Kerfing

[The Medway Handyman]

Anyone got much experience of kerfing a board so it bends?

147 x 28 redwood. I'm looking at an inwards bend - concave?

I'm wondering what kind of radius you can get?

Any info/tips appreciated.

[The Natural Philosopher]

soak it in ammonia for a few days. It will bend like blotting paper.

Nail up while still floppy.

[Stuart Noble]

And be about as much use I expect.

[Cicero]

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Plenty of cuts (1" intervals if you've got the patience)on the outer face to go into a bay or similar as a skirting. Use a fine tenon saw and cut to a depth of approximately 3/4 of thickness of board. Support the board well if it's a long board when you come to place it in position.

As a general indicator my bay is about 12' wide and the segment is about

30" deep at its centre. It helps if you can do the job (if it's a bay) in two parts because you can get the correct outer angle where it meets the other skirting and you can adjust the length of the second piece by checking how much the first piece covers.

Cic.

[gunsmith]

Ever tried steaming? No need to make all those cuts.

[Anna Kettle]

Yes I was very successful when I steamed some 12" old oak floorboards using a wallpaper stripper, then screwed them into position immediately. Definitely worth trying before you start to make cuts in the wood

Anna

[The Medway Handyman]

Did you enclose them in something to retain the steam?

[boltmail]

Softwood doesn't generally steam-bend well.

For steam bending properly, you'd need to (a) build a box and (b) substitute something like oak (which steam bends well). If you get into extreme radiuses you need to strap the outside to stop the outer cells exploding. In terms of what is possible, the tightest I've done is about a 12" radius in ex 1" oak. That was without strapping, and it wasn't the limit.

If you have the ability to buy, or tools to saw, thin slices, lamination is simpler.

Kerfing will work,but only if only the face is visible (and it's interior).

[Anna Kettle]

No just held the flat steamer end against the timber for a few minutes

Anna

[John Rumm]

or convex if looking from the other side ;-)

Probably about a 8" radius or perhaps a bit tighter. You can do a test with a thin lath of the same stuff - see how much a bit a couple of mm wide will bend.

Depends on exactly what you want to achieve. Steam can work if you make up a steaming tube of some description - a length of soil pipe can work well for smaller sizes. Laminating is another option.

An index peg mounted on a table saw can make it relatively easy. Cut the first kerf against the peg, then the next by running the peg in the first kerf and so on.

[Nige Danton]

I've steamed softwood torus skirtings to fit curved walls by putting them inside a poly tube made from a couple of builders bags (folded and stapled together).

-- Nige Danton

[Stuart Noble]

Assuming you have a fine blade. TCT blades are a bit wide I would have thought.

[The Natural Philosopher]

Nope. After it dries it will be perfectly woodlike, and retain its shape forever.

That's how they make curved chair backs..

[Stuart Noble]

Yes, you're right. Not the easiest stuff to work with on a d-i-y basis though

[Rick Hughes]

The joinery firm who made the double bull nose step for my stairs used the thickness of the table saw blade, and 2/3 rd depth of the wood..

The distance apart will depend on bend radius ... sides of the kerf obviously must not meet.

Looks to be about 150mm radius.

The other way is to steam it ...

[Rick Hughes]

I steamed some supports for a boat hull repair .... improvised a steam box using a length of drain pipe blocked end to get a bit of steam build up. Plenty of articles on line about steaming.

BTW ... other way to do a curve is simply laminate up ... using multiple thin strips, glue and clamp around a former ..... often used for stairs.

[Frank Erskine]

formulae and advice...

[Andy Dingley]

Bollocks. If you're into doing this industrially, you're working with anhydrous ammonia and that's evil stuff. You can't just "soak" it in a bit of .880. It will also turn any hardwood timber with tannins in it to black.

[Andy Dingley]

Yellow plastic gaspipe is the best stuff. Flimsier plastic pipe does at a pinch.

Don't use any sort of iron (esp. wwith oak!) or you'll get staining.

What are you making, and what sort of bend do you need? If this is "wide", then kerfing is the way to go (I've mostly done it in MDF or ply). If it's chair backs, then steam. Steaming also needs hardwoods to work easily, and green ones at that - resinous softwoods are a sod.

For kerfing, go with "50:50" cuts from your favourite circular saw, leaving the min thickness at least 2 kerf widths thick, otherwise it tends to crimp.

[The Medway Handyman]

I'm thinking of kerfing a 147 x 28 deck board to follow the edge of a curved deck, so I suppose wide would describe it. It would be concave looking at the face (back won't be seen).