Stack Marking – more:
Robert Paul Gurney shows marking and measuring with a technique designed to get the best results possible from your router.
I am going to discuss using the stack system in combination with the router. This is one of the most powerful joinery tools in the modern workshop; the router is fast and accurate.
Setting cutter depth
There are many jigs available (both store bought and homemade) but nothing could be simpler than using set-up blocks in a stack to set the depth of your router cut. With the router upside down, place the desired stack next to the exposed router bit. Use a spare set-up block that bridges across the stack and the exposed router bit. Adjust the cutter until you can’t see any light under the spare set-up block and the stack.
Setting the perpendicular fence
Housing joints of some sort or another are chief among the routing repertoire. Cut them accurately and place them well and the dreaded glue-up will be a less stressful event. There are many elaborate jigs you can make for making cuts square to an edge, but you don’t need anything more than a straight piece of MDF with a square fence (photo 1). The straightedge should extend past the fence by half the router base plus another 50mm or so for a clamping surface. If you have a workpiece that is wider than your right-angle template then you can use a longer straightedge against the template.
With all router right-angle templates where the router base rides against a straightedge, you need to accurately measure the distance from the edge of the router bit to the edge of your router base. Not all router bases are concentric, so it is wise to pick a consistent point on the base that you measure against.
To get a precise distance from your router bit to the edge of the router base you need a test cut. On a piece of scrap, make a test cut and use your dial calliper to measure this distance (photo 2).
You won’t have to do this every time because you can write the dimension down and use it next time you use the cutter. I use that dimension on subsequent cuts but re-confirm it each time I do another project. There are two dimensions you will need: the width of the cutter (photo 3) and the dimension to one marked point on the router base (photo 4). I write these numbers down (usually on the router’s storage box).
When you have located your shoulder line with the stack, you can temporarily mark it with the saddle square. From this point, with your dial calliper set, you can offset the template from the saddle square. This gives you the first position for the right-angle template. If the joint needs to be wider than the cutter, you will need to adjust the right-angle template again. The adjustment will be the difference between your cutter and the intended dimension.
To make the adjustment, clamp a saddle square against the back of the right-angle template, unclamp the right-angle template, place a stack of the intended dimension against the saddle square and clamp the right-angle template in the new position. against the stack.
If a cut is too close to the end of a workpiece to use the right-angle template, use the router fence instead. I will discuss this in more detail later.
Setting the stops is much the same as setting the right-angle template. I use two simple aids, as shown in the photo below. They are made of a piece of MDF that has two parallel edges and one edge perpendicular to them. A clamping bar fastened to them is all that it needs.
Cutting parallel to an edge
Two measurements are needed to set the fence on your router for parallel cuts. The first measurement is from the edge of the workpiece to the nearest edge of your cut. The second measurement is the one for
the far side of the cut which is calculated by subtracting the intended width of the groove from the width of the cutter.
Place the stack between the fence and the cutter and rotate the bit clockwise until it pushes the stack out to its most concentric position (see diagram A). When you get the right position the block moves a fraction. This is the point where you tighten down the fence. If the fence sits outside the router base, the stack may be prone to tipping. You can simply hold your hand or a piece of scrap under the fence. For the far side cut, you use the same techniques but add in the difference between the cutter and the intended cut width.
Router table: rabbets
Going directly from a test cut to a final pass is the key to cutting rebates on the router table. There are two types of fences used on the router table: one is a pivoting fence and the other is a sliding fence. They both can be set the same way with the stack. You will need some kind of reference piece – I use MDF with a very straight edge. Lay this piece on your router table against the bit with your desired stack between it and the fence. Approximate the position of the fence then rotate the bit backwards until the reference board no longer moves. (diagram B). You can now lock the fence in position.
Sliding dovetails are typically cut by matching the male part to a previously cut female housing cut. This means holding the male part upright against a router fence and making successive adjustments and cuts until you have a well-fitted and centred tail. The trouble with this is that you haven’t been able to precisely locate the divider or shelf. It has to be based on an imaginary centreline. It also involves a lot of trial-and-error cuts until the joint fits.
Contrary to the traditional way of cutting this joint, I find it better to cut the tail part first. This allows me to make my adjustments to the groove using the stack. You will need two dimensions (see diagram C), which you will get from a test cut just as you did with the housing joint. These dimensions vary with every different depth setting of the router bit so they will have to be done each time.
You can set the position of the mating piece by adding dimension ‘a’ into the stack. Dimension ‘b’ is used to adjust the right-angle template to get an accurate groove width. For all these measurements, the dial caliper is best. I find this method a little easier and more accurate than the traditional method.
If the brutality of the router is not what you want or require, you can use a stack to gain the same results. By measuring from your plane fence to the edge of the cutter, you can set your cuts very accurately.
The stack is designed to gain precision to 1/100mm but all joinery needs a lag: room for friction, swelling and glue. However, this does not need to lead to guesswork and sloppiness. By placing shims in the stack you can get exact locations. I use 1/2000in shims to allow for this lag.