Sometimes it is necessary to bend timber to an appropriate radius, some Victorian built houses have both internal and external rounded corners instead of the square corners that we have today. Whilst plastering a radius is difficult, bending either a skirting board or dado rail is far more difficult and time consuming than a simple mitre joint. There are two methods of bending wood, one is steam bending where the wood is placed in a vessel for a few hours and steamed then removed and held in a mould until it has dried out, the other is kerf cutting. Both methods will be described below.
The simplest method is kerf cutting which is achieved by simply cutting slots into the wood to be bent allowing it to bend to an appropriate radius. A chop saw is ideal for this as you can easily cut slots into the timber which is to be bent.
The cuts should be on the side of the wood that needs compressing so for a internal corner the cuts will be on the front of the piece of wood and for external corners the cuts will be on the back of the piece of wood. You must not cut more than 2/3 of the thickness of the wood or the wood will easily break. Wood glue can be put into the kerfs to help hole the bend in place. Kerf cutting is often found in old houses as it requires less time and equipment than steam bending and is the chosen method by most joiners, steam bending is often done by boat makers.
The skirting at the bottom of this concrete pillar has been kerf cut
Steam bending wood
Steam bending can be very effective but needs more equipment than Kerf cutting, here I will describe the method and show how to make a basic steamer. Some woods bend better than others, most hardwoods bend far better than softwoods! A general rule of thumb for steam bending is to steam the timber for 1 hour per inch thickness of the wood. A mould or jig is also necessary to hold the wood until it dries out again otherwise you are in for a long period of holding it!
Steam bending can be dangerous and should only be attempted by experienced DIY enthusiasts, thick heat resistant gloves are recommended as the heat can easily scald unprotected skin on contact. A steam bender can easily be made from some PVC pipe and fittings depending on what size of wood you need to bend.
Here I am using some 4 inch soil pipe to make a steamer for bending a piece of Dado rail.
To make a steam bender you will need-
Start by cutting the soil pipe to the correct length to accommodate the piece of wood to be bent
glue a soil pipe cap in one end of the pipe and then drill a small hole in the soil pipe for the steam to escape.
glue a soil pipe access plug in the other end
Drill a further two holes spaced out so that two 5 inch long stainless steel bolts can be pushed through the pipe then the wood can suspend on the bolts rather than resting on the soil pipe. This is so that the steam can penetrate the wood from all sides! Cover the bolts with plastic to prevent the metal touching the wood or it may mark the wood.
Ensure that the hole drilled for the bolts is the correct size (not too big) and then seal both holes with heat resistant silicone.
Drill a hole the correct size for fitting the steam pipe, all these will vary depending on which steamer you are using, but I'd use a tank connector fitting and then use the correct diameter of plastic pipe..
Drill a hole the correct size for fitting the steam pipe, all these will vary depending on which steamer you are using, but I'd use a tank connector fitting and then use the correct diameter of plastic pipe.
You now have a very basic vessel for steaming your wood!
For the steam generator there are many different options from using a gas stove and steel kettle to a electric wall paper stripper. Personally I'd go for the wall paper stripper as it is the safest method, keep checking it does not boil dry and keep a kettle full of water handy to top it up!
Be extremely careful when removing the wood from the vessel as it will be very hot, a pair of thick heat resistant gloves and a pair of wooden tongs is highly recommended! Whilst your wood is cooking you can set about making a mould or jig to hold it in place, there are no set rules for mould making except the mould should be clean and smooth as any rough hard patches will be transferred to the wood and will increase the amount of work involved.
Flexible plywood is extremely useful as you can simply bend this wood with little effort to the desired shape then screw supporting battens across it to make it hold that shape, then simply bend your piece of steamed wood around it and clamp it in place until it cools.
Here is the profile of the wall which we need the Dado rail to fit-
Cut a piece of flexi plywood the correct length and push it into the profile of the wall-
Then using some pieces of strong timber (3 inch by 2 inch etc) fasten pieces of timber to the plywood to make it retain this shape-
You now have a jig the correct profile for bending your piece of steamed wood, ensure the jig is sufficiently strong so that it will not go out of shape. When clamping the wood to the jig use some off cuts of wood to place between the clamps and the wood itself to prevent damage from the clamps.