There are four layout rules, or systems, in timber framing today. Within those, there are countless combinations in-between. These layout systems are used when you are laying out or marking the joinery on your timbers before cutting them. There are pros and cons to each system.
Scribe rule is the most difficult to master, but once you see how it works and can visualize what is happening, it is an incredibly powerful method. This method is ideal if you have organic, out of square, twisted or bowed timbers. You can take care of all of them with this technique. The timbers are stacked on top of each other where they will be located in the frame. String lines, plumb bobs, bubble scribes, and laser lines are used to locate cut marks.
- You can easily take care of irregular, round, and organic timbers
- It is one of the most rewarding methods to use
- Takes the most skill and time to master
- More material handling than the other methods
- Timbers are not interchangeable
The timbers are cut and planed with a four-sided, larger planer, by a sawyer or yourself, hence the name “Mill Rule”. The material is square, flat, and straight, and will only need sanding to finish it. With the material being so close to dimension, no square rule compensation or scribing is needed. It is just a matter of pulling the dimensions and marking your timbers. The planing process usually takes 1/4” off each side so an 8×8 will be cut to 7.5”x7.5”.
- It cuts down on time during the layout and cutting process. Sometimes it will offset the costs of itself if you are paying someone to cut your frame.
- All the timbers are constant, and therefore can be interchangeable. Knee braces are the best example.
- It isn’t a flexible system if you have out of square or rough-cut wood.
- It does have an added cost of the planning and transportation, which isn’t the best for someone who is cutting their own timbers.
With mapping, you take detailed measurements of the different pieces and layout the joinery to match them. You must employ some logic and care with this technique. For example, to have the dimensions to lay out a post, you will need to have cut all the preceding timbers, or at least laid them out so you can capture the dimensions where the joinery is located on the timbers.
- This is a very flexible method that allows you quite a bit of leeway on the sizes of your timbers.
- It mixes well with the other methods.
- Keeping track of all the measurements through a frame can be tricky and can lead to mistakes if not careful.
The Square Rule method is predicated on the theory that within each timber, a square and straight timber is sitting there waiting for you. Working with that theory, you can lay out your frame using irregular or rough sawn timbers with a chalk line and a little head scratching. Most of the time when you either cut or purchase rough sawn material it doesn’t come as ordered. An 8×8 post could end up being 7 ⅞” x 8 ⅛” but within that timber lies perfect 7 ¾” x 7 ¾” timber ready for you to cut. You are notching the timbers to standard dimensions to aid in having unified measurements throughout the frame.
For example, you will notch all the 8×10 beams to 9 ½”.
- You can deal with a lot of variations in timber sizes and account for any twisting or bowing in the timber by using a chalk line
- Allows you to standardize dimensions, which speeds up the layout process
- Time-consuming to layout and cut all the haunches, housing, and shoulders.