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

Having set the forum on fire with the publishing of the last two projects, the audience's anticipation of this third installment is palpable

Readers are no doubt thinking: "The first project he nailed together some scrap pine, the second project he nearly completed a fruit bowl, will this third project be a long and painful attempt at making a sawhorse when he could buy one from the local hardware store for 20 bucks"

Read on to have these questions and more answered...

Yes this project is definitely the construction of an overly complicated sawhorse, but remember the physical object is merely a vehicle used to learn and apply the concepts. When you think about it any old fool, armed with only a kinetheodolite, a burette and a large hadron collider, could make one of these sawhorses with ease, but that is not the point, it's the Knowledge that we thirst for.


Here is a Sketchup graphic of the sawhorse in a three view:

Attachment 202123

There is one thing missing in this graphic, in addition to the top beam and the fours legs, the sawhorse will also include stretchers spanning between the legs on each side. Where they attach to the leg there will be a mortise and tenon joint. The stretchers are the same height all the way around and are set at about a third of the way from the floor to the top beam.

So, after this sneak preview, let's recap. At this stage we are old hands at constructing sloped boxes, making them all line up at the corners and joining then with wooden joinery. But let's imagine that this box was very large and needed some form of internal bracing to withstand the forces of nature. Our reinforcement is likely to begin with a post placed along the inside corners of our hopper, now our hopper is square in plan so when a square section piece is placed against the corner, in a vertical orientation, it should all fit snug like this:

Attachment 202124

However this is not much help at this stage because a bracing post needs to travel along the corner of the hopper at slope. When placed along the corner at slope this happens:

Attachment 202125

Now our post is only supporting the corner of our hopper at one point, the arris. So what kind of shape do we need our post to be (in cross section) so that it is flush to both sides of the hopper? It turns out that this is what we need:
Attachment 202126

So in this project, the third in Chris's series, one of the main points of study is to shape our sawhorse legs to the correct cross section so that they would sit neatly inside a hopper that was sitting snugly on the outside. This will have the effect that any section through the leg, parallel to the floor, will be a square. Note in the graphic above that the footprints of the legs on the floor and where they but against the underside of the beam, they are indeed a square. Now we know what to do let's start doing it - after much backwards and forwards with a jointer plane we end up here:

Attachment 202127

Next we can work on the mortices where the legs insert into the top beam:

Attachment 202128

All four complete:

Attachment 202129

The mortices are a compound slope, sloping diagonally inwards to the centre, this is what it looks like as the leg is inserting:


Attachment 202130


I said that stretchers would be required and this is the second main focus of the study. The stretchers are the same height all around and tenon into the leg so the tenons must be offset so they can cross over each other inside the leg. Here is one tenon complete:

Attachment 202131

The marking out for the mortices on the leg is quite involved. This following photo shows the layout complete for one face of the leg. The outside rectangle is the footprint of the stretcher cross section and the two smaller squares are where the tenon pokes through, the upper square for the higher tenon, the lower square for the other crossing at right angles and going underneath. This layout is required on every face of every leg:

Attachment 202132

Then they all need to be chopped out:

Attachment 202133

Finally, all the parts you receive when you purchase your sawhorse in kit form:

Attachment 202134

Or if expensive shipping is no problem for you, they can send it assembled:

Attachment 202135

So! Need a sawhorse? Don't be tempted by those cheap and nasty jobs from the hardware store, meet us over at the Carpentry Study Group and we can make our own.

Regards

Derek