How do you curve plywood?

@rickw55,

Thanks. Seems though to me that the wood that wasn't kerf'ed would crack when bent at such an angle. Does it need to be moistened and bent slowly in stages?

admin wrote:

@rickw55,

Thanks. Seems though to me that the wood that wasn't kerf'ed would crack when bent at such an angle. Does it need to be moistened and bent slowly in stages?

No, there's no need for moistening or for bending slowly in saw kerf bending. Here's a link to a description of the technique from a Lost Art Press blog posted about a year ago. Slainte.

There are also thinner bendable plywoods that are made for bending.  They have been shown on "This Old House" in several episodes.

You can see the kerf cuts at the bend in the photo if you look more closely at it.

@Wood fellow,

Do you refer to the dark lines along the upper edge of the curves? I speculated they might be pencil marks indicating the kerfs, which were positioned on the OUTER side of the curve.

My subsequent inquiry might sound naive, but once you've kerfed the plywood for bending, can it flex in either direction, depending on which side is intended for the customer's view?

admin wrote:

@Wood fellow,

My subsequent inquiry might sound naive, but once you've kerfed the plywood for bending, can it flex in either direction, depending on which side is intended for the customer's view?

in my limited experience, if you flex it the toward the uncut side, you will likely loosen some of the strips between the kerfs.

Not the pencil lines. Zoom in on the photo to see the kerfs on the ply. You can bend the ply in or out.

The stuff they sell locally is called WiggleBoard.  It comes in short or long grain versions.  Meaning all the plies are aligned at either 1-90, or 180-270.  They must be doing something else with it as it bends easier than 8mm material would. I saw the kerfs in the corner also, however, it does not look like a great joint.  There is either some black tar in there, or it is a gap.  There are a lot of nails along the corner.
 

Added later 13 min 58 s:

This is a pic of some plywood being vac bagged with a shopvac, you can lay up to 3 layers of 1/8".  That is two layers in a 4x24 sheet to be.  You can get really tight curves in 1/8" if you go with the easy bend.  On should be able to get down to a 6 inch radius.  You need a mechanical bending moment.  But you can laminate it with a shopvac.  The shown example would have about 13000 pounds bearing on it, at 2 psi.  7 times more with a proper system, but it isn't necessary.  It is half a hull bent over a parabolic form, with gravity supplying the bending force.