Technical Thursdays - Router Table Joints archive
Thursday 20 February 2014
John Bullar machines joints the easy way
Joints cut on router tables range from one-off specials with standard cutters, to batch produced joints using dedicated cutters. The router table is essentially a scaled-down version of the spindle moulder - ideal for small-scale precision work. In this article we will look at some examples of router table joints with tips on what to watch out for.
Know your tableStep 1
Router tables range in size from small bench-top models to large floor-standing beasts, like the one shown here. The size only matters if you are handling long pieces of wood. What is most important for accurate joint work is that the table and router mounting are sturdy enough not to bend or vibrate while you cut the joints
Beneath the router table you need to fix a heavy-duty router. It can be very fiddly to raise and lower the router using its own plunge springs because it is working upside down. That is why larger router tables like this one are often fitted with a rise and fall platform - it gives you fine control to adjust the cutter height from above the table
A large diameter cutter with a wide flat top is ideal for use with the router table because it can remove an even thickness of waste wood from the underside of a large joint. The cutter has a half inch shaft for fitting into a heavy-duty router. That way it can work hard without vibration
At the back of the router table is a straight, vertical fence. The fence has a gap in the middle that the cutter can be set back into. Having only part of the cutter in front of the fence enables you to work on joints that are narrower than the full width of the cutter
Wide tenonsStep 5
Before cutting joints on the router table, the wood needs to be well prepared with straight sawn ends, flat planed faces and straight edges. Then, when you run the end of the wood across the cutter, it will remove a straight even rebate, which in this case forms the shoulders of a short wide tenon
By withdrawing the fence backwards in stages after each cut, you can turn a short wide tenon into a long wide tenon. It is important to keep the movement small so the cutter is removing a narrow rebate each time
Sliding fencesStep 7
You may have noticed the sliding fence, shown here at the back of the photo (see gallery image 7). It runs along a guide rail on the main fence, allowing you to push wood safely in a straight even motion. The sliding fence is an option on some router tables, and I think it is well worth having if you are going to use the table for cutting joints. If your table doesn't have a sliding fence, you can us a square of plywood or MDF instead
The square of plywood runs along the main fence, pushing the workpiece in front of it. By moving the work across the cutter at right angles, this acts as a cheap but effective sliding fence
Straight or spiralStep 9
Most router cutters nowadays have twin tungsten carbide edges as shown here on the right. However, although it lasts well, tungsten carbide cannot hold as sharp an edge as high-speed steel, like the twin fluted spiral cutter on the left. People often use spiral cutters for joints because they give a cleaner finish with better chip removal and less grab. However, they are expensive and they wear out more quickly with heavy use
This joint cut in elm used a spiral router bit to make the deep slot which would be likely to chatter with a straight cutter. Sometimes with joints like this, after removing the bulk of material on the router table, it is easiest and safest to square up the corners on the workbench using a chisel
Finger joints'Comb joints' or 'finger joints' are simple and effective end-to-end glued joints, ideal for solid wood. You can buy multi-bladed comb cutters for miniature joints, or make your own larger joints with a single cutter.
Half inch diameter straight cutters are workhorses of the router world, used by joiners and kitchen fitters. This means there are plenty of competitively priced ones around and mostly of good quality
Half inch cutters also happen to be an ideal size for cutting heavy finger joints on the router table with the workpiece clamped to a sliding fence. Special one-off joints are one area where the router table comes into its own. While other fixed purpose router jigs are great for repetitive joints, the router table is a universal tool. The number and types of joints it can make are up to your imagination and experience
The finger joints cut in oak here, also form a square socket around a vertical post. This makes a strong joint with three pieces of oak all the right angle to each other
The finger joint and socket joint are glued up and clamped at the same time so there are no gaps or excess tightness in any part of the joint
Scribed jointsThe vertical parts of a panelled cupboard door frame are known as stiles, while the horizontal parts are called rails. Another speciality of the router table is the 'stile and rail joint' - sometimes called a 'scribed joint' because the traditional technique is to scribe round the edge profile of the stile to mark the end of the rail.
Stile and rail cutters come in various forms but commonly have a set of two specially shaped cutters and a guide bearing all bolted onto one shaft. These can be dismantled and reassembled in a different order to make the second half of the joint, as you will see below
On the inside edge of each stile and rail is a groove to hold the panel, and this is cut by the upper cutter on the set. The ogee shaped edge on the inside of the frame surrounds the panel. This is made by the lower cutter on the set
After shaping the edges of two stiles and two rails for each door, the stile and rail cutters set is dismantled by releasing the top nut. This allows each cutter to be pulled off and the order reversed. However, it is essential that cutters are not turned over so the cutting edges still run in the same direction. Remember to turn the router off by the plug before dismantling the cutters
Now the same cutter has been re-assembled in a different order, it can be used to shape the ends of the horizontal rails that fit between the stiles. The shape made by the ogee cutter at the top of the shaft is symmetrical. Because the wood is now face-up, the ogee curved rail end will fit the ogee on the inside edge of the stile. The guide bearing in the middle runs on the edge of what has now become a wide stub tenon. The straight cutter at the bottom makes a shoulder on the back of the tenon
The two halves of the joint fit perfectly together, leaving a slot for the panel to sit in and the appearance of a mitre where the two inside mouldings meet. Aside from their many other uses, router tables are versatile joint making jigs. They are great for one-off joints using standard cutters, or for use with specialised joint cutters that cannot be operated in a handheld router.