The Chair – A Glimmer of Light
I need to explain why I have been so bloody minded about persevering with the drilling and sawing strategy.
The arms and backrest are being shaped in a different way to the legs and stretchers/rails. The front and rear rails were shaped to fit the legs because I could not be sure of the angle of the mortice and tenon joints. The M&T joints are also internal joints and any gaps could be filled with the epoxy used to glue them together.
By contrast, the arms and backrest are known angles, however their joinery is on the outside where it is visible. The joinery here must be spot on. The connecting sections were purposefully made square and oversize. They will be joined and then shaped (in contrast to the legs, which were shaped and then joined).
In spite of being as careful as I could in squaring the square end sections, I realise that there will be some deviation, or that I should assume that there is some deviation for a worst case scenario. Consequently, I must find a way to saw the joinery from one reference side. In my mind, working inwards from two sides will create errors, even if they are small. This will lead to gaps. If the joinery is perfectly square from the reference side then it should not matter what the opposite side looks like: the parts will fit, and the outsides are going to be removed anyway.
The ability to drill perfectly square from the reference side is one example. This was demonstrated to work reliably. The irony is that the jig I made will drill a hole with greater accuracy (for the purposes here) than the best drill press could!
The ability to saw to the circumference of the hole is important because the wood is too hard and too thick to file to shape, and anyway I have always sawn dovetails to the line, never deliberately played "safe" and left room to pare away waste. I believe in this instance that, with a guide, I should be able to saw to the optimum spot (melding into the edge of the hole). Not only that but, done from the reference side, it should allow for a square joint all the way through the work piece.
Some terminology at this point: I am not sure what to call the finger joint parts. The joint is sort of like a dovetail, but tail and pin does not apply here. Why do I care? Because the joint I have been practicing will have a counterpart, that is, a "male" finger that fills this "female" section. Both end in a round. And the fingers are also separated by a round.
I returned to the workshop this afternoon for a little more practice. First I tried carving the finger, that is, marking it out and paring from both sides. It was quickly apparent that this was not going to work and was a LOT of effort.
I had an idea about the errors that occurred previously. What was in common was a saw cut to the one side of the guide and the guide was positioned at the side of a board. My thought was that the clamp I used was pulling it over slightly at that spot because it could not be centred on the guide. I simply used a different clamp.
With everything else exactly as before, this is what I achieved ...
Other side ...
I was very happy with this. All that was needed was a little cleanup with a 3/16" round chainsaw file.
There was time to try a male finger. All I had to hand was a small piece of Jarrah waste. This was just enough.
I covered the Jarrah with blue tape and marked it from the female finger (this is how I plan to match the arm and backrest, as if it was a dovetail joint - another reason why the reference side must be able to create the non-reference side). The guide was clamped to the Jarrah and the sides sawn out. This left a pointed end, which was shaped with a file ...
I had deliberately sawn the male finger a fraction oversize. This was rasped to fit (just needed a few strokes) ...
Tools ...
And the Record clamp that helped ..
A few more practice runs are needed before the real thing.
Regards from Perth
Derek
February 2014