let you buy it on a cash account. Some suppliers will accommodate.

-- 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"

View robscastle's profile

robscastle

5381 posts in 2376 days


#26 posted 12-21-2017 08:23 AM

Drop by, ... yeah if that could happen sorry about that.

-- Regards Rob

View runswithscissors's profile

runswithscissors

2866 posts in 2197 days


#27 posted 12-23-2017 05:56 AM

A heat gun works fine on plywood. Bend so the face veneers run the long way. 1/8” (3 mm) needs no kerfing to bend. As big as your piece is, you’ll need to clamp one edge (as in your photo), and sandwich the other edge between sticks to get a uniform bend. The heat gun softens the glue sufficiently so that the glue lines aren’t a problem. NO NEED FOR MOISTURE. It just raises the grain. Ideally, I like to apply the heat to the inside of the bend, but since you’re bending over a form, you’ll have to heat from the outside of the bend. Shouldn’t be a problem with ply that thin. If you bend 2 of those, and laminate them over your form, you’ll get a very rigid, strong, 6mm lid for your trunk. And it won’t lose its bent shape.

For a panel that large, I’d try to find old fashioned movie lights. They throw out a heck of a lot of heat, and spread it over a large area instead of concentrating it in a small spot. Wear welding goggles. And leather gloves. Apply heat for a minute or 2, then gradually start bending. You can feel the wood start to yield as the heat does its job.

Really, what you are trying to do is very easy with the right approach.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

View AlaskaGuy's profile (online now)

AlaskaGuy

4626 posts in 2481 days


#28 posted 12-23-2017 07:05 AM

I remember seeing some youtube videos on bending wood on hot pipes and some video on hot pipe bending when making shaker baskets. Might do a search on that.

-- Alaskan's for Global warming!

View HuntleyBill's profile

HuntleyBill

114 posts in 3262 days


#29 posted 12-23-2017 03:38 PM

I don’t have movie lights but i do have a heat gun. I will try that.

Also, I found some bendable plywood at Owl Lumber. I tried bending it around the radius and it snapped in half. I then soaked it in water for a few min and that made it possible to bend around the radius. Maybe bendable plywood is not so bendable without heat or water.

Anyway,this seems to work well enough.

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

View John Smith's profile (online now)

John Smith

1428 posts in 334 days


#30 posted 12-23-2017 04:48 PM

with all this info being tossed about, it makes me want to include
one of those trunks in my 2018 Bucket List. They look really good
on the back end of any vintage automobile.

Bill, here is the 1930 Buick Touring Sedan that I restored a few years ago.
a two year labor of love !! I just wish I had had the trunk to go with it.
the running boards are hickory with several coats of Petit Spar Varnish
and the wood spokes are original. I found a spare wheel on ebay and fixed that to the back.
the VIN was 30-000009 . . . . #9 off the assembly line in 1930. pretty cool.

.

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

View HuntleyBill's profile

HuntleyBill

114 posts in 3262 days


#31 posted 12-23-2017 06:14 PM

VERY nice John. I love those wheels! As you can see in my profile picture, mine is a 1930 Model A. Te trunk I am making is designed to fit the trunk rack that is widely available from the parts suppliers.

My Model A took me 5 years to do. It was a mess. But they are fun to drive and everywhere we go we get smiles and waves. Especially from the kids.

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

View Andybb's profile

Andybb

1371 posts in 775 days


#32 posted 12-23-2017 07:24 PM

There is a technique here for making a bag out of heavy plastic to steam bend the wood.

-- Andy - Seattle USA

View runswithscissors's profile

runswithscissors

2866 posts in 2197 days


#33 posted 12-24-2017 02:00 AM

Oooohh! Model As are my favorite car. Most fun to drive of any vehicle I’ve ever had. When I was in high school, I bought one for $40. Then my buddy bought one for $40. Then we found one at a local garage for $40, and we bought that one together to use for parts. After selling mine, I started driving the one we had pulled all the parts off of.

My first one had a rod bearing go, so I found an engine at another garage, plus a transmission. The engine cost me $5. I could have had the tranny for $2, but I didn’t need one. Parked under an apple tree, and used block and tackle to do the engine swap.

When I got out of the army in the early 60s, I found a nice Model A sedan with a very good body for $75 (darned inflation!). I was sorely tempted, but passed on it. Would have had to drive it over the Cascades from eastern Wash to Seattle, and was leery of putting on that many highway miles. They’d do 60 mph, but the unbalanced engines and babbit bearings didn’t thrive with that treatment. And of course the mechanical brakes were barely adequate.

Later, in graduate school, I bought a ‘58 Renault 4 CV (the one that looked like Charles Degaulle in profile) for $250. It had 28,000 mi. on it, and was worn out. What a piece of junk. I’d have been better off with the Model A

I still check them out on CL from time to time, but now they cost anywhere from $12,000 to over $20,000, depending on condition. Anything under $10,000 is usually a basket case.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

View Alex Lane's profile

Alex Lane

539 posts in 4062 days


#34 posted 12-24-2017 11:29 PM

You’ve certainly got a lot of expertise to choose from here on LJ! I didn’t read all the replies carefully so I’m sorry if I repeat someone else.

At my job building wooden wings for classic biplanes, we have to bend thin strips of wood to the shape of the airfoil profile of a wing. Our rule is 3 days in soak, and 3 days clamped in the form. Not sure how that translates to bending a sheet of plywood as large as yours, but perhaps it needs more time in soak and in the form?

See a pic here.

I couldn’t tell from your picture how many curved form pieces were supporting the plywood under the curve. I’d guess the more you have the better.

Best wishes on your project!

-- Lane Custom Guitars and Basses

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