Thread: Chris Hall's Carpentry Study Group - Second Project

If the relationship of these projects to carpentry (which after all pertains to the woodwork of built structures, in particular roofs) seems a little tenuous then bear with me as the projects will eventually progress to various roof models. At this stage we are merely exploring the geometrical relationships that occur in roofs via the expedient of another, simpler object. I suppose if you turn your hopper upside down it does look a little like a portion of a hip roof...


So if you remember, our last project dealt with determining three angles that would allow us to construct a hopper of a chosen slope. These three angles are the face cut and two different edge cuts depending on whether we wish the corners to meet as a but joint or a miter/mitre joint. The last project was nailed but if we were a pre iron-age society and didn't have the use of nails (but nevertheless could accurately mark and cut out our wooden parts with flint or bronze tools ) then we may wish to find a joinery solution that will hold our hopper together at the corners. The first cab off the rank will be a mortise/mortice and tenon joint here, but standard dovetail/finger joint options would also be available.

So the focus of study in this second project is determining the layout for the mortices in a sloped piece, when intersected by the tenon from another sloped piece. Now our tenons will be square in cross section (well rectangular but 90deg corners, you know what I mean) but when an orthogonal tenon intersects a plane at some slope to the tenon, the resulting 'hole' is no longer square but will be distorted so that a diamond or parallelogram results. The greater the slope, the greater the distortion, conversely as the slope more closely approximates 90 degrees or square, the less the distortion so that, obviously, in traditional box type carcase work, the mortice has the same shape as the tenon cross section.

In the following photo I have started to hollow out the mortice by first drilling with an auger bit, but hopefully the parallelogram shape of the mortice is apparent. Note that the mortice travels through the receiving board at an angle:

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And here is the board with mortices complete:

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I don't have a photo of the tenoned piece being completed but here is a photo showing the matching sides with cutout complete. Of course the lessons learnt from the first exercise have been retained - the surfaces apart from the mortice and tenon parts still need to be cut at the appropriate angle - the surfaces are butting together in the region of the mortice and tenon but for neatness, a mitred return has been added at the top of the hopper:

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So how does it look when it's all together? Here is a photo of the mating parts coming together. Note the blood stains, part of my ritual sacrifice decorating every wooden joint:

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And finally all together:





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A close up of a corner:

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The last addition to this project was to chamfer the bottom edges of the boards so that the bottom sits flush to the resting surface:

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Actually the last thing needed is a floor panel so that this could serve its intended purpose as a fruit bowl but the next exciting project always beckons...

So at the completion of the second project in chris' course we have mastered some very useful concepts that allow us to have our sloping boards meet neatly at the corners and be connected by joinery. What now? Assuming that this hopper was the outer surface of some object and it required an internal frame of some sort - what special considerations may come in to play now? That is the focus of the project number three which arrives in the shape of a sawhorse. See you soon for project three in the series.

Regards

Derek