Attempting to [CTRL]+Z a half blind draw-bored mortice and tenon

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This post could also be titled “How draw bored mortice and tenons took me from hero to zero in fifteen minutes”.

You need to understand that this project has taken me a lot of evenings with half an hour snatched here and there to finally get to the point of being ready to assemble. I had learned a lot of new things on this build so the assembly felt like the culmination of months of effort (well just over a month, but our feelings are rarely based on fact…).

The assembly came together fast and the results were spectacular. Each joint pulled in nice and tightly and seated squarely with it’s partner. My wife was helping with the assembly and I know that thoughts of amazement and appreciation for being married to a specimen such as I were running through her head. Then she got cold and went inside (it was late in the evening, the shed was unheated, and it was a Tasmanian winter). With the departure of my muse, it all started to fall apart.

I had plans drawn up. I had labelled each part. I had hieroglyphs at each joint which in LPPML (Lance’s proprietary pencil marking language) said “This part connects to this part, and no other part will do.”. And yet somehow I managed to get it wrong.

Whilst I prefer to research different techniques thoroughly before trying them, I had to wing this one. You see the glue had been applied, the four panels already assembled, and the side panels mounted to the font. It was only when attempting to complete the frame by adding the rear panel that I realised something was amiss. The glue was by that point well on its way to creating it’s cross linked hug of everlasting love. Thank-you Titebond III for your longer setting time, as the errant assembly was the first panel I glued up.

Being draw bored mortice and tenon joints, it was a little more complicated to separate the pieces than simply knocking them apart. An additional complicating factor was that these were half blind (is that even the correct term?), in that the pins never exited out the back of the mortice piece. Let’s then establish the problems presented for an undo operation:

  • The join was glued (tick-tock, tick-tock).
  • The join was pinned (can’t simply pull apart).
  • The pin holes are offset (can’t drill the pin out).
  • The pin is half blind (can’t drill the pin out of the mortice from each side).
  • There were four joints with two pins each (needed to be a relatively fast operation, remember tick-tock, tick-tock).

After a moment of despondency and a subsequent internal pep talk, I made a plan, and for better or worse started executing it.

A draw bored mortice and tenon, connecting the wrong parts.

First I sawed and pared the pins flush with the legs.

Then I selected a smaller drill bit which I hoped would leave the holes in both mortice and tenon unmarred, whilst removing the bulk of the pin. I proceeded to carefully drill them out as deep as the far side of the tenon.

Drilling the bulk of the pins away whilst leaving the holes unscathed in both parts.

Taking my Thor hammer I started with gentle taps and increased the blows to the point where I was channelling its namesake in my efforts to break the glue bond and sheer the pin remnants until it finally gave way. I do feel compelled to point out that bar one, every join separated with almost no damage. On the final one, I realised I had a good system, and the consternation had subsided sufficiently for me to document the process with photos. It is thus that you get to see a photo of the one that when spectacularly wrong. For balance I also included one that went to plan.

The final step was to drill out the remains of the pins from the blind holes.

Drilling the pin waste from the blind holes at the back side of the mortise socket.

With the disassembly complete I glued and clamped the split piece and went inside. I didn’t even bother cleaning the shed, which I generally do with religious fervour. My despondency was tempered somewhat by the fact that I had managed to rescue something that at the moment of notice had seemed insurmountable.

On the bright side, the next day I got up bright and early and put it all together. As I stood back admiring my work later in the day, after a little while my eyes narrowed, my brow furrowed and I let out an anguished “WHAT?”. But that’s for another instalment.

If you know of a better way to undo draw bored half blind M&Ts, I would love to hear from you.

Lance

June 2020

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