Sunday, February 03, 2019

Mortises

The earlier post about butt scratching over maximizing the strength of M/T joints in a thin leg led to this solution. I'm still not sure if it is the best but wood has been chopped and there ain't no going back.

I decided on using double tenons separated by a stub tenon as a way to minimize loss of wood in the leg. That decision meant a fairly complex markout. I've found the best way to attack that is to make a jig with the markout included.  The jig has an additional advantage of insuring at least one wall of the mortise is vertical.

It is easier to show the jig that to explain how it works:


The blue lines are for working one side of the leg, the red lines are for the other side.

The last mortises I had chopped were on the just finished Moravian workbench. I will not say you lose the feeling for chopping with a layoff but at least I do. The first couple of mortises were slow and ugly. With a little paring they will clean up and be usable.

That slow and ugly begs a question, why? That answer, I think, is too much force. If it has been a while it is easy to forget "go slow to go fast" and you lose your "ear". By the third set of mortises the "ear" had returned and the muscle memory had as well. Then it was narrow cuts, tap, tap, tap, to the "sound" and the mortises went very quickly with one pass to depth and with clean walls.

As with most things in life, going Conan on it isn't the answer and is usually counter productive.

I took a day off from work and the shop yesterday. It was a fine Winter day in Southern Arizona with temps in the valley in the low 70's. A perfect day for a short hike in Madera Canyon. Madera Canyon is about halfway between Tucson and the US/Mexican border in the Santa Rita Mountains. The canyon is a major resting stop for migrating birds so we saw lots of cameras with huge lens and not many migrating birds although there were a few. BTW, I'd hate to carry one of those huge suckers up and down the trails just for a few really bad photos. Anyway a beautiful day for a walk in a beautiful setting.

MsBubba by a stream while still in the lower Juniper-Oak area:


ken 

12 comments:

  1. Ken do you use the jig to keep the chisel plumb while you chop ala Paul Sellers?

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    Replies
    1. Ralph,

      Yep, that is one of the side benefits of the jig.

      ken

      Delete
  2. The hiking pic looks like a great area - very different from what I imagine that area to be like.

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    Replies
    1. Matt,

      Most folks only see the desert floor because that is where the roads are. Scattered throughout the desert are mountain ranges aka "sky islands". The mountains act as rain and snow catchers particularly the northwest slopes and can be very lush with changing ecosystems as you gain altitude. Starting with cactus, ironwood and mesquite in the low levels changing to Juniper and Oak as you go up the mountain and becoming Pine forest in the upper levels. Madera canyon is a prime example.

      ken

      Delete
  3. Steve D8:07 AM

    My comment from yesterday went into the ether.

    You mention that the desk legs are thin enough to give you concern but I can't get a feel from the pix. How small are they? My thought is you have grown accustomed to workbench legs.

    We hit 46F yesterday on dog walk and I was sweating like crazy. It's all in what you are used to.

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  4. Steve,

    The short stretcher side is ~45mm and the long stretcher side is ~65mm. I'll put off set from each other lower stretchers 250mm or so off the floor on three sides and maybe an "H" stretcher if I feel it is needed.which should help some. There could be some truth to the workbench legs, they do not move :-).

    46F and I'd be inside. So would the dogs, nose outside and a quick turn back. wussie dogs.

    ken

    ReplyDelete
    Replies
    1. Steve D8:45 AM

      45mm is plenty of meat. 10 or 12mm for mortices will be strong.

      Cabinet doors are less than 20mm and wood window sash is in the 45mm neighborhood. Both setups withstand plenty of use for many years.

      Delete
  5. It was 38 and snowing when I took my dog for a walk today. It's all what you are used to. If I lived in Minneapolis, I would think it was a heat wave.

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    Replies
    1. Andy,

      Ain't that the truth.

      In a week or so we will be past likely freezes and I will turn the solar pool heater on. Once that is done it will be just a few weeks till pool WX. Life is tough in the desert :-).

      ken

      Delete
  6. Anonymous6:34 AM

    Chopping the second mortise in a workbench leg, with the intent of doing half the work from each side, I realised the the two half mortises would meet with an offset in the middle, so I made a guiding bloc to pare that mortise and chop the next ones.
    My workbench is rock solid and nobody will see it.
    Sylvain

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  7. Sylvain,

    That is one of the advantages of through mortises, If marked correctly vertical is pretty easy. Are you doing the Sellers bench?

    ken

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  8. Anonymous5:32 AM

    I made it about one year and a half ago.
    Sylvain

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