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Compound Joinery
September 7-12, 2008

Many architectural designs involve complicated roof shapes and offer challenges to the carpenter. The knowledge required to build these designs increases the ability of the carpenter to actually design these complex shapes. In this workshop, the process we will use to explore this topic is a collection of lessons from various global traditions. The goal of the class will be to broaden the problem solving skills of the participants. Skills retained will vary individually, but a body of reference materials will provide proven methods and exercises for future problem solving.

Learning to draw is the basis of the entry level skill set. A building is defined by the various views used in architectural plans: Plan, Elevation, and Section.

The various parts of the roof (plates, rafters, hips, valleys, ridges, etc.) can be drawn into these views. Simple techniques, known as "developed drawing", can be used to produce graphic solutions for: lengths of pieces, cutting angles, and the locations of intersections. The process involves a manipulation of any given view into an auxiliary view that allows the desired object to be seen in True Shape and True Length. For example, a rafter in plan view does not measure True Length, a rafter viewed in the plane of the roof does. This exercise is based upon the right triangle: it ties the two-dimensional information given to the three-dimensional desired result and is one key to visualization. Accurately drawn at full size or known scale, this can be enough information to build anything…Anything!

Our drawing exercises will involve common architectural shapes and built solutions:

  • Plate and ridge with hip and jack rafters
  • Principle rafters, header, valley, jack rafters and jack purlins
  • Plates and ridges with irregular hip and jack rafters.

Compound Joints Picture Classroom Discussion

We will use various drawing techniques, including folding paper models, to introduce mathematical concepts and skills that can be used first in conjunction with, and eventually in place of, the developed drawings. This allows the carpenter to move directly (using a calculator) from the architectural plans to the sawhorses for layout with a framing square.

In this transition of skills, we will reinforce our study of the right triangle, beginning with a discussion of Pythagoras. We then consider ratios (rise/run and rafter length/run are examples), similar triangles and proportion and how these principles can be applied to short cut many of the calculations required. Trig relates the ratios found in a roof to the included angles of the roof and applies easily to right triangles (one of the three angles is 90 degrees): If each length of the three sides is known, then the other two angles can be found If one additional angle and one length are known, then we can find the other two lengths and the other angle.

If one wishes to derive the backing angle of the hip or valley from the roof pitch and plan view eave angles, trig works…no better than drawing but perhaps faster.

A tool, using trig and drawings, was developed for steel detailers and fabricators. This was call the "Martindale Angles". Modern timber framers discovered this tool and manipulated it to good advantage in the form of the "Hawkindale Angles". All work in this class will be tied to the Hawkindale Angles as these named angles have become part of the language of the advanced level modern timber framer, log builder, and carpenter.

Using the drawings and the math we will work in pairs to layout and cut large scale models (see photo below) based upon our exercises. Hands-on experiences reinforces the lessons. These models we will leave with you.

Participants should have experience with: basic drafting, roof math and calculator use, roof layout and cutting.

Compound Class Models

Be sure to see our gallery page for more photos from compound workshops.

Tentative Daily Outline

The goal of this week will be three completed roof models.
  • September 7 (Sunday)
    :: Dinner at 6:00 PM
    :: Introductions, overview, folding models, review of schedule and goals
  • September 8 (Monday)
    :: Power point presentation: vocabulary and techniques
    :: Model one drawings and math
    :: Model one layout
    :: Evening session independent study (bring a problem to study)
  • September 9 (Tuesday)
    :: Revisit math and techniques
    :: Continue layout, check, cut, assemble Model one
    :: Begin math and drawings Model two
    :: Evening session independent study
  • September 10 (Wednesday)
    :: Revisit and reinforce lessons
    :: Layout, check, cut and assemble model 2
    :: Evening: available but not scheduled
  • September 11 (Thursday)
    :: Reinforce techniques
    :: Math, drawing, layout, check model three
    :: Evening session: My wood is not square, what now?
  • September 12 (Friday)
    :: Cut and assemble Model 3
    :: Recap and comments from the class

Taught by Curtis Milton