Joinery in Bristol | The geometry of the splayed leg trestle | Are these the best small set of carpentry books there are?

"The ordinary stool or trestle affords one of the best examples of the application of geometry to joinery work, since it involves nearly all the geometrical principles connected with the determination of bevels, sections, projections and the true shapes of plane surfaces"

The 6 volume set of "Joinery and carpentry" by Hancock, Corkhill and Dowsett is a wonderful treatise on joinery, carpentry, furniture fitments, geometry, roofing and much more. It isn't just a how to about making joints or using tools like is often the case but actually has tonnes of reference images of traditional windows, doors, furniture, panelling and much more making it a really useful reference book for joiners.

The section below is one of my favourite from the books, partly as I endeavoured to make a set of trestles that I treasure dearly. It was a wonderful experience trying to work out the geometry and decipher these pages without help from the online world or the use of computer aided design. It contains incredible information in the 3 pages which I feel is being lost very quickly in the modern carpentry world. I've published it here in the hope that being on the internet will shine a small amount of light on it.

As you will read in the pages it offers two options for making a set of trestles. I chose to keep the legs in their square form, thus making them rhomboidal in horizontal section once they are splayed. This is the more complicated of the two methods but for me is the better as we are most often dealing with square timber in carpentry situations so it is good practice to understand how it intersects in different situations.

I made the trestles from reclaimed douglas fir. We took the roof off my friend George's house to do a loft conversion/dormer, it's a 1930's terraced house in St George, Bristol. The rafters were made from surprisingly lovely timber from big old growth trees and were either perfectly tangentially or radially sawn making them really stable for the trestles. After much de-nailing I could machine up the timber and get to the drawing board.

The quality of the timber is clear to see.

Cutting the top leg joints and the housings is relatively straight forward and there are tonnes of articles and books with plenty of information about that so I won't go into it here.

By far the most complicated part of the build was marking out for the through mortice and tenon joint between the stretches and the main legs. This could of course be done quite easily by using many carpentry tricks, such as setting the trestles up on a level surface and using a laser or a spirit level to mark a line across the rhomboidal legs, but the challenge I had set myself was to work it all out using geometry and trigonometry on paper. If I had decided to set the stretchers plumb and not parallel with the arris of the legs then this would have all been much simpler as it would have been a single bevel cut. However, as you rotate the stretcher to come parallel with the arris on the legs it becomes a compound joint, add to this the complications of marking the through mortice around the legs as they are rhomboidal in the horizontal plane and you have a real head scratcher.

The completed joint.

The completed trestles.